A comparison of Salmonella enteritidis phage types from egg-associated outbreaks and implicated laying flocks

Progression of Salmonella enteritidis phage type 4 strains in São Paulo State, Brazil

A total of 574 S. Enteritidis strains (383 from human sources and 191 from non-human sources) isolated between 1975-95, in São Paulo State, Brazil, were phagetyped. Among the strains isolated during the period of 1975-92, 80.9% of them belonged to phage type 8 (PT-8), but in 1993 strains of PT-4 accounted for 65.2% of all the S. Enteritidis isolates. In the following years, PT-4 strains accounted for 99.7% and 98.4% of phagetyped S. Enteritidis strains. The results obtained suggested that the current epidemic of S. Enteritidis in São Paulo State is clearly associated with the progression of PT-4 strains.

Application of random amplified polymorphic DNA analysis to differentiate strains of Salmonella enteritidis

A random amplified polymorphic DNA (RAPD) fingerprinting method has been developed to differentiate Salmonella enteritidis isolates. A total of 65 arbitrary primers were screened with S. enteritidis isolates of different phage types. This allowed selection of a panel of primers capable of detecting DNA polymorphisms among S. enteritidis isolates. This panel was used to examine a panel of 29 isolates of S. enteritidis which had been previously characterized by other subtyping methods, including phage typing (PT) (n = 7), ribotyping (RT) (n = 13), and pulsed-field gel electrophoresis (PFGE). Applied collectively, these three methods resolved the collection into 20 different subtypes. However, by the RAPD fingerprinting method alone, 14 RAPD subtypes were revealed. Eight isolates of S. enteritidis phage type 8 that failed to be discriminated by other typing methods (PT, RT, and PFGE) were resolved into three different subtypes by RAPD analysis. In contrast, isolates that were derived from the same sources were not differentiated by any of the subtyping methods employed, including PT, RT, PFGE, and RAPD analysis. This RAPD approach to S. enteritidis subtyping provided more discriminatory power than did any of several other subtyping methods applied individually. Once the challenging step of primer identification was accomplished, determinations of the appropriate concentrations of arbitrary primer, DNA template, and MG2+ ion were also necessary for optimal discriminatory power. The bacterial DNA used in this RAPD protocol was obtained by boiling the bacterial sample. This simple procedure yielded DNA that produced fingerprint patterns as consistent as those obtained from phenol-chloroform-extracted DNA. Clearly, when appropriately constituted primer sets are identified and employed, RAPD analysis provides a simple, rapid, and powerful subtyping method for S. enteritidis.

Phage conversion in Salmonella enterica serotype Enteritidis: implications for epidemiology

A model system for the study of phage conversion of Salmonella enterica serotype Enteritidis is reported. Temperate phages 1,2,3 and 6 from the phage typing scheme were used to convert several individually recognized phage types into others. Phage type 4 was converted to PT8, PT6a to PT4, PT6a to PT7, PT13 to PT13a and PT15 to PT11; some new phage lysis patterns were also detected. This model was used to examine the relationships between phage types within a previously defined clonal lineage, SECLIII, to establish whether or not Enteritidis like Salmonella enterica serotype Typhi and Salmonella enterica serotype Paratyphi B possessed type determining phages. We were able to convert PT1 to PT20, and PT15 to PT11.

Salmonella enteritidis: the egg and I

The world-wide clinical incidence of Salmonella Enteritidis has increased markedly. The increase is associated with the enhanced ability of the bacterium to systemically colonise layer chickens. Subsequent contamination and consumption of intact shell eggs from colonised layer hens, either directly or in foods containing raw or lightly cooked eggs, causes human disease. Despite investigation, no change in the biology of the bacterium has been correlated with increased colonisation in chickens. To date, no method of control at the production level has proven effective; consumer education is the best means of minimising the public health risk.

Effect of Eimeria tenella infection on Salmonella enteritidis infection in chickens

The effect of Eimeria tenella infection on the Salmonella enteritidis infection in chickens was investigated in three experiments. Each experiment consisted of an uninfected control, birds infected with E. tenella, birds infected with S. enteritidis, and birds infected with a combination of E. tenella and S. enteritidis. A dose of 2 x 10(4) sporulated oocysts of E. tenella was given to each chicken. In Experiment 1, each chicken was infected with 10(5) cfu/d of S. enteritidis for 3 consecutive d starting 1 d after coccidia exposure and necropsied 4, 7, 10, and 14 d after coccidial infection. In Experiments 2 and 3, each bird was infected with 10(2) cfu/d and 10(1) cfu/d of S. enteritidis respectively, for 2 d beginning 4 d after coccidia exposure, and were killed 7, 10, and 14 d postinfection with E. tenella. Results showed that interaction between S. enteritidis and E. tenella was significant in Experiments 1 and 2, but not in Experiment 3, manifesting that the cecal Salmonella population were significantly increased by coccidial infection in birds killed 4, 10, or 14 d after coccidia exposure in Experiment 1 and in birds killed 14 d after coccidial infection in Experiment 2. The dose size of S. enteritidis was an important factor for the synergistic relationship between S. enteritidis and E. tenella. Frequency of recovery of S. enteritidis in liver and spleen was not increased by E. tenella infection.

An approach to reduction of Salmonella infection in broiler chicken flocks through intensive sampling and identification of cross-contamination hazards in commercial hatcheries

A comparative study of salmonella contamination in eleven commercial hatcheries in the UK was carried out during 1992/93. The sampling protocol involved individual swabbing and culture from surfaces and items of equipment within each premises. This allowed the identification of many areas where salmonella control measures were not successful resulting in a cross-contamination hazard for eggs and chicks. Egg sanitisation and handling methods, design of incubator and whole building ventilation systems, control of dust, fluff and aerosol production, disinfection of surfaces and equipment and handling of waste were areas where improvements could be made. There were examples of successful reduction of salmonella in all key areas and these could be extended to provide general practical protocols for salmonella control. The sampling and culture techniques used in this study required less labour and were more rapid and sensitive than traditional methods so could be used in comparative investigations of other complex high throughput livestock and food processing operations.

Changes in human ecology and behavior in relation to the emergence of diarrheal diseases, including cholera

Human populations throughout the world can be found in diverse conditions. A proportion of the population of developing countries lives in deprived conditions characterized by ramshackle housing, lack of piped water and sanitation, and widespread fecal contamination of the environment. Enteric infections, particularly due to bacterial pathogenes, are readily transmitted under these circumstances. In contrast, the majority of inhabitants of industrialized countries live in a sanitary environment that generally discourages the transmission of enteric pathogenes, particularly bacteria. In both these ecologic niches, changes in human ecology and behavior are leading to the emergence of certain enteric infections. Relevant factors in developing areas include urbanization (leading to periurban slums), diminished breastfeeding, and political upheaval that results in population migrations. In industrialized areas, large-scale food production (e.g., enormous poultry farms), distribution, and retailing (e.g., fast-food chains) create opportunities where widespread and extensive outbreaks of food-borne enteric infection can ensue if a breakdown in food hygiene occurs.

Salmonella enteritidis in Canada

During the last few years the prevalence of Salmonella enteritidis in people in Canada has increased slightly from 9 to 12% of all Salmonella isolates. Nation-wide surveys showed a low prevalence of S. enteritidis in poultry flocks: S. enteritidis was isolated from environmental samples of 2.7% of layer flocks and of 3% of broiler flocks. The overall prevalence of S. enteritidis-contaminated eggs from two flocks with infected hens was less than 0.06%. With the exception of S. enteritidis phage type (PT) 4, which has not been isolated from poultry in Canada, the phage types that occur most commonly in poultry (PT 8, 13 and 13a) are also the most prevalent in people. Phage typing was the most effective method for subdividing S. enteritidis strains. Eighty-three percent of the S. enteritidis isolates from poultry and its environment were sensitive to antimicrobial agents. The reasons why strains of the same phage type differ in virulence need to be elucidated.