Food Microbiology: E. coli and Spoilage

Food Microbiology

• The science that deals microbes' desirable and undesirable effects on food products' qualities and safety.
• This includes food spoilage, food preservation, and food-borne infections.

Food Spoilage

• Damage to food makes it unsuitable for human consumption.
• Indicates food is contaminated with pathogenic or poisonous agents.
• Bacteria and fungi (yeast or molds) are the major causes of food spoilage.
• They digest or degrade various chemical constituents of food using various enzymes.

Microbial Growth in Food

• Influenced by intrinsic and extrinsic factors

Intrinsic Factors

• Factors include pH, moisture content, nutrient content, antimicrobial constituents, and biological structures.

pH

• Represents the negative logarithm of hydrogen ion concentration
• Most bacteria prefer neutral pH levels of (6.5-7.5).
• Fungi grow across a wider pH range, but prefer pH between 5 and 6.
• Neutrophiles grow optimally between pH 5.5 and 8, such as E.coli and Salmonella sp.
• Acidophiles grow optimally between pH 0 and 5.5 , such as Lactobacillus sp.
• Alkalophiles grow optimally between pH 8 – 10.5, such as Vibrio cholerae

Moisture Content

• The water requirement of microorganisms measured water activity (Aw).
• Water activity reflects the amount of free water in a food medium.
• Lack of free water inhibits microbial growth.
• Bacteria generally need higher Aw levels for growth than fungi.
• Gram-negative bacteria usually need higher Aw than gram-positive bacteria.

Nutrient Content

• Microorganisms require water, protein, carbohydrates, lipids, vitamins, nitrogen, sulfur, phosphorus, and minerals (Ca+2, Fe+2) for growth and reproduction.
• Foods such as milk, meat, and eggs are rich in nutrients and susceptible to microbial spoilage.

Antimicrobial Constituents

• The resistance of some foods to microorganisms is due to naturally occurring antimicrobial substances.
• Plant species may have essential oils.
• Cow’s milk contains lactoferrin.
• Eggs contain lysozyme.

Biological Structures

• Natural coverings on some foods provide protection against spoilage organisms.
• Example covering include fascia, skin, and other membranes on meat to prevent microbe entry.

Extrinsic Factors

• Factors include temperature of storage, presence and concentration of gases, and relative humidity.

Temperature of Storage

• Microorganisms can grow over a wide spectrum of temperatures.
• Temperature has a significant impact on microorganism viability.
• Bacteria can be grouped into three main categories based on ideal growth temperature.
• Psychrophiles can grow best at 20°C but grow down to -10°C.
  • These bacteria can cause food spoilage at low temperatures.
  • Several of these bacteria are found in water and soil.
• Mesophiles grow best between 20°C - 45°C.
  • The optimum growth temperature for mesophiles is 37°C.
  • Most pathogenic bacteria are mesophiles.
• Thermophiles grow at temperatures above 45°C.
  • The optimum growth temperature for thermophiles is between 50°C - 70°C.
  • Bacteria in this group are mostly spore formers.

Concentration of Gases

• CO2 and O2 are two crucial gases in modified atmosphere packaged (MAP) foods.
• Microorganisms are classified based on O2 requirement.
• Obligate aerobes are completely dependent on atmospheric O2 for growth.
• Obligate anaerobes grow only in the absence of oxygen and are killed or inhibited by O2's presence.
• Facultative anaerobes grow with or without oxygen.
• Microaerophiles require lower levels of oxygen (2 to 10%) for growth and are damaged by normal atmospheric levels of O2 (20%).

Relative Humidity

• Refers to the amount of moisture in the food or the surrounding environment.
• Foods with low water activity placed in high humidity take up water, their Aw increases, and food spoilage occurs more easily.
• Ex: Dry grains stored in an environment with high humidity will take up water and undergo spoilage by molds.

Foodborne Infections

• Infections are caused by the entrance of a pathogenic microorganism into the host, colonization, and the reaction of the tissues to the presence of the organism, their multiplication, or any toxins they produce.
• Symptoms include nausea, vomiting, abdominal pain, diarrhea, fever, headaches and overall weakness.

Foodborne Pathogens

• The "Big 5," includes:
  • Norovirus
  • Hepatitis A virus
  • Salmonella spp.
  • Shigella spp.
  • Escherichia coli (E.coli) O157:H7

Norovirus (Norwalk Virus)

• A highly contagious virus that severely infects the gastrointestinal tracts of humans.
• Causes an illness known as acute viral gastroenteritis.
• Common symptoms are nausea, vomiting, diarrhea, and abdominal pain.
• Transmitted through direct contact or consuming contaminated food, water, or touching contaminated surfaces.
• Symptoms can begin in 12-48 hours after exposure to the virus (short incubation period).
• Norovirus gastroenteritis is a self-limiting disease that lasts one to six days and resolves without complication.

Hepatitis A (HAV)

• Communicable infectious disease triggered by Hepatitis A virus impacts liver function.
• The only food-borne illness preventable by a vaccine.
• Unlike hepatitis B and C, Hepatitis A does not develop into chronic hepatitis or liver cirrhosis.
• Symptoms include: nausea, vomiting, loss of appetite, fever, fatigue, darkened urine, jaundice, and right-upper abdominal pain.
• HAV has an incubation period (around 2-4 weeks).
• There is no cure or treatment.

Salmonella Spp

• Causes a serious infectious disease called Salmonellosis.
• Naturally found in the intestines of birds (especially chicken) and some mammals.
• Most Salmonella infections come from consumption of contaminated and undercooked poultry, eggs, or shellfish.
• Non-typhoidal Salmonella leads to relatively mild gastrointestinal illness.
• Symptoms appear 6-72 hours after exposure: diarrhea, abdominal cramps, nausea, vomiting, and fever.
• Most affected persons fully recover without medical treatment within 3-7 days; some patients require hospitalization due to severe dehydration or fever.
• Serious cases may require antibiotics to keep to infection from spreading.

Shigella Spp

• Shigellosis is (also called "bacillary dysentery”) is a highly contagious bacterial infection.
• Symptoms usually occur within 1-3 days: diarrhea (sometimes bloody), abdominal cramps or pain, nausea, vomiting, rectal tenesmus, and fever.
• Most cases of Shigella food poisoning resolve within a week and usually do not require hospitalization or cause any significant complications.
• Transmission primarily via direct contact from fecal matter; occurs via the hand-to-mouth route.
  • Thorough hand washing is key to preventing illness.
• Waterborne transmission occurs with wells, pools, or water parks become contaminated with human excrement.

Escherichia Coli (E. Coli) O157:H7

• Infections are among the most dangerous of food-borne illnesses.
• Most E. coli species are harmless, but some strains cause urinary tract infections, pneumonia, and other illnesses.
• E. coli bacteria are considered very hardy and can survive even on low temperatures.
• Humans need to ingest a very small number of E. coli organisms to become infected.
• Multiply in the large intestine and produce the Shiga toxin, which inflames the digestive tract, causes hemorrhagic colitis, bowel necrosis, seizures, severe anemia, kidney damage, renal failure, and death.
• Symptoms include: diarrhea, nausea, vomiting, and stomach cramps.
• A slight fever may develop.
• Infection can come from contaminated cattle manure or the feces of other warm-blooded animals in food and beverages.

Foodborne Infection vs. Intoxication

• Food-borne infection is the consumption of food contaminated with bacteria and has symptoms after in 8-16 hours.
• Intoxication is the consumption of food contaminated with bacterial toxins (symptoms appear after 1-6 hours).
• With both, patients usually recover within a day.

Risk Factors

• Improper cooking temperatures
• Improper hot/cold holding temperatures
• Poor employee health and hygiene
• Dirty and/or contaminated utensils and equipment
• Food from unsafe sources

Prevention Methods

• Clean: Keep hands clean with good hygiene and wash surfaces often.
• Separate: Do not cross-contaminate.
• Chill: Keep it cool and refrigerate promptly.
• Cook: Cook to proper temperatures.

Explore key aspects of food microbiology, including E. coli O157:H7 symptoms and dangers, and differentiating food-borne infection from intoxication. Also, learn about food spoilage, intrinsic factors affecting microbial growth, and water activity.