salmonella Flashcards
First recognised as
the agent of typhoid fever by Eberth in 1880
characteristics
Gram-negative motile non-sporing rod
Sterotypes
2400 different serotypes according to the Kauffman-White scheme
67 ‘O’ antigens, cell wall lipopolysaccharide
H antigens from flagella
Serotypes named according to particular combination of O and H antigens
Salmonella enterica 7 subspecies
I, II, IIa, IIIb, IV, V and VI
Most food poisoning strains come from which subspecies
1 - Salmonella Typhimurium
group 1
adapted to man
Salmonella serovars Typhi, Paratyphi
Cause enteric fever
group 2
adapted to animals serovar Dublin, Typhimurium: Cattle serovar Cholerae-suis: pigs serovars Galinarum, Pullorum: poultry Can cause enteric fever type diseases
group 3
non host- adapted
2400 serovars carried asymtomatically in animals and birds
cause food poisoning in humans
Incubation time
6- 48hr
symptom?
can last for ?
Chronic consequences
Nausea, vomiting, diarrhoea, abdominal cramp, fever, headache
May last for 1 -7 days
Chronic consequences may arise several weeks later e.g. arthritis
Fatality
usually less than 1% (compared with up to 10% with Typhi)
During Enteritidis outbreaks, 3.6% mortality in nursing homes among elderly
Virulence mechanisms
how many genes involve?
Located in ?
- 30 genes approx. involved in invasion phenotype
- Located in ‘pathogenicity island’ 35-40 kb
- Contact-dependent Type III secretion system delivers bacterial proteins to host cells
- Contact with enterocytes triggers formation of invasomes for attachment
- Bacterial signals cause polymerisation of host cell actin and cytoskeletal rearrangements
- Ruffles and blebs form on host cell surface and draw salmonellae into cells
- Salmonella multiplies in vacuoles
- Penetration of Salmonella into cytoplasm of epithelial cells triggers an influx of leucocytes at the infected area
- Release of prostglandins causes mucosal inflammation
- Bacterial cells release an enterotoxin within inflamed tissue which activates host adenyl cyclase enzyme
- This results in fluid loss from gut and diarrhoea
Salmonella Enteritidis
associated food
undercooked egg dishes
poultry meat
Salmonella Typhimurium associated food
Beef, dairy produce, pork lamb, chicken turkey
Other serotypes associated food
Cheese, salami, cream-filled desserts, shrimp, frog legs, yeast, coconut, sauces and salad dressing, cake mixes, dried gelatin, peanut butter, cocoa, and chocolate
Infectious dose
depends on serotype host susceptibility and food matrix
- Salmonella Anatum in eggnog: 10^6 – 10^7
- Salmonella Typhimurium in chocolate ~ 10 cells
Once salmonella in which food is hard to detect?
fatty food
Possible control measures in the poultry flock in 1980’s
Testing for infection
slaughter of positive flocks
Possible control measures in the poultry flock in 1997
Strict biosecurity and hygiene in poultry sheds
Vaccination against S. Enteritidis
Possible control measures in the poultry flock in The future
Competitive exclusion
Bacteriophage control
Broiler Production
Salmonella-free-parent stock
- -> Clean eggs taken to hatcheries, incubated for 21 d
- -> Chicks vaccinated at one day old
- -> Kept in broiler house for 43 days ~2.2 kg. Disinfection of house between batches
- -> Dispatched for slaughter
Zoonoses Order 1989
- Testing for Salmonella
- Compulsory slaughter of Salmonella-infected poultry
- Compensation for infected flocks
- Stricter reporting requirements
Egg Production
Breeding flocks
- -> Hatcheries
- -> Rearing farms 0-16 weeks
- -> Laying farms 16-72 weeks
- -> Packing centres
Lion Code of Practice
control points
Breeding Flocks Rearing farms Laying farms Feed Transport of eggs from the farm Packing centres Best before dates
