Food Poisoning Caused By Bacillus Species

We often think of Bacillus bacteria as being our friend in food processing with the type of enzymes that are produced for producing sugar, various protein hydrolysates and even for cleaning clothes. Unfortunately, they are not always benign and in some cases Bacillus bacteria are positively dangerous. We look at a few Bacillus species associated with food poisoning.

Bacillus cereus

Bacillus cereus is a Gram-positive, aerobic to facultatively anaerobic, spore-forming rod that is widely distributed in the environment and is best known as a cause of foodborne illness, though it can also produce serious opportunistic infections.

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1. Microbiologic Characteristics

• Gram stain: Gram-positive rods (may appear Gram-variable in older cultures)

• Spores: Oval, central to subterminal; environmentally resistant

• Motility: Motile (distinguishes it from Bacillus anthracis)

• Hemolysis: β-hemolytic on blood agar

• Catalase: Positive

• Habitat: Soil, dust, water, plants, food products

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2. Virulence Factors

• Toxins

  • Cereulide (emetic toxin)

  • Hemolysin BL (HBL)

  • Non-hemolytic enterotoxin (NHE)

  • Cytotoxin K

• Enzymes

  • Phospholipases

  • Proteases

  • Hemolysins

• Spores

  • Allow survival during cooking and food storage

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3. Clinical Syndromes

A. Food Poisoning

Two distinct toxin-mediated syndromes:

1. Emetic Syndrome

• Cause: Preformed cereulide toxin

• Incubation: 1–5 hours

• Symptoms: Nausea, vomiting

• Associated foods: Cooked rice, pasta, starchy foods

• Similar to: Staphylococcus aureus food poisoning

2. Diarrheal Syndrome

• Cause: Enterotoxins (HBL, NHE, CytK) produced in intestine

• Incubation: 8–16 hours

• Symptoms: Watery diarrhea, abdominal cramps

• Associated foods: Meat, vegetables, sauces

• Similar to: Clostridium perfringens

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B. Non-Gastrointestinal Infections (Opportunistic)

Occurs mainly in immunocompromised patients, IV drug users, or trauma cases:

• Bacteremia

• Endophthalmitis (severe, vision-threatening)

• Meningitis

• Wound infections

• Pneumonia

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4. Diagnosis

• Clinical diagnosis for food poisoning (self-limited)

• Culture:

  • Large Gram-positive rods

  • β-hemolytic colonies

• Toxin detection: Specialized assays (mainly research or outbreak investigations)

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5. Treatment

• Food poisoning: Supportive care only

• Systemic infections:

  • Resistant to β-lactams (β-lactamase producer)

  • Effective agents include:

    • Vancomycin

    • Clindamycin

    • Fluoroquinolones

    • Aminoglycosides

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6. Key Differentiation Points

Control Of Bacillus cereus

All foods which can support this bacteria need thorough cooking with rapid cooling afterwards if the food is to retain any shelf-life. The food also needs to be stored properly at the correct temperatures and in general avoid rewarming.

B. subtilis & B. licheniformis

Two other types of Bacillus bacteria have been linked to food poisoning but not that often. They are B. subtilis and B. licheniformis and are commonly found in meat, vegetables and some meat products especially pasties. Both these bacteria are spore-formers and they are linked to cases of nausea, vomiting and usually within one hour of consumption of the contaminated food. Sometimes diarrhoea occurs but after about 12 hours. There is a famous case of B. subtilis poisoning in 1994 where meat pasties were seasoned with contaminated black pepper because the spores had survived the cooking process.

References

Arnesen, L., A. Fagerlund, Granum, P. (2008) From soil to gut: Bacillus cereus and its food poisoning toxins. FEMS Microbiol. Rev. 32 pp. 579–606