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Environmental Survival of Salmonella Serotypes S. typhimurium. DT104 and S. enteritidis PT4: The Role of Surface Antigens

Institutions
Health Protection Agency
Start date
1998
End date
2000
Objective
This research project aims to gain a better understanding of those factors affecting the survival of Salmonella spp. in dry environments.

This study will gain a better understanding of the factors affecting the survival of Salmonella spp. in dry environments.

Strains of S. enteritidis PT4 and 6 and S. typhimurium DT104 will be examined and their behaviours will be compared with those of other sero- and/or phage types.

The study will also identify simple phenotypic markers that could be used to identify salmonella strains with enhanced survival.

A number of salmonella mutants, notably of surface antigens and global regulatory factors, will also be studied in an attempt to identify cellular mechanisms important in survival.

More information
During the infection process, salmonella enter intestinal epithelial cells by a complex mechanism initiated by contact between the cell surfaces.

In vitro cell adhesion and invasion assays have identified the host cellular processes leading to engulfment of the bacterium.

These include an increase in calcium ion influx, cytoskeletal rearrangements, localised ruffling at the cell surface, increased tyrosine kinase and protein phosphorylation.

Many genes encoded within 'pathogenicity islands' of salmonella are essential for successful invasion. These genes appear to be tightly regulated and require specific environmental signals for their expression.

The potential of S. enteritidis PT4 to elaborate six discrete fimbrial structures, hair-like proteinaceous antigens, which project from the bacterial cell structure has been demonstrated. At least two of these types, type 1 fimbriae and SEF17 fimbriae, possess adhesive properties, binding eukaryotic cell surface moieties and intracellular matrix components respectively.

Studies have demonstrated that there are several groups of S. enteritidis PT4 strains with regard to survival after exposure to various environmental stresses such as heat, acid, peroxide, air dying on surfaces and aerosolisation. Tolerant S. enteritidis isolates usually generate the so-called 'lacy' or convoluted colony phenotype when grown on various agar media following temperature reduction from 37°C to 20°C.

The 'lacy' colony phenotype generated by tolerant/virulent S. enteritidis isolates may be dependent upon expression of the SEF17 fimbriae. SEF17 null mutants and naturally occurring sensitive/virulent S. enteritidis isolates which do not express SEF17 do not generate the 'lacy' colony phenotype.

The expression of SEF17 is likely not only to be under the same regulatory control as those genes which contribute to bacterial survival and increased pathogenicity, but may also be part of the machinery of survival and increased pathogenicity.

Studies on S. typhimurium DT104 indicate that the majority of isolates produced the 'lacy' colonial phenotype and were very tolerant to a wide range of damaging environments and were particularly adept at surviving in the environment.

It has been shown that previously non-responsive PT4 and DT104 isolates may be induced to form 'lacy' colonies by change of media composition, notably by addition of hydrophobic compounds as supplements.

Whilst much research effort is aimed at resolving fundamental aspects of pathogenesis, little regard is given to two important factors which are essential for infection, namely

(i) survival of the bacteria in the environment and

(ii) the potentiation of colonisation and communicability between infected and non-infected individuals as a result of survival within a given environment.

Given that the bacterial cell surface is the point of contact between the bacterium and its environment, that factors at the cell surface are essential for the first stage of pathogenicity (adherence and invasion) and that the cell surface is a conduit for sensing and permitting bacterial responses to the environment, this project aims to examine the hypothesis that the bacterial cell surface and surface antigens plays a significant role in survival within the environment and potentiating infectivity.

Find more about this project and other FSA food safety-related projects at the Food Standards Agency Research webpage.

Funding Source
Food Standards Agency
Project number
B03012
Categories
Bacterial Pathogens
Viruses and Prions
Salmonella