L3: Intro to Food Microbiology

A set of 30 vocabulary flashcards covering the basics of food microbiology, including the roles of bacteria, fungi, viruses, and parasites, as well as the sources of food contamination.

What is Food Microbiology

The study of microorganisms that inhabit, create or contaminate food.

What is the importance of food microbiology (3 main)

• Microbial growth can cause food spoilage

• Microbes in food may cause disease (food poisoning) – topic of lectures 5 and 6

• Microbes may be used to produce fermented foods and drinks

Types of microorganisms found on/in food (6)

• Bacteria

• Fungi (Yeasts & Moulds)

• Parasites

• Algae

• Viruses

Which types of microorganisms cause food spoilage

Bacteria

Yeasts

Moulds

Which types of microorganisms cause food poisoning

All except yeasts (yeast very rare)

Bacteria

Moulds

Viruses

Algae

Parasites

Which types of microorganisms are used in food production

Bacteria

Yeasts

Moulds

Viruses (phages)

Are "Commercially sterile" foods actually fully sterile

No, may still have viable microorganisms present despite being processed eg. UHT milk

Bacterial Spoilage Example organisms and foods

Pseudomonas sp

Brochothrix thermosphacta

Shewanella putrefaciens that affect meats, dairy, fish, fruits & vegetables

Bacterial Food Poisoning example organisms and foods

Bacillus cereus, Campylobacter spp., Clostridium botulinum, C. perfringens, E. coli O157:H7/STEC, Listeria monocytogenes, Salmonella spp, S. aureus, and Vibrio parahaemolyticus

Meats, dairy products, fish, fruits & vegetables etc.

Food Production Bacteria and common foods they’re in

Microorganisms used in dairy products (yoghurt, cheese), fermented meat & fermented vegies, vinegar, cocoa, pre and probiotics

Lactobacillus sp

Lactococcus sp

Bifidobacterium sp

Leuconostoc sp.

Yeasts that cause Spoilage

Candida spp. and Zygosaccharomyces

Spoil dairy products, wine, meats, and fruits

Yeasts food poisoning- is this common or uncommon

Uncommon

Invasive food-borne yeast infections very rare

Yeasts in Food Production

Genera used for bread, beer, wine, and sake

Saccharomyces cerevisiae, Saccharomyces carlsbergensis, and Kloeckera sp.

Moulds involved in food poisoning

Production of mycotoxins in nuts, cereals, dried fruits, spices etc.; poisonous mushrooms

• e.g. Aflatoxins (Aspergillus flavus), Ochratoxin A (Penicillium verrucosum & Aspergillus ochraceus), Amatoxins (Amanita phalloides [death cap mushroom])

• invasive food-borne fungal infections rare, occur in immunosuppressed

Moulds involved in food spoilage

Penicillium, Botrytis, Aspergillus

Dairy products, fruits & vegetables, bread products

Aflatoxins

Mycotoxins produced by Aspergillus flavus commonly found in nuts, cereals, and dried fruits.

Ochratoxin A

A mycotoxin produced by Penicillium verrucosum and Aspergillus ochraceus

Commonly found in nuts, cereals, and dried fruits.

Amatoxins

Toxins produced by Amanita phalloides (death cap mushroom)

Moulds in Food Production

Fungi used to produce blue vein and Camembert cheeses (Penicillium roqueforti, Penicillium camemberti) and soy sauce (Aspergillus oryzae).

Do viruses cause food spoilage

NO, viruses cannot multiply in food

Viral Food Poisoning Examples

Norovirus, Hepatitis A, Hepatitis E, and Rotavirus, often found in shellfish, fruits, vegetables, ice and meat

Use of Viruses/phages in food production

1) Use of phages in biosanitisation to prevent biofilms on equipment

2) biopreservation to destroy biofilms on food

3) phage therapy to control animal or plant disease in primary production

Algae: food poisoning

Shellfish, fish

Ciguatera Fish Poisoning: Poisoning resulting from fish contaminated with dinoflagellates

Amnesic shellfish poisoning: from shellfish contaminated with diatoms

Food-borne Helminths

Parasitic worms such as Trichinella and Taenia found in raw or undercooked meats.

Food-borne Protozoa

Parasites such as Cyclospora, Cryptosporidium, Giardia, and Toxoplasma.

Parasites in food poisoning

meats, seafood, fruits and vegetables

• Helminths (e.g. Trichinella, Taenia etc.) – raw/undercooked meats

• Protozoa (e.g. Cyclospora, Cryptosporidium, Giardia, Toxoplasma) – food and water-borne

Origins of most microbes that cause food-borne disease and spoilage (3 broad)

Microbiota of livestock/produce

The farm environment

The food processing chain

Sources of microorganisms in food (5)

1. Air

2. Soil

3. Water

4. Plants

5. Animals

Sources of microorganisms in food (5)

1) Air

2 examples of airborne microbes

a) Airborne bacteria

b) Airborne fungi

Sources of microorganisms in food (5)

1) Air

a) Airborne bacteria - how transmitted

• Mainly carried on dust particles or water droplets

• Dust: especially Gram positive endospore producers with high resistance to dessication; Gram positive skin bacteria e.g. S. aureus

• Water droplets: Gram negative e.g. Pseudomonas spp.

Sources of microorganisms in food (5)

1) Air

a) Airborne bacteria

Dust bacteria is usually gram __

Gram positive endospore producers with high resistance to dessication

Gram positive skin bacteria e.g. S. aureus

Sources of microorganisms in food (5)

1) Air

a) Airborne bacteria

Water Droplet Bacteria is mainly gram __ + eg. species

Mainly Gram negative bacteria, such as Pseudomonas spp.

Sources of microorganisms in food (5)

1) Air

b) Airborne fungi - examples

• Mould spores evolved to disperse through the air

• Produce large numbers of spores (e.g. Penicillium and Aspergillus)

• Wind-dispersed, extremely abundant in outdoor air (e.g. Cladosporium)

Sources of microorganisms in food (5)

1) Air

b) Airborne fungi - Airborne Mould Spores

Spores evolved for wind dispersal, such as Penicillium, Aspergillus, and the abundant outdoor genus Cladosporium.

Sources of microorganisms in food (5)

1) Soil

A complex microflora that can transfer to foods, especially endospore producers like Bacillus and Clostridium.

Sources of microorganisms in food (5)

3) Water

• Marine bacteria in Seafood

eg. Vibrio, Staphylococci, Enterobacteriaceae, and Shewanella

• Faecal contamination of water by sewage e.g. Salmonella, Campylobacter, enteric viruses

• Contaminated process waters

Sources of microorganisms in food (5)

4) Plants - 3 categories

• Phylloplane flora = microorganisms found on the surface of leaves

• Rhizoplane flora = microorganisms found on the surface of roots

• Plant pathogens

Phylloplane flora are found on

Examples

= microorganisms found on the surface of leaves

(think P for Plant)

• Mainly yeasts and moulds e.g. Aureobasidium, Cladosporium

• Some bacteria e.g. Pseudomonas, Erwinia, Pantoea and Leuconostoc

Rhizoplane flora

= microorganisms found on the surface of roots

(think R for Roots)

• Less likely to have an effect on food than Phylloplane flora

Are Phylloplane flora or Rhizoplane flora more likely to have an effect on food

Phylloplane flora are more likely

• Plant pathogens

• Botrytis cinerea – grey mould on picked strawberries, noble rot on wine grapes

• Pectobacterium carotovorum (formerly Erwinia) – potato & onion soft rot

• Pantoea ananatis, Pantoea agglomerans – onion rot, other plant diseases

Sources of microorganisms in food (5)

5) Animals

3 main parts of animal that are a source

Skin

Nose and throat

GI tract

Sources of microorganisms in food (5)

5) Animals

a) skin

• Skin not a favourable niche for most microorganisms

• Dry, low pH (organic acids)

• Skin flora predominantly Gram positive bacteria e.g. Staphylococcus, Corynebacterium, Propionibacterium

• Transient microorganisms may be present but will not grow

Sources of microorganisms in food (5)

5) Animals

b) Nose and throat

• Exudates from the nose and throat transferred to foods. Food becomes a vector for infection.

• Potential source of Staphylococcus aureus

Sources of microorganisms in food (5)

5) Animals

c) GI tract

• Major source of microbial contamination on meat products

• Gut flora includes a large number of non-pathogenic and pathogenic microorganisms

• Faecal contamination of foods

Define “food microbiology” and provide three reasons why it is an important

field to study

List three groups of microbes which can cause food spoilage, and for each

group name two genera which contain species that cause food spoilage

Describe the sources of microorganisms from plants which may appear in

foods. In your answer provide some examples of such microorganisms, and

define the terms “phylloplane flora” and “rhizoplane flora”

Animal skin flora is predominantly gram ___

3 examples

Gram positive bacteria

Staphylococcus, Corynebacterium, Propionibacterium