Identification of environmental plasmid-bearing Vibriospecies isolated from polluted and pristine marine reserves of Hong Kong, and resistance to antibiotics and mercury

Fifty environmental isolates of Vibriospecies were isolated from water samples of Mai Po Nature Reserve and the Cape d’Aguilar Marine Reserve in Hong Kong and screened for the presence of plasmid. Mai Po is a wastewater-impacted area while the Cape d’Aguilar Marine Reserve is pristine natural marine water. Plasmid was found in Vibrioisolates from both sites at similar frequencies and each site showed distinctive plasmid profiles. These plasmid-bearing Vibrioisolates were identified as different species of the Vibriogenus by both biochemical test and subsequently full-length 16S rRNA sequences. Antibiotic resistance test showed that all these plasmid-bearing Vibrioisolates showed multiple resistance to 21 antibiotics tested. In addition, selective isolates also showed tolerance to 10 M Hg2+in culture medium and they generally harbored large plasmid(s) (>‰30 kb). Our results show that the high frequency of plasmid in Vibriospecies of both polluted and pristine environments may be ecologically important to the survival of these bacteria in the environment. The specific functioning of the cryptic plasmids remains the focus of current investigations.