Antimicrobial Susceptibility of Environmental Non-O1/Non-O139 Vibrio cholerae Isolates

Abstract

Vibrio cholerae serogroups O1 and O139 are the causative agents of cholera disease. There are more than 200 serogroups in this species that are termed V. cholerae non-O1/non-O139. Non-O1/non-O139 strains can cause gastroenteritis and cholera like diarrhea, wound infections, external otitis, and bacteraemia that may lead to mortality. Previous antimicrobial susceptibility studies were conducted mainly on O1/O139 serogroups and on clinical isolates. Our aim was to study and compare the antimicrobial susceptibilities of non-O1/non-O139 environmental strains isolated from chironomids, fish, and waterfowl. Significant differences were found in the antimicrobial susceptibilities between the environmental strains that were isolated from three different reservoir habitats. Significant increase in minimum inhibitory concentrations (MICs) of ampicillin and chloramphenicol was found in chironomid isolates from 2009 compared to those from 2005. V. cholerae isolates from different waterfowl species displayed the highest MIC values to chloramphenicol and trimethoprim-sulfamethoxazole (SXT), while chironomid isolates demonstrated the highest MIC values toward ampicillin. Isolates from fish and waterfowl showed high MIC values toward doxycycline. No significant differences were found between the MICs of isolates from the different waterfowl species. The percentage of antimicrobial resistance among V. cholerae isolates from waterfowl was the highest compared to the abundance of antimicrobial resistant isolates from chironomids or fish. The antimicrobial resistance genes can be carried on mobile genetic elements, thus, waterfowl may act as reservoirs for these elements and may spread them all over the globe. Data regarding treatment with antimicrobial agents toward V. cholerae non-O1/non-O139 serogroups is lacking and therefore further studies are needed.

Keywords: V. cholerae; antibiotics; antimicrobial susceptibility; chironomid; fish; resistance; waterbird; waterfowl.

FIGURE 1

MIC (average ± std. error) of the studied antimicrobial agents toward all V. cholerae strains. Ampicillin (n = 146), azithromycin (n = 141), chloramphenicol (n = 146), doxycycline (n = 144); SXT (n = 146). Bars with different letters are significantly different by repeated measures ANOVA with Bonferroni post hoc test (p < 0.05). SXT, Trimethoprim (TMP) and sulfamethoxazole.

FIGURE 2

Comparative analysis of MICs (average ± std. error) for each of the studied antimicrobial agents toward V. cholerae strains that were isolated from the three environmental reservoirs (waterfowl n = 47, fish n = 50, and chironomids n = 50). Bars with different letters are significantly different by One-way ANOVA with Tukey HSD test (p < 0.05). SXT, Trimethoprim (TMP) and sulfamethoxazole.

FIGURE 3

Comparative analysis of the MIC (average ± std. error) for each of the studied antimicrobial agents toward V. cholerae strains that were isolated from chironomids in 2005 (green bars, n = 18), and 2009 (blue bars, n = 32). Asterisks represent significant differences in MICs by Student’s t-test (p < 0.05). ns, no significant difference; SXT, Trimethoprim (TMP) and sulfamethoxazole.

FIGURE 4

Comparative analysis of MIC (average ± std. error) for each of the studied antimicrobial agents toward V. cholerae strains that were isolated from the three waterfowl species [black-crowned night herons (orange, n = 21), great cormorants (pink, n = 5), and little egrets (red, n = 22)]. No significant differences were found between MIC concentrations of the different strains that were isolated from different waterfowl species (p > 0.05).