Methylobacterium species: An increasingly important opportunistic pathogen

Methylobacterium species rarely cause human disease. Those isolated from humans are usually found as opportunistic pathogens in patients weakened by an underlying disease process. This report describes a case of Methylobacterium bacteremia in a 35-year-old woman with AIDS, compares the clinical presentation of this case with that of other previously reported cases of Methylobacterium infection, and provides a history of the Methylobacterium genus and its relevant taxonomy. Recommendations for presumptive identification include pink to orange colony growth on blood or Sabouraud agar but not on MacConkey agar; gram-negative, vacuolated bacillus or coccobacillus; growth at 25 degrees to 30 degrees C and not at 42 degrees C; and positive results on tests for oxidase and urease. Antibiotics with demonstrated efficacy against Methylobacterium species include amikacin, gentamicin, ciprofloxacin, trimethoprim-sulfamethoxazole, ceftizoxime, and ceftriaxone.