In vitro susceptibilities of the Bacteroides fragilis group to 14 antimicrobial agents in Korea

Plasmid-Related Resistance to Cefoxitin in Species of the Bacteroides fragilis Group Isolated from Intestinal Tracts of Calves

Species of the Bacteroides fragilis group are considered the most common anaerobe in human and animal infections and also harbor plasmids conferring resistance to several antibiotics. In this study, resistance to cefoxitin, plasmid profile and beta-lactamase production in species of the B. fragilis group isolated from intestinal tracts of calves were evaluated. One hundred sixty-one B. fragilis group bacteria isolated from calves with and without diarrhea were analyzed. Cefoxitin susceptibility was performed using an agar dilution method, beta-lactamase production by using a nitrocefin method, and plasmid extraction by using a commercial kit. Minimal inhibitory concentration values for cefoxitin ranged from 32 to > 512 microg/ml, and 47 bacteria (29.2%) were resistant to cefoxitin (breakpoint 16 microl). Only seven isolates harbored plasmids varying from 6.0 to 5.0 kb, and a 5.5-kb plasmid in B. vulgatus Bd26e and B. fragilis Bc5j might be related to cefoxitin resistance. beta-lactamase was detected in 33 (70.2%) isolates. The cepA gene was observed in total DNA and in the 5.5-kb plasmid. The plasmid presence in organisms isolated from cattle may be important in ecologic terms, and it needs further study.

Determinants of resistance in Bacteroides fragilis strains according to recent Brazilian profiles of antimicrobial susceptibility

Susceptibility profiles of 99 Bacteroides fragilis strains for 9 antimicrobial agents were defined by using an agar dilution method. The isolates were uniformly susceptible to imipenen and metronidazole. All isolates were resistant to ampicillin. The resistance rates to amoxicillin/clavulanate, cefoxitin, cefotaxime, chloramphenicol, clindamycin and tetracycline were 3.0, 12.1, 15.1, 1.0, 18.2 and 75.7%, respectively. Sixteen strains showed reduced susceptibility to metronidazole (MIC 2-4 mg/L) but none had nim genes using PCR. All strains were also investigated for the presence of cepA, cfiA, cfxA, ermF and tetQ genes by PCR methodology and 92.9, 4.9, 24.2, 2 and 64.6% of the strains were respectively found positive. These results reflect the importance of surveys of susceptibility profiles and the relevance of detecting major genetic determinants to monitor the dissemination of these genes.

Epidemiology and antimicrobial resistance of B. fragilis group organisms isolated from clinical specimen and human intestinal microbiota

Epidemiological aspects and the antimicrobial susceptibility profile of the Bacteroides fragilis group isolated from clinical and human intestinal specimens were examined in this study. B. fragilis group strains were isolated from 46 (37%) of 124 clinical specimens and the source of the samples was: Blood culture (3), intraabdominal infection (27), brain abscess (2), soft tissue infection (17), respiratory sinus (3), pleural aspirate (9), breast abscess (3), surgical infected wound (22), pelvic inflammatory disease (22), chronic otitis media (9) and miscellaneous (7). Intraabdominal and soft tissue infections were responsible for more than half of the clinical isolates. Susceptibility to penicillin, cefoxitin, tetracycline, metronidazole, chloramphenicol and clindamycin was examined. All isolates were susceptible to metronidazole and chloramphenicol. For clindamycin and cefoxitin the resistance rates observed were 21.7% and 10.9% respectively. Susceptibility profiles varied among the different species tested. A total of 37 species of B. fragilis group isolated from intestinal microbiota of individuals who had no antimicrobial therapy for at least 1 month before the sampling was also examined. All strains were also susceptible to chloramphenicol and metronidazole and the resistance rates to clindamycin and cefoxitin were 19.4% and 5.4% respectively. A few institutions, in Brazil, have monitored the antimicrobial susceptibility of B. fragilis group strains isolated from anaerobic infections. The resistance rates to cefoxitin and clindamycin and the variation in susceptibility patterns among the species isolated in this study emphasize the need for monitoring of susceptibility patterns of B. fragilis group organisms isolated, especially at our University Hospitals.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.

Longitudinal study of susceptibilities of species of the Bacteroides fragilis group to five antimicrobial agents in three medical centers

A total of 579 clinical isolates of the Bacteroides fragilis group collected from three Canadian hospitals were tested for susceptibility to five antimicrobial agents by using an agar dilution method. During the 4-year survey, isolates from intra-abdominal infections were collected from the following sites: abdominal abscesses (48%), peritoneal fluid (39%), blood (10%), and bile (3%). B. fragilis was the most prevalent species (35.4%), followed by B. thetaiotaomicron (19.2%), B. ovatus (15.9%), and B. vulgatus (11%). No metronidazole- or imipenem-resistant strains were found during the survey. Resistance profiles varied among the different species tested: 7.8, 2.9, and 7.3% of B. fragilis strains (n = 205) and 68.1, 17.2, and 9.4% of non-B. fragilis strains (n = 373) were resistant to cefotetan, cefoxitin, and clindamycin, respectively. B. fragilis and B. vulgatus demonstrated lower resistance rates than B. thetaiotaomicron, B. ovatus, B. distasonis, and B. caccae. During the study, rates of resistance to cefotetan and clindamycin fluctuated but rates of resistance to cefoxitin increased, particularly at one center. These data indicate a need to determine the susceptibility patterns of the B. fragilis group periodically at each hospital.

In vitro activity of FK037, a new parenteral cephalosporin, against anaerobic bacteria

The activity of FK037, a new parenteral cephalosporin, was compared with those of cefpirome, ceftazidime, and flomoxef against 322 recent clinical isolates of anaerobic bacteria. A fastidious facultative anaerobe, Gardnerella vaginalis, was also studied. FK037 inhibited 90% of isolates of Peptostreptococcus anaerobius, Peptostreptococcus asaccharolyticus, Clostridium perfringens, Mobiluncus spp., G. vaginalis, and Porphyromonas gingivalis at < or = 0.78 micrograms/ml. The MICs of FK037 for 50 and 90% of Bacteroides fragilis isolates were 25 and > 200 micrograms/ml, respectively; the activity of FK037 was comparable to those of cefpirome and ceftazidime but lower than that of flomoxef. The activity of FK037 against Fusobacterium nucleatum, Fusobacterium varium, and Bilophila wadsworthia decreased when inoculum size was increased from 10(6) to 10(8) CFU/ml. Little influence of inoculum size on the activity of FK037 was observed for other isolates tested. Medium pH affected the activity of FK037 against F. varium (MICs at pHs 5 and 7, 3.13 and 100 micrograms/ml, respectively) and Bacteroides gracilis (MICs at pHs 5 and 7, 12.5 and 1.56 micrograms/ml, respectively) but not against other organisms tested. FK037 was less resistant than flomoxef to hydrolysis by beta-lactamase group 2e derived from B. fragilis GAI 0558 and GAI 10150.

Susceptibilities of members of the Bacteroides fragilis group to 11 antimicrobial agents

The susceptibilities of 200 clinical isolates of the Bacteroides fragilis group to 11 antimicrobial agents were determined by the broth microdilution method of the National Committee for Clinical Laboratory Standards. All isolates were susceptible to imipenem and ticarcillin-clavulanic acid. The rates of resistance to cefoxitin and clindamycin were low (4 and 6%, respectively), while those to ceftizoxime and cefotetan were higher (10.5 and 24%, respectively).