Improved glutaminate-starch-penicillin agar for the isolation and enumeration of Aeromonas hydrophila from seawater by membrane filtration.

Glutaminate-starch-penicillin agar (GSP) in its original formula was found unsatisfactory for the detection and the enumeration of Aeromonas hydrophila from seawater by membrane filtration. It was also the case when GSP agar was adjusted to pH 8 or when ampicillin (10 mg/L) was incorporated to the original formula. The elevation of pH to 8 together with the addition of 10 mg/L ampicillin gave to the medium a high selectivity and permitted the detection of A. hydrophila from seawater. The numbers of A. hydrophila were monitored at 11 beaches along the coastline of Patras and the distribution of Aeromonas was not found homogenous. Low numbers of A. hydrophila were isolated from most samples tested, whereas high concentrations of A. hydrophila were isolated specifically from samples that were collected near sewage and fresh water inputs.