Food Poisoning

Define the term “gastroenteritis”:

Gastroenteritis refers to the inflammation of the stomach and intestines; can occur via processes other than bacteria (ie. IBS)

What are the 4 most common bacterial species that cause food poisoning? (Ranked from most common to least)

1) Campylobacter

2) Salmonella

3) Shiga toxin - producing E. coli (STEC)

4) Listeria monocytogenes

Where is Campylobacter commonly found? What animals is it associated with?

Commonly found as COMMENSAL gut bacteria in cattle, poultry, and swine

Campylobacter are considered “microaerophilic” bacteria… What does this mean?

Means that this bacteria REQUIRES lower amounts of oxygen in their environment than there is in the atmosphere

How can Campylobacter be identified on an agar plate? On a slide?

On agar:

• Have a silver / gray appearance on agar; slimy and spread out

On microscope:

• GRAM NEGATIVE

• Are described morphologically as CURVED rods

• Flagellated with TWO POLAR flagella (unique feature)

• Capsulated

What is one key feature of Campylobacter that differentiates it from Salmonella and E. coli? (Hint: either oxidase positive or negative)

Is oxidase POSITIVE instead of negative

What are the 2 Campylobacter species that are mentioned in this lecture? Which one is the most common cause of human infection?

C. jejuni and C. fetus

C. jejuni is the most common cause of human infection

In what ways can C. jejuni and C. fetus negatively effect ruminants?

** Note: these don’t ALWAYS cause infection, but when it is pathogenic, can cause -

• Reproductive failure (think fetus in C. fetus)

What is a virulence factor that is REQUIRED for Campylobacter to be infective?

MOTILITY; will not be infective otherwise

What is the correct full name for Salmonella? (genus and species)

Salmonella enterica

NOT typhimurium like is commonly thought

Where is Salmonella most commonly found? What species are the most common carriers?

Found as COMMENSAL gut bacteria in vertebrates

Most common reservoirs are reptiles and birds (chickens most well-known source)

** Note: host is determined by specific fimbriae

Is salmonella facultatively anaerobic or aerobic? What else about its lifestyle makes it unique to the other bacteria mentioned?

Facultative ANaerobic

Is also a facultative INTRAcellular pathogen

How can salmonella be identified on an agar plate? On a microscope?

On AP120E agar:

• Salmonella CANNOT ferment lactose, so on this medium, the agar will remain colorless (instead of pink, like it would for lactose-fermenting bacteria)

On microscope:

• NOT capsulated

• Most strains have flagella

Salmonella is grouped into 2 different types; what are these groups, and how are they differentiated between?

These groups are H antisera and O antisera, they are differentiated by what component of the bacterial cell is the antigen to the human body.

H antisera - antigen is flagella

O antisera - antigen is LPS from cell wall

Where is E. coli commonly found? What species does it usually associate with?

Is a common COMMENSAL bacteria of the gut in farm animals (MOSTLY CATTLE)

• Can colonize other animals, but only causes disease in humans

Is E. coli facultative aerobic or anaerobic?

Facultative ANaerobic

How can you identify E. coli on an agar plate?

AP120E agar:

• FERMENTS lactose, so agar will turn pink

Can also be grouped the same way as Salmonella, H antisera being flagella and O antisera being LPS

What is the main source of pathogenicity from E. coli in humans?

The Shiga toxin they produce (making this type of E. coli an STEC)

• Toxin is very harmful, especially for the young and old

• Infectious dose is very low

How is E. coli transmitted to humans? (2 main ways)

1) Undercooked meat

• Fecal contamination during slaughter → undercooked steak / burger → infection

2) Contaminated veggies

• Using manure from infected cattle to fertilize crops can cause this

What is the most well known STEC that causes disease in humans?

E. coli O157:H7

Describe how we classify pathogens in relation to how dangerous they are to humans / how difficult they are to treat…

Use a numbering system from 1-4, lowest number being lowest risk

Using the numbering system, how are the bacteria that were mentioned in this lecture ranked?

Campylobacter, Listeria, and Salmonella are category 2

STEC is category 3

• Because the toxin it produces is destructive, and treatment with abx causes more shiga toxin to be released

What are 3 things that make Listeria different from the rest of the bacteria covered in this lecture?

1) NOT COMMENSAL bacteria in animals, causes disease

2) GRAM +

3) Able to replicate in refrigerated temperatures

Is Listeria facultative aerobic or anaerobic?

Facultative ANaerobic

What do Listeria and Salmonella have in common?

Both facultative INTRAcellular pathogens

What is characteristic of Listeria’s flagella?

Poorly motile, causes Listeria organisms to move in a characteristic “tumbling” pattern

What species is Listeria mainly found in?

Ruminants, swine, birds, cats, and dogs

How can Listeria be transmitted to humans?

Usually found in:

• Pate (the food)

• Unpasteurized dairy products (soft cheese)

• Fish meat

• Cured meats (salami ☹ )

What makes Listeria so dangerous?

Other than causing the usual gastroenteritis symptoms, the bacteria doesn’t just stay in the gut…

• Migrates; can go to sites such as the CNS

• Can cause sepsis and / or meningitis

Is VERY dangerous for pregnant women and newborns