title: Evaluation of plasmid-encoded beta-lactamase resistance in Escherichia coli blood culture isolates.
abstract: The frequency of beta-lactam resistance was determined among 313 strains of Escherichia coli, 119 of Enterobacter/Klebsiella/Proteus spp., and 48 of Pseudomonas spp. isolated from blood cultures (at Turku University Central Hospital and Turku City Hospital) in 1983-1987. During this period the MIC50 of ampicillin for Escherichia coli increased from 8 to 32 micrograms/ml, the MIC90 of piperacillin from 16 to greater than 32 micrograms/ml and the MIC90 of cefuroxime from 4-8 to 16 micrograms/ml. Among 172 ampicillin-resistant isolates beta-lactamase-mediated resistance was characterized by DNA hybridization with TEM-1, SHV-1, OXA-1, OXA-2, PSE-1, PSE-2 and PSE-4 beta-lactamase probes and by isoelectric focusing. Beta-lactamase types found were TEM-1, TEM-2, SHV-1 and OXA-1. Isoelectric focusing did not show any other plasmid-mediated beta-lactamase varieties. Piperacillin-resistant strains showed mostly TEM-1 activity, but also produced OXA-1 and chromosomal beta-lactamase. Interestingly, a decrease in cefuroxime susceptibility in Escherichia coli occurred in a few OXA-1 producing strains as well as in strains that produced only chromosomal beta-lactamase. Two Escherichia coli strains that overproduced chromosomal beta-lactamase had increased ceftazidime MIC values (8-16 micrograms/ml).
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002444:Cefuroxime / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D010878:Piperacillin / Q000494:pharmacology; D010957:Plasmids; D011549:Pseudomonas / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D018805:Sepsis / Q000382:microbiology; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D000667:Ampicillin; D001618:beta-Lactamases; D002444:Cefuroxime; D010878:Piperacillin