Homologous recombination between bacterial strains is theoretically capable of preventing the separation of daughter clusters, and producing cohesive clouds of genotypes in sequence space. However, numerous barriers to recombination are known. Barriers may be essential such as adaptive incompatibility, or ecological, which is associated with the opportunities for recombination in the natural habitat. Campylobacter jejuni is a gut colonizer of numerous animal species and a major human enteric pathogen. We demonstrate that the two major generalist lineages of C. jejuni do not show evidence of recombination with each other in nature, despite having a high degree of host niche overlap and recombining extensively with specialist lineages. However, transformation experiments show that the generalist lineages readily recombine with one another in vitro. This suggests ecological rather than essential barriers to recombination, caused by a cryptic niche structure within the hosts.

poultry-derived CTX-M E. coli in GB are different from major CTX-M sequence types causing disease in humans.

Cefotaximases (CTX-M) are a rapidly growing class A ␤-lactamase family that has been found among a wide range of clinical bacteria. One hundred and six isolates were selected from 278,308 Salmonella isolates based on resistance to ampicillin and cephalosporins and subjected to further characterization. Fourteen isolates were bla CTX-M PCR positive, and cefotaxime MICs for these isolates were >16 mg/liter. Furthermore, sequence analysis revealed the presence of type CTX-M9, -15, or -17 to -18. All 14 isolates presented different PFGE restriction profiles, although six Salmonella enterica serotype Virchow isolates formed a tight cluster. The bla CTX-M genetic determinants were present in transferable plasmids of ϳ63, 105, and >148 kb. Plasmid restriction analysis showed that both horizontal transfer of similar plasmids among different clones and transfer of genes between different plasmids were likely mechanisms involved in the spread of bla CTX-M genes. We have found that CTX-M enzymes have emerged in community-acquired infections both linked to foreign travel and domestically acquired. This is the first report of a CTX-M enzyme in Salmonella in the United Kingdom. Also, it represents the first report of a bla CTX-M gene in Salmonella enterica serotype Stanley and a bla CTX-M-15 gene in Salmonella enterica serotypes Anatum, Enteritidis, and Typhimurium.Antimicrobials are essential for the treatment of invasive infections caused by Salmonella spp. However, it is well known that these organisms have been successful at acquiring resistance to a broad range of commonly used antimicrobials (5, 6). Extended-spectrum cephalosporins and fluoroquinolones are often used in the treatment of invasive cases of salmonellosis. However, the utilization of these drugs in treating complicated Salmonella infections is becoming seriously compromised by the increasing development of fluoroquinolone and extendedspectrum cephalosporin resistance. A recent example of this is treatment failure due to in vivo acquisition of a plasmid containing the bla CTX-M-3 gene by Salmonella enterica serotype Anatum (12).Cefotaximases (CTX-M) are class A ␤-lactamases that in general present higher levels of hydrolytic activity against cefotaxime than against ceftazidime. Ceftazidime MICs for organisms producing these enzymes are sometimes in the susceptible range. Many laboratories use ceftazidime resistance alone as an indicator of extended-spectrum ␤-lactamase production. For this reason, CTX-M-producing isolates may be missed by routine susceptibility testing performed by clinical microbiology laboratories. CTX-M enzymes comprise a rapidly growing family distributed both over wide geographic areas and among a wide range of bacteria of clinical significance. There are five major CTX-M groups (groups 1, 2, 8, 9, and 25) (3).In order to assess the current presence of organisms and genes of concern in England and Wales, the present work aimed to screen a large collection of Salmonella isolates of human origin with for the presence of bla CTX-M genes. S...

In order to monitor epidemiological trends, Cryptosporidium-positive samples (n=4509) from diarrhoeic patients were typed. Compared to the previous 4 years, the proportion of Cryptosporidium hominis cases in 2004-2006 increased to 57·3%, while 38·5% were C. parvum. The remaining 4·2% cases included mixed C. parvum and C. hominis infections, C. meleagridis, C. felis, C. ubiquitum and a novel genotype. When the typing results were combined with enhanced surveillance data to monitor risk exposures, C. hominis was linked to urban dwelling, previous diarrhoea in the household, any travel especially abroad, and using a swimming or paddling pool. C. parvum was linked to having a private water supply, contact with surface water, visiting or living on a farm, and contact with farm animal faeces. The proportion of laboratory-confirmed indigenous cases acquired from direct contact with farm animals was estimated to be 25% for C. parvum and 10% of all reported Cryptosporidium cases.

Extended-spectrum ␤-lactamase (ESBL)-mediated resistance is of considerable importance in human medicine. Recently, such enzymes have been reported in bacteria from animals. We describe a longitudinal study of a dairy farm suffering calf scour with high mortality rates. In November 2004, two Escherichia coli isolates with resistance to a wide range of ␤-lactams (including amoxicillin-clavulanate and cefotaxime) were isolated from scouring calves. Testing by PCR and sequence analysis confirmed the isolates as being both bla CTX-M14/17 and bla TEM-35 (IRT-4) positive. They had indistinguishable plasmid and pulsed-field gel electrophoresis (PFGE) profiles. Transferability studies demonstrated that bla CTX-M was located on a conjugative 65-MDa IncK plasmid. Following a farm visit in December 2004, 31/48 calves and 2/60 cows were positive for E. coli with bla CTX-M . Also, 5/48 calf and 28/60 cow samples yielded bla CTX -and bla TEM -negative E. coli isolates that were resistant to cefotaxime, and sequence analysis confirmed that these presented mutations in the promoter region of the chromosomal ampC gene. Fingerprinting showed 11 different PFGE types (seven in bla CTX-Mpositive isolates). Six different PFGE clones conjugated the same bla CTX-M -positive IncK plasmid. One clone carried a different-sized, bla CTX-M -positive, transformable plasmid. This is the first report of bla CTX-M from livestock in the United Kingdom, and this report demonstrates the complexity of ESBL epidemiology. Results indicate that horizontal plasmid transfer between strains as well as horizontal gene transfer between plasmids have contributed to the spread of resistance. We have also shown that some clones can persist for months, suggesting that clonal spread also contributes to the perpetuation of resistance.Cefotaximases (CTX-M) are class A ␤-lactamases produced by a wide range of bacteria of clinical significance and in general present higher levels of hydrolytic activity against cefotaxime than against ceftazidime. CTX-M enzymes comprise a genetically diverse (five groups designated 1, 2, 8, 9, and 25 have been described) and rapidly growing family. These are the predominant extended-spectrum ␤-lactamases (ESBL) in human infections in parts of Eastern Europe, South America, and Japan. In the United Kingdom, the first report of a CTX-M enzyme was in a human clinical isolate of Klebsiella oxytoca with bla CTX-M9 in 2000 (1). Since then, CTX-M-producing Escherichia coli has emerged as a significant and developing problem, occurring in patients in the community as well as in those with recent hospital contact (16,19).In spite of this human situation, worldwide, there have been only a few recent reports of CTX-M-producing bacteria in animals (3,4,10,11,25,29). It is unclear whether it is primarily human or veterinary use of antibiotics that has provided the selective pressures necessary for this situation. In a recent letter, we described the first reported isolation of CTX-Mproducing E. coli from cattle in the United Kingdom. These resist...