A 4 month old infant presents with failure to thrive, progressive muscular weakness, and poor head control. On questioning, the mother states that she typically feeds the baby soy-based formula sweetened with honey. Which of the following organisms is most likely to be responsible for the child's presentation?

The baby has infant botulism (floppy baby syndrome), which is due to germination of Clostridium botulinum spores (found in honey) in the baby's gastrointestinal tract. Patients improve when honey is removed from the diet. This disorder is most common in children under the age of six months; older children and adults do not appear to be vulnerable to this form of botulism, but are susceptible to botulism caused by ingestion of preformed toxin. Clostridium difficile causes pseudomembranous colitis, especially after antibiotic therapy. Clostridium perfringens causes gas gangrene and gastroenteritis, and it is not associated with ingestion of honey. Clostridium tetani causes tetanus, and does not cause a food-borne illness in infants. Ref: Ray C.G., Ryan K.J. (2010). Chapter 29. Clostridium, Peptostreptococcus, Bacteroides, and Other Anaerobes. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.