Vibrio agar: a new plating medium for isolation of Vibrio cholerae

Distribution and antibiotic resistance of vibrio population in an urbanized tropical lake-the Vembanad-in the southwest coast of India

Among the diverse Vibrio spp. autochthonous to coastal ecosystems, V. cholerae, V. fluvialis, V. vulnificus and V. parahaemolyticus are pathogenic to humans. Increasing sea-surface temperature, sea-level rise and water-related disasters associated with climate change have been shown to influence the proliferation of these bacteria and change their geographic distribution. We investigated the spatio-temporal distribution of Vibrio spp. in a tropical lake for 1 year at a 20-day interval. The abundance of Vibrio spp. was much higher during the south-west monsoon in 2018, when the lake experienced a once-in-a-century flood. The distribution of Vibrio spp. was influenced by salinity (r = 0.3, p < 0.001), phosphate (r = 0.18, p < 0.01) and nitrite (r = 0.16, p < 0.02) in the water. We isolated 470 colonies of Vibrio-like organisms and 341 could be revived further and identified using 16S rRNA gene sequencing. Functional annotations showed that all the 16 Vibrio spp. found in the lake could grow in association with animals. More than 60% of the isolates had multiple antibiotic resistance (MAR) index greater than 0.5. All isolates were resistant to erythromycin and cefepime. The proliferation of multiple antibiotic-resistant Vibrio spp. is a threat to human health. Our observations suggest that the presence of a diverse range of Vibrio spp. is favoured by the low-saline conditions brought about by heavy precipitation. Furthermore, infections caused by contact with Vibrio-contaminated waters may be difficult to cure due to their multiple antibiotic resistances. Therefore, continuous monitoring of bacterial pollution in the lakes is essential, as is the generation of risk maps of vibrio-infested waters to avoid public contact with contaminated waters and associated disease outbreaks.

Detection, isolation, and identification of Vibrio cholerae from the environment

Microbiological techniques for sampling the aquatic realm have become increasingly sophisticated, especially with advances in molecular biology. These techniques have been used to detect microorganisms that cannot be cultured by conventional bacteriological methods. This has resulted in a deeper and a clearer understanding of the ecology and epidemiology of microorganisms. Important advances have been made in isolation, detection, and identification of Vibrio cholerae over the past decade. The understanding that V. cholerae, like several other pathogenic bacteria, can enter into a state known as "viable but nonculturable" (VBNC) provided important clues on the epidemiology of the pathogen and its ability to cause sudden explosive epidemics at multiple places almost simultaneously. The advances in techniques have also allowed investigators to discern the intricate aspects of the ecology of this pathogen in the aquatic world. In this unit, we present the most accepted methods for the isolation and detection of V. cholerae.

Culture media for the isolation and enumeration of pathogenic Vibrio species in foods and environmental samples

The genus Vibrio now includes a large number of species. Clear evidence is only available for the aetiological role of V. cholerae, V. vulnificus and V. parahaemolyticus in foodborne diseases. Until recently, V. cholerae serogroup 0:1 was accepted as the cause of epidemic cholera. However, the designation of outbreaks of diarrhoeal diseases caused by V. cholerae 0:139 as clinical cholera has lead to renewed interest in Non 0:1 serogroups of V. cholerae. A wide range of enrichment and selective media for the isolation of vibrios has been developed. These media are reviewed with respect to their ability to recover and differentiate the target vibrios. Alkaline peptone water (APW) remains the recommended enrichment medium for vibrios in parallel with either salt polymyxin broth (SPB) or glucose teepol (or sodium dodecylsulphate) salt broth (GTSB) when tests for V. parahaemolyticus are required. Thiosulphate citrate bile salt agar (TCBS) in parallel with polymyxin mannose tellurite (PMT) or sodium dodecylsulphate polymyxin sucrose agar (SPS) are the recommended selective plating media.

Cholera

Despite more than a century of study, cholera still presents challenges and surprises to us. Throughout most of the 20th century, cholera was caused by Vibrio cholerae of the O1 serogroup and the disease was largely confined to Asia and Africa. However, the last decade of the 20th century has witnessed two major developments in the history of this disease. In 1991, a massive outbreak of cholera started in South America, the one continent previously untouched by cholera in this century. In 1992, an apparently new pandemic caused by a previously unknown serogroup of V. cholerae (O139) began in India and Bangladesh. The O139 epidemic has been occurring in populations assumed to be largely immune to V. cholerae O1 and has rapidly spread to many countries including the United States. In this review, we discuss all aspects of cholera, including the clinical microbiology, epidemiology, pathogenesis, and clinical features of the disease. Special attention will be paid to the extraordinary advances that have been made in recent years in unravelling the molecular pathogenesis of this infection and in the development of new generations of vaccines to prevent it.

Differential medium for Vibrio cholerae

A differential medium designed for rapid presumptive identification of Vibrio cholerae was described and shown to be useful for enumeration of viable cholera vibrios in the presence of other intestinal bacteria.