The effect of a combination of Iso-Sensitest agar and ampicillin on the detection of enterobacter beta-lactamase.
The ampicillin MICs for faecal strains of E. cloacae (n = 11) and Enterobacter species not identified to species level (n = 3) were noticed to be two-fold to four-fold lower on Iso-Sensitest than on Mueller-Hinton II agar. The levels of inducible beta-lactamase on Iso-Sensitest, Mueller-Hinton, and a selective MacConkey-based agar, with and without ampicillin, were determined. The level produced on Iso-Sensitest with ampicillin was comparable to that induced by Mueller-Hinton alone. We conclude that when routine procedures for the detection of beta-lactamase-based resistance are evaluated, not only should care be taken to choose the right antibiotics, but also different combinations of beta-lactams and agar should be tested.
Osterblad
M
M
Antimicrobial Research Laboratory, National Public Health Institute, Turku, Finland. Monica.Osterblad@utu.fi
Huovinen
P
P
D000362:Agar / Q000494:pharmacology*; D000667:Ampicillin / Q000494:pharmacology*; D003470:Culture Media / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004754:Enterobacter / Q000187:drug effects* / Q000201:enzymology; D004790:Enzyme Induction; D008826:Microbial Sensitivity Tests; D010406:Penicillins / Q000494:pharmacology*; D001618:beta-Lactamases / Q000096:biosynthesis / Q000187:drug effects* / Q000378:metabolism
D003470:Culture Media; D010406:Penicillins; D000667:Ampicillin; D000362:Agar; D001618:beta-Lactamases