Study of medically important Vibrios in the sewage of Katmandu Valley, Nepal.

A total of 42 samples were collected from the different sites of sewer system of Kathmandu Valley during rainy summer season (June to September 2008) using Moore's technique. Samples (on Moore's swabs) were submersed in alkaline peptone water (pH 8.6) and transported to Research Laboratory of National Institute of Tropical Medicine and Public Health Research, Kathmandu in cold condition (ice chest) followed by incubation at 37 degrees C for 8 hours. After incubation, culture was done on thiosulfate-citrate-bile salt-sucrose (TCBS) agar and incubated at 37 degrees C for overnight (15 hrs). Both yellow and green colonies measuring from 2 to 9 mm in diameter on TCBS agar were subjected for gram staining, biochemical testing as well as sero-typing using antisera (poly O1, Ogawa and Inaba) (Denka Seiken Co. Ltd, Japan). Altogether 46 medically important Vibrios were isolated from 42 samples studied. The isolates were identified as V. cholerae (n = 20; 43.5%), V. vulnificus (n = 11; 23.9%), V. parahaemolyticus (n = 5; 10.9%), V. furnissi (n = 5; 10.9%), V. fluvialis (n = 3; 6.5%) and V. alginolyticus (n = 2; 4.3%). Of the 20 V. cholerae isolates, 13 (65.0%) and 7 (35.0%) isolates were V. cholerae O1 and non-O1, respectively. Among the V. cholerae O1 (n = 13), classical Hikojima strain was most frequently isolated (n = 10) followed by V. cholerae O1 Ogawa (El Tor = 2 and classical = 1). High frequency of V. cholerae isolation from sewer system of Kathmandu Valley is an indication of possible outbreak of cholera anytime in future and, therefore, demands improvement in sanitary condition, supply/consumption of safe drinking water and personal hygiene.