Project leader: Dr S. Bertrand, Dr. W. Mattheus and Dr R. Vanhoof
Collaborating center : C. Wildemauwe (Unité de typage par Phages - Brussels)
Salmonella are gram-negative, aerobic, non-sporing rods that readily grow on simple culture media.
Salmonella can infect a diverse range of animal hosts, from insects, reptiles and birds to mammals, including man and can be present and persist in the environment. The presence of Salmonella in other habitats (water, food and natural environment) is explained by faecal contamination.
The genus Salmonella consists of two species: S. enterica and S. bongori (V).
The species S. enterica is divided into six subspecies: subspecies enterica (I), subspecies salamae (II), subspecies arizonae (IIIa), subspecies diarizonae (IIIb), subspecies houtenae (IV), and subspecies indica (VI). The actual number of serovars in all Salmonella species and subspecies is 2501 (Kauffmann-White scheme 2001).
Most isolates of Salmonella from warm-blooded animals belong to subspecies enterica (I). The other subspecies are found in cold-blooded animals and environment. Serovar names are no longer considered as species names and therefore are not printed in italics. S. typhimurium becomes S. enterica subspecies enterica serovar Typhimurium or Salmonella Typhimurium. Only serovars of S. enterica subspecies enterica are given names (usually geographical names). Serovars of other subspecies are designated by their O:H formula.
All Salmonella serovars are considered potential pathogens in most animal species. The pathogenicity of some serovars appears to be limited to a narrow range of animal hosts such as S. Dublin in cattle, S. Typhi in human and S. Gallinarum (fowl). Other serovars such as S. Typhimurium can affect many species.
Human infection with Salmonella may be expressed as acute gastroenteritis, enteric fever, bacteraemia or localized metastatic infection at almost any site.
A chronic carrier state may occasionally occur after infection with Salmonella, and is characterized by a prolonged excretion of the organism in faeces or urine.
The National Reference Center receives the human Salmonella isolates of more than 200 clinical laboratories. Current manufacturing and distribution practices play an important role in the occurrence of foodborne infections. Free movement of people can also be effective in distributing the disease nationally and internationally.
The aim of our national surveillance program (in collaboration with the Epidemiology Division of our Institute) is to document the occurrence and trends of serovars, to detect and investigate local, regional, national or even international outbreaks (in collaboration with the Enter-net network), to find and eliminate the source(s), and to suggest preventive actions.
All Salmonella isolates sent to the Reference Center are cultured on Kligler and tested for dulcitol and inositol fermentation to orient the serotyping and to verify the accuracy of identification performed by the original laboratory.
The serotyping is performed with the slide agglutination test (commercial antisera) according the scheme of Kauffmann-White. When necessary, additional biochemical tests are realized to confirm the identification or to differentiate between the subspecies.
The most important serovars are regularly randomly sampled for antimicrobial susceptibility testing. The susceptibility is determined by the disk diffusion method following EU-CAST recommendations. The following antibiotics are tested: ampicillin, cefotaxime, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfonamides, tetracycline, trimethoprim, trimethoprim + sulfamethoxazole.
Phage typing is also performed on Enteritidis, Typhimurium, Hadar and Virchow serovars. The phage typing is realised in the unit "phage typing" of the division according to the recommendations of the Central Public Health Laboratory Service ( London ).
Pulse Field gel Electrophoresis (PFGE) is used to investigate outbreaks.wiv-isp: www.wiv-isp.be see our compendium CNR and our compendium LMM (FR-NL)National Reference Centrum: http://nrchm.wiv-isp.be