Cholera outbreak in South Africa, 2008-2009: laboratory analysis of Vibrio cholerae O1 strains

Abstract

Background: A total of 720 Vibrio cholerae O1 strains were recovered for investigation from an outbreak of cholera in South Africa between November 2008 and April 2009.

Methods: Strains were characterized by serotype testing. Antimicrobial susceptibility testing. Genetic diversity of 248 strains was investigated using pulsed-field gel electrophoresis (PFGE) analysis. Extended characterization was performed on 90 strains. Molecular analysis included: polymerase chain reaction (PCR) identification of ctxA and tcpA genes, sequencing the ctxAB gene, and investigation of molecular mechanisms conferring antimicrobial resistance.

Results: The majority of strains were characterized as serotype Ogawa. Strains showed multidrug resistance. Approximately 1.0% of strains displayed extended-spectrum β-lactamase (ESBL) activity. Strains showed very similar PFGE patterns. Ninety strains selected for extended characterization showed the following results: Strains possessed the cholera toxin (CT) and all were PCR positive for the tcpA-El Tor variant. Sequencing of the ctxB gene matched the B-1 allele. Strains harbored the SXT element. Strains that displayed ESBL activity possessed a 140-kilobase-pair plasmid that produced the TEM-63 β-lactamase. Nalidixic acid-resistant strains harbored mutations in GyrA (Ser83-Ile) and ParC (Ser85-Leu).

Conclusions: These data highlight the rapid development of antimicrobial resistance and spread of V. cholerae O1 El Tor variants expressing the classical CT within South Africa.

Keywords: SXT element; South Africa; TEM-63 β-lactamase; Vibrio cholerae O1 El Tor variant; cholera outbreak; classical cholera toxin; multidrug-resistant.