EFFECT OF ALUM ON FREE-LIVING AND COPEPOD-ASSOCIATED VIBRIO-CHOLERAE O1 AND O139

The effects of alum [KAl(SO4)(2)] on free-living and copepod-associate d Vibrio cholerae O1 and O139 were investigated by using plate counts and immunofluorescence direct viable counting (DVC). Growth of alum-tr eated cells in 0.5 parts per thousand Instant Ocean seawater was inhib ited, i.e., no growth was obtained on Luria-Bertani (LB) agar or thios ulfate-citrate-bile salt-sucrose (TCBS) agar. However, a significant n umber of the inhibited cells maintained viability, as measured by DVC. In comparison, a significant number of V. cholerae organisms associat ed with zooplankton, most of which were crustacean copepods, were viab le but nonculturable, with only a small number of cells retaining cult urability on LB and TCBS agar. Both DVC and viable plate counts (CFU) were significantly greater for V. cholerae O1 and O139 associated,vith zooplankton than for V. cholerae in water alone, i.e., without copepo ds. It is concluded that alum is an effective coagulant but not an eff ective killing agent for V. cholerae and that association with copepod s offers protection for V. cholerae O1 and O139 against alum and chlor ine treatments.