Serovar Typhimurium Definitive Phage Type Research Articles

The occurrence ofSalmonellaspp. in duck eggs on sale at retail or from catering in England

Human salmonellosis outbreaks in England and Northern Ireland due to Salmonella enterica serovar Typhimurium definitive phage type (DT) 8 have been identified as associated with the consumption of duck eggs since 2010. This study has shown that Salmonella spp. was detected in 1·4% of ducks egg samples providing baseline data for risk assessors, regulators and the food industry. This may be helpful in communicating risks associated with the consumption of this product as well as evaluating risk management options to control food safety including vaccination of ducks.

Complete Proteome of a Quinolone-Resistant Salmonella Typhimurium Phage Type DT104B Clinical Strain

Salmonellosis is one of the most common and widely distributed foodborne diseases. The emergence of Salmonella strains that are resistant to a variety of antimicrobials is a serious global public health concern. Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) is one of these emerging epidemic multidrug resistant strains. Here we collate information from the diverse and comprehensive range of experiments on Salmonella proteomes that have been published. We then present a new study of the proteome of the quinolone-resistant Se20 strain (phage type DT104B), recovered after ciprofloxacin treatment and compared it to the proteome of reference strain SL1344. A total of 186 and 219 protein spots were recovered from Se20 and SL1344 protein extracts, respectively, after two-dimensional gel electrophoresis. The signatures of 94% of the protein spots were successfully identified through matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). Three antimicrobial resistance related proteins, whose genes were previously detected by polymerase chain reaction (PCR), were identified in the clinical strain. The presence of these proteins, dihydropteroate synthase type-2 (sul2 gene), aminoglycoside resistance protein A (strA gene) and aminoglycoside 6'-N-acetyltransferase type Ib-cr4 (aac(6')-Ib-cr4 gene), was confirmed in the DT104B clinical strain. The aac(6')-Ib-cr4 gene is responsible for plasmid-mediated aminoglycoside and quinolone resistance. This is a preliminary analysis of the proteome of these two S. Typhimurium strains and further work is being developed to better understand how antimicrobial resistance is developing in this pathogen.

Genomic Analysis ofSalmonella entericaSerovar Typhimurium Definitive Phage Type 104

Genomic Analysis of<i>Salmonella enterica</i>Serovar Typhimurium Definitive Phage Type 104

Revival of an old problem: an increase inSalmonella entericaserovar Typhimurium definitive phage type 8 infections in 2010 in England and Northern Ireland linked to duck eggs

Salmonella enterica serovar Typhimurium definitive phage type (DT) 8 is uncommon in humans in the UK. In July 2010, the Health Protection Agency reported an excess isolation rate of pan-susceptible S. Typhimurium DT8 in England and Northern Ireland. By the end of October, this amounted to 81 laboratory-confirmed human cases for all regions of England and Northern Ireland in 2010, an increase of 26% and 41% on 2009 and 2008, respectively. Descriptive epidemiological investigation found a strong association with infection and consumption of duck eggs. Duck eggs contaminated with S. Typhimurium DT8 were collected from a patient's home and also at farms in the duck-egg supply chain. Although duck eggs form a small part of total UK eggs sales, there has been significant growth in sales in recent years. This is the first known outbreak of salmonellosis linked to duck eggs in the UK since 1949 and highlighted the impact of a changing food source and market on the re-emergence of salmonellosis linked to duck eggs. Control measures by the duck-egg industry should be improved along with a continued need to remind the public and commercial caterers of the potential high risks of contracting salmonellosis from duck eggs.

Zoonotic Cryptosporidiosis from Petting Farms, England and Wales, 1992–2009

To the Editor: Visits to petting farms in England and Wales recently have increased in popularity. Petting farms are commercial operations at which visitors, mainly families and organized groups, are encouraged to have hands-on contact with animals. The ≈1,000 petting farms in the United Kingdom collectively receive >2 million visitors per year, with peak visitor times during school and public holidays. Commercial farms also may host farm visits on single days for group and school visits. The farm attraction business is a substantial part of the rural economy, generating >£12 million annually (1). During 1992–2009, a total of 55 outbreaks of infectious intestinal disease associated with petting farms in England and Wales was reported to the Health Protection Agency. Verocytotoxin-producing Escherichia coli O157 (VTEC O157) caused 30 (55%) of these outbreaks (244 persons were affected [range 2–93, mean 8 persons] and 84 were hospitalized); Salmonella enterica serovar Typhimurium definitive phage type 104 caused 2 (3%) of the outbreaks. A total of 23 (42%) petting farm outbreaks were caused by Cryptosporidium spp. (1,078 persons were affected [range 2–541, mean 45 persons] and 29 were hospitalized). We report on these cryptosporidiosis outbreaks as a reminder of the risk to petting farm visitors. Contributory factors reported in the cryptosporidiosis outbreaks included direct contact with preweaned lambs, calves, kids, or animal feces (e.g., diarrhea in lambs, a recognized risk factor for cryptosporidiosis; 11/23 [48%]) and inadequate hand washing facilities (7/23 [30%]). Of outbreaks in which hand washing facilities were inadequate, thumb sucking by children was also noted in 1; in another, alcohol-based hand gels and sanitizers, which are ineffective against Cryptosporidium spp., were used. Cryptosporidium spp. are coccidian parasites that infect a wide range of farm livestock, including cattle, sheep, goats, pigs, horses, and deer, but are mainly a veterinary problem in neonatal ruminants. C. parvum, for example, is a common agent in the etiology of the neonatal diarrhea syndrome of calves, lambs, and goat kids. Widespread asymptomatic carriage of this parasite exists in livestock in the United Kingdom (2). In humans, cryptosporidiosis occurs most commonly in children <5 years of age, can be life threatening in immunocompromised persons, and is caused predominantly by C. hominis and C. parvum parasites. Fecal–oral transmission can occur directly from animal to person and from person to person or indirectly through contaminated food or water (2). Typing of Cryptosporidium spp. has been undertaken by the UK Cryptosporidium Reference Unit since 1999. C. parvum was identified from human feces in 12 (75%) of the 16 petting farm outbreaks since 1999 (feces were not submitted for typing in 4). Additionally, Cryptosporidium spp. oocysts were detected and confirmed as C. parvum from suspected sources (lambs, calves) in 4 (33%) of these 12 outbreaks and linked by GP60 subtype to human cases in 3 outbreaks. Zoonotic risk factors in case–control studies of sporadic cryptosporidiosis cases in England and Wales also have identified an association between C. parvum infection and touching farm animals or visiting a farm (3). In petting farm outbreaks, Cryptosporidium spp. displayed a seasonal pattern, as did VTEC O157. Cryptosporidiosis outbreaks occurred more often in springtime (18 vs. 5; p = 0.0001) than did VTEC O157 outbreaks, which occurred more frequently during the summer (25 vs. 5; p<0.00001), especially in August (Figure). During spring 2010, two additional C. parvum outbreaks associated with contact with lambs at petting farms were reported in England. Control measures included restricting bottle feeding of lambs and enhancing the supervision of hand washing. The associations with outbreaks of cryptosporidiosis in spring and contact with young farm animals also has been reported in Scotland (4). Figure Outbreaks of cryptosporidiosis and verocytotoxin-producing Escherichia coli O157 linked to petting farms, England and Wales, 1992–2009. Despite the 2 separate seasonal peaks of infection, care should be exercised throughout the year. The importance of careful attention to hygiene and supervision of children visiting farms and the need for appropriate facilities, such as those for hand washing, are covered in the UK Health and Safety Executive standards; operators of petting farms are expected to meet these standards (5). These guidelines also apply to commercial farms hosting open days. A good practice reminder on managing the risks from VTEC O157 in a petting farm context was published by the Health Protection Agency, Health and Safety Executive, and the Local Government Regulation (6). Guidance on the control of VTEC O157 infections for farms open to public access applies equally to most gastrointestinal pathogens, including Cryptosporidium spp. The need for a sound approach to managing hygiene control measures at petting farms cannot be overemphasized.

AcrAB-TolC directs efflux-mediated multidrug resistance in Salmonella enterica serovar typhimurium DT104.

Multidrug-resistant Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) strains harbor a genomic island, called Salmonella genomic island 1 (SGI1), which contains an antibiotic resistance gene cluster conferring resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides, and tetracyclines. They may be additionally resistant to quinolones. Among the antibiotic resistance genes there are two, i.e., floR and tet(G), which code for efflux pumps of the major facilitator superfamily with 12 transmembrane segments that confer resistance to chloramphenicol-florfenicol and the tetracyclines, respectively. In the present study we determined, by constructing acrB and tolC mutants, the role of the AcrAB-TolC multidrug efflux system in the multidrug resistance of several DT104 strains displaying additional quinolone resistance or not displaying quinolone resistance. This study shows that the quinolone resistance and the decreased fluoroquinolone susceptibilities of the strains are highly dependent on the AcrAB-TolC efflux system and that single mutations in the quinolone resistance-determining region of gyrA are of little relevance in mediating this resistance. Overproduction of the AcrAB efflux pump, as determined by Western blotting with an anti-AcrA polyclonal antibody, appeared to be the major mechanism of resistance to quinolones. Moreover, chloramphenicol-florfenicol and tetracycline resistance also appeared to be highly dependent on the presence of AcrAB-TolC, since the introduction of mutations in the respective acrB and tolC genes resulted in a susceptible or intermediate resistance phenotype, according to clinical MIC breakpoints, despite the presence of the FloR and Tet(G) efflux pumps. Resistance to other antibiotics, ampicillin, streptomycin, and sulfonamides, was not affected in the acrB and tolC mutants of DT104 strains harboring SGI1. Therefore, AcrAB-TolC appears to direct efflux-mediated resistance to quinolones, chloramphenicol-florfenicol, and tetracyclines in multidrug-resistant S. enterica serovar Typhimurium DT104 strains.

Molecular characterisation of an outbreak strain of multiresistant Salmonella enterica serovar Typhimurium DT104 in the UK

A major national outbreak of multiresistant Salmonella enterica serovar Typhimurium definitive phage type 104 (MR DT104) occurred in England and Wales in the summer of 2000. Isolates of MR DT104 were characterised by antimicrobial resistance type (R-type), pulsed-field gel electrophoresis (PFGE), plasmid profiling and fluorescent amplified fragment length polymorphism (fAFLP) analysis. Results of R-type, PFGE and fAFLP showed that summer 2000 outbreak-associated isolates were indistinguishable from most MR DT104 isolates collected in England and Wales during the 1980s and 1990s. However, outbreak-associated isolates all had an additional 2-MDa plasmid (PP D), and this distinct profile allowed outbreak cases to be distinguished from background MR DT104 infections, thereby facilitating the epidemiological investigation by improving the specificity of the case definition. The study demonstrated the highly clonal nature of MR DT104 and the importance of a hierarchical approach to molecular subtyping for outbreak investigations.

A national outbreak of multi-resistant Salmonella enterica serovar Typhimurium definitive phage type (DT) 104 associated with consumption of lettuce.

Between 1 August and 15 September 2000, 361 cases of Salmonella enterica serotype Typhimurium definitive phage type (DT) 104, resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, spectinomycin and tetracycline (R-type ACSSuSpT), were identified in England and Wales residents. Molecular typing of 258 isolates of S. Typhimurium DT104 R-type ACSSuSpT showed that, although isolates were indistinguishable by pulsed-field gel electrophoresis, 67% (174/258) were characterized by a particular plasmid profile. A statistically significant association between illness and consumption of lettuce away from home was demonstrated (OR = 7.28; 95% CI=2.25-23.57; P=0.0006) in an unmatched case-control study. Environmental investigations revealed that a number of food outlets implicated in the outbreak had common suppliers of salad vegetables. No implicated foods were available for microbiological testing. An environmental audit of three farms that might have supplied salad vegetables to the implicated outlets did not reveal any unsafe agricultural practices. The complexity of the food supply chain and the lack of identifying markers on salad stuffs made tracking salad vegetables back to their origin extremely difficult in most instances. This has implications for public health since food hazard warnings and product withdrawal are contingent on accurate identification of the suspect product.

Factors affecting haemolysin production and congo red binding in Salmonella enterica serovar Typhimurium DT 98.

Differences in haemolysin expression were observed in a strain of Salmonella enterica serovar Typhimurium definitive phage type (DT) 98 cultured under various conditions. Haemolysin expression was optimal in cultures grown micro-aerobically. The zones of haemolysis were wider after longer periods of incubation. Haemolysin production varied after growth in the following media (greatest to least): brain heart infusion (BHI) broth > nutrient broth (NB)>trypticase soy broth (TSB)> M-9 glucose medium. Haemolysin production correlated directly with Congo red binding in nutrient broth. On Congo red blood agar, colonies were smaller, with dark centres and wider zones of haemolysis. Culture-cell-free haemolysin activity was higher, but cell-bound haemolysin activity was very low in growth medium supplemented with Congo red. Boiled tea extract at 25% v/v (of 25% w/v tea infusion) in PBS and nutrient broth was bactericidal to S. Typhimurium DT 98. The addition of boiled tea extract to growth medium inhibited haemolysin production by S. Typhimurium DT 98 at higher concentrations (6-12.5% v/v) but stimulated haemolysin production at lower concentrations (1.5-3% v/v). The pre-treatment of bacterial cell suspensions with lower concentrations of tea extract (1.5-3% v/v) also altered the Congo red binding, which showed an inverse correlation in nutrient broth.

Characterization of multidrug-resistant Salmonella enterica serovar Typhimurium isolated in Japan.

A total of 221 isolates of multidrug-resistant Salmonella enterica serovar Typhimurium in Japan were characterized in the present study. The results revealed that clonal serovar Typhimurium definitive phage type 104 strains prevailed and that these strains had drug resistance patterns, integron types, and pulsed-field gel electrophoresis patterns similar to those predominant among isolates in Western countries.