Detection of virulence genes in vibrio cholerae isolated from diseased seabass, lates calcarifer in east coast, Malaysia

Vibrio cholerae is the aetiological agent for cholera disease, a major public health concern due to the zoonotic ability of the infection. Vibrio cholerae encodes two major virulence factors which is the cholera toxin (CT) and toxin co-regulated pilus (TCP). It also encodes other virulence factors, such as the hemolysin encoded by the hlyA gene and ToxRVC. This study was conducted to detect the presence of virulence genes in Vibrio cholerae in East Coast Malaysia. A total of thirty-eight isolates of Vibrio cholera were revived from glycerol stock stored in -80˚C freezer. Blood hemolysis test was done by inoculating the bacterial samples on 5% sheep blood agar and incubated at 35˚C for 24h. The boiling method was done to extract the bacterial DNA. Then, a Polymerase chain reaction (PCR) was done to detect the presence of twelve types of virulence genes, namely tdh, trh-tdh, tlh, vvha, chiA, luxR, toxR(Vh), toxR(Vc), hlyA, cola, VcgEP2 and VcgP1 Interestingly, 95% (19/20) of the Vibrio cholerae isolated from Kuala Pahang showed beta hemolysis. The bacteria isolates were grouped into 10 groups of virulence genes frequency. Group I consist of ToxRVC, luxR, hlyA, and colA were the most abundant and detected in 70% (14/20) of Vibrio cholerae isolates from Pahang. The environmental condition and horizontal gene transfer might be responsible for the presence of virulence genes in Vibrio cholerae.
Keywords: Vibrio cholerae, Cholera, Virulence factors, hlyA gene, ToxRVC gene