Aeromonas infections and their treatment

With advances in the identification and molecular taxonomy of Aeromonas spp., these organisms, which are widely distributed in the environment, are increasingly being recognised as human pathogens. Clinical infections include gastroenteritis, skin and soft tissue infections and bacteraemia. Antibiotic resistance poses a potential problem in the antimicrobial therapy of infections cased by Aeromonas spp. While most strains are susceptible to chloramphenicol, ciprofloxacin, co-trimoxazole and the aminoglycosides, the activity of amoxycillin/clavulanate and the acylureidopenicillins is inconsistent. Addition of a beta-lactamase inhibitor does not significantly enhance the activity of the acylureidopenicillins. Aztreonam and the carbapenems, imipenem and meropenem remain highly active. Although resistance to the first and second generation cephalosporins is variable, more than 90% of Aeromonas spp. are susceptible to the third generation agents. Of potential significance is the identification of chromosomally-encoded inducible beta-lactamases, associated with resistance to extended spectrum penicillins, cephalosporins, monobactams and carbapenems, in clinical isolates of Aeromonas spp. Two distinct enzymes are produced: the A1 enzyme, a serine beta-lactamase behaving as a group 1 cephalosporinase, and the A2 enzyme, a metallo beta-lactamase which hydrolyses a wide range of beta-lactam agents including the carbapenems. The clinical relevance of these enzymes in Aeromonas spp. is unclear.