Presumptive identification of Candida species other than C. albicans, C. krusei, and C. tropicalis with the chromogenic medium CHROMagar Candida

BACKGROUND: CHROMagar Candida (CaC) is increasingly being reported as a medium used to differentiate Candida albicans from non-albicans Candida (NAC) species. Rapid identification of NAC can assist the clinician in selecting appropriate antifungal therapy. CaC is a differential chromogenic medium designed to identify C. albicans, C. krusei, and C. tropicalis based on colony color and morphology. Some reports have proposed that CaC can also reliably identify C. dubliniensis and C. glabrata. METHODS: We evaluated the usefulness of CaC in the identification of C. dubliniensis, C. famata, C. firmetaria, C. glabrata, C. guilliermondii, C. inconspicua, C. kefyr, C. lipolytica, C. lusitaniae, C. norvegensis, C. parapsilosis, and C. rugosa. RESULTS: Most NAC produced colonies that were shades of pink, lavender, or ivory. Several isolates of C. firmetaria and all C. inconspicua produced colonies difficult to differentiate from C. krusei. Most C. rugosa isolates produced unique colonies with morphology like C. krusei except in a light blue-green color. C. glabrata isolates produced small dark violet colonies that could be differentiated from the pink and lavender colors produced by other species. All seventeen isolates of C. dubliniensis produced green colonies similar to those produced by C. albicans. CONCLUSION: C. glabrata and C. rugosa appear distinguishable from other species using CaC. Some NAC, including C. firmetaria and C. inconspicua, could be confused with C. krusei using this medium

Persistence of Pigment Production by Yeast Isolates Grown on CHROMagar Candida Medium

We evaluated the persistence of pigmentation in yeast isolates grown on the chromogenic medium CHROMagar Candida over 7 days. Candida, Cryptococcus, and Trichosporon isolates were inoculated alone or mixed onto duplicate sets of plates and incubated at 30 and 35°C. Candida albicans and Candida krusei were readily identified throughout the reading period, but Candida glabrata was difficult to differentiate from other species until the 3- or 4-day time point. Candida tropicalis produced colonies similar to those of rare Cryptococcus and Trichosporon species, and mixed cultures were often difficult to identify as such

Enterobacter cloacae infection characteristics and outcomes in battlefield trauma patients.

Enterobacter cloacae is a Gram-negative rod with multidrug-resistant potential due to chromosomally-induced AmpC β-lactamase. We evaluated characteristics, antibiotic utilization, and outcomes associated with battlefield-related E. cloacae infections (2009-2014). Single initial and serial E. cloacae isolates (≥24 hours from initial isolate from any site) associated with a clinical infection were examined. Susceptibility profiles of initial isolates in the serial isolation group were contrasted against last isolate recovered. Characteristics of 112 patients with E. cloacae infections (63 [56%] with single initial isolation; 49 [44%] with serial isolation) were compared to 509 patients with bacterial infections not attributed to E. cloacae. E. cloacae patients sustained more blast trauma (78%) compared to non-E. cloacae infections patients (75%; p<0.001); however, injury severity scores were comparable (median of 34.5 and 33, respectively; p = 0.334). Patients with E. cloacae infections had greater shock indices (median 1.07 vs 0.92; p = 0.005) and required more initial blood products (15 vs. 14 units; p = 0.032) compared to patients with non-E. cloacae infections. Although E. cloacae patients had less intensive care unit admissions (80% vs. 90% with non-E. cloacae infection patients; p = 0.007), they did have more operating room visits (5 vs. 4; p = 0.001), longer duration of antibiotic therapy (43.5 vs. 34 days; p<0.001), and lengthier hospitalizations (57 vs. 44 days; p<0.001). Patients with serial E. cloacae had isolation of infecting isolates sooner than patients with single initial E. cloacae (median of 5 vs. 8 days post-injury; p = 0.046); however, outcomes were not significantly different between the groups. Statistically significant resistance to individual antibiotics did not develop between initial and last isolates in the serial isolation group. Despite current combat care and surgical prophylaxis guidelines recommending upfront provision of AmpC-inducing antibiotics, clinical outcomes did not differ nor did significant antibiotic resistance develop in patients who experienced serial isolation of E. cloacae versus single initial isolation

Tetracycline Susceptibility Testing and Resistance Genes in Isolates of Acinetobacter baumannii-Acinetobacter calcoaceticus Complex from a U.S. Military Hospital▿

Infections with multidrug-resistant Acinetobacter baumannii-Acinetobacter calcoaceticus complex bacteria complicate the care of U.S. military personnel and civilians worldwide. One hundred thirty-three isolates from 89 patients at our facility during 2006 and 2007 were tested by disk diffusion, Etest, and broth microdilution for susceptibility to tetracycline, doxycycline, minocycline, and tigecycline. Minocycline was the most active in vitro, with 90% of the isolates tested susceptible. Susceptibilities varied significantly with the testing method. The acquired tetracycline resistance genes tetA, tetB, and tetA(39) were present in the isolates

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 (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

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