food microbiology for lab technicians

1. FOOD MICROBIOLOGY

2. A Brief History
• Early Food Preservation
• 900 AD – “Food Poisoning” Recognized
• 1795-Appert Developed Canning
• 1854-1864-FOOD MICROBIOLOGY BECOMES
A SCIENCE

3. Why Study Food Microbiology?
• Provide Clean, Safe, Healthful Food to
Consumer
• Food Permits Growth
• Control of Microbial Growth
• Prevent Food Spoilage
• Prevent Food-borne Illnesses
• Food Preservation and Production

4. Food-Borne Illness
• Estimated burden of food – borne illnesses
– $6.9 Billion/Year Cost of FBI
• CDC Estimates
– 76 Million Cases of FBI Annually
– 325,000 Hospitalizations
– 5,000 Deaths

5. Common symptoms of food born illnesses
• Nausea
• Vomiting:
• Diarrhea:
• Abdominal cramps:
• Fever
• Headache
• Muscle aches
• Fatigue
• Dehydration
• Other symptoms: chills, weakness, dizziness, and in severe cases,
organ damage or neurological symptoms

6. Agents of Disease (Foodbourne Pathogens)
BACTERIA
– E coli
– Salmonella spp.,
– Vibrio cholera,
– Bacillus cereus,
– Clostridium botulinum,
– Listeria monocytogenes,
– Staphylococcus aureus
VIRUSES
– Enteroviruses,
– Norwalk virus,
– Hepatitis virus
PROTOZOA
– Giardia lamblia,
– Cryptosporidium parvum,
– Entamoeba histolyticum,
– Cyclospora cayetanesis
HELMINTHS
– Tapeworms (Beef, Fish and Pork),
– Flukes (Fish and Shellfish),
– Roundworms and Hookworms

7. Public health impact of food born illnesses
• Healthcare Burden:
• Economic Costs:
• Morbidity and Mortality:
• Public Awareness and Concern: This can lead to
avoiding certain foods or brands, and increased demand
for food safety regulations and oversight.
• Social Disruption: closures of food establishments,
• Long-Term Health Impacts: foodborne bacteria can lead
to reactive arthritis, kidney failure, or neurological
disorders in susceptible individuals.
• Global Health Security: outbreaks (COVID 19) often
crossing international borders through the global food
supply chain.

8. What Organism Causes the
Most Cases of Food-Borne
Illness Annually?
Campylobacter

9. What Organism Causes the
Most Deaths Due to Food-
Borne Illness?
Salmonella

10. Intrinsic and Extrinsic Factors
• Intrinsic
– pH
– Moisture Content
– Oxidation-reduction Potential
– Nutrient Content
– Antimicrobial Constituents
– Biological Structures

11. pH
• Effects of pH
– Enzymes
– Nutrients
• Other Environmental Factors
– Temperature
– Salt
– Age
• No known pathogen grows below pH of 4.6
– Clostridium botulinum

12. Moisture
• Remove and/or Bind Moisture
– Humectants
– Dehydration
• Water Activity – Aw
• Most Fresh Foods - Aw > 0.99
0 1
Pure water
No water

13. Microbial Growth and Aw
• Halophilic 0.75
• Xerophilic molds 0.61
• Osmophilic yeasts0.61
• Lowest Aw for Pathogen Growth
– 0.86
– Stapholococcus aureus

14. Oxidation- Reduction Potential
• O/R Potential - Eh
– “…ease with which the substrate loses or gains
electrons.”
• Loss of electrons – oxidized
• Gain of electrons – reduced
• Aerobic
• Anaerobic
• Microaerobic
• Facultative anaerobes

15. Others
• Nutrients
– Fastidius vs non-fastidious
• Biological Structure
• Antimicrobial Factors
– Naturally occurring factors

16. Extrinsic Factors
• Temperature
• Relative Humidity
• Gases in the Environment
• Presence of Other Microorganisms

17. Temperature
• Microorganisms grow over a wide range of Temperatures
• Psychrotrophs are microorganisms capable of growth at
low temperatures, typically between 0°C and 20°C.
• Mesophiles are microorganisms that thrive at moderate
temperatures, usually between 20°C and 45°C, including
many human pathogens.
• Thermophiles are microorganisms adapted to high
temperatures (between 45°C-80°C). often found in hot
springs and deep-sea vents.
• Psychroduric - survive at low temperatures but do not
necessarily grow or reproduce under such conditions.
• Thermoduric - survive exposure to high temperatures,
even though they may not necessarily thrive or grow well
under those conditions.

18. Other Factors
1. Relative Humidity of Environment
– Can change the Aw
– Water activity (Aw) is a measure of the
amount of water available for microbial growth
and chemical reactions within a food product.

19. Environmental Gasses
• Oxygen: promotes aerobic microorganisms and spoilage by oxidation.
• Carbon Dioxide. elevated levels can inhibit the growth of aerobic
spoilage organisms and slow down enzymatic reactions, However,
excessive carbon dioxide levels can also lead to undesirable changes in
texture, flavor, and appearance of food products.
• Nitrogen (N2): often used in modified atmosphere packaging to displace
oxygen and create an anaerobic environment, which inhibits the growth
of aerobic spoilage microorganisms and slows down oxidative reactions.
• Ethylene (C2H4): a natural plant hormone produced by some fruits and
vegetables as they ripen. does not cause food spoilage, it can accelerate
the ripening and senescence of certain fruits and vegetables, leading to
faster deterioration and shorter shelf life if not controlled properly during
storage and transportation.
• Sulfur Dioxide used as a preservative in dried fruits and wine to inhibit
microbial growth and prevent oxidation. It can also have antimicrobial
and antioxidant effects, helping to extend the shelf life of certain food
products.

20. Presence of Other Microorganisms
• Competitive Exclusion: one species outcompetes another
species for nutrients or space, leading to the suppression or
elimination of the less competitive species.
• General Microbial Antagonism: inhibition or suppression of
microbial growth by one microorganism against another;
through production of antimicrobial compounds
(bacteriocins), competition for nutrients or space, and
alteration of environmental conditions.
• Lactic Acid Antagonism: inhibitory effect exerted by lactic
acid bacteria (LAB) against other microorganisms. In
fermented products such as yoghurt,

21. Other apllications of bacteria in
food microbiology
• Microbes that we can exploit
• Bacteria—cheese, yogurt, vinegar,
• Yeasts—bread, beer, liqueurs, wine
• Molds—cheeses
• Bacteria in agriculture Rhizobium spp:
• Nitrogen fixation in root nodules of legumes
• Bacteria used in engineering produce that is
resistant to adverse environmental conditions,
pests pathogens and spoilage