Borderline susceptibility to antistaphylococcal penicillins is not conferred exclusively by the hyperproduction of beta-lactamase.
Staphylococcus aureus strains bearing the 17.2-kb beta-lactamase plasmid pBW15 and belonging to phage group 94/96 exhibit borderline susceptibility to the antistaphylococcal penicillins. Borderline susceptibility within phage group 94/96 is thought to be mediated by the hyperproduction of type A staphylococcal beta-lactamase. Evaluation of 84 non-94/96 phage type S. aureus strains that also produced the type A enzyme identified 7 additional hyperproducing strains. However, none of these isolates contained pBW15, and only one met the criteria for borderline susceptibility. To determine the role of pBW15 and the 94/96 phage type in the expression of borderline susceptibility, pBW15 was transformed in two plasmid-free, penicillin-susceptible strains, one of which belonged to phage group 94/96. Penicillin MICs for both transformants and quantitative beta-lactamase activity were comparable to those for the parent pBW15-containing strain. A fourfold difference in the oxacillin MICs for the 94/96 and non-94/96 phage type transformants (1.0 and 0.25 microgram/ml, respectively) was identified, and only the 94/96 phage type transformant met the criteria for borderline susceptibility. Chromosomal DNA from borderline-susceptible phage group 94/96 strains did not hybridize with a probe for mecA, and the beta-lactam binding affinity of PBPs 1, 2, 3, and 4 from a penicillin-susceptible 94/96 phage type strain and a non-94/96 phage type strain were comparable. Although hyperproduction of the type A beta-lactamase appears to be necessary for the expression of borderline susceptibility within certain phage group 94/96 strains, beta-lactamase production of a comparable magnitude by a group of S. aureus strains belonging to other phage types does not confer borderline susceptibility. These data suggest that borderline susceptibility is not solely due to the hyperproduction of beta-lactamase.
Barg
N
N
Department of Medicine, Vanderbilt University Medical School, Nashville, Tennessee 37202.
Chambers
H
H
Kernodle
D
D
D001426:Bacterial Proteins; D001434:Bacteriophage Typing; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000096:biosynthesis; D015342:DNA Probes; D006602:Hexosyltransferases; D008826:Microbial Sensitivity Tests; D002267:Muramoylpentapeptide Carboxypeptidase / Q000096:biosynthesis; D009693:Nucleic Acid Hybridization; D010403:Penicillin Resistance / Q000235:genetics*; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000494:pharmacology*; D010458:Peptidyl Transferases; D010641:Phenotype; D010957:Plasmids; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
D001426:Bacterial Proteins; D002352:Carrier Proteins; D015342:DNA Probes; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001618:beta-Lactamases