Laura A. McDermott

National Survey on the Susceptibility of Bacteroides fragilis Group: Report and Analysis of Trends for 1997-2000

The results of a multicenter US survey using the National Committee for Clinical Laboratory Standards currently recommended methodology for measuring in vitro susceptibility of 2673 isolates of Bacteroides fragilis group species were compared from 1997 to 2000. The test panel consisted of 14 antibiotics: 3 carbapenems, 3 beta-lactam-beta-lactamase inhibitors, 3 cephamycins, 2 fluoroquinolones, clindamycin, chloramphenicol, and metronidazole. Declines in the geometric mean minimum inhibitory concentrations were seen with imipenem, meropenem, ampicillin-sulbactam, and the cephamycins. Increased geometric means were observed with the fluoroquinolones and were usually accompanied by an increase in resistance rates. Bacteroides distasonis shows the highest resistance rates among beta-lactam antibiotics, whereas Bacteroides vulgatus shows the highest resistance levels among fluoroquinolones. B. fragilis shows the lowest resistance rates for all antibiotics. All strains were susceptible to chloramphenicol and metronidazole concentrations <8 microgram/mL. The data underscore the need for species identification and continued surveillance to monitor resistance patterns.

Candidaemia associated with decreased in vitro fluconazole susceptibility: is Candida speciation predictive of the susceptibility pattern?

BACKGROUND Candidaemia is often treated with fluconazole in the absence of susceptibility testing. We examined factors associated with candidaemia caused by Candida isolates with reduced susceptibility to fluconazole. METHODS We identified consecutive episodes of candidaemia at two hospitals from 2001 to 2007. Species identification followed CLSI methodology and fluconazole susceptibility was determined by Etest or broth microdilution. Susceptibility to fluconazole was defined as: full susceptibility (MIC < or = 8 mg/L); and reduced susceptibility (MIC > or = 32 mg/L). Complete resistance was defined as an MIC > 32 mg/L. RESULTS Of 243 episodes of candidaemia, 190 (78%) were fully susceptible to fluconazole and 45 (19%) had reduced susceptibility (of which 27 were fully resistant). Of Candida krusei and Candida glabrata isolates, 100% and 51%, respectively, had reduced susceptibility. Despite the small proportion of Candida albicans (8%), Candida tropicalis (4%) and Candida parapsilosis (4%) with reduced fluconazole susceptibility, these species composed 36% of the reduced-susceptibility group and 48% of the fully resistant group. In multivariate analysis, independent factors associated with reduced fluconazole susceptibility included male sex [odds ratio (OR) 3.2, P < 0.01], chronic lung disease (OR 2.7, P = 0.01), the presence of a central vascular catheter (OR 4.0, P < 0.01) and prior exposure to antifungal agents (OR 2.2, P = 0.04). CONCLUSIONS A significant proportion of candidaemia with reduced fluconazole susceptibility may be caused by C. albicans, C. tropicalis and C. parapsilosis, species usually considered fully susceptible to fluconazole. Thus, identification of these species may not be predictive of fluconazole susceptibility. Other factors that are associated with reduced fluconazole susceptibility may help clinicians choose adequate empirical anti-Candida therapy.

In vitro activities of newer quinolones against bacteroides group organisms.

ABSTRACT The activities of BMS-284576, clinafloxacin, moxifloxacin, sitafloxacin, trovafloxacin, imipenem, cefoxitin, and clindamycin against 589 Bacteroides fragilis group isolates were determined. The activity of BMS-284576 was comparable to that of trovafloxacin. Sitafloxacin and clinafloxacin were the most active quinolones, and moxifloxacin was the least active. B. fragilis was the most susceptible of the species, and Bacteroides vulgatus was the most resistant. Association of specific antibiotic resistance with Bacteroides species was noted for all quinolones.

Activity of Ceftolozane-Tazobactam against a Broad Spectrum of Recent Clinical Anaerobic Isolates

ABSTRACT We evaluated in vitro activity of ceftolozane-tazobactam (TOL-TAZ), formerly CXA-201, against recent clinical anaerobic isolates with emphasis on the Bacteroides fragilis group. Ceftolozane-tazobactam showed good activity against B. fragilis species and intermediate to limited activity against other species of Bacteroides. Ceftolozane-tazobactam showed very good activity against Prevotella spp., Fusobacterium spp., and Propionibacterium spp., varying activities against Gram-positive cocci, and limited activity against Clostridium spp.

In Vitro Activities of Doripenem, a New Broad-Spectrum Carbapenem, against Recently Collected Clinical Anaerobic Isolates, with Emphasis on the Bacteroides fragilis Group

ABSTRACT Doripenem was evaluated against 527 recent clinical isolates, i.e., 404 Bacteroides fragilis isolates and 123 gram-positive anaerobe isolates. Against B. fragilis, doripenem was as active as imipenem, meropenem, and piperacillin-tazobactam and more active than ertapenem or ampicillin-sulbactam. Doripenem was active against isolates resistant to ertapenem, ampicillin-sulbactam, cefoxitin, clindamycin, and moxifloxacin. All of the gram-positive isolates tested were susceptible to doripenem.

In Vitro Activity of Ceftaroline against a Broad Spectrum of Recent Clinical Anaerobic Isolates

ABSTRACT The in vitro activity of ceftaroline was compared with those of ceftriaxone, clindamycin, imipenem, metronidazole, moxifloxacin, tigecycline, and vancomycin against 514 clinical anaerobic isolates using Clinical and Laboratory Standards Institute (CLSI) standard methodology. Ceftaroline demonstrated good to excellent activity against Gram-positive anaerobic pathogens and limited activity against Gram-negative pathogens, particularly Bacteroides fragilis group isolates.

Comparative In Vitro Activities of Clinafloxacin and Trovafloxacin against 1,000 Isolates of Bacteroides fragilis Group: Effect of the Medium on Test Results

ABSTRACT The in vitro antibacterial activities of clinafloxacin, trovafloxacin, ciprofloxacin, and cefoxitin against 1,000 clinical isolates of Bacteroides fragilis group were compared by agar dilution in brucella blood agar (BBA) and Wilkins Chalgren agar (WCA). Significantly higher geometric mean MICs for the three quinolones and cefoxitin (P < 0.001) were obtained in BBA than in WCA. Regardless of medium, clinafloxacin was slightly more active than trovafloxacin. The activity of clinafloxacin and trovafloxacin was greater than that of cefoxitin against B. distasonis, B. ovatus, and B. thetaiotaomicron but lower against B. vulgatus. High cross resistance between trovafloxacin and clinafloxacin was observed.

Comparison of the semisolid agar antifungal susceptibility test with the NCCLS M38-P broth microdilution test for screening of filamentous fungi.

ABSTRACT Antifungal susceptibility testing of pathogenic molds is being developed. A simple screening semisolid agar antifungal susceptibility (SAAS) test accurately measures susceptibilities of yeasts. The performance of the SAAS screening test for filamentous fungi was assessed by comparing MICs of four antifungals (amphotericin B [AMB], AMB lipid complex [ABEL], itraconazole [ITZ], and posaconazole [POS]) for 54 clinical mold isolates with the results of the National Committee for Clinical Laboratory Standards (NCCLS) proposed broth microdilution method (M38-P). The SAAS test utilized inocula stabbed into tubes of 0.5% semisolid heart infusion agar. In both tests MICs were read after incubation at 35°C for 48 h. The isolates tested were Aspergillus fumigatus, Aspergillus niger, Aspergillus flavus, other Aspergillus spp., Fusarium spp., Penicillium sp., Mucor sp., Scedosporium prolificans, Trichophyton sp., and an unidentified dematiaceous mold. Concordance of test results was determined as the percent agreement of MICs ± 1 dilution. The overall agreement between the tests for each drug was as follows: AMB, 94%; ABEL, 83%; ITZ, 94%; POS, 94%. For the Aspergillus spp., all but one were susceptible to ITZ by SAAS test; all were susceptible to POS (MIC range, 0.25 to 4 μg/ml). Three of six non-Aspergillus molds that were resistant to AMB and ABEL by SAAS (MIC ≥ 2 μg/ml) were also resistant by the NCCLS test. The SAAS test compared favorably to the NCCLS broth microdilution test for molds, and most of the clinical isolates tested were susceptible to all four drugs.

In Vitro Evaluation of the Activity of Imipenem-Relebactam against 451 Recent Clinical Isolates of Bacteroides Group and Related Species

ABSTRACT We evaluated the in vitro activity of imipenem-relebactam (imipenem-MK7655) against 451 recent clinical isolates within the Bacteroides group and related species. Relebactam did not enhance or inhibit the activity of imipenem against Bacteroides fragilis or other Bacteroides species. No synergistic or antagonistic effect was observed. The MICs of imipenem-relebactam were equal to or within one dilution of the MICs of these isolates to imipenem.

Differences in the Molecular Epidemiology and Antibiotic Susceptibility of Clostridium difficile Isolates in Pediatric and Adult Patients.

ABSTRACT The rising incidence of Clostridium difficile infections (CDIs) in adults is partly related to the global spread of fluoroquinolone-resistant strains, namely, BI/NAP1/027. Although CDIs are also increasingly diagnosed in children, BI/NAP1/027 is relatively uncommon in children. Little is known about the antibiotic susceptibility of pediatric CDI isolates. C. difficile was cultured from tcdB-positive stools collected from children diagnosed with CDI between December 2012 and December 2013 at an academic childrens hospital. CDI isolates were grouped by restriction endonuclease analysis (REA). MICs were measured by agar dilution method for 7 antibiotics. Susceptibility breakpoints were based on guidelines from CLSI and/or the European Committee on Antimicrobial Susceptibility Testing (EUCAST). MICs and REA groupings of C. difficile isolates from 74 adult patients (29 isolates underwent REA) from a temporally and geographically similar adult cohort were compared to those of pediatric isolates. Among 122 pediatric and 74 adult isolates, respectively, the rates of resistance were as follows: metronidazole, 0% and 0%; vancomycin, 0% and 8% (P = 0.003); rifaximin, 1.6% and 6.7% (P = 0.11); clindamycin, 18.9% and 25.3% (P = 0.29); and moxifloxacin, 2.5% and 36% (P = <0.0001). Only 1 of 122 (0.8%) BI/NAP1/027 isolates was identified among the children, compared to 9 of 29 (31%) isolates identified among the adults (P = <0.0001). The 3 moxifloxacin-resistant pediatric isolates were of REA groups BI and CF and a nonspecific group. The 2 rifaximin-resistant pediatric isolates were of REA groups DH and Y. The 21 clindamycin-resistant pediatric isolates were distributed among 9 REA groups (groups A, CF, DH, G, L, M, and Y and 2 unique nonspecific REA groups). These data suggest that a diverse array of relatively antibiotic-susceptible C. difficile strains predominate in a cohort of children with CDI compared to adults.