Class 1 integron-borne, multiple-antibiotic resistance encoded by a 150-kilobase conjugative plasmid in epidemic vibrio cholerae O1 strains isolated in Guinea-Bissau

Abstract

In the 1996-1997 cholera epidemic in Guinea-Bissau, surveillance for antimicrobial resistance showed the emergence of a multidrug-resistant strain of Vibrio cholerae O1 during the course of the epidemic. The strain was resistant to ampicillin, erythromycin, tetracycline, furazolidone, aminoglycosides, trimethoprim, and sulfamethoxazole. Concomitant with the emergence of this strain, we observed a resurgence in the number of registered cholera cases as well as an increase in the case fatality rate from 1.0% before the emergence of the multiple-drug-resistant strain to 5.3% after the emergence of the strain. Our study shows that the strain contained a 150-kb conjugative multiple-antibiotic resistance plasmid with class 1 integron-borne gene cassettes encoding resistance to trimethoprim (dhfrXII) and aminoglycosides [ant(3")-1a]). The finding of transferable resistance to almost all of the antibiotics commonly used to treat cholera is of great public health concern. Studies should be carried out to determine to what extent the strain or its resistance genes have been spread to other areas where cholera is endemic.

FIG. 1

Number of cases of cholera and number of deaths reported during the cholera epidemic in Guinea-Bissau in 1996–1997.

FIG. 2

Integron structure and resistance gene cassettes found in V. cholerae O1. The PCR primers used and the amplicons obtained are shown below the integron structure, with the bold line representing the amplicon sequenced. att1 is a site which is responsible for recombination, and qacEΔ1 and sul1 encode resistance to disinfectants and sulphonamides, respectively. The individual gene cassettes are shown together with their recombination sites (59-bp element).

FIG. 3

RFLP analysis of the 150-kb plasmid isolated from V. cholerae O1 strains isolated during cholera outbreaks in Guinea-Bissau. The explanations of the lanes include the strain designation and RFLP type unless stated otherwise. Lanes: a, HindIII-digested phage lambda DNA (weight marker); b, reference strain 1075/25; c, F2189, type E; d, F2196, type F; e, 9862, type A; f, 9868, type D; g, C230, type D; h, C231, type D; i, C233, type D; j, C235, type D; k, C236, type D; 1, C240, type D; m, HindIII-digested phage lambda DNA (weight marker).

FIG. 4

Examples of BglI ribotypes of V. cholerae O1 strains associated with cholera outbreaks in Guinea-Bissau. Unless stated otherwise, the explanations of the lanes include the strain designation, ribotype, and year of isolation. Lanes: A, 1-kb molecular weight standard; B, 1407, ribotype Ia, 1987; C, C235, type II, 1997; D, 1445, type Ia, 1992; E, 1452, type Ia, 1992; F, 1482, type Ia, 1992; G, F2107, type II, 1994; H, F2196, type II, 1994; I, F2189, type II, 1994; J, 1-kb molecular weight standard.