Epidemiology and Infection

Research Article

Multiply antibiotic-resistant Vibrio cholerae O1 biotype El Tor strains emerge during cholera outbreaks in Zambia

J. C. L. MWANSAa1 c1, J. MWABAa1, C. LUKWESAa1, N. A. BHUIYANa2, M. ANSARUZZAMANa2, T. RAMAMURTHYa3, M. ALAMa2 and G. BALAKRISH NAIRa2

a1 University Teaching Hospital, Department of Pathology and Microbiology, Lusaka, Zambia

a2 International Centre for Diarrhoeal Disease Research, ICDDR,B, Dhaka, Bangladesh

a3 National Institute of Cholera and Enteric Diseases, Beliaghata, Calcutta, India

SUMMARY

Antibiotic resistance data, made available from laboratory records during eight cholera outbreaks between 1990 and 2004 showed Vibrio cholerae serogroup O1 to have a low level of resistance (2–3%) to tetracycline during 1990–1991. Resistance increased for tetracycline (95%), chloramphenicol (78%), doxycycline (70%) and trimethoprim–sulphamethoxazole (97%) in subsequent outbreaks. A significant drop in resistance to tetracycline and chloramphenicol followed the adoption of a national policy to replace tetracycline with erythromycin for treating cholera. Sixty-nine strains from cholera outbreaks in Zambia between 1996 and 2004, were examined for antibiotic resistance and basic molecular traits. A 140 MDa conjugative, multidrug-resistant plasmid was found to encode tetracycline resistance in strains from 1996/1997 whereas strains from 2003/2004 were resistant to furazolidone, but susceptible to tetracycline, and lacked this plasmid. PCR revealed 25 of 27 strains from 1996/1997 harboured the intl1 class 1 integron but lacked SXT, a conjugative transposon element. Similar screening of 42 strains from 2003/2004 revealed all carried SXT but not the intl1 class 1 integron. All 69 strains, except two, one lacking ctxA and the other rstR and thus presumably truncated in the CTX prophage region, were positive for important epidemic markers namely rfbO1, ctxA, rstR2, and tcpA of El Tor biotype. Effective cholera management is dependent on updated reports on culture and sensitivity to inform the choice of antibiotic. Since the emergence of antibiotic resistance may significantly influence strategies for controlling cholera, continuous monitoring of epidemic strains is crucial.

(Accepted August 10 2006)

(Online publication November 23 2006)

Correspondence:

c1 *Author for correspondence: Dr J. C. L. Mwansa, University Teaching Hospital, Department of Pathology and Microbiology, Lusaka, Zambia. (Email: jclmwansa@yahoo.ca)

Metrics