Food Poisoning

How should we address food poisoning from a one-health stand-point?

Food poisoning is therefore often considered to be best addressed using a "One Health" approach where we should consider the role of animals, humans and the environment in the spread of these infections

What is gastroenteritis?

Inflammation of the stomach and intestines

Food poisoning can be caused by…

• Bacteria

• Food / Water contaminated by heavy metals

• Parasites

What are the top three species causing bacterial GI disease?

• What is the least common?

• Campylobacter is by far the most common cause of food poisoning

• Salmonella is the 2nd most common cause of food poisoning

• Shiga toxin producing E. coli (STEC) is the 3rd most common cause of food poisoning

• Listeria monocytogenes is by far the least common cause of food poisoning

Where are campylobacter most often found?

What are their growth requirements?

How do colonies appear in a culture?

How do the bacteria themselves appear?

• Campylobacter is commonly found in the gut of cattle, poultry and swine

• They are microaerophilic, so need a lower amount of oxygen than in air

• They can be identified by their distinctive colony appearance and Gram stain

• Silvery gray, shiny, no distinct colonies, continuous growth

• Campylobacter are Gram negative CURVED rods, unlike Salmonella and E. coli which are not curved

• Campylobacter are flagellated with polar flagella, unlike Salmonella and E. coli which have peritrichous flagella

What main test will differentiate campylobacter and from salmonella and E. coli?

Oxidase test

• Catalase positive and OXIDASE POSITIVE (Salmonella and E. coli are oxidase negative)

Describe features of campylobacter transmission.

• Campylobacter have capsules

• Campylobacter doesn't always cause infection in animals, it is sometimes a gut commensal

• The infectious dose is quite low compared to Salmonella for example

• C. jejuni is the most common cause of human infection

• C. jejuni and C. fetus cause reproductive failure in ruminants

• Campylobacter remains outside intestinal epithelial cells (lECs)

• Motility is required for Campylobacter infectivity

Where are salmonella most often found?

What are their growth requirements?

What tests can help identify them?

How do the bacteria themselves appear?

• Salmonella is commonly found in the gut of vertebrates

• They are facultative anaerobes

• They are catalase positive and oxidase negative

• They can be identified using API20E

• Salmonella DO NOT ferment lactose

• Appears yellow on MacConkey agar

• Most strains DO NOT have a capsule

• Most strains are flagellated

How can salmonella be grouped?

• Salmonella can be grouped using serology

• Specific H antisera can differentiate according to flagella antigens

• Specific O antisera can differentiate according to LPS in the cell wall

• If there is a capsule then Vi antisera can differentiate capsule type

What are the most common reservoirs for salmonella?

• What determines the hosts?

• Does salmonella cause disease in these hosts?

• The most common reservoirs for salmonella are reptiles and birds

  • Hosts are determined by the fimbriae type

  • Often causes NO disease in these animals

Salmonella is a ______ _______ pathogen.

facultative intracellular

How can salmonella spread to eggs?

Salmonella Enteritidis can infect the ovaries of a chicken and be spread vertically (To eggs which can infect humans)

What is significant about “Red Lion” eggs?

• Are salmonella free, vaccinated chickens means the eggs can be eaten raw

Many types of E. Coli are not _____, however the ____ ____ producing E. coli called ___ or __________ E. Colic (EHEC) does cause zoonotic food poisoning.

zoonotic, shiga toxin, STEC, enterohemorrhagic

Where is E. coli most often found?

What are their growth requirements?

What tests can help identify them?

How do the bacteria themselves appear?

• E. coli is commonly a commensal in the mammalian gut

• They are facultative anaerobes

• They are catalase positive and oxidase negative

• They can be identified using API20E

• Most E. coli ferment lactose

• Appear red/pink colonies on MacConkey agar

• Most strains are flagellated

How can E. coli be grouped?

• Specific H antisera can differentiate according to flagella antigens

• Specific O antisera can differentiate according to LPS in the cell wall

What is the main reservoir for STEC?

• Does it cause disease in these animals?

• The STEC reservoir is farm animals, notably, cattle

• STEC are less common in other animals such as chickens, sheep, pigs, deer or other wildlife

• Animals are typically NOT sick

What is the significance of the Shiga toxin produced by E. coli?

The Shiga toxin produced can be extremely harmful to humans - especially the very young/old and/or the immunocompromised

• Additionally infectious dose is quite low

How can STEC be introduced to the external surface of meat?

• Faecal contamination during slaughter introduces STEC onto the external surface of meat

• If we were to nick the bowels for examples

• When we "mince" up that meat and make beefburgers, we put what was on the outside, in

• Makes it more dangerous than other types of meat

How can STEC be introduced to vegetables and other crops?

If we use manure from colonised cattle to fertilise crops, we can introduce STEC into lettuce and other vegetables

What clinical syndromes may STEC cause?

STEC can cause haemorrhagic colitis and/ or haemolytic uremic syndrome (HUS)

What is the most well known STEC?

The most well known STEC is E. coli 0157:H7 but other non-0157 STEC are becoming more prominent

How are pathogens classified?

Using a number system (1-4), one being lower and higher being greater risk

• We classify pathogens according to how dangerous they are to humans and/or how difficult they are to treat if humans become infected

What are some category 2 pathogens?

• Campylobacter, Listeria, Salmonella

What are some category 3 pathogens?

• Why are they classified in this way?

STEC

• The toxin it produces is so destructive and treatment with antibiotics can cause more toxin to be released

Where is Listeria most often found?

What are their growth requirements?

What tests can help identify them?

How do the bacteria themselves appear?

• NOT commensal in animals, causes disease in animals and humans

• They are facultative anaerobes

• Also facultative intracellular pathogens like salmonella

  • Listeria are notably able to replicate at refrigeration temperatures

• They are catalase positive and oxidase negative

• Listeria is a GRAM POSITIVE coccobacillus (unlike Campylobacter, Salmonella and E. coli

• Have flagella, but poorly motile at 37C

  • Move in a characteristic, tumbling motion

What are the main reservoirs for listeria?

• Listeria is found mainly in ruminants, swine, birds, cats and dogs

• Listeria is found in pâté, unpasteurised dairy products like soft cheese, fish and cured meats

• Since they can survive colder temperatures

Why is the transmission of Listeria so significant and why does it have such a high mortality rate?

• Listeria are facultative intracellular pathogens, but they don't just stay in the Gl tract

• They can migrate to sites such as the central nervous system and cause sepsis and /or meningitis

• Although Listeria causes relatively few infections, it is noteworthy because it has a very high mortality rate

• Particularly dangerous for pregnant woman and newborns