Food borne infections and toxins

Any sickness that is caused by the consumption of foods or beverages that are
contaminated with certain infectious or non-infectious agents

Children < 5y carry 40% of disease burden

Salmonella enterica subsp. enterica serovar Typhi

• Sanitation
• Hygiene
• Clean water
• Sewerage

We eat some foods raw (vegetables) or “pink” (meat)
Some foods can develop bacterial toxins when left after cooking
Cooked food may be contaminated from raw food or faeces

• Norovirus
• Campylobacter spp.
• Salmonella spp.
• Listeria monocytogenes
• Escherichia coli

salmonella

listreia and clotridium
(norovirus high as well)

SS RNA calicivirus
Small infective dose
Highly survivable in the environment

RT-qPCR BUT:
• Cannot discriminate infectious or non-infectious norovirus

rapid: incubate day
resolve 3 days

• Infants/young children
• Transplant patients / immunosuppressed
• Elderly

• Broadening and blunting of villi /
shortening of microvilli
• Specific intestinal lesions completely
resolve within two weeks

Person-to-person
Foodborne
Waterborne
Environment

cook 80+ degrees and disinfections

Curved Gram-negative rod
• C. jejuni (poultry)
• C. coli (pigs)
• C. upsaliensis (dogs)

culture of faecal sample
• Microaerophilic, thermophilic
(42oC), 48h
• Blood / charcoal agar with
antibiotic
if can culture- probably the cause in humans, but easily culturable in animals with no problems

colonise SI
incubate 5 days
inflam, enteritis
CS
resolve in a week

Endemic in animals – carried sub-clinically by birds and many animals
• Eating contaminated food (raw poultry especially)
• Contact with carrier pets / farm animals
Chickens regularly colonised – factory processing promotes carcass contamination
• Freezing allows survival

cooking kills
freezing doesnt

Gram-negative rod
• Salmonella enterica subsp enterica ser. Typhimurium / Enteriditis

culture of faecal sample
• Facultative anaerobe, normophilic
• Enrichment broth (selenite) 24h
• Selective media (XLD) 24h
• Serovar typing

Kaufmann-White scheme
• O = lipopolysaccharide antigen
• H = flagella antigen

incubate= 1 day
adhere and invades intestinal epithelium
intestinal inflam
immunocompetent patient= self limiting, confined to terminal ileum and colon
sysmtpoms subside in few days, can shed for >1 month

Foodborne
Water borne
Animal contact

cooking kills
vaccines can reduec carriage

gram positive rod

culture of faecal sample
• Facultative anaerobe, psychrophilic
• Selective culture needed
• Characteristic motility at 4oC

Incubation time: 2 - 3 days (non-invasive) / 1 - 2 weeks (invasive)
Resolution: 2 - 3 days

fac intracellular pathogen:
invades and multiplies within mammalian cells
cross intestinal wall at peyers patches
prolonged speticaemia

Pregnant women
• 20 times more likely to contract listeriosis
• Experience fever and fetal issues

Foodborne
• Contaminated raw meat
• Unpasteurised milk
• Cheese using unpasteurised milk
• Foods containing raw vegetables

Vertical transmission during pregnancy

cooking kills

Shiga-toxin producing E. coli
(also enterohaemorrhagic/ verotoxigenic)
O157:H7 serotype

culture faecal sample

calves: diarrhoea, haemorrhagic colitis
cow carry subclinically

incubate: days
resolve: week

effaced microvili with e coli on pedestals nearby
toxin production-> haemorrhagic colitis and haemolytic uraemic syndrome

raw meat
animal contact

cooking kills e coli

Incubation time: 12 h
Resolution: 12 h

heat stable toxins produced in some strains

Bacillus cereus
• Produces a heat-stable toxin

contaminated meat

Vibrio parahaemolyticus
• Waterborne pathogen, shellfish

sale direct to consumer legal in most UK eg farm side- BANNED IN SCOTLAND
must register with FSA

USA= governed by state

Infants and young children
Older adults
Pregnant women
Immunosuppressed

healthy people can still become ill

Animals healthy and free from brucellosis + TB
Farm complies with hygiene rules and routinely inspected twice a year
Product labelled with appropriate health warning (including raw milk as ingredient)
Verification sampling programme of raw drinking milk

limit bacterial total count
few coliforms
MO salmonella, capylo, STEC
few coagulase + staphs
listeria below limi throughout the proposed shelf life

Salmonella= absent
Enterobacterales below cut-off

bacteria:
Salmonella spp. and L. monocytogenes isolated
Salmonella spp., C. jejuni, and L. monocytogenes from 33.3% faecal samples
Genetic association for Salmonella from faecal / raw food samples from same
household

• Hand hygiene with food, pet and faecal material
• Keep young children away from raw food
• Store away from human food and use separate utensils
• Disinfection of surfaces, utensils used for preparation
• At risk individuals in the house?

• Pro-commensal (favour competition) e.g. probiotics
• Anti-pathogen e.g. vaccines, antimicrobials
• Exposure reduction e.g. biosecurity