Optimization of a Method for Testing Ballast Water for Enterococci and an Investigation on the Occurrence of Antibiotic Resistance in Vibrio cholerae

Abstract

Several methods of enumerating Enterococci in water are suggested in the literature, notably membrane filtration and mEA plating. To establish optimal growth conditions, including incubation time, (24 and 48 hr) and temperature (35°C and 41°C), samples of 0.1 mL, 1 mL and 10 mL filtered water collected from Lake Artemisia, MD, USA were amended with known concentrations of Enterococcus faecalis (ATCC 29212), filtered using 0.45 µm membrane filters, and incubated on mEA agar under different conditions: 35°C/24h, 35°C/48h, and 41°C/48h, following U. S. Environmental Protection Agency guidelines. Results demonstrated no significant difference among the volume and time of incubations used but a significant difference in the temperatures employed.

Being the etiological agent of cholera, V. cholerae is a major public health problem in several developing countries. The prevalence of β-lactamase-producing strains and their isolation from life-threatening infections as well as the environment is alarming and presents a major therapeutic challenge for clinicians. The extended-spectrum β-lactamase profile of a collection of 210 V. cholerae O1 strains isolated from clinical and water samples was investigated. The strains were collected during ongoing epidemiological and ecological cholera surveillance in the provinces of Chhatak and Mathbaria in Bangladesh, between March 2009 and April 2012. Resistance to penicillins, monobactams, carbapenems, second-, third- and fourth- generation cephalosporins were tested by disk diffusion. Genotypic analysis of the resistance determinants was performed by PCR to detect ESBL (blaCTX, blaTEM, blaSHV), carbapenemases (blaIMP, blaSPM, blaVIM, blaBIC, blaNDM, blaKPC, blaAIM, blaSIM, blaDIM, and blaGIM). All strains were sensitive to the 4th-generation beta-lactam cefepime. This is the first report documenting such extensive resistance to monobactams and third-generation cephalosporin in V. cholerae.