Bacillus cereus group - other than B. anthracis

• B. cereus
• B. mycoides
• B. thuringiensis

Gram Stain

• Gram positive large spore forming bacilli (aerobic/facultative)

Clinical Significance

These organisms are widely distributed in nature, especially soil environments. Their spores may contaminate dried foods (spices/tea/flour/powders).

B. cereus is an opportunistic pathogen that can cause bacteremia, endocarditis, brain abscesses, and pneumonia in predisposed individuals (especially IVDU/malignancy/alcoholism).  It has also been associated with severe ocular or wound infections (gangrene like) following trauma, burns or surgery.  Neonates are prone to infection with this organism, especially umbilical stump infections or ventilator associated pneumonia.  It can also cause food-borne illnesses (diarrheal/vomiting type).

B. thuringensis (an insect pathogen) and B. mycoides have been associated with wound, burn, and ocular infections.

 

Usual Susceptibility Pattern

The majority of isolates exhibit broad beta-lactam resistance (penicillins and cephalosporins).

Carbapenems may test susceptible but induction of chromosomal metalloenzymes results in elevated MICs (imipenem may retain activity).  

They are usually susceptible to aminoglycosides, tetracyclines, linezolid, and vancomycin (elevated MICs reported in neonates).

Susceptibility to macrolides, clindamycin, and quinolones is variable.

Daptomycin MICs are often elevated – possibly due to resistance in spores with reversion to susceptibility on germination.

TMP/SMX resistance is inherent but may not be easily detected by routine testing.

Empiric Therapy
Clinically Significant Infections:
Vancomycin
or
Linezolid