CTX-M-producing E. coli are a rapidly developing problem in the UK, with CTX-M-15 particularly common. The diversity of producers and geographical scatter of referring laboratories indicates wide dissemination of blaCTX-M genes. Because of the public health implications, including for the treatment of community-acquired urinary tract infections, the spread of these strains--and CTX-M-15 beta-lactamase in particular--merits close monitoring.

The risk for diarrhea-associated HUS was higher for children infected with Escherichia coli O157 phage type (PT) 2 and PT21/28 than for those infected with other PTs.

A total of 88 uropathogenic Escherichia coli isolates, including 68 isolates from urine and 20 isolates from blood, were characterized by multilocus sequence typing (MLST). MLST has identified an important genetic lineage of E. coli, designated sequence type 131 (ST-131), represented by 52 of these isolates, 51 of which were resistant to extended-spectrum cephalosporins. ST-131 appears to be a drug-resistant uropathogenic strain of E. coli responsible for causing urinary tract infections and bacteremia and is widely disseminated among both community and hospital patients from different geographical areas in the northwest of England. Application of MLST has helped to define the population biology which may underpin the epidemiology of pathogenic E. coli strains. The portability of MLST allows the accurate monitoring of this antibiotic-resistant uropathogenic strain of E. coli and will enhance surveillance for this important group of organisms.Urinary tract infection (UTI) is the most common laboratory-confirmed bacterial infection encountered in medical practice in Europe and North America (9). Escherichia coli is a major cause of UTI, and it accounts for approximately 70 to 95% of community-acquired cases and 50% of all hospitalacquired infections (9). These organisms are responsible for significant social and economic costs for both communities and public health resources. It has been estimated that 150 million cases of UTI occur on a global basis per year and cost about 6 billion dollars for national health resources (6).UTI due to E. coli can progress to bacteremia, which is associated with significant mortality. E. coli is recognized as the one of the two most common causes of bacteremia in England and Wales, and the Health Protection Agency reported 32.5 bacteremia cases per 100,000 subjects in 2005 (7). There is no comprehensive surveillance for community-acquired UTIs in England, and currently, there is only voluntary national surveillance for bacteremia; therefore, it is very difficult to estimate the true incidence of UTI infections and monitor the spread of these organisms (12).In recent years, there has been an increase in the occurrence cephalosporin-resistant strains of E. coli causing UTI and invasive infections (10). These organisms, which are often also resistant to other widely used antibiotics such as fluoroquinolones and trimethoprim, have particular clinical significance due to the limited therapeutic options that are available. Furthermore, the prevention and control of the spread of uropathogenic E. coli infections are hampered by a poor understanding of the population biology of these pathogens. The potential of particular lineages of antibiotic-resistant or uropathogenic E. coli to disseminate and cause disease is unknown. Improved strain characterization and phylogenetic analysis would improve our understanding of the epidemiology of this pathogen and will allow the development of a rapid assay for monitoring of uropathogenic E. coli.Multilocus sequence typing (MLST) is a DNA sequencebas...

Objectives: Uropathogenic and invasive Escherichia coli O25:H4-ST131 isolates producing CTX-M-15 extended-spectrum b-lactamase (ESBL) enzymes have recently been shown to be disseminated across the globe. In the UK, many CTX-M-15 ESBL-producing E. coli strains have been previously defined as belonging to the epidemic strains A -E, as determined by PFGE. The present study was carried out to define the relationship between these two groups of pathogenic E. coli.Methods: Multilocus sequence typing and PFGE were used for molecular characterization of a collection of 61 ESBL-producing E. coli isolates from across the UK.Results: Strains A to E all belonged to the ST131 clone, further underscoring the epidemiological importance of this lineage. Conclusions:The future spread of the ST131 clone, and its UK variants, should be monitored closely and the pathogenic mechanisms explaining their success should be investigated.Keywords: multilocus sequence typing, MLST, molecular epidemiology, uropathogenic Escherichia coli, UPEC, extended-spectrum b-lactamases, PFGE IntroductionEscherichia coli is one of the two most common causes of bacteraemia in England and Wales 1 and causes the majority of urinary tract infections (UTIs) worldwide. The widespread use of antibiotics has selected for drug-resistant strains, with current concern centred on those with fluoroquinolone resistance and extended-spectrum b-lactamases (ESBLs). ESBL-producing E. coli-principally with CTX-M-type enzymes, particularly CTX-M-15-increasingly cause UTIs in the community and longterm care and hospital settings in the UK.2,3 Five major epidemic E. coli strains (A-E) with CTX-M-15 b-lactamase were identified in the UK, based on their PFGE banding patterns, along with many clonally diverse producers of the enzyme. Epidemic strain A is nationally distributed, being particularly dominant in parts of Lancashire, Shropshire, Hampshire and Ulster. Most strain A-E isolates are resistant to oxyiminocephalosporins and, through co-production of OXA-1 b-lactamase, also to b-lactamase inhibitor combinations; in addition, most isolates are resistant to fluoroquinolones, trimethoprim, tetracyclines and amikacin. Strain A is susceptible to gentamicin, the others are generally resistant. A few strain A isolates in the north-west (NW) of England possess plasmid-mediated AmpC b-lactamase and consequently have enhanced resistance to cephamycins and cephalosporin/b-lactamase inhibitor combinations. 4 This rise in E. coli with CTX-M enzymes is not unique to the UK and several recent studies using multilocus sequence typing (MLST) have identified a globally disseminated O25:H4-ST131

I d e n t if i ca t i o n of en t e ro p a t h oge n i c Escherichia co/iSummary. Strains of Escherichia coli from sporadic cases of diarrhoea and belonging to serotypes 044 : H 18,055 : H7,O 1 1 lab : H2 1,011 1 ab : H25 or 0 126 : H27 were examined for virulence properties. With the exception of 0 1 1 lab: H25 these are considered to be classical enteropathogenic E. coli (EPEC) serotypes. The strains had been isolated in Britain from the faeces of children < 3 years old. Of the serotypes examined, 7 of 13 044 : H 18 strains, all of 10 0 1 1 lab : H21 strains and 13 of 21 0126 : H27 strains belonged to the enteroaggregative class of E. coli (EAggEC) that attached to HEp-2 cells in the characteristic aggregative pattern and hybridised with the EAggEC probe. They also caused mannose-resistant haemagglutination of rat erythrocytes, a property which may be a useful marker for their identification. Strains of 044 : H18 with similar properties were also isolated from three small outbreaks in Britain, one of which involved elderly patients. EAggEC have not been considered previously as aetiological agents of diarrhoea in developed countries and have rarely been reported as belonging to EPEC serotypes. All 15 055 : H7 strains and seven of eight 0 1 1 lab: H25 strains were also considered to be potentially diarrhoeagenic as they gave localised attachment (LA) to HEp-2 cells that resulted in a positive fluorescence actinstaining test. This test is considered to correlate with the attaching-and-effacing virulence mechanisms of EPEC in vivo. None of the strains in this study hybridised with the EPEC adherence-factor (EAF) probe. Neither the aggregative EPEC nor the LA-positive EAFnegative EPEC described here would be identified in epidemiological surveys when the EAF probe is used in the absence of cell tests.