Prevalence and mechanism of resistance to 'third-generation' cephalosporins in clinically relevant isolates of Enterobacteriaceae from 43 hospitals in the UK, 1990-1991.

In a UK survey of the occurrence of extended spectrum beta-lactamases, 96 hospitals submitted a total of 3951 non-selected, non-duplicate isolates of Enterobacteriaceae from 100 patients in each hospital, 206 of these cultures being mixed and, therefore, discarded. These isolates were initially screened for strains likely to produce extended-spectrum beta-lactamases (ESBLs) by MIC determination of beta-lactams followed by a bioassay, then disc approximation test and isoelectric focusing (IEF). Isolates were further examined using two pairs of PCR primers for both blaTEM and blaSHV genes. The ability of isolates to transfer resistance to both cefotaxime and ceftazidime by conjugation and transformation were examined. Four hundred and nine cefotaxime/ceftazidime-resistant isolates (10.9%) were identified from the 3745 submitted isolates, of which 338 (9.0%) were Enterobacteriaceae, 29 Escherichia coli, 35 Klebsiella spp. and seven Hafnia alveii. IEF suggested that 17 isolates produced an ESBL, which was confirmed in most cases by PCR and hydrolysis, five isolates produced an SHV enzyme by IEF, but not confirmed by PCR, and 11 had isoelectric points in the range 8-9 suggesting a possible AmpC enzyme. Only two isolates transferred the determinants. In the case of the Klebsiella spp., 19 of the 24 ceftazidime-resistant/clavulanate-sensitive isolates were positive by PCR for a blaSHV gene. No isolates were identified as carrying blaTEM, although eight isolates had isoelectric points of 5-6.3, suggesting the presence of a possible TEM beta-lactamase. The results for the H. alveii isolates suggest that either an AmpC-like enzyme or a transferable beta-lactamase which is not TEM/SHV is present. This study shows that a wide range of genotypically and phenotypically different isolates of Enterobacteriaceae producing ESBL-like enzymes is present throughout the UK at a frequency of about 1% of unselected isolates. It is important that surveillance of resistance to these clinically important antibiotics is maintained as the occurrence of localized or more widespread outbreaks caused by bacteria producing ESBLs is to be expected.

Activity of 13 beta-lactam agents combined with BRL 42715 against beta-lactamase producing gram-negative bacteria compared to combinations with clavulanic acid, tazobactam and sulbactam.

The activity of six cephalosporins, six penicillins and one monobactam combined with BRL 42715, clavulanic acid, sulbactam or tazobactam at 0.1, 0.5, 1, 2, 5 and 10 mg/L was determined for 45 beta-lactamase producing Gram-negative bacteria. The combination of BRL 42715 with any of the agents was more active than any of the other inhibitor and beta-lactam combinations. Unlike the other beta-lactamase inhibitors, BRL 42715 enhanced the activity of the beta-lactams for strains that constitutively expressed Richmond & Sykes Class I beta-lactamase and against strains expressing extended-spectrum plasmid-mediated beta-lactamases.

Activity of meropenem against imipenem-resistant bacteria and selection in vitro of carbapenem-resistant Enterobacteriaceae.

The activity of meropenem against 106 imipenem-resistant (MIC > or = 8 mg/l) clinical isolates, and the frequency of resistance to meropenem and imipenem among 24 Enterobacteriaceae was determined. Both agents selected colonies on agar but 20-80% were susceptible after one subculture and 72% of the mutants reverted to susceptibility 1 to 6 months after selection. All isolates and stable mutants were inhibited by > 1 mg/l meropenem, although the MIC of imipenem was 4-16 mg/l. Three of six Xanthomonas maltophilia isolates were susceptible to meropenem (MICs 2-4 mg/l). Pseudomonas aeruginosa lacking outer membrane protein D2 were resistant to meropenem, although isolates with substantially reduced expression of this protein were susceptible. None of the imipenem-resistant gram-positive bacteria were susceptible to meropenem. There was no clear correlation between altered outer membrane protein expression and decreased susceptibility to carbapenems, and there was no apparent involvement of plasmid or chromosomal beta-lactamase.