Low Prevalence of carbapenem-resistant Enterobacteriaceae among wounded military personnel.

Multidrug-resistant organisms (MDROs) are a global health problem that affect both civilian and military populations. Among wounded warriors, MDROs further complicate the care of trauma-related infections, resulting in extended duration of hospitalization, as well as increased morbidity and mortality. During the wars in Iraq and Afghanistan, extended spectrum ß-lactamase-producing Enterobacteriaceae were frequently isolated from wounded warriors. The potential emergence of difficult-to-treat carbapenem-resistant Enterobacteriaceae represented a serious challenge for clinicians. We examined carbapenem-resistant Enterobacteriaceae prevalence among wounded military personnel over a 6-year period (2009-2015). Among 4090 Enterobacteriaceae isolates collected, 16 (0.4%) were carbapenem-resistant, of which the majority was Enterobacter aerogenes (44%) followed by Klebsiella pneumoniae (37%), and Escherichia coli (19%). Five isolates (31%) collected from 2 patients were carbapenemase-producers with one associated with an infection. All 5 carbapenemase-producing isolates were resistant to all tested carbapenems and each carried one carbapenemase gene (4 with blaKPC-3 and 1 with blaNDM-1). Overall, although a large number of Enterobacteriaceae isolates were collected, only a small proportion was carbapenem-resistant and data indicate a lack of a cluster. Due to these limited numbers, it is difficult to make any conclusions regarding the association between carbapenem resistance, antibiotic exposure, and clinical outcomes.

In Vitro activity of Manuka Honey and polyhexamethylene biguanide on filamentous fungi and toxicity to human cell lines.

Soft-tissue invasive fungal infections are increasingly recognized as significant entities directly contributing to morbidity and mortality. They complicate clinical care, requiring aggressive surgical debridement and systemic antifungal therapy. To evaluate new topical approaches to therapy, we examined the antifungal activity and cytotoxicity of Manuka Honey (MH) and polyhexamethylene biguanide (PHMB). The activities of multiple concentrations of MH (40%, 60%, 80%) and PHMB (0.01%, 0.04%, 0.1%) against 13 clinical mould isolates were evaluated using a time-kill assay between 5 min and 24 h. Concentrations were selected to represent current clinical use. Cell viability was examined in parallel for human epidermal keratinocytes, dermal fibroblasts and osteoblasts, allowing determination of the 50% viability (LD50) concentration. Antifungal activity of both agents correlated more closely with exposure time than concentration. Exophiala and Fusarium growth was completely suppressed at 5 min for all PHMB concentrations, and at 12 and 6 h, respectively, for all MH concentrations. Only Lichtheimia had persistent growth to both agents at 24 h. Viability assays displayed concentration-and time-dependent toxicity for PHMB. For MH, exposure time predicted cytotoxicity only when all cell types were analyzed in aggregate. This study demonstrates that MH and PHMB possess primarily time-dependent antifungal activity, but also exert in vitro toxicity on human cells which may limit clinical use. Further research is needed to determine ideal treatment strategies to optimize antifungal activity against moulds while limiting cytotoxicity against host tissues in vivo.

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.

BACKGROUND: The 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. METHODS: We 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. RESULTS: Using 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. CONCLUSION: PCR/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.

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.

Antimicrobial resistance acquisition after international travel in U.S. travelers.

BACKGROUND: Prior studies have shown an increase in multidrug-resistant (MDR) E. coli colonization from two percent in U.S.-based to 11 % in deployed, healthy military personnel. It is unclear if colonization with MDR organisms occurs through deployment exposures or risks related to routine overseas travel. This study prospectively evaluates rates and risk factors associated with MDR gram-negative bacterial and methicillin-resistant S. aureus (MRSA) colonization after international travel. METHODS: Participants traveled internationally for five or more days. Pre- and post-travel, colonizing bacteria from oropharyngeal, nares, groin, and peri-rectal (PR) areas were collected using BD CultureSwab™ MaxV(+). Identification and susceptibilities were done utilizing the BD Phoenix™ Automated Microbiology System. Non-MDR pre- and post-travel MDR bacteria within a subject were compared by pulsed-field gel electrophoresis (PFGE). A questionnaire solicited demographics and potential risk factors for MDR acquisition. RESULTS: Of 58 participants, 41 % were male and median age was 64 years. Pre- and post-travel swabs were obtained a median of ten and seven days before and after travel, respectively. Itineraries included 18 participants traveling to the Caribbean and Central America, 17 to Asia, 16 to Africa, 5 to Europe, 4 to South and North America. Seventeen of 22 travelers used atovaquone/proguanil for malaria prophylaxis. The only MDR organism isolated was extended-spectrum ß-lactamase (ESBL)-producing E. coli in five (9 %) participants post-travel (all PR and unrelated by PFGE). There were no statistically significant associations between exposure risks and new ESBL-producing E.coli colonization. Of 36 participants colonized with E. coli pre- and post-travel, new resistance was detected: TMP/SMX in 42 % of isolates (p < 0.01), tetracycline in 44 % (p < 0.01), and ampicillin-sulbactam in 33 % (p = 0.09). No participants were colonized with MRSA pre- or post-travel. CONCLUSION: Consistent with prior studies, new antimicrobial resistance was noted in colonizing E. coli after international travel. Nine percent of participants acquired new strains of ESBL-producing E.coli without identified risks.

Phenotypic and genotypic changes over time and across facilities of serial colonizing and infecting Escherichia coli isolates recovered from injured service members.

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 ß-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.

Biofilms and persistent wound infections in United States military trauma patients: a case-control analysis.

BACKGROUND: Complex traumatic injuries sustained by military personnel, particularly when involving extremities, often result in infectious complications and substantial morbidity. One factor that may further impair patient recovery is the persistence of infections. Surface-attached microbial communities, known as biofilms, may play a role in hindering the management of infections; however, clinical data associating biofilm formation with persistent or chronic infections are lacking. Therefore, we evaluated the production of bacterial biofilms as a potential risk factor for persistent infections among wounded military personnel. METHODS: Bacterial isolates and clinical data from military personnel with deployment-related injuries were collected through the Trauma Infectious Disease Outcomes Study. The study population consisted of patients with diagnosed skin and soft-tissue infections. Cases (wounds with bacterial isolates of the same organism collected 14 days apart) were compared to controls (wounds with non-recurrent bacterial isolates), which were matched by organism and infectious disease syndrome. Potential risk factors for persistent infections, including biofilm formation, were examined in a univariate analysis. Data are expressed as odds ratios (OR; 95% confidence interval [CI]). RESULTS: On a per infected wound basis, 35 cases (representing 25 patients) and 69 controls (representing 60 patients) were identified. Eight patients with multiple wounds were utilized as both cases and controls. Overall, 235 bacterial isolates were tested for biofilm formation in the case-control analysis. Biofilm formation was significantly associated with infection persistence (OR: 29.49; CI: 6.24-infinity) in a univariate analysis. Multidrug resistance (OR: 5.62; CI: 1.02-56.92), packed red blood cell transfusion requirements within the first 24 hours (OR: 1.02; CI: 1.01-1.04), operating room visits prior to and on the date of infection diagnosis (OR: 2.05; CI: 1.09-4.28), anatomical location of infected wound (OR: 5.47; CI: 1.65-23.39), and occurrence of polymicrobial infections (OR: 69.71; CI: 15.39-infinity) were also significant risk factors for persistent infections. CONCLUSIONS: We found that biofilm production by clinical strains is significantly associated with the persistence of wound infections. However, the statistical power of the analysis was limited due to the small sample size, precluding a multivariate analysis. Further data are needed to confirm biofilm formation as a risk factor for persistent wound infections.

Resistance patterns and clinical significance of Candida colonization and infection in combat-related injured patients from iraq and afghanistan.

BACKGROUND: Penetrating wounds with environmental contamination are associated with a range of infectious complications, including fungus. This is the first study to examine the epidemiology, resistance patterns, and outcomes of Candida infections and colonization in United States military patients injured in Iraq and Afghanistan. METHODS: Clinical information associated with initial unique and serial Candida isolates collected from patients (June 2009-October 2013) through the Trauma Infectious Disease Outcomes Study (TIDOS) was evaluated. Susceptibilities were performed using Sensititre YeastOne (YO-9) plates and interpreted by Clinical Laboratory and Standards Institute (CLSI) and adjusted-European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. RESULTS: The analysis included 127 patients with 131 unique Candida isolates, of which 102 were Candida albicans and 29 non-albicans Candida spp. Overall, 99% of patients were male with a median age of 23 and an injury severity score of 22. Injuries were primarily due to blasts (77%) and sustained among personnel serving in Afghanistan (89%). There was a median of 7 days from injury to Candida isolation, and 74 isolates were associated with infection. In the multivariate analysis, non-albicans Candida spp were associated with prior antifungal exposure, blood isolates, and wound isolates (P < .01). Nonsusceptibility by CLSI and EUCAST criteria was associated with non-albicans Candida spp (P < .05). Patients with Candida isolation had a 7.1% mortality rate, compared with 1.4% from the overall TIDOS population. CONCLUSIONS: Candida isolation from patients with penetrating war injuries may identify a population at higher risk for death. Prospective studies are needed to determine whether targeted antifungals and surgical management will affect this mortality rate.

Staphylococcus aureus colonization of healthy military service members in the United States and Afghanistan.

BACKGROUND: Staphylococcus aureus [methicillin-resistant and methicillin-susceptible (MRSA/MSSA)] is a leading cause of infections in military personnel, but there are limited data regarding baseline colonization of individuals while deployed. We conducted a pilot study to screen non-deployed and deployed healthy military service members for MRSA/MSSA colonization at various anatomic sites and assessed isolates for molecular differences. METHODS: Colonization point-prevalence of 101 military personnel in the US and 100 in Afghanistan was determined by swabbing 7 anatomic sites. US-based individuals had received no antibiotics within 30 days, and Afghanistan-deployed personnel were taking doxycycline for malaria prophylaxis. Isolates underwent identification and testing for antimicrobial resistance, virulence factors, and pulsed-field type (PFT). RESULTS: 4 individuals in the US (4 isolates- 3 oropharynx, 1 perirectal) and 4 in Afghanistan (6 isolates- 2 oropharynx, 2 nare, 1 hand, 1 foot) were colonized with MRSA. Among US-based personnel, 3 had USA300 (1 PVL+) and 1 USA700. Among Afghanistan-based personnel, 1 had USA300 (PVL+), 1 USA800 and 2 USA1000. MSSA was present in 40 (71 isolates-25 oropharynx, 15 nare) of the US-based and 32 (65 isolates- 16 oropharynx, 24 nare) of the Afghanistan-based individuals. 56 (79%) US and 41(63%) Afghanistan-based individuals had MSSA isolates recovered from extra-nare sites. The most common MSSA PFTs were USA200 (9 isolates) in the US and USA800 (7 isolates) in Afghanistan. MRSA/MSSA isolates were susceptible to doxycycline in all but 3 personnel (1 US, 2 Afghanistan; all were MSSA isolates that carried tetM). CONCLUSION: MRSA and MSSA colonization of military personnel was not associated with deployment status or doxycycline exposure. Higher S. aureus oropharynx colonization rates were observed and may warrant changes in decolonization practices.

Detection of methicillin-resistant and methicillin-susceptible Staphylococcus aureus colonization of healthy military personnel by traditional culture, PCR, and mass spectrometry.

BACKGROUND: Methicillin-resistant (MRSA) and methicillin-susceptible (MSSA) Staphylococcus aureus colonization is associated with increased rates of infection. Rapid and reliable detection methods are needed to identify colonization of nares and extra-nare sites, particularly given recent reports of oropharynx-only colonization. Detection methods for MRSA/MSSA colonization include culture, PCR, and novel methods such as PCR/electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). METHODS: We evaluated 101 healthy military members for S. aureus colonization in the nares, oropharynx, axilla, and groin, using CHROMagar S. aureus medium and Xpert SA Nasal Complete PCR for MRSA/MSSA detection. The same subjects were screened in the nares, oropharynx, and groin using PCR/ESI-TOF-MS. RESULTS: By culture, 3 subjects were MRSA-colonized (all oropharynx) and 34 subjects were MSSA-colonized (all 4 sites). PCR detected oropharyngeal MRSA in 2 subjects, which correlated with culture findings. By PCR, 47 subjects were MSSA-colonized (all 4 sites); however, 43 axillary samples were invalid, 39 of which were associated with deodorant/anti-perspirant use (93%, p < 0.01). By PCR/ESI-TOF-MS, 4 subjects were MRSA-colonized, 2 in the nares and 2 in the oropharynx; however, neither of these correlated with positive MRSA cultures. Twenty-eight subjects had MSSA by PCR/ESI-TOF-MS, and 41 were found to have possible MRSA (S. aureus with mecA and coagulase-negative Staphylococcus (CoNS)). CONCLUSION: The overall 3% MRSA colonization rate is consistent with historical reports, but the oropharynx-only colonization supports more recent findings. In addition, the use of deodorant/anti-perspirant invalidated axillary PCR samples, limiting its utility. Defining MRSA positivity by PCR/ESI-TOF-MS is complicated by co-colonization of S. aureus with CoNS, which can also carry mecA.

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

BACKGROUND: The 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. METHODS: GNB 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. RESULTS: The 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. CONCLUSION: Healthy 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.

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.

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.

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 (bla(OXA-23-like), bla(OXA-24-like), bla(OXA-58-like), and bla(OXA-51-like)) and metallo-ß-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. bla(OXA-23-like) and bla(OXA-24-like) were the primary resistance genes found. bla(OXA-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.

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

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.

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.

Aminoglycoside resistance and susceptibility testing errors in Acinetobacter baumannii-calcoaceticus complex.

Antimicrobial resistance is depleting the pharmacopeia of agents clinically useful against Gram-negative bacilli. As the number of active agents diminishes, accurate susceptibility testing becomes critical. We studied the susceptibilities of 107 isolates of the Acinetobacter baumannii-calcoaceticus complex to amikacin, gentamicin, and tobramycin using disk diffusion, Etest, as well as the Phoenix, Vitek 2, and MicroScan automated systems, and compared the results to those obtained by broth microdilution. Genes encoding aminoglycoside-modifying enzymes (AMEs) were detected by multiplex PCR, and clonal relationships were determined by pulsed-field gel electrophoresis. Tobramycin was the most active aminoglycoside (27.1% of isolates were susceptible). Disk diffusion and Etest tended to be more accurate than the Vitek 2, Phoenix, and MicroScan automated systems; but errors were noted with all methods. The Vitek 2 instrument incorrectly reported that more than one-third of the isolates were susceptible to amikacin (a very major error). Isolates were polyclonal, with 26 distinct strains, and carried multiple AME genes unrelated to the strain type. The presence of the ant(2")-Ia gene was statistically associated with resistance to each aminoglycoside. The AME genotype accounted for the resistance profile observed in a minority of isolates, suggesting the involvement of multiple resistance mechanisms. Hospital pharmacy records indicated the preferential use of amikacin over other aminoglycosides in the burn intensive care unit, where aminoglycoside resistance is prevalent. The resistance in that unit did not correlate with a predominant strain, AME genotype, or total annual aminoglycoside consumption. Susceptibility to tobramycin increased, even though susceptible isolates carried AME genotypes predicting the inactivation of tobramycin. Determination of the relative contribution of multiple concurrent resistance mechanisms may improve our understanding of aminoglycoside resistance in the Acinetobacter baumannii-calcoaceticus complex.

Prospective study of bacterial and viral contamination of exercise equipment.

OBJECTIVE: Transmission of bacterial and viral pathogens is known to occur by hand contact with fomites. Exercise equipment in public facilities may serve as such fomites. It is not known whether equipment disinfection might reduce microorganism colonization. We performed studies to address these issues. DESIGN: Observational study of bacterial and viral culture results from hand-contact surfaces of exercise equipment, pre-exercise and postexercise; prospective study of viral culture results before and after intervention with disinfection solution. SETTING: Two fitness centers in a military community. INTERVENTION: One week trial of twice-a-day equipment disinfection. MAIN OUTCOME MEASURES: Type and number of bacteria and type of viruses present on equipment before and after exercise; prevalence of viral culture positivity on equipment before and after intervention. RESULTS: Bacterial cultures of body contact surfaces on equipment revealed benign bacterial species (coagulase-negative staphylococci, diphtheroids, and so forth) but no pathogenic bacteria whether obtained pre-exercise or postexercise, or whether from aerobic versus weight training equipment. Viral cultures revealed the presence of viruses (generally rhinoviruses) on 63 of 100 (63%) hand-contact surfaces of equipment. Weight equipment was significantly more often contaminated than aerobic equipment (73% vs. 51%; P = 0.026). Disinfection of equipment did not lower the prevalence of virus isolation (48% positive before cleaning; 86% positive after cleaning). CONCLUSIONS: There is little risk of exposure to pathogenic bacteria on exercise equipment. Such equipment may commonly serve as fomites for the transmission of viruses. These data do not suggest that disinfection of exercise equipment will offer significant protective effects against virus exposure.