In Vitro Antimicrobial Susceptibility of Anaerobic Bacteria Isolated from Clinical Specimens

Abstract

The minimal inhibitory concentrations of 601 clinical isolates of anaerobic bacteria to 10 different antimicrobial agents were determined by an agar-dilution technique. Nearly all strains were resistant to kanamycin and gentamicin, although moderate activity to both drugs was noted with Fusobacterium sp., anaerobic cocci, some strains of Bacteroides melaninogenicus, and nonsporeforming gram-positive bacilli. Chloramphenicol at 12.5 ,ug/ml inhibited all but three of the strains tested. Tetracycline at 6.25 ,ug/ml had high activity against all groups tested, with the exception that only 39% of strains of Bacteroidesfragilis were inhibited at this concentration. Excluding certain species of Bacteroides, the majority of anaerobes were inhibited by penicillin at 3.1 ,ug/ml or less and by cephalothin at 12.5 ,ug/ml or less. Lincomycin at 6.2 ,ug/ml or less was active against nearly all strains. Erythromycin at a concentration of 3.1 ,ug/ml was active against B. fragilis; however, erythromycin was less active against the other groups. Most of the minimal inhibitory concentrations of lincomycin exceeded those of clindamycin by fourfold; Rifampin inhibited virtually all strains at 3.1 /Ag/ml.

Susceptibility of the Bacteroides fragilis group in the United States in 1981

“…Our study confirms the widespread resistance to tetracycline in Bacteroides species that was first recognized in the 1960s (6,10,13). This high resistance rate may be explained by an efficient tetracycline resistance transfer system which is stimulated by the presence of low levels of the drug (12,17,25,27 …”

“…Thus, the clinical use of clindamycin, erythromycin, or the streptogramins may increase the frequency of clindamycin resistance in Bacteroides species. The 6% resistance rate in this survey may reflect a real increase over that reported in the early 1970s, when lower resistance rates were reported (1,6,10,13,16,22,23).…”

“…These organisms are usually considered together on the basis of taxonomy and because of increased antibiotic resistance as compared with other anaerobic bacteria (1,6,7,13,24). Of the group, B. fragilis emerges as the most important pathogen; it has the highest frequency of isolation from serious infections and is the most common anaerobic bacterium that invades the bloodstream.…”

“…Most strains of the B. fragilis group are resistant to penicillin G and cephalosporins, including cephalothin, cefazolin, and cefamandole, on the basis of the presence of constitutive ,B-lactamases (13,14,24,25). Furthermore, the isolation rate of resistant strains seems to be increasing (4,17).…”

Differentiation of Fluorescent Pseudomonads by Their Effect on Milk Agar

“…P. aeruginosa is the commonest and most clinically significant species. The other two species are occasionally associated with serious infections (Gilardi, 1972 and 1976;Martin, Maker and Washington, 1973) but, more significantly, they may be confused with P. aeruginosa in the laboratory (Falkiner, Keane and Taylor, Brown and Scott-Foster (1970) devised a simple milk medium to distinguish between P. aeruginosa and P. fluorescens. Colonies of P. aeruginosa were surrounded by a clear zone due to hydrolysis of the casein, and formed a green pigment that diffused into the medium.…”