Wendy C. Zera

Multidrug-resistant gram-negative bacteria colonization of healthy US military personnel in the US and Afghanistan

BackgroundThe US military has seen steady increases in multidrug-resistant (MDR) gram-negative bacteria (GNB) infections in casualties from Iraq and Afghanistan. This study evaluates the prevalence of MDR GNB colonization in US military personnel.MethodsGNB colonization surveillance of healthy, asymptomatic military personnel (101 in the US and 100 in Afghanistan) was performed by swabbing 7 anatomical sites. US-based personnel had received no antibiotics within 30 days of specimen collection, and Afghanistan-based personnel were receiving doxycycline for malaria chemoprophylaxis at time of specimen collection. Isolates underwent genotypic and phenotypic characterization.ResultsThe only colonizing MDR GNB recovered in both populations was Escherichia coli (p=0.01), which was seen in 2% of US-based personnel (all perirectal) and 11% of Afghanistan-based personnel (10 perirectal, 1 foot+groin). Individuals with higher off-base exposures in Afghanistan did not show a difference in overall GNB colonization or MDR E. coli colonization, compared with those with limited off-base exposures.ConclusionHealthy US- and Afghanistan-based military personnel have community onset-MDR E. coli colonization, with Afghanistan-based personnel showing a 5.5-fold higher prevalence. The association of doxycycline prophylaxis or other exposures with antimicrobial resistance and increased rates of MDR E. coli colonization needs further evaluation.

Carbapenem Susceptibility Testing Errors Using Three Automated Systems, Disk Diffusion, Etest, and Broth Microdilution and Carbapenem Resistance Genes in Isolates of Acinetobacter baumannii-calcoaceticus Complex

ABSTRACT The Acinetobacter baumannii-calcoaceticus complex (ABC) is associated with increasing carbapenem resistance, necessitating accurate resistance testing to maximize therapeutic options. We determined the accuracy of carbapenem antimicrobial susceptibility tests for ABC isolates and surveyed them for genetic determinants of carbapenem resistance. A total of 107 single-patient ABC isolates from blood and wound infections from 2006 to 2008 were evaluated. MICs of imipenem, meropenem, and doripenem determined by broth microdilution (BMD) were compared to results obtained by disk diffusion, Etest, and automated methods (the MicroScan, Phoenix, and Vitek 2 systems). Discordant results were categorized as very major errors (VME), major errors (ME), and minor errors (mE). DNA sequences encoding OXA beta-lactamase enzymes (blaOXA-23-like, blaOXA-24-like, blaOXA-58-like, and blaOXA-51-like) and metallo-β-lactamases (MBLs) (IMP, VIM, and SIM1) were identified by PCR, as was the KPC2 carbapenemase gene. Imipenem was more active than meropenem and doripenem. The percentage of susceptibility was 37.4% for imipenem, 35.5% for meropenem, and 3.7% for doripenem. Manual methods were more accurate than automated methods. blaOXA-23-like and blaOXA-24-like were the primary resistance genes found. blaOXA-58-like, MBLs, and KPC2 were not present. Both automated testing and manual testing for susceptibility to doripenem were very inaccurate, with VME rates ranging between 2.8 and 30.8%. International variability in carbapenem breakpoints and the absence of CLSI breakpoints for doripenem present a challenge in susceptibility testing.

Methicillin-Resistant Staphylococcus aureus in Wound Cultures Recovered from a Combat Support Hospital in Iraq

BACKGROUND Staphylococcus aureus infections complicate care of combat-related injuries and can independently result in skin and soft-tissue infections during deployments or training. Community-associated methicillin-resistant S. aureus (CA-MRSA) strains seem to produce severe disease but retain susceptibility to many oral antimicrobials. This study characterizes 84 MRSA isolates recovered from wound cultures at a combat support hospital in Iraq. METHODS MRSA strains recovered from December 2007 through March 2009 were analyzed. Antimicrobial resistance testing was determined by broth microdilution and the BD Phoenix Automated Microbiology System. The genotypic pattern was analyzed by pulsed-field gel electrophoresis and polymerase chain reaction identification of resistance and virulence genes. RESULTS No MRSA isolates from wound cultures were resistant to vancomycin. The most active oral antistaphylococcal agents were tetracycline (95% susceptibility), trimethoprim-sulfamethoxazole (94%), and clindamycin (94%). Of agents not typically recommended as monotherapy, 98% of isolates were susceptible to rifampin, 91% to moxifloxacin, and 60% to levofloxacin. The most common pulsed-field type (PFT) was USA300 (79%). The typical staphylococcal cassette chromosome mec IV elements carrying the CA-MRSA resistance genes were present in 88% of the isolates. Panton-Valentine leukocidin virulence genes were identified in 88% of isolates, including 100% of PFT USA300. The virulence gene associated with an arginine catabolic mobile element was present in 75% of isolates, including 94% of PFT USA300. CONCLUSION This study is the first genotypic and phenotypic characterization of CA-MRSA recovered from wound cultures in a deployed combat hospital. The pattern noted was similar to that seen in soldiers stationed in the United States.

Phenotypic and Genotypic Changes over Time and across Facilities of Serial Colonizing and Infecting Escherichia coli Isolates Recovered from Injured Service Members

ABSTRACT Escherichia coli is the most common colonizing and infecting organism isolated from U.S. service members injured during deployment. Our objective was to evaluate the phenotypic and genotypic changes of infecting and colonizing E. coli organisms over time and across facilities to better understand their transmission patterns. E. coli isolates were collected via surveillance cultures and infection workups from U.S. military personnel injured during deployment (June 2009 to May 2011). The isolates underwent antimicrobial susceptibility testing, pulsed-field gel electrophoresis, and multiplex PCR for phylotyping to determine their resistance profiles and clonality. A total of 343 colonizing and 136 infecting E. coli isolates were analyzed, of which 197 (57%) and 109 (80%) isolates, respectively, produced extended-spectrum β-lactamases (ESBL). Phylogroup A was predominant among both colonizing (38%) and infecting isolates (43%). Although 188 unique pulsed-field types (PFTs) were identified from the colonizing isolates, and 54 PFTs were identified from the infecting isolates, there was a lack of PFT overlap between study years, combat zones, and military treatment facilities. On a per-subject basis, 26% and 32% of the patients with serial colonizing isolates and 10% and 21% with serial infecting isolates acquired changes in their phylogroup and PFT profiles, respectively, over time. The production of ESBL remained high over time and across facilities, with no substantial changes in antimicrobial susceptibilities. Overall, our results demonstrated an array of genotypic and phenotypic differences for the isolates without large clonal clusters; however, the same PFTs were occasionally observed in the colonizing and infecting isolates, suggesting that the source of infections may be endogenous host organisms.

Epidemiology and antimicrobial susceptibilities of wound isolates of obligate anaerobes from combat casualties.

Data from recent conflicts related to war wounds and obligate anaerobes are limited. We define the epidemiology and antimicrobial susceptibility of obligate anaerobes from Iraq and Afghanistan casualties (6/2009-12/2013), as well as their association with clinical outcomes. Susceptibility against eleven antibiotics (7 classes) was tested. Overall, 59 patients had 119 obligate anaerobes identified (83 were first isolates). Obligate anaerobes were isolated 7-13 days post-injury, primarily from lower extremity wounds (43%), and were largely Bacteroides spp. (42%) and Clostridium spp. (19%). Patients with pelvic wounds were more likely to have Bacteroides spp. and concomitant resistant gram-negative aerobes. Seventy-three percent of isolates were resistant to ≥1 antimicrobials. Bacteroides spp. demonstrated the most resistance (16% of first isolates). Patients with resistant isolates had similar outcomes to those with susceptible strains. Serial recovery of isolates occurred in 15% of patients and was significantly associated with isolation of Bacteroides spp., along with resistant gram-negative aerobes.

Resistance Patterns and Clinical Significance of Candida Colonization and Infection in Combat-Related Injured Patients From Iraq and Afghanistan

Among combat-injured patients from Iraq and Afghanistan, 5% had Candida spp. isolated from wounds. The crude mortality rate of 7.1% was similar to invasive mold infections, and may serve as a marker of those at higher risk for death.

Effect of HMG-CoA reductase inhibitors on antimicrobial susceptibilities for Gram-Negative rods

Epidemiologic evidence suggests a beneficial effect of HMG‐CoA reductase inhibitors (statins) in sepsis, and in‐vitro data exist for antimicrobial activity of statins against some bacteria and fungi. We examined whether statin exposure at physiologic concentrations enhances activity of selected antimicrobials against Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli. Broth microdilution was performed with and without dose‐ranging concentrations of lovastatin, fluvastatin, atorvastatin, pravastatin and simvastatin. No effects on antimicrobial activity were demonstrated.

The use of PCR/Electrospray Ionization-Time-of-Flight-Mass Spectrometry (PCR/ESI-TOF-MS) to detect bacterial and fungal colonization in healthy military service members

BackgroundThe role of microbial colonization in disease is complex. Novel molecular tools to detect colonization offer theoretical improvements over traditional methods. We evaluated PCR/Electrospray Ionization-Time-of-Flight-Mass Spectrometry (PCR/ESI-TOF-MS) as a screening tool to study colonization of healthy military service members.MethodsWe assessed 101 healthy Soldiers using PCR/ESI-TOF-MS on nares, oropharynx, and groin specimens for the presence of gram-positive and gram-negative bacteria (GNB), fungi, and antibiotic resistance genes. A second set of swabs was processed by traditional culture, followed by identification using the BD Phoenix automated system; comparison between PCR/ESI-TOF-MS and culture was carried out only for GNB.ResultsUsing PCR/ESI-TOF-MS, at least one colonizing organism was found on each individual: mean (SD) number of organisms per subject of 11.8(2.8). The mean number of organisms in the nares, groin and oropharynx was 3.8(1.3), 3.8(1.4) and 4.2(2), respectively. The most commonly detected organisms were aerobic gram-positive bacteria: primarily coagulase-negative Staphylococcus (101 subjects: 341 organisms), Streptococcus pneumoniae (54 subjects: 57 organisms), Staphylococcus aureus (58 subjects: 80 organisms) and Nocardia asteroides (45 subjects: 50 organisms). The mecA gene was found in 96 subjects. The most commonly found GNB was Haemophilus influenzae (20 subjects: 21 organisms) and the most common anaerobe was Propionibacterium acnes (59 subjects). Saccharomyces species (30 subjects) were the most common fungi detected. Only one GNB (nares E. coli) was identified in the same subject by both diagnostic systems.ConclusionPCR/ESI-TOF-MS detected common colonizing organisms and identified more typically-virulent bacteria in asymptomatic, healthy adults. PCR/ESI-TOF-MS appears to be a useful method for detecting bacterial and fungal organisms, but further clinical correlation and validation studies are needed.

Lack of doxycycline antimalarial prophylaxis impact on Staphylococcus aureus tetracycline resistance

There is concern that susceptibility of Staphylococcus aureus to tetracyclines may decrease due to use of antimalarial prophylaxis (doxycycline). We examined characteristics related to tetracycline resistance, including doxycycline exposure, in S. aureus isolates collected via admission surveillance swabs and inpatient clinical cultures from United States military personnel injured during deployment (June 2009-January 2012). Tetracycline class resistance was determined using antimicrobial susceptibility testing. The first S. aureus isolate from 168 patients were analyzed, of which 38 (23%) isolates were resistant to tetracyclines (class). Tetracycline-resistant isolates had a higher proportion of resistance to clindamycin (P=0.019) compared to susceptible isolates. There was no significant difference in tetracycline resistance between isolates collected from patients with and without antimalarial prophylaxis; however, significantly more isolates had tet(M) resistance genes in the doxycycline exposure group (P=0.031). Despite 55% of the patients receiving doxycycline as antimalarial prophylaxis, there was no association with resistance to tetracyclines.

Oral antibiotics for infections due to multidrug-resistant Gram-negative organisms

Abstract We determined minimum inhibitory concentrations of rifampicin, nitrofurantoin, amoxicillin–clavulanic acid, and cefdinir, plus a combination of amoxicillin–clavulanic acid and cefdinir by broth microdilution for mainly wound isolates of Escherichia coli and Klebsiella pneumoniae. E. coli and K. pneumoniae susceptibilities increased by combining amoxicillin–clavulanic acid and cefdinir.