Antimicrobial susceptibilities of Vibrio cholerae strains isolated from cholera patients admitted
to the Infectious Diseases Hospital, Calcutta, India for 6 years were analysed to determine the
changing trends; 840 V. cholerae strains isolated in 1992–1997 were included in this study.
Among V. cholerae serogoup O1 and O139, ampicillin resistance increased from 1992 (35 and
70%, respectively) to 1997 (both serogroups 100%). Resistance to furazolidone and
streptomycin was constantly high among V. cholerae O1 strains with gradual increase in
resistance to other drugs such as ciprofloxacin, co-trimoxazole, neomycin and nalidixic acid. V.
cholerae O139 strains exhibited susceptibilities to furazolidone and streptomycin comparable
with those of O1 strains. However, after initial increase in resistance to chloramphenicol and
co-trimoxazole, all the V. cholerae O139 strains became susceptible to these two drugs from
1995 onwards. Both V. cholerae O1 and O139 remained largely susceptible to gentamicin and
tetracycline. V. cholerae non-O1, non-O139 strains, in contrast, exhibited high levels of
resistance to virtually every class of antimicrobial agents tested in this study especially from
1995. Kruskal–Wallis one-way analysis showed that V. cholerae O1 Ogawa serogroup exhibited
significant yearly increase in resistance to nine antibiotics followed by non-O1 non-O139 and
O139 strains to six antibiotics and two antibiotics respectively. Interesting observation
encountered in this study was the dissipation of some of the resistant patterns commonly found
among V. cholerae non-O1 non-O139 or O1 serogroups to the O139 serogroup and vice versa
during the succeeding years.