Chromobacterium violaceum

Chromobacterium violaceum is a Gram-negative, facultative anaerobic, non-sporing coccobacillus. It is part of the normal flora of water and soil of tropical and sub-tropical regions of the world. It produces a natural antibiotic called violacein. It grows readily on nutriet agar, producing distinctive smooth low convex colonies with a dark violet metallic sheen (due to violacein production). Its full genome was published in 2003.

Biochemistry

C. violaceum ferments glucose, trehalose, N-acetylglucosamine and gluconate but not L-arabinose, D-galactose or D-maltose.

Medical significance

C. violaceum rarely infects humans, but when it does it causes skin lesions, sepsis and liver abscesses that may be fatal. Care must be taken because Burkholderia pseudomallei is commonly misidentified as C. violaceum by many common identification methods. The two are readily distinguished because B. pseudomallei produces large wrinkled colonies.

C. violaceum produces a number of natural antibiotics:

• Aztreonam is a monobactam antibiotic that is active against gram-negative aerobic bacteria including Pseudomonas aeruginosa. It is marketed as Azactam.
• Violacein is active against amoebae and trypanosomes;
• Aerocyanidine is active against Gram-positive organisms;
• Aerocavin is active against Gram-positive and Gram-negative organisms.

Treatment

Infection caused by C. violaceum is rare, therefore there are no clinical trials evaluating different treatments. Antibiotics that have been used to successfully treat C. violaceum include pefloxacin, ciprofloxacin, amikacin, and co-trimoxazole. Other antibiotics that appear to be effective in vitro include chloramphenicol and tetracycline. For theoretical reasons, infection would not be expected to respond to penicillins, cephalosporins or aztreonam, although carbapenems like meropenem or imipenem may possibly work.

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