In-vitro antimicrobial susceptibility and beta-lactamases of ampicillin-resistant Escherichia coli in Hong Kong.

Three hundred and forty isolates of ampicillin-resistant Escherichia coli isolated from blood, bile and urine were collected during 1984 and 1988 in the Prince of Wales Hospital, Hong Kong and MICs of 21 beta-lactam antibiotics were determined. beta-Lactamases were identified by isoelectric focusing, and TEM-1 was found in 89.1% of isolates, PSE-1 in 3.2%, and OXA-1 in 2.9% of strains. Ten isolates (2.9%) possessed both TEM-1 and PSE-1. Five isolates (1.5%) produced only chromosomal enzymes and one produced an unidentified enzyme which focussed at pI 6.0. All but seven of 274 TEM-1 producers and all nine OXA-1 producers reacted with oligonucleotide probes in a colony blot technique. All isolates contained plasmids and 229 of 318 (72.0%) isolates transferred the ampicillin resistance factor. Of 42 transconjugants of TEM-1 producers selected for study, 39(92.9%) had only a single transferable plasmid bearing the TEM-1 gene.