COLIFORM BACTERIA IN SEA WATER AND SHELLFISH: I. LACTOSE FERMENTATION AT 35.5° AND 44 °C

Abstract

Of 6452 coliform strains isolated from sea water and shellfish specimens by membrane filtration (MF) and Violet Red Bile (VRB) agar techniques, 4728 (73.3 per cent) fermented lactose with the production of acid and gas within 48 hours at 35.5 °C; these cultures were incubated in Eijkman medium, in a water-bath at 44 °C, for 48 hours. Gas-positive tests were recorded for 94.6 per cent of Escherichia coli type I strains and 37.7 per cent of E. coli type II strains; 6.7 per cent of the "non-faecal" strains (represented by 10 coliform biotypes) were also gas-positive at 44 °C. The capacity of selected strains to ferment lactose at higher temperatures (44.5° to 46.0 °C) was also studied.A total of 1724 (26.7 per cent) of the cultures produced completely typical coliform colonies on MF membranes or VRB agar plates but were incapable of rapid lactose fermentation at 35.5 °C on subsequent isolation. Aerobacter biotypes were predominant (77 per cent), and 47.4 per cent of the cultures liquefied gelatin. The probable effect of lactose-degraded coliform bacteria on coliform density estimates made by the MF technique is discussed.