Susceptibility testing of anaerobic bacteria: evaluation of the redesigned (Version 96) bioMérieux ATB ANA device.

We compared the susceptibility results for 200 clinical anaerobes with nine antibiotics obtained by using a new ATB ANA (bioMérieux) device against those obtained by the National Committee for Clinical Laboratory Standards (NCCLS) standard agar dilution method. For better evaluation of the device, we added some resistant Bacteroides fragilis group strains from our own collection: 3, 6, and 12 strains that were resistant to imipenem, ticarcillin plus clavulanic acid, and co-amoxiclav, respectively, and 2 other strains with decreased susceptibility to metronidazole. For some strains that did not grow on ATB S medium, tests were performed by using West-Wilkins medium supplemented with 1.5% agar. The new ATB ANA device made clinical categorization of the investigated strains possible, according to French (Committee of the Antibiogram of the French Society of Microbiology) or U.S. (NCCLS) breakpoints, with the following respective results: category agreement, 94.3 and 94.9%; minor errors, 4.8 and 3.8%; major errors, 0.4 and 0.8%; and very major errors 4.6 and 4.2%. The ATB ANA device was able to detect low-level metronidazole-resistant B. fragilis strains according to the French breakpoints but not the NCCLS ones. For B. fragilis and beta-lactamase-positive Prevotella strains, the clustering effect of amoxicillin MICs around the French breakpoints led to more frequent minor errors. ATB ANA is a very convenient method to determine the antibiotic susceptibilities of anaerobes. Results obtained by ATB ANA correlated well with those obtained by the reference method.

[In vitro activity of 10 antibiotics including pristinamycin and its two components (RP 12536 and 27404) against strict anaerobes]. / Activité in vitro de 10 antibiotiques dont la pristinamycine et ses deux composants (RP 12536 et RP 27404) sur les anaérobies stricts.

The activities of the pristinamycin and its two components (RP 12536 and RP 27404) were investigated using the reference agar dilution method M11A3, on 175 anaerobic strains in comparison with that of erythromycin, clindamycin, metronidazole, amoxycillin either alone or combined with clavulanic acid, piperacillin, cefoxitin, cefotetan and cefotaxime. beta-lactamase production was detected for all the 55 B. fragilis group strains and 8/12 Prevotella and 2/18 Fusobacterium strains, respectively. On the whole anaerobes, resistance rates (%) were respectively: RP 27404 (69), RP 12536 (64), pristinamycin (5) erythromycin (31), clindamycin (17), metronidazole (7) amoxycillin (24), amoxycillin-clavulanic acid (2), piperacillin (7), cefoxitin (14), cefotetan (21) and cefotaxime (27). RP 27404 and 12536 had low activities on anaerobes but acted synergistically as pristinamycin. The greatest anti-anaerobic potencies were obtained with amoxycillin-clavulanic acid combination, pristinamycin, metronidazole and piperacillin. As resistance was not found for pristinamycin among Prevotella, Fusobacterium, Gram+ rods and Peptostreptococcus, this streptogramin may be an appropriate agent for the treatment of periodontitis, pulmonary, ENT, gynecologic and soft tissue infections where these anaerobes are frequently involved.

In vitro evaluation of activities of nitazoxanide and tizoxanide against anaerobes and aerobic organisms.

The antibacterial activities of nitazoxanide and its main metabolite, tizoxanide, were tested against a broad range of bacteria, including anaerobes. Metronidazole, amoxicillin, amoxicillin-clavulanic acid, piperacillin, cefoxitin, imipenem, and clindamycin were used as positive controls. MICs were determined by reference agar dilution methods. The 241 anaerobes were all inhibited by nitazoxanide, with the MICs at which 90% of isolates are inhibited (MIC90S) being between 0.06 and 4 mg/liter with the exception of those for Propionibacterium species, for which the MIC90 was 16 mg/liter. The MIC90s of nitazoxanide were 0.5 mg/liter for the Bacteroides fragilis group (80 strains), 0.06 mg/liter for Clostridium difficile (21 strains), and 0.5 mg/liter for Clostridium perfringens (16 strains). Metronidazole showed a level of activity comparable to that of nitazoxanide except against Bifidobacterium species, against which it was poorly active, and Propionibacterium species, which were resistant to metronidazole. The other antibiotics showed various levels of activity against anaerobes, with imipenem along with nitazoxanide being the most active agents tested. Tizoxanide was less effective than nitazoxanide except against the B. fragilis group, against which its activity was similar to that of nitazoxanide. Under aerobic conditions, nitazoxanide demonstrated poor activity against members of the family Enterobacteriacae and Pseudomonas, Staphylococcus, and Enterococcus species. The same results were obtained when culture was performed under anaerobic conditions with the notable exception of the results against Staphylococcus aureus. The MICs of nitazoxanide were in the range of 2 to 4 mg/liter for 34 clinical isolates of S. aureus, 12 of which were methicillin resistant, while tizoxanide was not effective.

[In vitro activity of a new fluoroquinolone, marbofloxacin (RO 09-1168) against strictly anaerobic bacteria and some bacteria from human fecal flora]. / Activité in vitro d'une nouvelle fluoroquinolone, la marbofloxacine (RO 09-1168) sur les anaérobies stricts et quelques bactéries de la flore fécale humaine.

As recommended by the EEC, the in vitro activity of a veterinary quinolone has to be evaluated on human strains isolated from the gut and especially against anaerobes. Thus, the MICs for Marbofloxacin were determined by the reference agar method (Norma NCCLS M11 A3) using Wilkins Chalgren medium for the 124 anaerobic strains and Mueller Hinton agar for E. coli, Proteus, Enterococcus and Lactobacillus. On the whole aerobes, the activity of Marbofloxacin was equal or slightly greater to that of ofloxacin. The modal MIC was 0.03 mg/l for Enterobacteriaceae, 2 mg/l and 16 mg/l for Enterococcus and Lactobacillus strains, respectively. Considering the anti-anaerobic activity of this new drug, in comparison with that of ofloxacin, MICs for ofloxacin were generally one log2 higher for Gram negative bacilli and two log2 higher for Gram positive bacilli. Modal MICs for marbofloxacin were 0.12 mg/l for Clostridium perfringens, 0.5 mg/l for Bacteroides fragilis, Fusobacterium, Prevotella, and Peptostreptococcus strains, 1 mg/l for Bifidobacteria, 2 mg/l for non-fragilis members of the B. fragilis group, and 4 mg/l for C. difficile strains, respectively. It appears in vitro that Marbofloxacin was a more potent agent than ofloxacin on the whole anaerobes.

[In vitro activity of carbapenems (biapenem, imipenem and meropenem) and some other antibiotics against strict anaerobic bacteria]. / Activité in vitro des carbapénèmes (biapénème, imipénème et méropénème) et de quelques antibiotiques sur les anaérobies stricts.

During 1994, the in vitro antibiotic susceptibility of 306 anaerobic bacteria was performed in 4 hospitals, by the reference agar dilution method. Among the 129 B. fragilis group strains, only two B. fragilis strains were resistant to the three carbapenems and all beta-lactams, even combined with beta-lactamase-inhibitors while metronidazole resistance could not be detected. Evolution in antibiotic resistance rates could be assessed only for piperacillin whose resistance rates increased to 20%. beta-lactamase production was detected respectively for 27% of Prevotella and 17% of Fusobacterium strains. No beta-lactamase activity was seen among Gram positive anaerobes. On the whole anaerobic strains resistance rates were: biapenem, imipenem, meropenem and piperacillin-tazobactam 0.7, amoxicillin-clavulanic acid or metronidazole 2, piperacillin 11.3, amoxicillin 31%, respectively. The three carbapenems demonstrated a good in vitro activity against most anaerobes with few differences between them.

[Comparison of two routine techniques for the evaluation of the susceptibility to antibiotics of strict anaerobic bacteria: E test AB Biodisk and ATB ANA Biomerieux]. / Comparaison de deux techniques permettant d'apprécier la sensibilité aux antibiotiques des anaérobies stricts en routine: E test AB Biodisk et ATB ANA BioMérieux.

A simple, rapid and reliable method that can be used to test individual isolates in routine is needed. Two systems are now marketed in France. As these two methods have not been studied extensively and never compared, the aim of our study was to evaluate them concurrently. For that 56 anaerobes were collected, including 31 Bacteroides fragilis group strains. The MIC's of 10 antibiotics were determined by the reference agar method. All results were further interpreted in SIR categories. Agreements of the results obtained for each method were assessed comparatively to the reference method results. For E Test and ATB ANA respectively, agreements of results were: 93 and 92.8 p. cent, major discrepancies (R/S): 4.2 and 5.7 p. cent, very major discrepancies (S/R): 3.7 and 1.5 p. cent. Clindamycin was involved in one-third of the discrepancies observed with E test. This study shows that E test and ATB ANA demonstrated interesting alternatives for the susceptibility testing of anaerobes.