THE HIDDEN CARBAPENEMASE OF AEROMONAS-HYDROPHILA

It has been presumed that there are just two beta-lactamases in the mo tile Aeromonas species, a carbapenemase and a cephalosporinase, based on the premise that all beta-lactamases can be detected by hydrolysis of the chromogenic cephalosporin, nitrocefin. However, when it was rec ently found that a non-motile species of Aeromonas that causes furuncu losis in salmon, contained three beta-lactamases, one of which was a c arbapenemase which could not be detected with nitrocefin, it was hypot hesised that genetic exchange could occur between fish pathogens and h uman pathogens resulting in the transfer of the carbapenemase-encoding gene. This could have a potentially serious impact on intensive thera py units where carbapenems are employed. The purpose of this study was to determine whether the human pathogen Aeromonas hydrophila demonstr ated the same beta-lactamase profile. After anion and cation exchange chromatography had been employed to separate the beta-lactamases of a clinical strain of A. hydrophila, three different beta-lactamases were found, one of which is a carbapenemase which does not hydrolyse nitro cefin. It is, therefore, probable that many strains of Aeromonas spp. contain a similar array of beta-lactamases which include a carbapenema se that cannot be detected with nitrocefin. Similar carbapenemases may well remain hidden in other species of bacteria unless appropriate te chniques to detect the enzymes are employed.