Cefoxitin is both an inhibitor of class A beta-lactamase of Xanthomonas campestris pv. campestris str. 17 and an inducer of its gene.
In Xanthomonas campestris pv. campestris (Xcc), the chromosomally encoded class A β-lactamase (Bla(xcc)) is expressed at a high basal level in the absence of an inducer and its expression is inducible by ampicillin. Like most of the class A β-lactamases, Bla(xcc) cannot digest the β-lactam ring of cefoxitin. However, Xcc exhibits high basal resistance to cefoxitin. A promoter activity assay with P(blaxcc)-lacZ transcriptional fusion from a plasmid and western blotting using anti-Bla(xcc) polyclonal antibodies demonstrated that a sublethal concentration of cefoxitin can induce expression of the bla(xcc) gene. Cefoxitin can be used as an inducer to study bla(xcc) expression in bla(xcc)-deficient mutants such as Xcbla and XcampR. Addition of cefoxitin to the Bla enzyme solution blocks β-lactamase activity, suggesting that cefoxitin is an inhibitor of Bla(xcc). This explains why there is no β-lactamase activity in cefoxitin-induced Xcc. A significant synergistic effect was also observed between cefoxitin and other β-lactam antibiotics. A homology model demonstrated that the methoxy-group in the β-lactam ring of cefoxitin tends to displace the conserved catalytic water molecule into the active cavity of Bla(xcc), thus leading to formation of a stable but inactive acyl-Bla(xcc) intermediate.
Department of Biotechnology and Laboratory Science in Medicine, National Yang-Ming University, Taipei 112, Taiwan.
Yang
Y
Tsuey-Ching
David
D
Hecht
Jeffrey J P
JJ
Tsai
Rouh-Mei
RM
Hu
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D019677:Artificial Gene Fusion; D002440:Cefoxitin / Q000494:pharmacology*; D020536:Enzyme Activators / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D017930:Genes, Reporter; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic / Q000187:drug effects; D016959:Xanthomonas campestris / Q000187:drug effects* / Q000201:enzymology*; D001618:beta-Lactamases / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D047090:beta-Lactams / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D047090:beta-Lactams; D002440:Cefoxitin; D001618:beta-Lactamases