Antibacterial usage in English NHS hospitals as part of a national Antimicrobial Stewardship Programme.

Antimicrobial resistance (AMR) has become a global problem for health care services, with fewer antimicrobials entering the market and some pathogenic organisms becoming resistant to commonly used antimicrobials. Antimicrobial stewardship (AS), including evidence-based standard setting, education and communication, and audits of practice, has become a key method of preventing the rise in the rise in AMR. Data on antibiotic consumption are often obtained through prospective and retrospective point prevalence audits of antibiotic usage, but such studies are very resource intensive and only provide a snapshot of consumption. The objective of the study reported here was to examine longitudinal total antibacterial usage at a national level and cross-sectional usage at an individual hospital trust level using a commercial database that captures antimicrobial prescribing from at least 99% of English hospital Trusts.

Enhanced surveillance of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia in children in the UK and Ireland.

OBJECTIVE: To determine the incidence and demographic features of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia in children in the UK and Ireland and to characterise MRSA isolated from cases. DESIGN: Prospective surveillance study. SETTING: Children aged <16 years hospitalised with bacteraemia due to MRSA. METHODS: Cases were ascertained by active surveillance involving paediatricians reporting to the British Paediatric Surveillance Unit and by routine laboratory surveillance. Patient characteristics were obtained using questionnaires sent to reporting paediatricians. MRSA isolates were characterised using molecular and phenotypic techniques including antimicrobial susceptibility testing. RESULTS: 265 episodes of MRSA bacteraemia were ascertained, involving 252 children. The overall incidence rate was 1.1 per 100 000 child population per year (95% CI 0.9 to 1.2): 61% of the children were aged <1 year (a rate of 9.7 cases per 100 000 population per year (95% CI 8.2 to 11.4)) and 35% were <1 month. Clinical data were obtained from 115 cases. The clinical presentation varied, with fever present in only 16% of neonates compared with 72% of older children. A history of invasive procedure was common, with 32% having had intravascular lines and 13% having undergone surgery. 62% of patients for whom data were available were receiving high-dependency care (46% in SCBU/NICU and 16% in PICU). Of 93 MRSA isolates studied, 73% belonged to epidemic strains widely associated with nosocomial infection in the UK and Ireland. CONCLUSIONS: MRSA bacteraemia in children was relatively uncommon and was predominantly seen in very young children, often those receiving neonatal or paediatric intensive care. Bacteraemia predominantly involved well-documented epidemic strains of MRSA associated with nosocomial infection.

Antimicrobial susceptibility of Pseudomonas aeruginosa: results of a UK survey and evaluation of the British Society for Antimicrobial Chemotherapy disc susceptibility test.

A survey was conducted in 1999, first to establish the prevalence of antibiotic resistance among clinical isolates of Pseudomonas aeruginosa in the UK and secondly to test whether the use of the standardized British Society for Antimicrobial Chemotherapy (BSAC) disc testing method improved the accuracy of routine susceptibility testing for this organism. Twenty-five hospitals were each asked to collect up to 100 consecutive, clinically significant isolates of P. aeruginosa and to test their susceptibility to amikacin, gentamicin, ceftazidime, imipenem, meropenem, ciprofloxacin, piperacillin and piperacillin/tazobactam using the new BSAC disc method. A total of 2194 isolate reports were available for analysis and 10% of the isolates represented, plus those with unusual resistances, were re-tested centrally for quality control purposes. The zone distributions were essentially unimodal, indicating the absence of major populations with acquired resistance. The results indicated that resistance rates to the beta-lactam, aminoglycoside and quinolone agents tested in P. aeruginosa in the UK remain low (<12%), and were mostly unchanged since a previous survey conducted in 1993. High resistance rates were nevertheless reported for isolates from cystic fibrosis patients. The accuracy of susceptibility testing using the new BSAC disc testing method was better than in previous studies, when Stokes' method was most frequently used. Critically, the proportion of resistant isolates incorrectly reported as susceptible was reduced significantly; nevertheless, depending on the antibiotic, up to 49% of the isolates reported as intermediate or resistant were found susceptible on central re-testing.

IMP-4, a novel metallo-beta-lactamase from nosocomial Acinetobacter spp. collected in Hong Kong between 1994 and 1998.

Between 1994 and 1998, 97 imipenem-resistant Acinetobacter isolates were identified at the Prince of Wales Hospital, Hong Kong, China. A bla(IMP) PCR product was obtained from 23 of 35 viable cultures; 12 isolates belonged to genomic DNA group 3, 8 belonged to group 2 (Acinetobacter baumannii), 2 belonged to group 13TU, and 1 belonged to group 1. The bla(IMP) homologues were sequenced from two isolates from genomic DNA group 2 and one isolate each from groups 3 and 13TU. The four sequences included an identical 738-bp open reading frame, predicted to encode a polypeptide of 246 amino acids, with 95.6% homology to IMP-1 and 89.3% homology to IMP-2. The new enzyme, designated IMP-4, was partially purified. It had a pI of 8.0 and was strongly active against imipenem and meropenem, with V(max) values 53 and 8% of that for penicillin G, respectively. Strong activity was also seen against oxyimino-aminothiazolyl cephalosporins but not against aztreonam. Hydrolytic activity was inhibited by EDTA but not by clavulanate or tazobactam. Carbapenem MICs for most bla(IMP)-positive isolates were 4 to 32 microg/ml, but one isolate with the intact gene was susceptible, with imipenem and meropenem MICs of 0.25 and 0.5 microg/ml, respectively. The latter isolate did not produce the band with a pI of 8.0, and gene expression was inferred to have been lost. None of the isolates studied in detail contained extrachromosomal DNA, and carbapenem resistance was not transmissible to Escherichia coli. Nevertheless, the presence of bla(IMP-4) in different genomic DNA groups implies horizontal transfer, and sequences resembling a GTTRRRY integrase-dependent recombination motif were identified in the flanking regions of bla(IMP-4).

Type characterisation and antibiotic susceptibility of Burkholderia (Pseudomonas) cepacia isolates from patients with cystic fibrosis in the United Kingdom and the Republic of Ireland.

The spread of Burkholderia cepacia among cystic fibrosis (CF) patients in the UK prompted an investigation into whether an epidemic strain was responsible. A total of 366 B. cepacia isolates from 178 CF patients in 17 centres was examined by ribotyping and pulsed-field gel electrophoresis (PFGE). Associations were also sought between antibiotic resistance and strain type. More than 50 ribotype patterns were found but one, termed ribotype 1, was identified from 68 patients in eight centres. One centre had a single patient with this type while, in others, most or all patients harboured this organism. Small clusters of apparent cross-colonisation within centres were also evident for some other ribotypes. PFGE confirmed that ribotype 1 isolates were genetically similar. Ribotype 1 isolates were not markedly more resistant to antimicrobial agents than were other isolates, and the MICs of individual antibiotics were no more tightly clustered for ribotype 1 isolates than for others. Most isolates were resistant to ciprofloxacin, amikacin, gentamicin, tobramycin, carbenicillin, cefuroxime, cefotaxime, imipenem, biapenem, chloramphenicol, tetracycline, trimethoprim and sulphamethoxazole, but > or = 77% were susceptible to ceftazidime, piperacillin, piperacillin/ tazobactam and meropenem. We conclude that numerous strains of B. cepacia colonise CF patients in the UK and Ireland but that one epidemic strain has spread in at least eight centres. Isolates of this strain appear homogenous in total genomic profile but very variable in antibiotic susceptibility.

Role of efflux pump(s) in intrinsic resistance of Pseudomonas aeruginosa: active efflux as a contributing factor to beta-lactam resistance.

Wild-type strains of Pseudomonas aeruginosa are more resistant to various beta-lactam antibiotics as well as other agents than most enteric bacteria. Although resistance to compounds of earlier generations is explained by the synergism between the outer membrane barrier and the inducible beta-lactamase, it was puzzling to see significant levels of resistance to compounds that do not act as inducers or are not hydrolyzed rapidly by the chromosomally encoded enzyme. This intrinsic-resistance phenotype becomes enhanced in those strains with the so-called intrinsic carbenicillin resistance. In the accompanying paper (X.-Z. Li, D. M. Livermore, and H. Nikaido, Antimicrob. Agents Chemother. 38:1732-1741, 1994), we showed that active efflux played a role in the resistance, to various non-beta-lactam agents, of P. aeruginosa strains in general and that the efflux was enhanced in intrinsically carbenicillin-resistant strains. We show in this paper that, in comparison with the drug-hypersusceptible mutant K799/61, less benzylpenicillin was accumulated in wild-type strains of P. aeruginosa and that the accumulation levels were even lower in intrinsically carbenicillin-resistant strains. Deenergization by the addition of a proton conductor increased the accumulation level to that expected for equilibration across the cytoplasmic membrane. In intrinsically carbenicillin-resistant isolates, there was no evidence that either nonspecific or specific permeation rates of beta-lactams across the outer membrane were lowered in comparison with those of the more susceptible isolates. Furthermore, these carbenicillin-resistant isolates were previously shown to have no alteration in the level or the inducibility of beta-lactamase and in the affinity of penicillin-binding proteins. These data together suggest the involvement of an active efflux mechanism also in the resistance to beta-lactams. Hydrophilic beta-lactams with more than one charged group did not cross the cytoplasmic membrane readily. Yet one such compound, ceftriaxone, appeared to be extruded from the cells of more-resistant strains, although with this compound effects of proton conductors could not be shown. We postulate that wild-type strains of P. aeruginosa pump out such hydrophilic beta-lactams either from the periplasm or from the outer leaflet of the lipid bilayer of the cytoplasmic membrane, in a manner analogous to that hypothesized for multidrug resistance protein of human cancer cells (M.M. Gottesman and I. Pastan, Annu. Rev. Biochem. 62:385-427, 1993).

Cloning and sequence analysis of the gene for a carbapenem-hydrolyzing class A beta-lactamase, Sme-1, from Serratia marcescens S6.

Serratia marcescens S6 produces a pI 9.7 carbapenem-hydrolyzing beta-lactamase that is probably encoded by the chromosome (Y. Yang, P. Wu, and D. M. Livermore, Antimicrob. Agents Chemother. 34:755-758, 1990). A total of 11.3 kb of genomic DNA from this strain was cloned into plasmid pACYC184 in Escherichia coli. After further subclonings, the carbapenem-hydrolyzing beta-lactamase gene (blaSme-1) was sequenced (EMBL accession number Z28968). The gene corresponded to an 882-bp open reading frame which encoded a 294-amino-acid polypeptide. This open reading frame was preceded by a -10 and a -35 region consistent with a putative promoter sequence of members of the family Enterobacteriaceae. This promoter was active in E. coli and S. marcescens, as demonstrated by primer extension analysis. N-terminal sequencing showed that the Sme-1 enzyme had a 27-amino-acid leader peptide and enabled calculation of the molecular mass of the mature protein (29.3 kDa). Sequence alignment revealed that Sme-1 is a class A serine beta-lactamase and not a class B metalloenzyme. The earlier view that the enzyme was zinc dependent was discounted. Among class A beta-lactamases, Sme-1 had the greatest amino acid identity (70%) with the pI 6.9 carbapenem-hydrolyzing beta-lactamase, NMC-A, from Enterobacter cloacae NOR-1. Comparison of these two protein sequences suggested a role for specific residues in carbapenem hydrolysis. The relatedness of Sme-1 to other class A beta-lactamases such as the TEM and SHV types was remote. This work details the sequence of the second carbapenem-hydrolyzing class A beta-lactamase from an enterobacterial species and the first in the genus Serratia.