1. Bacillus cereus

2. Bacillus sp. characteristics
Gram positive rod
Aerobic
Central, ellipsoidal spores
Two different diseases
Two different toxins
Many similarities to C. perfringens
~65,000 cases/year; 85 lab confirmed
Vegetative cells not remarkably resistant to heat

3. Bacillus sp. Over 100 species Six species in “B. cereus group”
B. anthracis
B. thuringiensis (Bt)
B. mycoides, pseudomycoides, weihenstephanensis
B. cereus and thuringiensis are indistinguishable except for Bt toxin production
Top three all highly related as well
Only the first that food microbiology is concerned with

4. Ecology and reservoir Similar to other spore-forming organisms
Widespread, ubiquitous
Soils and plants
Vegetables, starch, spices, ~30% positive
Meat products and milk (cross-contaminated with Bacillus from environment)

5. Growth characteristics
Fairly generic characteristics
Temperature, generally 4-48 oC, optimum oC
pH for growth (not terribly acid resistant)
Salt resistant; up to ~7.5%
Water activity for growth >0.95
Spore D100~3-200 min

6. Diseases Characteristics Diarrheal Emetic Dose required 105-107
(cells/gram)
Toxin production in
Small intestine
Food
Toxin type
Protein enterotoxin
Cyclic peptide emetic toxin
Incubation period
8-16 h
0.5-5 h
Duration of illness
12-24 h
6-24 h
Symptoms
Abdominal pain, watery diarrhea, nausea
Nausea, vomiting, malaise
Food associated
Meat products, vegetables, puddings, sauces, milk and milk products
Fried and cooked rice, pasta, pastry, noodles
From Doyle and Beuchat Food Microbiology

7. Characteristics of toxin
Emetic
Cereulide; cyclic structure, 3 repeats of (D-O-Leu-D-Ala-L-O-Val- L-Val)
Resistant to heat, pH, proteolysis
Stable after 121 oC for 30 min
pH 2-11
Produced optimally at oC, late exponential to stationary phase
Enterotoxins
Sensitive to heat, proteolysis, strong acid
Haemolytic enterotoxin (Hbl) has three subunits (B, L1, L3)
Non-haemolytic enterotoxin (Nhe); 99% of strains
Cytotoxin K (CytK)
Foods with >106 organisms generally have sufficient toxin

8. Association with foods (I)
Widespread (as expected)
Variety of foods associated
Diarrheal disease
milk, meats, vegetables, fish
Emetic disease
Rice
other starchy foods such as potatoes, pasta
cheese products

9. Association with foods (II)
Heat processing may select for (as Clostridium)
More common in pasteurized milk than raw, however:
Low numbers (< 103 generally)
Toxin production not favored in low temperature milk
Sweet curdling or bitty cream
“Chinese Restaurant Syndrome”
Rice prepared in bulk; spores survive
Rice not properly cooled to below 8 oC
Grow and produce emetic toxin
Reheating does not inactivate toxin

10. Outbreaks Mighty Taco, Buffalo, NY, 2016
Pellegrino Food Products (Warren, PA)

11. Staphylococcus aureus

12. Staphylococcus aureus
Gram positive cocci
Irregular clumps; grape-like
Facultative anaerobes
Non-spore forming
Intoxication; heat stable toxin
Organism isn’t dramatically heat stable
Mild, short-duration illness; usually due to contaminated food handlers
Salt-tolerant (much lower aw than other organisms)
Resistant to drying
~240,000 cases/yr ; estimated only 1/1000 cases get reported

13. Growth and toxin production
Enterotoxin production
Factor
Optimum
Range
Temperature
35-37
7-48
35-40
10-45 pH A:
Other: 6-7
NaCl %
0-20%
0.5% aw
>0.99
Oxygen
Aerobic
Aerobic/anaerobic
Taken from Adams and Moss, Food Microbiology

14. Characteristics of toxin
10 known enterotoxins (classified serologically)
SEA to SEI
No SEF (declassified)
Three SEC’s (SEC1, SEC2, SEC3)
SEA most common in foodborne outbreaks
SED, SEB also but much less frequent
Isolates may produce multiple SE’s
Called an enterotoxin (is technically a neurotoxin)
Binds receptors in gut that stimulate emetic response in brain
Resistant to proteolytic enzymes; heat (preformed toxin can be resistant to subsequent heating; mushroom outbreak)

15. Ecology of S. aureus Primarily: Also:
Skin, skin glands, mucus membranes of warm-blooded animals
CDC: 25% of skin/nares of healthy humans
Think: skin contact, nasal drippings, sneezing
Also:
Animals
Mastitis (inflammation of mammary tissue)
Dust, air, food contact surfaces, environment

16. Foods associated Meats, poultry, egg products, bakery products…
Common features (one or more of following):
Poor personal hygiene; foods made by hand
Preparation of foods far in advance
Inadequate cooking or heating of foods
Slow cooling of contaminated foods (large batches)
Prolonged use of warming plates
Is a poor competitor with other organisms
Most of these are inhibited by aw of 0.86
“Keep hot foods hot (>140o F), cold foods cold (<40o F)”

17. Characteristics of disease
Short incubation period, 1-10 hours; 4 h typical
About 1-5 mg toxin required (approx cells in food)
Nausea, vomiting, stomach cramps; diarrhea sometimes
Recovery complete in 1-2 days
Death uncommon; although ~4% of children and elderly by severe dehydration

18. Outbreaks July 2011, Crowne Plaza Hotel, Portland, OR
July 17: 7 guests, vomiting, diarrhea, cramps between 1 ¾ and 3 ¾ hours after breakfast
Linked to hollandaise sauce (butter, pasteurized eggs, lemon juice) on eggs benedict
Made at 5:15 am, “held in a stove” until 11 am; no food sample left to test
SEA+SEB S. aureus isolated from 2 cases and one chef; PFGE indistinguishable