Antimicrobial Resistance in Shigellosis, Cholera and Campylobacteriosis

Cholera is caused by strains of V. cholerae O1 or O139. V. cholerae has many serotypes, but only toxigenic strains (which produce cholera toxin, or CT) belonging to these two serotypes have caused epidemic diarrhoea. V. cholerae belongs to the Vibrionaceae family of bacteria, which are normal inhabitants of fresh and salt water; thus, an understanding of cholera requires an understanding of the bacteria’s role in the environment as well as in the human host. Other species of Vibrio cause diarrhoea or systemic illness, and some may even produce cholera toxin, but they do not cause epidemic diarrhoea. Patients with cholera excrete large numbers of the bacteria in their faeces. The bacteria are easily cultured using special media for their isolation (TCBS or TTGA), and their presence can also be detected using rapid immunoassay methods at the bedside (SMART Test or coagglutination tests). Specimens for culture should be placed in transport medium (e.g. Cary Blair) if they cannot be cultured immediately; they are then stable for several days and can be sent to a regional laboratory. After isolation, standard tests, including agglutination with specific O1 or O139 antiserum, are available to confirm identity. V. cholerae is a motile, curved, Gram-negative rod. If trained technicians and the proper microscope are available, motility is helpful for rapid diagnosis, since the bacteria can be readily visualized. Serogroup O1 has been subdivided into 3 serotypes (Ogawa, Inaba, and Hikojima) based on differences in factors A, B, and C of the O antigen, and also into two biotypes (classical and El Tor). An individual strain of O1 V. cholerae will thus have both a serotype and a biotype designation (for example a strain might be serotype Ogawa, biotype El Tor). All recent isolates of serotype O1 belong to the El Tor biotype, but there is frequent switching between Ogawa and Inaba serotypes in various locations. Hikojima strains are very rare and are not important from a public health standpoint. The clinical illnesses caused by Ogawa and Inaba strains are indistinguishable. Introduction