title: Emergence of resistance to beta-lactam agents in Pseudomonas aeruginosa with group I beta-lactamases in Spain.
abstract: The contribution of induction and stable derepression of chromosomal class I beta-lactamases to beta-lactam antibiotic resistance was studied in clinical isolates of Pseudomonas aeruginosa collected from patients treated with beta-lactam antibiotics. Multiple isolates from the same patient were characterized by O-serotyping as a primary screen, combined with pyocin typing. Sonicated extracts of cells were assayed for chromosomal and plasmid-mediated beta-lactamases by isoelectric focusing and cloxacillin inhibition studies. The specific beta-lactamase activity, basal and induced, with cefoxitin was determined to differentiate strains with inducible or derepressed production of the enzyme. Beta-lactamase induction was performed in each strain against the beta-lactam agents used in the therapy of each patient. The observations showed that induction against older penicillins such as penicillin, amoxicillin, and amoxicillin/clavulanate resulted in a moderate to strong increase in beta-lactamase activity, whereas the results obtained with first-generation cephalosporins varied with the beta-lactam agent tested. Third-generation cephalosporins were weak inducers of beta-lactamases, and their use as therapy preceded the appearance of strains that produce chromosomal group I beta-lactamases constitutively. These strains showed a remarkable reduction in sensitivity to ureidopenicillins, carboxipenicillins, third-generation cephalosporins, and monobactams, but not to carbapenems.
authors.affiliation: Department of Immunology, Microbiology, and Parasitology, School of Pharmacy, University of Basque Country, Vitoria-Gasteiz, Spain.
authors.forename: K
authors.initials: K
authors.lastname: Colom
authors.forename: A
authors.initials: A
authors.lastname: Fdz-Aranguiz
authors.forename: E
authors.initials: E
authors.lastname: Suinaga
authors.forename: R
authors.initials: R
authors.lastname: Cisterna
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D006801:Humans; D019081:O Antigens / Q000276:immunology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D012703:Serotyping; D013030:Spain; D001618:beta-Lactamases / Q000096:biosynthesis / Q000502:physiology*; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D019081:O Antigens; D047090:beta-Lactams; D001618:beta-Lactamases