Multilocus Sequence Typing and Virulence Potential of Vibrio parahaemolyticus Strains Isolated from Aquatic Bird Feces

Abstract

Vibrio parahaemolyticus is a Gram-negative, foodborne pathogenic bacterium that causes human gastroenteritis. This organism is ubiquitously present in the marine environment. Detection of V. parahaemolyticus in aquatic birds has been previously reported; however, the characterization of isolates of this bacterium recovered from these birds remains limited. The present study isolated and characterized V. parahaemolyticus from aquatic bird feces at the Bangpu Recreation Center (Samut Prakan province, Thailand) from 2016 to 2017, using multilocus sequence typing (MLST) and genome analysis. The results showed that V. parahaemolyticus was present in 34.9% (76/218) of the collected bird fecal samples. Among the ldh-positive V. parahaemolyticus isolates (n = 308), 1% (3/308) were positive for tdh, 1.3% (4/308) were positive for trh, and 0.3% (1/308) were positive for both tdh and trh. In turn, the MLST analysis revealed that 49 selected V. parahaemolyticus isolates resolved to 36 STs, 26 of which were novel (72.2%). Moreover, a total of 10 identified STs were identical to globally reported pathogenic strains (ST1309, ST1919, ST491, ST799, and ST2516) and environmental strains (ST1879, ST985, ST288, ST1925, and ST260). The genome analysis of isolates possessing tdh and/or trh (ST985, ST1923, ST1924, ST1929 and ST2516) demonstrated that the organization of the T3SS2α and T3SS2β genes in bird fecal isolates were almost identical to those of human clinical strains posing public health concerns of pathogen dissemination in the recreational area. The results of this study suggest that aquatic birds are natural reservoirs of new strains with high genetic diversity and are alternative sources of potentially pathogenic V. parahaemolyticus in the marine environment. IMPORTANCE To our knowledge, infection of foodborne bacterium V. parahamolyticus occurs via the consumption of undercooked seafood contaminated with pathogenic strains. Aquatic bird is a neglectable source that can transmit V. parahaemolyticus along coastal areas. This study reported the detection of potentially pathogenic V. parahamolyticus harboring virulence genes from aquatic bird feces at the recreational center situated near the Gulf of Thailand. These strains shared identical genetic profile to the clinical isolates that previously reported in many countries. Furthermore, the strains from aquatic birds showed extremely high genetic diversity. Our research pointed out that the aquatic bird is possibly involved in the evolution of novel strains of V. parahaemolyticus and play a role in dissimilation of the potentially pathogenic strains across geographical distance.

Keywords: Vibrio parahaemolyticus; aquatic bird feces; multilocus sequence typing; virulence genes; whole-genome analysis.

FIG 1

Phylogenetic tree of 49 V. parahaemolyticus isolates from aquatic bird fecal samples. The black circles in front of the names represent isolates possessing virulence genes. Bold letters represent isolates with sequence types (STs) identical to those available in the pubMLST database (https://pubmlst.org).

FIG 2

Geographical position of previously reported V. parahaemolyticus STs that were isolated from aquatic bird feces in Thailand (https://pubmlst.org).

FIG 3

Population snapshot of V. parahaemolyticus isolates from bird feces and related STs from the pubMLST database. (A) eBURST diagram of all STs of the bird feces isolates and related STs from the pubMLST database. (B) Clonal complex (CC) 2516 with single-locus variants (SLVs). (C) CC8 with SLVs. Yellow color represents STs of bird feces isolates detected in this study. Red and blue colors represent STs of clinical and environmental isolates, respectively, from the pubMLST database.

FIG 4

Phylogenetic tree of 32 V. parahaemolyticus strains from GenBank and five isolates from bird fecal samples. (A) The codon tree was constructed using whole-genome sequencing data by an algorithm installed in PATRIC (34). (B) The multilocus sequence typing tree was constructed based on seven housekeeping gene sequences using MEGA 7.0 (80).