title: Mechanism of resistance of an ampicillin-resistant, beta-lactamase-negative clinical isolate of Haemophilus influenzae type b to beta-lactam antibiotics.
abstract: The mechanism of non-beta-lactamase-mediated beta-lactam resistance in a clinical isolate of Haemophilus influenzae type b was studied. This clinical isolate showed up to a 32-fold increase in MICs of a wide variety of beta-lactams, including moxalactam and cefotaxime, although no beta-lactamase activity was detected, even after attempted induction. Transformation of broad-spectrum beta-lactam resistance into ampicillin-susceptible H. influenzae RDnov was accomplished. Examination of the outer membrane protein profile of the resistant parent by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of Triton X-100-extracted membranes revealed an unusual major outer membrane protein band at a molecular weight of 45,000. This outer membrane protein profile did not transform with beta-lactam resistance. Permeability differences were noted between the resistant strain and the nonisogenic susceptible strain of H. influenzae, although these penetration differences were not transformed. Comparison of the penicillin-binding protein profile of a resistant transformant with that of a susceptible parent with both whole-membrane preparations and whole-cell labeling, revealed a major reduction in binding affinity to penicillin-binding proteins 3a and 3b (molecular weights, 68,000 and 65,000, respectively). Thus, alteration in penicillin-binding proteins 3a and 3b correlated with the beta-lactam resistance.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002463:Cell Membrane Permeability; D002701:Chloramphenicol / Q000494:pharmacology; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000201:enzymology; D006602:Hexosyltransferases; D008826:Microbial Sensitivity Tests; D008970:Molecular Weight; D002267:Muramoylpentapeptide Carboxypeptidase / Q000378:metabolism; D010400:Penicillin G / Q000378:metabolism; D010403:Penicillin Resistance; D046915:Penicillin-Binding Proteins; D010458:Peptidyl Transferases; D014169:Transformation, Bacterial; D001618:beta-Lactamases / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D046915:Penicillin-Binding Proteins; D002701:Chloramphenicol; D000667:Ampicillin; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001618:beta-Lactamases; D010400:Penicillin G