nitrocefin and Gram-Negative-Bacterial-Infections

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.

Topics: Aerobiosis; Anaerobiosis; beta-Lactamases; Cephalosporins; Culture Media; Gram-Negative Anaerobic Bacteria; Gram-Negative Bacterial Infections; Humans; Indicators and Reagents; Microbial Sensitivity Tests; Penicillins

Imipenem-induced beta-lactamase (level of expression, specific activity and kinetic parameters (Vmax and Km) in response to nitrocefin) and outer membrane proteins (OMPs) (hydrophobicity, permeability and electrophoretic pattern) were characterized in, one beta-lactam sensitive (PAC-9), one resistant (PAC-1) and two resistant laboratory mutants (PAC-9M, PAC-9M2) of Comamonas acidovorans strains. Beta-lactamases from both mutant strains showed different Vmax values compared to the parental strains. Beta-lactam resistance was found to be associated in PAC-1 with inducible beta-lactamase production and OMP alteration by the appearance of a 102-KDa protein. Moreover, PAC-1 was less permeable to nitrocefin than PAC-9. These data indicate that C. acidovorans resistance to beta-lactam resulted from synergy between beta-lactamase and OMP alterations.

Topics: Aminoglycosides; Anti-Bacterial Agents; Bacterial Outer Membrane Proteins; beta-Lactam Resistance; beta-Lactamases; Cell Membrane Permeability; Cephalosporins; Gram-Negative Aerobic Rods and Cocci; Gram-Negative Bacterial Infections; Humans; Microbial Sensitivity Tests