The Impact of Water Intrusion on Pathogenic Vibrio Species to Inland Brackish Waters of China

Abstract

The estuary is the ecological niche of pathogenic <i>Vibrio</i> spp. as it provides abundant organic and inorganic nutrients from seawater and rivers. However, little is known about the ecology of these <i>Vibrio</i> species in the inland brackish water area. In this study, their co-occurrence and relationships to key environmental constraints (salinity and temperature) in the Hun-Tai River of China were examined using the most probable number polymerase chain reaction (MPN-PCR) approach. We hereby report 2-year continuous surveillance based on six water indices of the Hun-Tai River. The results showed that seawater intrusion maximally reached inland as far as 26.5 km for the Hun-Tai River. Pathogenic <i>Vibrio</i> spp. were detected in 21.9% of the water samples. In particular, <i>V. cholerae</i>, <i>V. parahaemolyticus</i>, and <i>V. vulnificus</i> were isolated in 10 (10.4%), 20 (20.8.5%), and 2 (2.08%) samples, respectively. All <i>V. parahaemolyticus</i> strains were <i>tdh</i> gene negative, 10% were positive for the <i>trh</i> gene. Multi-locus sequence typing (MLST) divided <i>V. parahaemolyticus</i> strains into 12 sequence types (STs) for the Hun-Tai River. Five STs were respectively present in various locations along the Hun-Tai River. The PCR assay for detecting six virulence genes and <i>Vibrio</i> seventh pandemic island I and II revealed three genotypes in 12 <i>V. cholerae</i> isolates. The results of our study showed that seawater intrusion and salinity have profound effects on the distribution of pathogenic <i>Vibrio</i> spp. in the inland river, suggesting a potential health risk associated with the waters of the Hun-Tai River used for irrigation and drinking.