title: Characterization of novel Mycobacterium tuberculosis and Mycobacterium smegmatis mutants hypersusceptible to beta-lactam antibiotics.
abstract: Our laboratory previously constructed mutants of Mycobacterium tuberculosis and Mycobacterium smegmatis with deletions in the genes for their major beta-lactamases, BlaC and BlaS, respectively, and showed that the mutants have increased susceptibilities to most beta-lactam antibiotics, particularly the penicillins. However, there is still a basal level of resistance in the mutants to certain penicillins, and the susceptibilities of the mutants to some cephalosporin-based beta-lactams are essentially the same as those of the wild types. We hypothesized that characterizing additional mutants (derived from beta-lactamase deletion mutants) that are hypersusceptible to beta-lactam antibiotics might reveal novel genes involved with other mechanisms of beta-lactam resistance, peptidoglycan assembly, and cell envelope physiology. We report here the isolation and characterization of nine beta-lactam antibiotic-hypersusceptible transposon mutants, two of which have insertions in genes known to be involved with peptidoglycan biosynthesis (ponA2 and dapB); the other seven mutants have insertions which affect novel genes. These genes can be classified into three groups: those involved with peptidoglycan biosynthesis, cell division, and other cell envelope processes. Two of the peptidoglycan-biosynthetic genes (ponA2 and pbpX) may encode beta-lactam antibiotic-resistant enzymes proposed to be involved with the synthesis of the unusual diaminopimelyl linkages within the mycobacterial peptidoglycan.
authors.affiliation: Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Flores
authors.forename: Linda M
authors.initials: LM
authors.lastname: Parsons
authors.forename: Martin S
authors.initials: MS
authors.lastname: Pavelka
mesh_terms: D004251:DNA Transposable Elements; D017353:Gene Deletion; D016254:Mutagenesis, Insertional; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D010457:Peptidoglycan / Q000096:biosynthesis; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D010457:Peptidoglycan; D001618:beta-Lactamases
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