2. Foodborne Illnesses - Gram Positive Pathogens

What is a spore?

• Produced by bacteria, moulds and yeasts

  • Endospore, endo = inside

  • moulds also use it to reproduce

• Resistant structures

• Role in spoilage and disease

• Dormant structure: no metabolic activity

• DNA is present in the core

• Different protective layers

Gram positive vs Gram negative

What are spores resistant to?

• Wet heat

• Dry heat

• UV and gamma radiation

• Extreme dessication

• Oxidative chemicals

Listeria monocytogenes

• Gram +

• Motile rod

• Facultative anaerobe

• Ubiquitous pathogen (an organism that causes disease and is widespread and abundant in its environment)

• Salt tolerant (Awmin = 0.92)

• Grows in chilled foods (Tmin = 0 C)

Different Listeria species

• There are 6 listeria species: only L. monocytogenes is pathogenic for humans

• The invasive listeriosis has had 4 confirmed cases per million people

• Of all confirmed cases 16-30% die.

What can Listeriosis do to you?

• Mild intestinal illness:

  • Gastro-enteritis, mild flu-like illness

  • Incubation time: <1 day - 48h, lasts 1-3 days

• Severe illness

  • Stillbirth (fetus), septicemia, meningitis

  • Incubation time: <1 day - 3 months

YOPI

Consumers considered most vulnerable to foodborne illness include the young (0-5 years), older (65+ years), pregnant, and immunocompromised -

L. monocytogenes in foods

• Deli meats

• Soft cheese

• Raw milk

• Pate

• Smoked and lightly processed fish

• Ready to eat foods

Does MAP & vacuum packaging prevent growth of L. monocytogenes?

No

Prevention of growth of L. monocytes

• Restrict outgrowth during storage:

  • pHmin = 4.3

  • Awmin = 0.92

• Heat the product

  • D-value in milk = 1-2 s at 71.7 C

  • Pasteurization (15s at 71.7 C) sufficient to inactivate L. monocytogenes

Staphylococcus aureus characteristics

• Gram +

• Coccus

• Growth range: 7-48C

• Facultative anaerobic bacterium

• Remarkably salt tolerant (Awmin = 0.83)

• Bad competitor

Toxin in Staphylococcus

• Produced by 50-70% of the strains

• Produced in the food

• Heat stable

Symptoms in Staphylococcus

• Mild symptoms, vomiting

• Incubation time: 0.5-6h

• duration 1-2 days

Staphylococcus aureus on food

• Low level of initial contamination

• additional growth needed for toxin production

  • Temperature abuse

  • Protein-rich food, limited microbial competition

    • Heated foods, which are recontaminated

    • Meats that are salted (awmin = 0.83), salmon

Which pathogen has a higher disease burden per case?

L. monocytogenes

How are spores formed?

• Due to stress response induced by nutrient limitation

  1. vegetative cell

  2. sporulating cell

  3. spores (released when cell lyses)

Waking up of spores

• Known as germination: spore → vegetative cells

  • Nutrients trigger germination because environment becomes favourable

• Outgrowth occurs: reproduction of vegetative cells

Spore formers

• Food spoilage

  • Bacillus subtillis

• Food pathogens

  • Bacillus cereus

  • Clostridium botulinum

  • Clostridum perfringens

• Non-food related pathogens

  • Bacillus anthracis

  • Bacillus thuringiensis

Where is Bacillus cereus found? (Resevoir) and what does it contaminate?

Soil

Contaminates:

• Raw food, like cereals and vegetables

• Found in dust in food processing environments

Bacillus Cereus characteristics

• Can form spores, hence is found even in cooked foods

  • Spores can even germinate when not stored properly.

• Forms toxins.

• Gram positive

• Facultative anaerobe

• Spore forming rods

Food poisoning by Bacillus cereus

• Diarrhoeal Syndrome

  • Similar to Clostridium perfringens food poisoning

  • Caused by enterotoxins produced by the bacteria growing in the small intestine of the host.

  • Appears 8-16 hours after consumption and last 12–24 hours.

  • Abdominal pain, watery diarrhoea, nausea

• Emetic syndrome:

  • Similar to Staphylococcus aureus

  • caused by a toxin which is acid and heat resistant

    • Known as cereulide, a cyclic peptide toxin

  • Is preformed in food (toxins are there before consumption)

  • incubates for 0.5-5 hours

  • is dominated by nausea and vomiting, lasting 6-24 hours

Bacillus cereus in foods

• Ubiquitous

• Associated with boiled and fried rice that has been held at warm temperatures.

• Meat products, vegetables, soups, puddings, sauces, dried herbs and pasta.

When are B. cereus toxins produced?

Late exponential/early stationary phase

Clostridium perfringens illness

• Onset of illness 8-16 hours after food consumption, lasting between 12 and 24 hours

• Symptoms include abdominal pain, profuse watery diarrhoea

• Caused by an enterotoxin released by vegetative cells sporulating in the host small intestine

• Can also cause wound infections

Clostridium p. in foods

• Usually Linked to meat products such as stews, meat gravies, roast joints, and pies

• Vegetables, spices and herbs

• Cooking kills vegetative cells but not heat-resistant spores

Clostridium perfringens characteristics

• Rod shaped

• Gram positive

• Oval spores

• non-motile

• Catalase negative

• largely anaerobic (can survive in oxygen)

Clostridium botulinum in foods

• Found in aquatic muds, soil

• Frequently linked to home produced foods rather than commercial. (or underprocessed foods)

• Involving: vegetables and fish

Clostridium botulinum characteristics

• Gram positive

• Rod shaped

• Motile

• Spore forming

• Obligately anaerobic

• Neurotoxin producer

• It can be activated in the gut of humans

Clostridium botulinum illness

• Causes botulism

• Due to neurotoxin

• Toxin types that cause botulism: A, B, E & F (F in rare cases)

pH and Clostridium botulinum

The consensus is that a pH around 4.7 represents an absolute minimum for C. botulinum to grow

Infant botulism

Infant botulism differs from the classical foodborne syndrome in that it results from the colonization of the infant's gut with Clostridium botulinum and the production of toxin in situ (within the body). This requires the ingestion of viable spores, not pre-formed toxin

• Often caused by honey, thefore kids under a year should not consume honey

Characteristics of viruses

• Small (25-300 nm = 0025-0.3 micrometer))

• Genome: DNA or RNA (never both)

• Proteins coating or surrounding the genome

• Capsid (protein shell)

• needs external host to multiply

• No growth in foods

• Host specific

Do viruses or bacteria cause more outbreaks?

Viruses, which are mostly caused by the norovirus or hepatitis A

Norovirus (NV)

• Calicivirus family

• Gastroenteritis: vomiting, diarrhoea

• Incubation time: 15-50h

• Duration:24-48h

• No vaccination possible

• Low dose pathogen: 1-10 particles sufficient to cause disease

Contamination cycle of Norovirus

• Human: will multiply the norovirus in intestine and virus leaves body through faeces.

• Faeces go into the sewage and virus can get in water

• Water might be used for irrigation of fruits & vegetables.

• Water might be used to grow shellfish

• Virus might also spread from hand to food

Hepatitis A

• Picornavirus family

• Invasive virus:

  • Anorexia, fever, malaise, nausea, vomiting

  • Liver damage: dark urine, jaundice

• Incubation time: 2-6 weeks

• Duration: 8 weeks

• Vaccination possible

• Same routes as norovirus

Determination of presence of viruses

• Tissue culture (not for human NV, therefore often surrogate/model viruses used in infectivity assays)

• Electron-microscopy (high Detection limit)

• Immunologic methods (high DL)

• DNA techniques such as RT-PCR

High detection limit = many virus particles need to be present

Preventative measures to prevent viruses from spreading

• use of uncontaminated water

• hygiene

• strict rules food workers

• heating if possible

Problems with spore formers

• They are ubiquitous: raw material, environment, equipment

• They survive during mild processing (not sterilization)

Which bacteria will NOT grow under vacuum?

Campylobacter, pseudomonas and bacillus