Comparison of effects of medium composition and atmospheric conditions on detection of Bilophila wadsworthia beta-lactamase by cefinase and cefinase plus methods.
The influence of growth medium and incubation conditions on the detection of Bilophila wadsworthia beta-lactamase was tested with Cefinase and Cefinase Plus disks. The tests involved aerobic and anaerobic incubation with conventional disk and quantitative tube assays. The production of beta-lactamase was correlated with penicillin G, ampicillin, and ampicillin-sulbactam MICs and inhibition zones on penicillin (2-U) disks. The strains were grown on (i) brucella agar (brucella), (ii) brucella agar supplemented with 1% pyruvate (brucella-pyruvate), and (iii) brucella agar supplemented with 1% taurine (brucella-taurine). With the aerobic disk assay, 100, 100, and 7% of strains were positive after 30 min from growth on brucella-pyruvate, brucella, and brucella-taurine plates, respectively; of strains grown on brucella-taurine, 54% remained negative by the Cefinase assay, and 23% remained negative by the Cefinase Plus assay at 2 h. In quantitative assays, the strains became positive after 30 min from brucella-pyruvate plates and after 1 h from brucella plates. The intensities of the reactions were strongest with brucella-pyruvate plates under anaerobic test conditions. Anaerobic incubation enhanced beta-lactamase detection of growth on brucella-taurine: at 3 h, 85% of strains were positive in comparison to 38% with aerobic incubation. All beta-lactamase-negative strains were susceptible to penicillin G and ampicillin; all beta-lactamase-positive strains were resistant to ampicillin and, with the exception of two strains, penicillin G. In conclusion, beta-lactamase production correlated with susceptibility to penicillin G and ampicillin. Brucella agar supplemented with 1% pyruvate was the most reliable medium for testing B. wadsworthia beta-lactamase, and anaerobic incubation expedited positive results. Brucella agar supplemented with taurine was unsuitable for B. wadsworthia beta-lactamase testing. Cefinase and Cefinase Plus results were in agreement, but Cefinase Plus yielded faster reactions.
Summanen
P H
PH
Research Service, VA Wadsworth Medical Center, Los Angeles, California 90073, USA. PHSummanen@aol.com
D000332:Aerobiosis; D000693:Anaerobiosis; D002511:Cephalosporins / Q000378:metabolism; D003470:Culture Media; D006089:Gram-Negative Anaerobic Bacteria / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D010406:Penicillins / Q000494:pharmacology; D001618:beta-Lactamases / Q000378:metabolism*
D002511:Cephalosporins; D003470:Culture Media; D007202:Indicators and Reagents; D010406:Penicillins; D001618:beta-Lactamases; C021720:nitrocefin