Food-borne bacterial infections

Question 1

Defences against infection in the gastrointestinal tract

Answer 1

• Mouth-saliva,lysozyme
• Oesophagus-peristalsis
• secretory IgA in small intestine

Question 2

How do pathogens overcome defences to cause disease?

Answer 2

• fatty foods (lowers dose)
• proton pump inhibitors decrease stomach HCL
• high/low infectious dose
• survive acid stress

Question 3

food-borne disease

Answer 3

results from contamination of food by pathogens

Question 4

food poisoning

Answer 4

results from microorganisms having grown on the food to produce:

a) a sufficiently large population to produce an infective dose
b) toxins in the food

Question 5

bacterial causitive agent examples

Answer 5

salmonella, campylobacter, shigella, vibrio cholerae

Question 6

Toxin-type food poisoning

Answer 6

• staphylococcus aureus -enterotoxin

- clostridium botulinum -neurotoxin

Question 7

Infection-type food poisoning

Answer 7

• ->salmonella, E.coli -GI symptoms

- ->Listeria monocytogenes - systemic symptoms

Question 8

Reported cases highest no in uk from

Answer 8

campylobacter

Question 9

Diarrhoeal diseases =

Answer 9

greatest single cause of human morbidity and mortality in world

Question 10

Salmonella

Answer 10

• motile, non-sporing, gram-ve rods
• facultative anaerobes
• salmonella enterica >2000 serotypes

S.Typhi - human, systemic infection (typhoid fever) - no animal source-bloodstream and reticuloendothelial system infection

Question 11

Typhoid and Enteric Fever

Answer 11

-associated with lack of health services
Caused by:
-salmonella typhi
-salmonella paratyphi A, B, C

Question 12

Pathogenesis

Answer 12

• localised invasion of intestinal mucosa - facultative intracellular parasites
• type III secretion systems essential for virulence
• bacteria pass through M cells, taken up by macrophages, multiply and lyse macrophages

Question 13

Survival strategies of Salmonella sp in macrophages

Answer 13

1. prevent fusion of lysosome

2. survival in phagosome

Question 14

Campylobacter

Answer 14

• C.jejuni - slender, motile, gram -ve curved or spiral rods

- Microaerophillic

Question 15

Sources of campylobacter

Answer 15

• common gut inhabitants of animals/meats
• meat infected with gut contents at slaughter
• survive well on chickens processed rapidly and staying moist
• cross contamination

Question 16

C.jejuni and C.coli in man

Answer 16

• acquired from animals via food/contact

- acute infective bacterial diarrhoea

Question 17

pathogenesis

Answer 17

• facultative intracellular parasites
• invade mucous membranes of gut
• produce cytotoxins (cause tissue destruction)

Question 18

General preventative measures

Answer 18

1. Prevention of contamination of food
2. Prevention of growth of pathogens
3. rejection of suspected foods

Question 19

Salmonella

Answer 19

• facultative anaerobe
• grows between 5-47 degrees C
• symptoms after 12-36 hours
• lasts 2-6days
• avoid through heat treatment (Eg pasteurisation)

Question 20

Campylobacter

Answer 20

• microaerophilic
• grows between 30-47C
• fever, Diarrhoea,cramps last 3days-3weeks