Eradicating Helicobacter pylori infection

Cara N. Wilder, Ph.D.

Helicobacter pylori is a Gram-negative, microaerophilic bacterium known to inhabit the stomach lining of at least 50% of the human population. This pathogen is transmitted to humans through the consumption of contaminated food and water, as well as through direct contact with infected individuals. Once ingested, H. pylori will colonize the surface of stomach epithelial cells, resulting in either asymptomatic carriage or complications including chronic gastritis, peptic ulcers, or stomach cancer.

The most common treatment of H. pylori infections is through the use of a triple regimen that combines two antibiotics (clarithromycin, amoxicillin) and a proton pump inhibitor (PPI). Though this treatment is effective in most patients, recent reports have indicated that successful bacterial eradication is decreasing due to the emergence of clarithromycin-resistant strains. To aid in the treatment of these antibiotic-resistant infections, many clinicians have turned toward the use of second-line treatments such as a bismuth-containing quadruple therapy (EBMT) or a moxifloxacin-containing triple therapy (MEA). However, little is known regarding the efficacy of these second-line therapies.

In a recent study, Kim et al. sought to evaluate the rate of H. pylori reinfection following EBMT or MEA treatment. In this analysis, 648 patients who failed bacterial eradication through the standard triple therapy were treated with either the EBMT or the MEA second-line therapies. At four weeks following treatment, patients were examined for H. pylori colonization through either the ¹³C urea breath test or by invasive analysis. From this investigation, the annual reinfection rate from EBMT and MEA treatment was found to be 4.45% and 6.46%, respectively. Overall, the long-term reinfection rate of H. pylori remained low following both second-line treatments, suggesting that there is no significant evidence that reinfection of H. pylori is related to the eradication program.

Read the published article

Prevention of Toxoplasmosis

Histopathology of active toxoplasmosis of myocardium.
Photo courtesy of  EP Ewing Jr. and CDC

Cara N. Wilder, Ph.D.

Toxoplasma gondii is a ubiquitous obligate, intracellular parasitic protozoan known to cause toxoplasmosis in a number of warm-blooded animals, including humans. This protist is transmitted to humans through the consumption of undercooked meat from infected animals, the ingestion of food or water contaminated with oocytes from infected cat feces, or by transplacental transmission. In healthy individuals, toxoplasmosis is relatively asymptomatic and self-limiting. However, this illness can silently affect pregnant women and result in severe consequences for the fetus including neurological impairment, chorioretinitis, or death. T. gondii can also affect immune-compromised individuals, resulting in cerebral or extra-cerebral toxoplasmosis.

Currently, the CDC considers toxoplasmosis to be one of the leading causes of death attributed to foodborne illness. Moreover, T. gondii infection in domestic animals represents a significant economic and public health threat due to the potential for foodborne outbreaks. Unfortunately, treatment of toxoplasmosis is difficult due to both the severe side-effects of the drug as well as the potential for re-infection. Thus, the development of effective preventative treatments is of great importance.

In recent study, Wang et al. analyzed the protective efficacy of recombinant T. gondii protein disulfide isomerase (PDI) as a potential target for the development of a novel vaccine. This particular antigen was chosen as a candidate vaccine target as it is soluble, demonstrates conserved homology among the three distinct clonal lineages of T. gondii strains, and is highly expressed on the outer surface of T. gondii tachyzoites. In this study, BALB/c mice were intranasally immunized with varying concentrations of recombinant T. gondii PDI (rTgPDI), and the resulting immunological response was evaluated by lymphoproliferative assays and by cytokine and antibody measurements. In addition to this analysis, immunized mice were also challenged with tachyzoites from T. gondii strain RH. Following this challenge, the survival time of the mice was assessed and the number of brain and liver tachyzoites enumerated.

From these analyses, the group discovered that immunization with 30 µg of rTgPDI demonstrated higher levels of anti-PDI antibody production, a strong lymphoproliferative response, and high levels of cytokine production as compare to the other doses tested. Further, mice immunized with rTgPDI demonstrated enhanced survival times and reduced levels of tachyzoites as compared to control mice. Overall, the results from the study demonstrated that immunization with rTgPDI elicited a protective immune response against T. gondii tachyzoites, thus suggesting that this recombinant protein may be a promising candidate for the development of a vaccine to prevent toxoplasmosis.

Read the published article

Rapid diagnosis of typhoid from blood cultures

Image of Salmonella enterica, courtesy of the CDC

Cara N. Wilder, Ph.D.

Typhoid fever is a life-threatening illness caused by the Gram-negative bacterium, Salmonella enterica subsp. enterica serovar Typhi. This foodborne pathogen is commonly contracted though the consumption of food or water that has been handled by a person shedding S. Typhi, or through the contamination of these products with sewage. Once ingested, the bacteria will inhabit the intestinal tract and bloodstream, resulting in a variety of complications including high fever, stomach pains, septicemia, and death.

Typhoid fever is common throughout most of the developing world, particularly in parts of Asia, Africa, and Latin America. Unfortunately, a number of people within these countries do not have access to a reliable laboratory diagnosis as the appropriate clinical facilities and techniques are not available. Thus, there is an urgent need for an inexpensive, easy-to-use, portable technique that can rapidly and safely diagnose typhoid fever independent of a hospital setting.

In a recent study, Castonguay-Vanier et al. investigated the accuracy and efficacy of a technique combining blood culture amplification of S. Typhi with a S. Typhi antigen rapid diagnostic test (RDT) developed by Standard Diagnostics (Cat. No. 15FK12). When tested against 23 Gram-negative reference pathogens, this assay was able to detect S. Typhi, as well as Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Ndolo. The precision of this assay was further analyzed through the examination of 6,456 blood cultures from 3,028 patients. From this prospective study, the group found that the sensitivity, negative predictive value, specificity, and positive predictive value were 96.7%, 99.5%, 97.9%, and 87.9%, respectively, for patients with proven S. Typhi bacteremia. Overall, these results suggest that the combination of blood culture amplification of S. Typhi with an S. Typhi RDT is promising as an effective, sensitive, and inexpensive tool for the rapid diagnosis of typhoid fever.

Read the published article now

Characterization of Arcobacter species using multi-locus sequence typing

Cara N. Wilder, Ph.D.

Arcobacter is a genus of aerotolerant, Campylobacter-like bacteria first isolated from aborted bovine fetuses by Ellis et al. in 1977. Since then, Arcobacter species have been discovered in a variety of sources, including food, water, animals, and agricultural run-off. In recent years, the prevalence of Arcobacter butzleri and Arcobacter cryaerophilus in food, raw milk, and water has suggested the potential of these organisms to be spread by contaminated consumable products. This is particularly disconcerting as these species are considered to be pathogenic, causing a variety of symptoms such as abdominal pain, nausea, and septicemia.

To aid in the identification, characterization, and epidemiology of Arcobacter strains, Miller et al. developed a multi-locus sequence typing (MLST) scheme based on the analysis of partial, defined sequences from seven Arcobacter housekeeping genes (aspA, atpA(uncA), glnA, gltA, glyA, pgm, and tkt). In this study, a sample set of 374 strains comprising five known Arcobacter species was isolated from a diverse array of sources and geographical regions. The analysis of these strains yielded almost 300 sequence types and 1176 alleles across the seven loci. Overall, this extensive set of genomic sequence data may aid with strain discrimination as well as help track sporadic Arcobacter-related gastroenteritis and potential outbreaks.

Read the published article

Rapid Detection of Cronobacter spp.

Image of Cronobacter sakazakii, formerly known as
Enterobacter sakazakii. Photo courtesy of CDC and Dr. JJ Farmer.

Cara N. Wilder, Ph.D.

Cronobacter sakazakii is a Gram-negative, foodborne pathogen associated with the use of powdered infant formula. In infants, this bacterium has been found to cause invasive infections with high fatality rates, including neonatal meningitis, sepsis, and necrotizing enterocolitis. Due to the severity of these infections, it is imperative that rapid and sensitive detection assays are available for the microbiological testing of powdered infant formula.

Currently, the routine procedure for the detection of Cronobacter spp. is both arduous and time intensive. To improve upon this, Cai et al., developed a novel molecular-based assay that targets the Cronobacter ompA gene through real-time PCR integrated with high resolution melting (HRM) analysis. This innovative methodology is not only faster than current procedures, reducing detection time from several days to less than 24 hours, it is also probe-free and reduces the risk of PCR carry over. To analyze the specificity and sensitivity of this assay, 11 Cronobacter isolates and 25 reference strains were examined. In this analysis, only Cronobacter spp. produced a positive signal. Moreover, the assay detection limit was found to be 10² CFU/mL, indicating that the assay is highly sensitive. Overall, this established method may provide a rapid, sensitive, and specific molecular tool for the direct detection of Cronobacter spp. in powdered infant formula.

 Read the published article

Identification of Enterococcus species using an automated microarray-based nucleic acid test

Image of Enterococcus sp. Photo courtesy of Janice Haney Carr.

Cara N. Wilder, Ph.D.

Enterococcus faecalis is a Gram-positive commensal bacterium known to inhabit the gastrointestinal tract of humans and animals. In immunologically compromised individuals, E. faecalis is a leading cause of urinary tract infections and nosocomial bacteraemia. This latter condition is of particular concern as it can lead to septic shock or the hematogenous spread of bacteria to other parts of the body, resulting in high rates of mortality and organ failure.

Unfortunately, the treatment of E. faecalis infection is not straightforward as a number of strains exhibit intrinsic and acquired resistance to a variety of antibiotics, including aminoglycosides, cephalosporins, and penicillins. Presently, these drug-resistant strains are commonly treated with vancomycin; however, in some instances the extended use of this antimicrobial drug has resulted in the emergence of vancomycin-resistant strains. To make matters worse, current treatment options for vancomycin-resistant strains is limited. Therefore, the rapid identification of vancomycin-resistant strains is imperative to the successful treatment of infection.

In recent years, advances in diagnostics have yielded a number of sensitive assays for the detection of E. faecalis, including fluorescent in situ hybridization (FISH), matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS), and the microarray-based Verigene Gram-Positive Blood Culture test (BC-GP) (Nanosphere). This latter method was recently validated through an examination of 12 Gram-positive targets including E. faecalis, as well as associated drug-resistance determinants. In this study, Buchan et al. used the Verigene BC-GP test to analyze 1,252 positive blood culture broths collected from five clinical centers throughout the United States. The resultant data indicated that the BC-GP test can sensitively and specifically identify E. faecalis and other leading causes of Gram-positive bacteremia directly from positive blood cultures. Further, this assay was capable of detecting the genetic markers vanA and vanB, which confer resistance to vancomycin. Overall, the Verigene BC-GP assay may prE. faecalis, ultimately enhancing public health.
ovide diagnosticians with a more sensitive means of detecting vancomycin-resistant

Read the published article now

Rapid and sensitive detection of blaKPC in Klebsiella pneumoniae

Cara N. Wilder, Ph.D.

Klebsiella pneumoniae is a Gram-negative bacterium found within the mouth, skin, and intestines. Although this organism is a common inhabitant of the human microflora, it can behave as an opportunistic pathogen in immunologically compromised individuals, causing a variety of clinical diseases including pneumonia, thrombophlebitis, and septicemia. Current therapies for K. pneumoniae infection include treatment with β-lactam antibiotics such as third-generation cephalosporins, carbapenems, and penicillins.

Over the last decade, a number of K. pneumoniae strains exhibiting multidrug resistance have emerged in numerous healthcare settings, resulting in prolonged hospitalization and increased mortality. These strains were found to produce Klebsiella pneumoniae carbapenemase (KPC), which is a β-lactamase enzyme that confers resistance to all β-lactam antibiotics. More troubling was the discovery that KPC is encoded by the Tn₃-type transposon-localized gene, bla_KPC. Mobilization of this genetic element has permitted the diffusion of bla_KPC between various plasmids, allowing for inter-species dispersion via horizontal transfer. To date, plasmids harboring bla_KPC have been isolated among Enterobacteriaceae genera commonly found in the human microbiome, including Klebsiella pneumoniae, Enterobacter spp., and Escherichia coli. Regrettably, these strains are often not detectable through routine susceptibility screening and are easily disseminated, further contributing to escalating morbidity and mortality rates.

In order to control the spread of KPC strains, a rapid and sensitive diagnostic tool is necessary. In a recent report, Mosca et al. evaluated the performance of NucliSens EasyQKPC (bioMérieux, France), which is a new molecular assay designed to rapidly detect the presence of the bla_KPC gene via real-time nucleic acid sequenced-based amplification (NASBA™). In this study, 38 non-duplicate, carbapenem-resistant K. pneumoniae isolates were first analyzed using the modified Hodge test (MHT) and the carbapenemase inhibitor test, which are traditional culture-based methods often recommended for the detection of carbapenem-resistant strains. While all strains exhibited the production of KPC when examined by the carbapenemase inhibitor test, only 84% of the strains evaluated by MHT exhibited carbapenemase-production. In contrast, NucliSens EasyQKPC was able to detect the bla_KPC gene in each of the isolates evaluated. The accuracy of this assay was confirmed when each of the isolates tested positive for the presence of the gene following PCR analysis. Overall, NucliSens EasyQKPC provides a sensitive and reliable assay for the identification of the bla_KPC gene, allowing for the rapid detection of KPC strains in clinical samples.

Read the published article now

Use of bacteriotherapy to resolve Clostridium difficile infection

Clostridium difficile

Cara N. Wilder, Ph.D.

Antibiotic treatment of hospitalized patients poses a serious risk for the colonization of Clostridium difficile. Infection with this anaerobic, spore-forming bacterium is characterized by a wide spectrum of symptoms including diarrhea, fulminant pseudomembranous colitis, and death. Though treatment of C. difficile with antibiotics is often effective, a number of treated patients experience a relapse in infection following the cessation of antibiotic therapy. It is believed that these recurrent infections may be linked to a condition termed dysbiosis, which is characterized by a general imbalance of the intestinal microflora resulting from continuous antibiotic exposure.

In recent years, the use of a probiotic-based approach has been proposed as a promising therapy for the treatment of C. difficile infections. To determine the ideal combination of probiotic strains that both resolves C. difficile disease and restores a healthy intestinal microflora, Lawley et al. employed the use of a C. difficile murine infection model that parallels many aspects of human disease. In the study, the murine model was infected with an epidemic strain of C. difficile that was able to out-compete health-associated intestinal bacteria, allowing for the maintenance of dysbiosis. Following the establishment of infection, the group used fecal-transplantation as a model to identify a mixture of six phylogenetically-diverse bacteria that were able to trigger the expansion of health-associated intestinal microflora and resolve C. difficile infection within the mice. Overall, the results from this study highlight the therapeutic potential of probiotic bacteriotherapy in the treatment of C. difficile and other forms of dysbiosis.

Read the published article now

Preventing aspergillosis through immunization

Aspergillus fumigatus. Photo courtesy of
David Gregory and Debbie Marshall

Cara N. Wilder, Ph.D.

Over the last 20 years, Aspergillus fumigatus has become one of the most frequent causes of invasive fungal infection in immunologically compromised patients. This infection, termed aspergillosis, is associated with a wide spectrum of symptoms, including allergic reactions, organ failure, and lung infection. In most patients, A. fumigatus predominantly affects the lungs, resulting in an often fatal illness termed invasive pulmonary aspergillosis (IPA).

Current therapies for aspergillosis include treatment with antifungal drugs such as Amphotericin B or Triazole medications (Voriconazole, Posaconazole, Itraconazole). Unfortunately, these therapies have had limited success in treating IPA, and are often associated with serious toxicities. This is further compounded by the growing number A. fumigatus strains that have developed resistance against antifungal drugs, thus making the eradication of aspergillosis increasing more difficult. In response to these concerns, many research laboratories have focused their efforts on the development of new strategies targeted toward the prevention and treatment of such infections.

In one vaccine discovery program, Ito et al. used an immunochemical and mass spectrometric approach to identify an antigenic target for the development of a candidate vaccine that provides immunization against A. fumigatus. Following nasopulmonary inoculation of immunocompetent mice with viable A. fumigatus conida, Asp f 3 was identified as a potential antigenic target based on immunodominance during infection. Upon the analysis of this allergen, it was determined that subcutaneous immunization with full-length and truncated recombinant Asp f 3 offered protection against A. fumigatus infection. This was further confirmed following the examination of the lungs of vaccinated survivors, which were deemed free of hyphae and exhibited minimal infiltration of mononuclear cells. Overall, the findings from this study indicate that recombinant Asp f 3 is an effective immunogen and promising candidate for the development of a novel vaccine to prevent aspergillosis.



Read the published article now

Response of Campylobacter jejuni to Erythromycin Exposure

Campylobacter jejuni. Photo courtesy of Dr. Patricia Fields
and Dr. Collette Fitzgerald.

Cara N. Wilder, Ph.D.

Campylobacter jejuni is a Gram-negative, motile bacterium that is commonly present in the intestinal tract of both domestic and wild animals. In humans, C. jejuni causes a foodborne infection termed campylobacteriosis, which results in symptoms that range from mild enteritis to fever, headache, and bloody diarrhea. In some cases, Campylobacter infection has been associated with Guillain-Barré syndrome, which is a post-infection autoimmune disorder that damages nerve tissue.

Although most cases of campylobacteriosis are self-limiting, antibiotic treatment may be necessary for patients that are either immunologically compromised, or exhibit severe or persistent infection. The most common antimicrobial therapy used to treat campylobacteriosis is erythromycin, which is a macrolide antibiotic that inhibits bacterial protein translation. However, due the regular use of this antibiotic in animal production and veterinary medicine, an increasing number of C. jejuni isolates have become drug-resistant. In many of these strains, the mechanism of resistance is frequently conferred by target modification or through the expression of antibiotic efflux pumps.

Though the genetic basis of erythromycin resistance has been well-studied, the initial response and adaptive mechanisms directly following erythromycin exposure is not well understood. To analyze this, Xia et al. performed a competitive microarray hybridization study that examined the genome-wide transcriptional response of a sensitive and resistant strain of C. jejuni upon exposure to inhibitory and sub-inhibitory doses of erythromycin. Following treatment with erythromycin, the resistant strain of C. jejuni exhibited little to no differential gene expression. In contrast, a number of genes were differentially regulated in the sensitive strain, including the up-regulation of genes associated with motility, and the down-regulation of genes associated with energy production and conversion. Moreover, the inactivation of several differentially expressed genes appeared to negatively affect host colonization and the ability to tolerate high levels of oxygen. Overall, these results provide new insight into the adaptive response of C. jejuni to antibiotic treatment, and my help provide further understanding into the mechanisms underlying the emergence of antibiotic resistance.



 Read the published article now

Survival mechanisms of Burkholderia cepacia complex cells grown in biofilms

Burkholderia cepacia. Photo courtesy of Janice Haney Carr
and CDC

Cara N. Wilder, Ph.D.

The Burkholderia cepacia complex (Bcc) is a group of Gram-negative bacteria composed of 17 closely related species. Of these strains, Burkholderia cenocepacia is an opportunistic pathogen frequently associated with high rates of transmission and mortality among immune-compromised people, such as those suffering from cystic fibrosis. Unfortunately, infections caused by B. cenocepacia and other Bcc strains are very difficult to eradicate due to a variety of  intrinsic antibiotic-resistance mechanisms including the expression of multidrug efflux pumps, inducible β-lactamases, altered penicillin-binding proteins, and the ability to form biofilms.

In particular, biofilms are multicellular microbial communities that can form on various environmental, clinical, and abiotic surfaces. These groups of sessile cells are often more tolerant to antibiotics than free-living, planktonic cells due to decreased growth rates, differential gene expression, and reduced penetration of the biofilm. Thus, upon exposure to antibiotic therapies, a small subpopulation of cells within the biofilm is able to persist by entering a dormant multidrug-tolerant state. Following the removal of the antibiotic, these “persister cells” are then able to reestablish growth and create a new biofilm.

To elucidate the mechanisms behind the emergence of persister cells in Bcc biofilms, Acker et al. analyzed B. cenocepacia biofilms following treatment with Tobramycin, a bactericidal antibiotic known to induce the formation of harmful reactive oxygen species (ROS). Through the use of transcriptome analysis, flow cytometry, ROS-staining, and inhibitor studies, the group discovered that surviving persister cells were able to escape cell death through the down-regulation of the tricarboxylic acid (TCA) cycle, allowing cells to avoid ROS production, and through the activation of the glyoxylate shunt, which is an anaplerotic pathway of the TCA cycle. This finding may provide novel approaches for the treatment of Bcc biofilms as the glyoxylate shunt is absent in humans, and inhibition of this pathway prior to treatment with Tobramycin was found to decrease the number of persisters. Thus, this pathway may be an ideal target for combination therapy.

Read the published article now

 

Preventing Acinetobacter baumannii infection through active and passive immunization

Cara N. Wilder, Ph.D.

Multidrug-Resistance -- A growing concern throughout the world

Within the last two decades, multidrug-resistant strains have emerged as a common cause of drug-resistant infection throughout the world, resulting in prolonged hospitalizatin and high mortality rates. ATCC understands the danger and growing concern behind the spread of these strains, and we would like to help support your research in this field. For the several weeks, we will highlight various emerging multidrug-resistant strains, and some of the current research being performed with these superbugs. For more information, on these strains, subscribe to our eNewsletter or visit our website at www.atcc.org.

 

Preventing Acinetobacter baumannii infection through active and passive immunization

Acinetobacter baumannii is an opportunistic pathogen typically associated with a wide variety of complications, including pneumonia, localized tissue infections, septicemia, and death. This bacterium commonly infects individuals with a compromised immune system, and has become a predominant cause of infection in intensive care units, healthcare settings, and combat zones.


Within the last two decades, multidrug-resistant strains of A. baumannii have emerged as a common cause of drug-resistant infection throughout the world, resulting in prolonged hospitalization, extensive healthcare cost, and high mortality rates despite treatment. More troubling is the recent evolution of clinical variants that are pan-drug resistant, demonstrating resistance to every FDA-approved antibiotic. In response to these concerns, government agencies and research laboratories have focused their efforts on the development of new strategies targeted toward the prevention and treatment of such infections.




A CDC microbiologist working with Acinetobacter baumannii.
Photo courtesy of James Gathany and CDC.

In one vaccine discovery program, Luo et al. used a screening mechanism to identify an antigenic target for the development of a candidate vaccine that provided both active and passive immunization against A. baumannii. Following the intravenous infection of mice, OmpA was identified as a potential antigenic target based on humoral immunodominance during infection. Upon the analysis of this outer membrane protein, it was found that OmpA was highly conserved among numerous clinical isolates and demonstrated minimal homology with the human proteome. Additionally, vaccination of immune-compromised mice with an emulsification of recombinant OmpA and aluminum hydroxide adjuvant induced high titers of anti-OmpA antibodies, and demonstrated improved survival and reduced bacterial burden in intravenously infected mice. The activity of anti-OmpA antibodies was further confirmed through passive transfer studies, which recapitulated protection. Overall, the results from this study indicate that recombinant OmpA is an effective immunogen and promising candidate for the development of a novel vaccine to prevent A. baumannii infections.


Read the published article now

Impact of White-Nose Syndrome

Cara N. Wilder, Ph.D.

Photo provided by Dr. Winkler and

Dr. Sikes, CDC

Bats are an essential part of our ecosystem, providing valuable services including insect control, pollination, and seed dispersal for countless plant species. In the United States, each of the 45 indigenous bat species are insectivorous, predating on nocturnal insects that are often very damaging to commercial agriculture^1-4. For example, a single colony of big brown bats has been estimated to consume as many as 1.3 million agricultural pests yearly, significantly contributing to the disruption of insect population cycles and the preservation of commercial crops⁵. In fact, scientists throughout the United States estimate that bats are worth at least $3.7-$53 billion per annum in reduced pesticide use and crop damage^4,6.

Regrettably, bat populations throughout the world are in rapid decline due to the emergence and spread of Geomyces destructans. This fungal pathogen, which causes a fungal skin infection termed white-nose syndrome (WNS), has devastated populations of cave-hibernating bats throughout North America, resulting in bat declines exceeding 75%^7,8. Since its initial documentation in 2006, WNS is estimated to have killed over 6 million bats⁷.

Presently, numerous state and federal agencies, tribes, organizations, and individual researchers are working toward further understanding the dynamics and transmission of this G. destructans in the hopes of finding a novel method to prevent the further spread of this devastating disease. In an effort to aid research efforts related to WNS, ATCC now offers the fully-sequenced G. destructans, strain 20631-21, deposited by the USGS National Wildlife Health Center, and the associated genomic DNA. Sequencing for this strain has also been published by The Broad Institute.

Help save our bats by getting started on your research today!

• ATCC^® MYA-4855™ -- Geomyces destructans strain 20631-21
• ATCC^® MYA-4855D™ -- Genomic DNA from Geomyces destructans strain 20631-21

Register to view the ATCC Webinar featuring Dr. David, Blehert, head of diagnostic microbiology at the U.S. Geological Survey – National Wildlife Health Center (NWHC; Madison, WI).

References

1. Kalka, M. B., Smith, A. R. & Kalko, E. K. Bats limit arthropods and herbivory in a tropical forest. Science 320, 71, doi:10.1126/science.1153352 (2008).
2. Williams-Guillen, K., Perfecto, I. & Vandermeer, J. Bats limit insects in a neotropical agroforestry system. Science 320, 70, doi:10.1126/science.1152944 (2008).
3. Kunz, T. H., Braun de Torrez, E., Bauer, D., Lobova, T. & Fleming, T. H. Ecosystem services provided by bats. Annals of the New York Academy of Sciences 1223, 1-38, doi:10.1111/j.1749-6632.2011.06004.x (2011).
4. Boyles, J. G., Cryan, P. M., McCracken, G. F. & Kunz, T. H. Conservation. Economic importance of bats in agriculture. Science 332, 41-42, doi:10.1126/science.1201366 (2011).
5. Whitaker Jr., J. O. Food of the big brown bat Eptesicus fuscus from maternity colonies in Indiana and Illinois. Am. Midl. Nat. 134, 346-360 (1995).
6. International, B. C. All About Bats, <www.batcon.org>
7. A Coordinated Response to the Devastating Bat Disease, <http://whitenosesyndrome.org/>
8. Blehert, D. S. et al. Bat white-nose syndrome: an emerging fungal pathogen? Science 323, 227, doi:10.1126/science.1163874 (2009).

 

 

 

 

The Effect of Horizontal Gene Transfer on the Emergence of Multi-Drug Resistant Bacteria in Nosocomial Infections

Cara N. Wilder, Ph.D.

The discovery of antibiotics in the early twentieth century has revolutionized the treatment of infectious diseases. However in recent decades, the frequency of nosocomial infections caused by multidrug-resistant bacterial strains has steadily escalated worldwide, resulting in increased morbidity, mortality, and health-care expense^1-2. This phenomenon can be attributed to a combination of microbial evolution and clinical practices that enhance the transmission of multidrug-resistant strains, including the continuous overuse and misuse of antibiotics, the increased employment of invasive medical devices and procedures, and ineffectual infection control practices³. These selective pressures have required bacterial species to evolve an extraordinary gamut of mechanisms designed to counteract antibiotic function, including the production of antibiotic-modifying and -inactivating enzymes, efflux pumps, and genomic and ribosomal modifications of target sites^4-5.

Antibiotic resistance in bacterial strains can be achieved through either genetic mutation or by the acquisition of a laterally transmitted mobile genetic element harboring an antibiotic-resistance gene cassette⁶. This latter mechanism, termed horizontal gene transfer, can occur through cell contact-dependent DNA transfer (conjugation), the uptake of naked DNA from the surrounding environment (transformation), or by phage-dependent transfer of bacterial genetic elements (transduction). In particular, conjugation has been implicated in a vast number of reports of bacterial gene transfer in the environment, including the horizontal transfer of antibiotic resistance genes. It is predicted that this transfer system may be more predominant as the associated mobile genetic elements transferred are of a very wide host range.

Studies have shown that horizontal gene transfer can occur in both intra- and inter-species populations, with foreign DNA representing up to one-fifth of any given bacterial genome⁷. This natural selection process has been particularly prominent in the emergence of deadly multidrug-resistant strains such methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae^8-10. Numerous surveillance studies have identified the emergence of these resistant strains as a major trend in nosocomial infections among high-risk patients, and are attributed to more than 70% of these infections^11-13.

Overall, the worldwide clonal spread of multidrug-resistant organisms within and between hospitals has fueled the extensive rise in resistance, severely limiting therapeutic options and substantially increasing the incidence of incurable infection. Unless this rise in multidrug-resistance can be reversed, the effectiveness and utility of antibiotics may be a matter of years or decades, effectively plunging infection control toward a pre-antibiotic era¹⁴.

Prominent Strains of Multidrug-Resistant Bacteria

Extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae – Gram-negative bacilli within the Enterobacteriaceae family that produce extended-spectrum β-lactamase. An example of this includes strains of Escherichia coli and Klebsiella pneumoniae that produce New Delhi metallo-β-lactamase-1 (NDM-1). NDM-1 is a carbapenemase β-lactamase that inactivates carbapenem antibiotics as well as a wide range of other antibiotics through the destruction of the β-lactam ring, thus deactivating the antibacterial properties.

ATCC^® NDM-1 Strains:

·         Klebsiella pneumoniae (ATCC^® BAA-2146™)

·         Enterobacter cloacae (ATCC^® BAA-2468™)

·         Escherichia coli (ATCC^® BAA-2469™)

·         Klebsiella pneumoniae subsp. pneumoniae (ATCC^® BAA-2470™)

·         Klebsiella pneumoniae subsp. pneumoniae (ATCC^® BAA-2472™)

Methicillin-resistant Staphylococcus aureus (MRSA) – Any strain of Staphylococcus aureus that has developed resistance to β-lactam antibiotics, including methicillin. These strains harbor the SCCmec genomic island containing the mecA resistance gene, which encodes a penicillin binding protein (PBP) that does not bind methicillin or other β-lactam antibiotics. This enables the PBP to catalyze the transpeptidase reaction, consequently completing cell wall synthesis in the presence of antibiotics.

ATCC^® MRSA Strains:

·         Methicillin-Resistant Staphyloccus aureus Panel organized by SCCmec type (MP-2™)

·         Methicillin-Resistant Staphyloccus aureus Panel organized by Pulse-field type (MP-3™)

Vancomycin-resistant enterococci (VRE) – Bacterial strains of the genus Enterococcus that are resistant to the antibiotic vancomycin. This phenotype is possible through the presence of various resistance genes, including vanA, vanB, vanC, vanD, vanE, and vanF. Resistance involves the alteration of vancomycin target sequences: the terminal amino acid residues of NAM/NAG-peptide subunits. Modification of these sequences decreases the binding affinity of vancomycin, allowing antibiotic resistance.

 

ATCC^® VRE Strains:

·         Vancomycin-Resistant Enterococci Panel (MP-1™)

References

1.     Harbarth S, et al. Control of multiply resistant cocci: do international comparisons help? Lancet Infect. Dis. 1: 251-261, 2001.

2.     Blondeau JM, Tillotson GS. Antimicrobial susceptibility patterns of respiratory pathogens – a global perspective. Semin. Respir. Infect. 15: 195-207, 2000.

3.     Jones RN, Phaller MA. Bacterial resistance; a worldwide problem. Diagn. Microbial. Infect. Dis. 31: 379-388, 1998.

4.     Levy SB. Active efflux, a common mechanism for biocide and antibiotic resistance. J. Appl. Microbial. Suppl. S1: 65S-71S, 2002.

5.     Gold HS, Moellering RC Jr. Antimicrobial-drug resistance. N. Engl. J. Med. 335: 1445-1453, 1996.

6.     Normark BH, Normark S. Evolution and spread of antibiotic resistance. J. Intern. Med. 252: 91-106, 2002.

7.     Davison J. Genetic exchange between bacteria in the environment. Plasmid 42(2): 73-91, 1999.

8.     Wielders CCL, et al. mecA Gene is Widely Disseminated in Staphylociccus aureus Population. J. Clin. Microbiol. 40(11): 3970-3975, 2002.

9.     Palmer KL, et al. Horizontal Gene Transfer and the Genomics of Enterococcal Antibiotic Resistance. Curr. Opin. Microbial. 13(5): 632-639, 2010.

10.   Bush K, Fisher JF. Epidemiological expansion, structural studies, and clinical challenges of new β-lactamases from Gram-negative bacterial. Annu. Rev. microbial. 65: 455-478, 2011.

11.   Wiener J, et al. Multiple antibiotic-resistant Klebsiella and Escherichia coli in nursing homes. JAMA 281: 517-523, 1999.

12.   Dzidic S, Bedekovic V. Horizontal gene transfer-emerging multidrug resistance in hospital bacteria. Acta. Pharmacol. Sin. 24(6): 519-526, 2003.

13.   Muto CA, et al. SHEA Guideline for Preventing Nosocomial Transmission of Multidrug-Resistant Strains of Staphylococcus aureus and Enterococcus. Infection Control and Hospital Epidemiology 24(5): 362-386, 2003.

14.   Wellington EMH, et al. The role of the natural environment in the emergence of antibiotic resistance in Gram-negative bacteria. Lancet Infec. Dis. 13(2): 155-165, 2013.