Background. Bloodstream infections due to extended-spectrum b-lactamase (ESBL)-producing Enterobacteriaceae have been associated with increased hospital costs, length of stay, and patient mortality. However, the role of routine inpatient surveillance for ESBL colonization in predicting related infection is unclear.Methods. From 2000 through 2005, we screened 17,872 patients hospitalized in designated high-risk units for rectal colonization with vancomycin-resistant enterococci and ESBL-producing Enterobacteriaceae using a selective culture medium. In patients with a bloodstream infection due to ESBL-producing Enterobacteriaceae (ESBL-BI) during the study period, surveillance results were evaluated for evidence of antecedent ESBL-producing Enterobacteriaceae colonization.Results. The rate of ESBL-producing Enterobacteriaceae colonization doubled during the 6-year study period, increasing from 1.33% of high-risk patients in 2000 to 3.21% in 2005. Among patients with ESBL-producing Enterobacteriaceae colonization, 49.6% also carried vancomycin-resistant enterococci. The number of ESBL-BIs increased 14-fold in 5 years, from 9 cases in 2001 to 40 cases in 2005. Of 413 patients colonized with ESBLproducing Enterobacteriaceae, 35 (8.5%) developed a subsequent ESBL-BI. Of concern, more than one-half of all ESBL-BIs occurred in patients who were not screened. These 56 patients received a diagnosis of ESBL-BI in the emergency department, when hospitalized in low-risk medical units, or at transfer from an acute or long-term health care facility.Conclusions. Colonization with ESBL-producing Enterobacteriaceae is increasing at a rapid rate, and routine rectal surveillance for ESBL-producing Enterobacteriaceae may have clinical implications. However, in our experience, over one-half of patients with an ESBL-BI did not undergo screening through our current surveillance measures. As a result, targeted screening for ESBL-producing Enterobacteriaceae among additional patient populations may be integral to future ESBL-BI prevention and management efforts.

Bloodstream infections with Acinetobacter baumannii are occurring with increasing frequency, resulting in significant morbidity and mortality. The attributable mortality rate for infections ranges from 8 to 43% (11, 26), and A. baumannii continues to emerge as a health care-associated pathogen (35). Carbapenems, tetracyclines, and polymyxins are the most frequently active drugs against such strains (3,12,35). However, carbapenem-intermediate or -resistant A. baumannii (CIRA) strains are becoming increasingly prevalent (27), with few therapeutic options for the treatment of infections with this organism.Among the tetracyclines, tigecycline is less active than minocycline against Acinetobacter spp. on a weight-per-weight basis (14); however, intravenous minocycline is not currently available in the United States. Therefore, tigecycline is likely the tetracycline of choice for the treatment of infections caused by CIRA. Prior investigations reveal that tigecycline is bacteriostatic against CIRA (24), but drug combinations with tigecycline at the achievable serum concentrations have not been sufficiently evaluated in vitro.This study sought to determine the change in the activity of tigecycline against CIRA with increasing concentrations of drug. Additionally, we explored the activities of tigecycline in combination with other antimicrobial agents with activity against CIRA, including ampicillin-sulbactam, ciprofloxacin, levofloxacin, rifampin, polymyxin B, amikacin, meropenem, and imipenem. All combinations were modeled from average, steady-state, free, and serum concentrations. Finally, we describe the predictive value of the antimicrobial activities of doxycycline and minocycline for the antimicrobial activity of tigecycline. MATERIALS AND METHODSBacterial strains. Isolates of A. baumannii complex were obtained from clinical specimens submitted to the clinical microbiology laboratory at Northwestern Memorial Hospital (Chicago, IL). One isolate per patient per calendar year was obtained, in accordance with the criteria of the CLSI (formerly the NCCLS) (21).

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.Linezolid provides high rates of clinical cure and microbiological success in complicated infections due to Enterococcus spp., including vancomycin-resistant Enterococcus faecium (3). However, the emergence of resistance during linezolid treatment has been reported for clinical strains of Enterococcus (1,2,7,9,12,13). Clinical resistance to linezolid is associated with a G2576T mutation in domain V of 23S rRNA genes of Enterococcus, and the level of linezolid resistance is directly related to the number of 23S rRNA genes containing this mutation (11,15). Both laboratory and clinical strains of E. faecium with linezolid MICs of 4 g/ml have been shown to carry the G2576T mutation (10,14). Accurate detection by susceptibility testing methods of decreased susceptibility due to G2576T mutation in one or two genes is necessary since this can be a prelude to higher levels of linezolid resistance associated with extensive use of the antibiotic (14).In this study we compared the performance of five different susceptibility testing methods, E-test, disk diffusion, Vitek 2 system, MicroScan WalkAway broth microdilution, and agar dilution, for the detection of decreased linezolid susceptibility of Enterococcus faecalis and E. faecium due to presence of the G2576T mutation.Strain selection. collected during this period. All strains were identified to the species level by using the Vitek 2 system. When the Vitek 2 system failed to identify the strains, identification was obtained by manual biochemical reactions (8). The strains were recovered from blood, urine, respiratory specimens, and various body fluids and tissues. Three well-characterized strains of linezolid-resistant E. faecium (strains 38-13, 45-24, and 38-42) and one strain of lineozlidresistant E. faecalis (strain 41-31) were kindly provided by Paul Schreckenberger of the Loyola University Medical Center, Maywood, IL.Susceptibility testing. E-test linezolid strips with a concentration gradient corresponding to 0.016 to 256 g/ml were utilized with Mueller-Hinton agar as described by the manufacturer (AB Biodisk, Piscataway, N.J.). E-test MICs were determined as 80% growth inhibition, and measured E-test MICs were rounded up to the next twofold dilution for the categorical interpretation. Disk diffusion testing was performed with 30-g linezolid disks (BBL, Becton Dickinson) using Clinical and Laboratory Standards Institute (CLSI; formerly National Committee for Clinical Laboratory Standards) standards (4), and 80% growth inhibition was utilized to measure diameters of growth inhibition zones. Agar dilution testing (0.5...

Drug resistance is emerging in many important microbial pathogens, including Candida albicans. We performed fungal susceptibility tests with archived isolates obtained from 1984 through 1993 and fresh clinical isolates obtained from 1994 through 1997 by testing their susceptibilities to fluconazole, ketoconazole, and miconazole and compared the results to the rate of fluconazole use. All isolates recovered prior to 1993 were susceptible to fluconazole. Within 3 years of widespread azole use, we detected resistance to all agents in this class. In order to assess the current prevalence of resistant isolates in our hematologic malignancy and transplant patients, we obtained rectal swabs from hospitalized, non-AIDS, immunocompromised patients between June 1995 and January 1996. The swabs were inoculated onto sheep’s blood agar plates containing 10 μg of vancomycin and 20 μg of gentamicin/ml of agar. One hundred one yeasts were recovered from 97 patients and were tested for their susceptibilities to amphotericin B, fluconazole, flucytosine, ketoconazole, and miconazole. The susceptibility pattern was then compared to those for all clinical isolates obtained throughout the medical center. The antifungal drug histories for each patient were also assessed. The yeasts from this surveillance study were at least as susceptible as the overall hospital strains. There did not appear to be a direct linkage between prior receipt of antifungal agent therapy and carriage of a new, drug-resistant isolate. Increased resistance to newer antifungal agents has occurred at our medical center, but it is not focal to any high-risk patient population that we studied. Monitoring of susceptibility to antifungal agents appears to be necessary for optimizing clinical therapeutic decision making.

Nine selected isolates of Candida albicans were tested for their susceptibilities to amphotericin B and fluconazole by using three methods to assess the effect of incubation time and buffer concentration. By using a microdilution method with 0.0165 M 3-(N-morpholino)propanesulfonic acid (MOPS) and a 24-h incubation time, all of the isolates were found to be susceptible to amphotericin B and fluconazole. After 48 h of incubation, all isolates were still susceptible to amphotericin B. Seven of the nine isolates were resistant to fluconazole, and for the remaining two isolates, MICs increased by fourfold or more but the isolates remained susceptible (MIC, <10 g/ml). The nine isolates, along with three control strains, were further tested against amphotericin B and fluconazole by a standard broth macrodilution method with both 0.165 and 0.0165 M MOPS. The susceptibility results for fluconazole by the broth macrodilution method with the lower MOPS concentration correlated with the results of the 24-h broth microdilution method for determination of susceptibility or resistance in eight of nine tests and with the results of the 48 h broth microdilution method in three of nine tests. The results of the broth macrodilution method with the standard MOPS concentration did not correlate with any of the results obtained by the 24-h broth microdilution but correlated with results of seven of nine tests by the 48-h broth microdilution method. All nine test strains appeared to be susceptible when they were examined by a flow cytometric method. For clinical yeast susceptibility testing in microdilution panels, the 0.0165 M MOPS concentration combined with 24 h of incubation appeared to be the method of choice. The lower MOPS concentration may also be a useful modification to the tentative broth macrodilution method of the National Committee for Clinical Laboratory Standards. Use of the higher buffer concentration or longer incubation time may lead to false in vitro resistance for agents like fluconazole.