Beta-Lactamase Activity in Anaerobic Bacteria

The susceptibility pattern of 265 anaerobic bacteria from clinical isolates to 10 antimicrobial agents was investigated by the agar dilution technique. Penicillin G, in a concentration of 16 pg/ml, was active against most organisms, important exceptions being 12% of Bacteroides melaninogenicus and 24% of B. fragilis strains. The susceptibility of strains to ampicillin was similar to their susceptibility to penicillin G. Carbenicillin, at -128 ug/ml, inhibited all but a few strains. Cefamandole was less active than the penicillins; 82% of B. melaninogenicus, 32% of B. fragilis, and 75% of Fusobacterium strains were inhibited by <16 ,ug/ml. A trend towards tetracycline resistance was seen in many bacterial groups, especially Bacteroides, Fusobacterium, and Clostridium. All organisms were susceptible to chloramphenicol and clindamycin in concentrations of -16 pug/ml and -4 pug/ml, respectively. Erythromycin was less active than clindamycin against all strains tested. Metronidazole and tinidazole were active against most anaerobes, but resistance of a few strains in each group was encountered. The increased resistance of B. melaninogenicus strains to penicillin, and emergence of anaerobes resistant to >16 pug of imidazole per ml may have therapeutic implications.

supporting

confidence: 89%

“…Penicillin resistance has been observed in Bacteroides species other than Bacteroides fragilis (12,15,19) as well as in some Clostridium species (19). In addition, many anaerobes have become resistant to tetracycline (13,15,16), and clindamycin-resistant Bacteroides strains have recently appeared (11).…”

mentioning

confidence: 99%

Susceptibility of Anaerobic Bacteria to Ten Antimicrobial Agents

Appelbaum

Chatterton

1978

“…Even in the six isolates with MICs greater than 32 ,ug of cefoxitin per ml, no enzymatic activity could be demonstrated with cefoxitin as a substrate. This result is in direct contrast to the finding of Weinrich and Del Bene (23). These workers have claimed that they can measure rates of hydrolysis of cefoxitin by B. fragilis ,B-lactamase that in some cases exceed those of cephamandole and even cephaloridine.…”

Section: Discussion Based On Screening Of 79 Clinical Isolates It Iscontrasting

confidence: 61%

Cefoxitin Resistance to Beta-Lactamase: a Major Factor for Susceptibility of Bacteroides fragilis to the Antibiotic

Darland

Birnbaum

1977

Toluene-treated cell suspensions of Bacteroides fragilis were used to screen clinical isolates for the production of f3lactamase. Approximately one-third of the isolates possessed considerable cephalosporinase activity. A significant correlation was found between f3lactamase production and resistance to cephalosporin antibiotics. Several isolates were resistant to cefuroxime and cefamandole and produced enzymes capable of hydrolyzing these antibiotics. However, none of the 79 strains tested could hydrolyze the cephamycin derivative, cefoxitin. A large percentage (>90%) of the strains were susceptible to cefoxitin. Therefore, resistance to lactamase hydrolysis is a major factor for the effectiveness of cefoxitin against B. fragilis. Detailed studies of four isolates suggest that two different enzymes may be produced. Both are cephalosporinases but differ with regard to cellular distribution and substrate specificity. Cefoxitin is not a substrate for either enzyme, but it is an excellent competitive inhibitor (Ki -0.1 FM).Cephalosporins are broad-spectrum antibiotics with activity against most gram-positive and gram-negative bacteria. Among the exceptions to this general rule are members of the gram-negative species Bacteroides fragilis. Martin et al. (11) in a study of 195 clinical isolates, found that only 9% were susceptible to 25 ,g or less of cephalothin per ml. Although cephaloridine has generally proven to be more effective, Kislak (9) found only 50% of 40 isolates to be sensitive to 25 ug or less per ml. These observations have since been confirmed by others (21,22).Recently, cefoxitin (a semisynthetic cephamycin analogue) was demonstrated to be considerably more effective against B. fragilis than the cephalosporins now in use (21,22). Over 95% of the strains tested by the two groups were susceptible to 32 ,ug or less of cefoxitin per ml. Of the several hypotheses available to explain the effectiveness of cefoxitin against this group of bacteria, perhaps the most attrac-

“…These beta-lactamases possess a high degree of activity against CM. Although the ability of CX to act as an inducer of beta-lactamases has been reported previously (4,10,12,20,25), its superiority over similar drugs as an inducer and the enhanced activity of the induced enzyme for CM has not been reported. This phenomenon resembles methicillin induction of penicillinase in Staphy- (5,14,18).…”

Section: Discussionmentioning

confidence: 95%

Emergence of Resistance to Cefamandole: Possible Role of Cefoxitin-Inducible Beta-Lactamases

1979

170

102

Selection of resistance to cefamandole has been observed, and the drug has failed to protect animals lethally infected with certain Enterobacteriaceae that appeared to be highly susceptible in vitro. Using spectrophotometric assays, some of these organisms were found to produce beta-lactamases highly active against cefamandole. Cefoxitin, a poor enzyme substrate, was found to be superior to both cephalothin and cefamandole in induction of these enzymes. A simple disk induction test was developed and used to examine 147 Enterobacteriaceae for production of these beta-lactamases. The enzymes were found in 69% of cephalothin-resistant, cefamandole-susceptible strains and in only 3% of strains susceptible to both cephalothin and cefamandole. They were most prevalent among isolates of Enterobacter, indole-positive Proteus, and Serratia. Since selection of resistance and therapeutic failures have occurred most often among these genera, the relationship between presence of inducible enzymes and outcome of therapy should be examined further in humans.Cefamandole (CM;6,11,26) and cefoxitin (CX; 3, 24) possess a greater spectrum of antibacterial activity than previously marketed cephalosporins. Possible bases for the expanded spectrum of these new compounds include their resistance to a variety of beta-lactamases and/ or greater intrinsic activity, i.e., better penetration into the cell and attachment to target proteins (3,5,11,20,22,26). However, results of a recent study with these new drugs showed significant discrepancies between in vitro and in vivo tests, especially with CM (9). Animals infected with organisms appearing to be susceptible to CM in vitro failed to respond to therapy with the drug. Furthermore, in vivo selection of resistant mutants was observed in several instances. The purpose of this investigation was to analyze strains used in the previous study to determine if beta-lactamase production might be responsible for the discrepancies observed. MATERIALS AND METHODSAntibiotics. All drug solutions (weight compensated for purity) were prepared the day of use. Working standards were prepared from the following anti- Beta-lactamase assays. Beta-lactamase activity was evaluated by direct spectrophotometric methods (19) on whole cells. Cells from a 24-h Mueller-Hinton agar culture (Difco) were suspended in phosphate buffer (pH 7) so as to give 109 colony-forming units per ml. Fresh drug solution was added to the cell suspension to give a final concentration of 100 ,M, and, after incubation for 4 h at 37°C in air, the cells were removed by filtration (Millipore membrane filter). Plate counts of the drug-cell suspensions indicated no loss in viability during the 4-h incubation. The concentration of active drug remaining in the filtrate was determined by reading the optical density of the solution at the wavelength of maximal absorption associated with the beta-lactam ring (Beckman DB-GT). This wavelength varied between 255 and 270 nm for the different drugs tested. Drug solutions incubated similarly without cell...