Food Microbiology ch.30 BIOL 260

The good, the bad and the ugly

• Good = bacteria are important in food production

• Bad = some bacteria cause food spoilage

• Ugly = some bacteria cause food poisoning

Factors that influence growth in foods

• Temperature: Some microbes grow well I cooler temps (psychotrophs), others more slowly (thermophiles)

• Water Availability

  • Bacteria grow best in a hypotonic environment

  • Cannot tolerate a hypertonic environmen

• pH (bacteria can still grow on lower pH, just more slowly)

• Atmosphere

  • Presence or absence of oxygen

• Nutrients

  • More nutrients = more microbes

• Biological barriers

  • Foods that have skins, rinds, shells that protect from spoilage… prevent bacterial growth

• Antimicrobial chemicals

  • Some foods have naturally occurring enzymes (eggs whites have lysozyme that breaks down peptidoglycan)

Microbes in food production

• Lactic acid bacteria (cheeses, yogurts, sauerkraut)

• Yeast (wine, beer, breads)

• Molds (soy sauce, miso, cheese)

Mechanisms of pathogenesis

• Attachment: pili or adhesins

• Toxin production: two kinds

  • Increase secretion of ions and electrolytes (diarrhea)

  • Cause cell death and epithelial lining (Cytotoxins)(bloody diarrhea)

• Alterations in host cells

• Cell invasion: type 3 secretion systems bind to epithelial cells and insert effector proteins into host epithelial cells, this ruffles the host cell, the bacteria will be engulfed by the host cell and will multiply. Can also target M-cells (microfold cells) found in the small intestine

Foodborne intoxication

• results from ingestion of food that has had organisms grow in it and generate a toxin (exotoxin) that is liberated into the food.

  • Clostridium botulinum: this organism produces a neurotoxin that causes muscle paralysis.

  • Staphylococcus aureus: It can grow in food and produce a toxin that causes vomiting and diarrhea.

Foodborne infection

results from eating food that is contaminated with organisms, the organisms grow and multiply in the intestines, as they grow they may produce toxins, which generate symptoms of abdominal cramps, vomiting, and diarrhea.

Cytotoxin

Kills host cells (ex. Shiga toxin)

Endotoxin

• An endotoxin is part of the outer membrane of gram-negative bacteria.

It is specifically the lipid A portion of lipopolysaccharide (LPS).

Enterotoxin

a toxin that targets the intestines