Antimicrobial resistance and genotyping of Vibrio cholerae isolates collected from outbreaks in East Africa, 2006-2007

Original article


Salwa F. Ahmed 1, Momtaz O. Wasfy 1, Myriam Morcos 1, Guillermo Pimentel 1, Mubarak Mohamed 2, Sadiki F. Materu 3, Ammar Abdo Ahmed 4, Adam W. Armstrong 1 , John D Klena 1

1-US Naval Medical Research Unit-3, Cairo, Arab Republic of Egypt; 2-Central Public Health Laboratory, Ministry of Health, Sudan; 3-AMREF Laboratory Programme, Nairobi, Kenya; 4-Ministry of Health, Djibouti

Libyan J Infect Dis. Vol. 2, No.1. Jan-2008:37-44


Background/Objectives: Outbreaks of the Gram-negative bacterial pathogen Vibrio cholerae in parts of Africa are not uncommon. The purpose of this study was to determine the relationship of V.cholerae isolates circulating in Eastern and Horn of Africa nations during four cholera outbreaks beginning in 2006.
Materials and Methods: We investigated phenotypic and genetic properties associated with V. cholerae outbreaks in 82 isolates from Sudan (n=70), Somalia (n=6) and Djibouti (n=6) from 2006 to 2007. Isolates were cultured on TCBS agar medium at 37؛C for 18-24 h. Serotyping was performed on purified colonies using commercially available polyclonal antisera directed towards O1- or O139-specific antigens (Difco). Monoclonal antibodies specific for O1 Inaba or O1 Ogawa were used to determine the specific O1 type. Antimicrobial susceptibility testing (AST) was performed using commercially available discs (Beckton- Dikinson, Sparks, MD). Genomic DNA from all of the isolates were analyzed by SfiI and NotI macrorestriction profiling. A virulence gene profiling assay was also performed using genes to the cholera toxin subunit B, toxin co-regulated pilus, the zona occludans toxin and the haemolysin.
Results: All of the isolates except those from Somalia were serotyped as V. cholerae O1 El Tor Inaba, all six Somali isolates were O1 El Tor Ogawa. Resistance to sulfatrimethoxazole (SXT) was universal among the isolates, but only ten were resistant to ampicillin (Ap). These isolates were from Somalia (n=6), Djibouti (n=1), and Sudan (n=1). The Ap-resistant Sudan isolate was also resistant to tetracycline and was considered multidrug resistant (MDR). PCR identified a TEM-1 like resistance gene in only the Sudan isolate. All of the El Tor Inaba isolates, regardless of location,were indistinguishable using both SfiI and NotI enzymes. The only exception was the MDR Inaba isolate from Sudan which had a two band difference using SfiI. Analysis of representative isolates from each outbreak by multilocus sequence typing (MLST) failed to further discriminate between isolates.
Conclusion: It appears that two clones are responsible for the outbreaks
of cholera from Sudan to Djibouti from 2006-2007; one strain is V. cholerae O1 El Tor Ogawa described previously in this region of Africa. The second is a clone of V. cholerae O1 El Tor Inaba. To our knowledge, this is the first report of V. cholerae O1 El Tor Inaba in Sudan and Djibouti.

Keywords: Vibrio cholerae, outbreaks, East Africa, antimicrobial resistance, genotyping.