John R. Warren

Emerging Incidence of Enterococcus faecium among Hospital Isolates (1993 to 2002)

ABSTRACT Historically, most clinical microbiology laboratories report that 80 to 90% of enterococci are Enterococcus faecalis, whereas E. faecium accounts for 5 to 10% of isolates. At our medical center from 1993 to 2002, we evaluated the percentages of E. faecium among all enterococcal isolates and the percentages of E. faecium isolates that were vancomycin resistant. Over this 10-year period, the percentage of enterococci that were identified as E. faecium increased from 12.7 to 22.2% (P < 0.001) and the proportion of E. faecium that was vancomycin resistant increased from 28.9 to 72.4% (P < 0.001). Both the percentage of E. faecium among the enterococci and the proportion of vancomycin-resistant E. faecium increased significantly over this 10-year period.

In Vitro Activities of Various Antimicrobials Alone and in Combination with Tigecycline against Carbapenem-Intermediate or -Resistant Acinetobacter baumannii

ABSTRACT The activities of tigecycline alone and in combination with other antimicrobials are not well defined for carbapenem-intermediate or -resistant Acinetobacter baumannii (CIRA). Pharmacodynamic activity is even less well defined when clinically achievable serum concentrations are considered. Antimicrobial susceptibility testing of clinical CIRA isolates from 2001 to 2005 was performed by broth or agar dilution, as appropriate. Tigecycline concentrations were serially increased in time-kill studies with a representative of the most prevalent carbapenem-resistant clone (strain AA557; imipenem MIC, 64 mg/liter). The in vitro susceptibility of the strain was tested by time-kill studies in duplicate against the average free serum steady-state concentrations of tigecycline alone and in combination with various antimicrobials. Ninety-three CIRA isolates were tested and were found to have the following antimicrobial susceptibility profiles: tigecycline, MIC50 of 1 mg/liter and MIC90 of 2 mg/liter; minocycline, MIC50 of 0.5 mg/liter and MIC90 of 8 mg/liter; doxycycline, MIC50 of 2 mg/liter and MIC90 of ≥32 mg/liter; ampicillin-sulbactam, MIC50 of 48 mg/liter and MIC90 of 96 mg/liter; ciprofloxacin, MIC50 of ≥16 mg/liter and MIC90 of ≥16 mg/liter; rifampin, MIC50 of 4 mg/liter and MIC90 of 8 mg/liter; polymyxin B, MIC50 of 1 mg/liter and MIC90 of 1 mg/liter; amikacin, MIC50 of 32 mg/liter and MIC90 of ≥32 mg/liter; meropenem, MIC50 of 16 mg/liter and MIC90 of ≥128 mg/liter; and imipenem, MIC50 of 4 mg/liter and MIC90 of 64 mg/liter. Among the tetracyclines, the isolates were more susceptible to tigecycline than minocycline and doxycycline, according to FDA breakpoints (95%, 88%, and 71% of the isolates were susceptible to tigecycline, minocycline, and doxycycline, respectively). Concentration escalation studies with tigecycline revealed a maximal killing effect near the MIC, with no additional extent or rate of killing at concentrations 2× to 4× the MIC for tigecycline. Time-kill studies demonstrated indifference for tigecycline in combination with the antimicrobials tested. Polymyxin B, minocycline, and tigecycline are the most active antimicrobials in vitro against CIRA. Concentration escalation studies demonstrate that tigecycline may need to approach concentrations higher than those currently achieved in the bloodstream to adequately treat CIRA bloodstream infections. Future studies should evaluate these findings in vivo.

Fatal Case of Endocarditis Due to Weissella confusa

ABSTRACT This is the first reported case of endocarditis due to the Lactobacillus-like vancomycin-resistant gram-positive bacillus Weissella confusa. Full identification and susceptibility testing of Lactobacillus-like organisms recovered in blood culture should be performed for patients with clinical presentations that suggest endocarditis.

Risk Factors and Outcomes Associated With Non–Enterococcus faecalis, Non–Enterococcus faecium Enterococcal Bacteremia

OBJECTIVES To compare risk factors, clinical features, and outcomes in patients with Enterococcus avium, Enterococcus casseliflavus, Enterococcus durans, Enterococcus gallinarum, and Enterococcus mundtii bacteremia (cases) with those in patients with Enterococcus faecalis bacteremia (controls). DESIGN A retrospective case-control study. SETTING A 725-bed, university-affiliated, academic medical center. PATIENTS The clinical microbiology database at Northwestern Memorial Hospital from January 1994 to May 2003 was searched to identify cases; each case was matched to one control on the basis of date of admission. RESULTS Thirty-three cases were identified and matched with 33 controls. The mean duration of hospital stay was longer (29.7 vs 17.2 days; P = .03) and the mean time to acquisition of bacteremia was greater (16.5 vs 6.3 days; P = .003) for cases than controls. Cases were more likely to have underlying hematologic malignancies (P < .001), to have been treated with corticosteroids (P = .02), and to be neutropenic (P = .003). Controls were more likely to have an indwelling bladder catheter (P = .01), and cases were more likely to have the gastrointestinal tract as a source of infection (P = .007) and to have concurrent cholangitis (P = .002). There were no differences in severity of illness or in mortality rates. CONCLUSIONS Compared with patients with E. faecalis bacteremia, patients with non-E. faecalis, non-Enterococcus faecium enterococcal bacteremia were more likely to have a hematologic malignancy, prior treatment with corticosteroids, neutropenia, and cholangitis; longer duration of hospital stay was also identified as a clinical feature. However, non-E. faecalis, non-E. faecium species are not associated with any differences in mortality.

Catheter-related bloodstream infections caused by rapidly growing nontuberculous mycobacteria : a case series including rare species

Rapidly growing nontuberculous mycobacteria (RGMs) are responsible for a variety of clinical syndromes in humans including catheter-related blood stream infections (CRBSIs). Recently, we identified a cluster of RGM-associated CRBSI at our institution. We describe the epidemiologic and clinical patterns associated with these infections. We conducted a retrospective single-center review of RGM CRBSI between May 2004 and June 2005. RGMs isolated from blood cultures of 6 patients included Mycobacterium mucogenicum (2), Mycobacterium fortuitum (2), and the rare RGM species, Mycobacterium neoaurum (1) and Mycobacterium septicum (1). All of the patients had a long-term intravascular catheter (mean duration, 6.5 months). Bacteremia was resolved in all patients after catheter removal and appropriate antibiotics. None of the patients suffered a relapse of RGM CRBSI, and all survived to 1 year. RGMs are causative pathogens in both immunosuppressed and immunocompetent individuals with long-term intravascular catheters and blood stream infections. Recent trends at our center suggest that infections with these pathogens are rising.

Multidrug-resistant Pseudomonas aeruginosa cholangitis after endoscopic retrograde cholangiopancreatography: failure of routine endoscope cultures to prevent an outbreak.

BACKGROUND Nosocomial infections due to medical devices are of increasing concern to infection control practitioners. Attempts to prevent such infections have included surveillance cultures of endoscopes and bronchoscopes. In July 2002, the infectious disease consultation service was asked to see three patients with sepsis due to multidrug-resistant Pseudomonas aeruginosa after endoscopic retrograde cholangiopancreatography (ERCP). OBJECTIVE To describe an outbreak of multidrug-resistant P. aeruginosa sepsis after ERCP at an institution that performs routine surveillance cultures of endoscopes. DESIGN A traditional outbreak investigation supplemented by pulsed-field gel electrophoresis (PFGE) was undertaken, including a case-control analysis based on the hypothesis that all infected individuals had their ERCP performed with the same endoscope. SETTING A tertiary-care academic medical center. RESULTS The case-control analysis confirmed the hypothesis that undergoing ERCP with the implicated endoscope was associated with a culture positive for Pseudomonas (P = .01). The available strains were identical by PFGE. This outbreak occurred despite a negative surveillance culture of the implicated endoscope 1 month earlier. CONCLUSIONS Infectious morbidity can occur after endoscopy despite negative surveillance cultures. The practice of routine endoscope cultures does not prevent device-related infectious morbidity.

Evaluation of the Vitek 2 System for Rapid Identification of Clinical Isolates of Gram-Negative Bacilli and Members of the Family Streptococcaceae

Abstract. Accuracy of the Vitek 2 automated system (bioMérieux Vitek, USA) for rapid identification of bacteria was evaluated using a collection of 858 epidemiologically unrelated gram-negative and 99 gram-positive clinical isolates. Isolates were tested after subculturing to ensure purity. Conventional agar-based biochemical tests (Steers replicator) were used as a reference method of identification. Gram-negative bacteria were identified to the species level with 95.3% accuracy by the system (Enterobacteriaceae, 95.9%; and non-Enterobacteriaceae, 92.5%), and gram-positive isolates with 72% accuracy. Although Vitek 2 identified routine clinical isolates of gram-negative bacilli and Enterococcus faecalis and Enterococcus faecium reliably, rapidly, and reproducibly, improvement is required in the identification of less common species of enterococci and viridans group streptococci.

Stimulation of Epithelial Hyperplasia in Rat Urinary Bladder by Escherichia Coli Cystitis

Using heterotopically transplanted rat urinary bladder, experiments were conducted to develop a reproducible animal model of bacterial cystitis-associated urothelial hyperplasia without calculus formation, and to elucidate which bacterial component(s) might induce urothelial hyperplasia. Bladder instillation of live Escherichia coli (E. coli) resulted in persistent infection and inflammation and also diffuse urothelial hyperplasia. Instillation of killed E. coli also induced diffuse hyperplasia. Hyperplastic changes regressed following withdrawal of the killed E. coli treatment. Urothelial hyperplasia was also induced by repeated instillation of protein-rich lipopolysaccharide (LPS), the endotoxin derived from gram-negative bacterial wall component, but not by protein-free LPS. A finding common to bladders showing hyperplasia was the infiltration of neutrophils into intercellular spaces of the urothelium. We conclude that urothelial hyperplasia is induced by E. coli cystitis, that LPS plays a significant role in the hyperplastic response, and that neutrophils may mediate the response.

Comparison of Testing Methods for Detection of Decreased Linezolid Susceptibility Due to G2576T Mutation of the 23S rRNA Gene in Enterococcus faecium and Enterococcus faecalis

ABSTRACT E-test, Vitek 2, MicroScan, agar dilution, and disk diffusion were compared for detection of decreased linezolid susceptibility due to 23S rRNA gene G2576T mutation among 32 clinical Enterococcus strains initially reported as intermediate or resistant by E-test alone or Vitek 2 confirmed by E-test. Agar and broth dilution methods were in concordance with PCR detection of the mutation, and disk diffusion was somewhat less sensitive but equally specific.

Microheterogeneity of staphylococcal enterotoxin B

Abstract Four components have been demonstrated in staphylococcal enterotoxin B by isoelectric focusing in polyacrylamide gels. In a typical preparation their relative concentrations from the most to least cathodic were 6, 56, 31 and 7%. The components were not stable conformers nor were the differences in isoionic points due to bound ligand. A comparison of the measured isoionic points with values calculated for varying numbers of excess basic groups indicated that each component differed from the succeeding one by a single charge. Sequential conversion of the components from the more to the less alkaline forms was obtained by exposure to pH 9.0 at 37 °C. The data gave an excellent fit for two consecutive first-order reacions in whicc the specific reaction rate constants were nearly identical. The reaction was much slower at pH 7.3 and 37 °C and no change at all was observed over a period of 32 days at pH 9.0 and 1 °C. Amide hydrolysis is the mechanism for these conversions, but the rate is too slow to account for the appearance of four components during the comparatively short period of bacterial fermentation. It is suggested, therfore, that only the most cathodic component is synthesized by the organism and that this is converted to the other forms enzymatically.