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...

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Evidence of the possible role of wild mice in the epidemiology of Salmonella enteritidis infection on broiler breeder and layer breeder units was obtained by a bacteriological examination of local mice. Persistent S enteritidis infection in birds on these units had been a problem and a high proportion of the mice were found to carry salmonella. S enteritidis was isolated from the liver and the intestine of most of the mice, indicating a systemic infection. Three-week-old chicks were infected by contact with droppings from mice which had been infected experimentally with S enteritidis two and five months previously. Wild mice infected artificially or naturally excreted S enteritidis intermittently, with up to 10(4) organisms in some individual droppings. A naturally infected mouse which died after intermittently excreting small numbers of S enteritidis in its droppings for 19 weeks had 10(4) organisms/g of liver and 10(3)/g of macerated intestine and contents. S enteritidis was also found in fetal tissue in a naturally infected mouse suggesting the possibility that the organism might be transmitted vertically.

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This systematic review considers the relationship between arthropods commonly found in and around livestock premises and zoonotic bacteria. The principal focus is upon insects and arachnids on poultry units, where houses, litter and manure provide good conditions for the growth, multiplication and protection of flies, beetles and mites, and where zoonotic pathogens such as Salmonella and Campylobacter are prevalent. Other members of the Enterobacteriaceae and the taxa Clostridium, Helicobacter, Erysipelas and Chlamydiaceae are also discussed. Salmonella is widely distributed in the flies of affected livestock units and is detectable to a lesser degree in beetles and mites. Persistent carriage appears to be common and there is some field and experimental evidence to support arthropod-mediated transmission between poultry flocks, particularly carry-over from one flock to the next. Campylobacter may readily be isolated from arthropods in contact with affected poultry flocks, although carriage is short-lived. There appears to be a role for flies, at least, in the breaching of biosecurity around Campylobacter-negative flocks. The carriage of other zoonotic bacteria by arthropods has been documented, but the duration and significance of such associations remain uncertain in the context of livestock production.

Salmonella Typhimurium has been reported to contaminate egg production across the world, but where Salmonella Enteritidis is endemic it is this latter serovar that dominates egg-borne salmonellosis. However, Salmonella Typhimurium is a major food-borne pathogen so it is important to understand how it can impact the microbiological safety of eggs and what serovar-specific control strategies may be appropriate in the future as control over Salmonella Enteritidis continues to improve. To that end, the present review examines the published literature on Salmonella Typhimurium in laying hens and eggs, with particular reference to comparative studies examining different serovars. Experimentally Salmonella Enteritidis is more often isolated from egg contents and seems to adhere better to reproductive tract mucosa, whilst Salmonella Typhimurium appears to provoke a more intense tissue pathology and immune response, and flock infections are more transient. However, it is observed in many cases that the present body of evidence does not identify clear differences between specific behaviours of the serovars Typhimurium and Enteritidis, whether in laying hens, in their eggs, or in the laying environment. It is concluded that further long-term experimental and natural infection studies are needed in order to generate a clearer picture.

SUMMARYLogistic regression, supported by other statistical analyses was used to explore the possible association of risk factors with the fluoroquinolone (FQ)-resistance status of 108 pig finisher farms in Great Britain. The farms were classified as 'affected' or 'not affected' by FQ-resistant E. coli or Campylobacter spp. on the basis of isolation of organisms from faecal samples on media containing 1 mg.l -1 FQ. The use of FQ was the most important factor associated with finding resistant E. coli and/or Campylobacter, which were found on 79% (FQ-resistant E. coli) and 86% (FQ-resistant Campylobacter) of farms with a history of FQ use. However, resistant bacteria were also found on 19% (FQ-resistant E. coli) and 54% (FQ-resistant Campylobacter) of farms with no history of FQ use. For FQ-resistant E.

Epidemiological findings are reported from pig breeding units that were visited repeatedly and\ud sampled intensively for environmental Salmonella contamination. Eight pig breeding units\ud previously associated with Salmonella Typhimurium were visited during up to seven years. Samples\ud from voided faeces, surfaces, fomites and wildlife were cultured. Certain serovars were isolated\ud repeatedly on certain units, whilst others were detected only once or intermittently. A few serovars\ud were isolated consistently on some units but only intermittently on others. There was an association\ud between Salmonella in pens and in their immediate environment. S. Typhimurium was significantly\ud associated with growing pigs. Pens holding breeding stock for production herds were frequently\ud Salmonella-positive. Herds under common ownership showed similar serovar combinations.\ud Cleaning and disinfection was frequently ineffective. Wildlife serovars were typical of the associated\ud premises. On one unit, a low level of Salmonella was attributed to a small herd size, good cleaning\ud and disinfection and good rodent control. The study has shown that breeding herds are susceptible to\ud endemic infections with multiple Salmonella serovars and that cleaning, disinfection and vector\ud control may in many cases be inadequate. Finally, the prevalence of S. Typhimurium may be greater\ud in youngstock, which has important implications for public health