Bacillus cereus

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 http://www.schmidtandclark.com/bacillus-cereus

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

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)

Growth characteristics Fairly generic characteristics Temperature, generally 4-48 oC, optimum 28-35 oC pH for growth 4.9-9.3 (not terribly acid resistant) Salt resistant; up to ~7.5% Water activity for growth >0.95 Spore D100~3-200 min

Diseases Characteristics Diarrheal Emetic Dose required 105-107 105-108 (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

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 20-25 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

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

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

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

Staphylococcus aureus

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

Growth and toxin production Enterotoxin production Factor Optimum Range Temperature 35-37 7-48 35-40 10-45 pH 6.0-7.0 4.0-9.8 A: 5.3-6.8 Other: 6-7 4.8-9.0 NaCl 0.5-4.0% 0-20% 0.5% aw 0.98-0.99 0.83-0.99 >0.99 0.86-0.99 Oxygen Aerobic Aerobic/anaerobic Taken from Adams and Moss, Food Microbiology

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)

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

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)”

Characteristics of disease Short incubation period, 1-10 hours; 4 h typical About 1-5 mg toxin required (approx. 105-108 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

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