Walsh & Hoyt: Miscellaneous Gram-Negative Bacilli

Infections of the eyes and CNS are occasionally caused by gram-negative bacilli that do not belong to a common genus. A number of rare gram-negative aerobic bacilli cause human infection, including endophthalmitis, orbital cellulitis, meningitis, and brain abscess. Clinical laboratories often identify these organisms by their ability to ferment glucose (e.g., ""gram-negative nonfermenter"") or by their similarity to other, more common, organisms (e.g., ""Pseudomonas-like organism"") rather than by a genus and species. Rare gram-negative bacilli that may cause CNS disease of neuro-ophthalmologic significance include glucose fermenters, such as Aeromonas, Capnocytophaga, Cardiobacterium, and Plesiomonas shigelloides, and glucose nonfermenters or weak fermenters, such as Alcaligenes, CDC Group Ve organisms Chryseomonas luteola and Flavimonas oryzihabitans, and Eikenella. Most patients with CNS infections caused by these and other rare gram-negative bacilli are hospitalized, chronically ill, immunocompromised, or have some other factor that predisposes them to the infection; however, in utero transmission withsubsequent neonatal meningitis has also been documented. A 67-year-old previously healthy woman developed a homonymous hemianopia associated with signs of systemic infection; imaging studies showed a mass in the occipital lobe that was found to be an abscess from which Eikenella corrodens was cultured. Most of the rare gram-negative bacilli that cause infection in the CNS are sensitive to a wide variety of antibiotics; however, meningitis caused by Achromobacter and Alcaligenes species is associated with frequent development of hydrocephalus, a high mortality of about 77%, and significant neurologic sequelae in survivors.