Comparison of antibiotic resistance phenotype and genotype between tdh⁺ and tdh⁻ strains of Vibrio parahaemolyticus

  Objective  To compare the phenotypic and genotypic antibiotic resistance difference between tdh⁺ and tdh⁻ strains of Vibrio parahaemolyticus, and analyze the relationship between antibiotic resistance genotype and phenotype.

  Methods  The resistance patterns of 208 tdh⁺ and 73 tdh⁻ strains of V. parahaemolyticus to 16 antibiotics (7 kinds) commonly used in clinical treatment and aquaculture were determined using K-B test. The whole gene sequences of the strains were obtained by new generation sequencing technology. The mutations of antibiotic resistance genes and related genes in the genome were analyzed by sequence alignment. The relationship between phenotype and genotype was analyzed.

  Results  Both tdh⁺ and tdh⁻ strains were 100% sensitive to imipenem. The drug-resistance rates of tdh⁺ strains (0.48%, 8.65%) to cefepime and azithromycin were higher than that of tdh⁻ strains (0.00%, 4.11%); the drug-resistance rates of tdh⁻ strains to ampicillin, cefoxitin, ceftriaxone, ciprofloxacin, nalidixic acid, streptomycin, kanamycin, gentamicin, sulfamethoxazole, sulfamethoxazole, tetracycline, doxycycline and chloramphenicol were higher than those of tdh⁺ strains. The multidrug resistance rate of tdh⁻ strains (34.25%) was higher than that of tdh⁺ strains (19.23%). There were 5 types and 7 kinds of drug resistance genes, among which β - lactam gene (bla_CARB) was detected in all the tdh⁺ strains and tdh⁻ strains; the tetracycline resistance tet (34) gene carriage rates in tdh⁺and tdh⁻ strains were 99.52% and 98.63%, the quinolone resistance gene qnrS5 was detected only in tdh⁺ strain. The detection rates of folate metabolism inhibitors (sul2), tetracycline ［tet（35）、tet（59）］ and phenylpropanol (floR) resistance genes in tdh⁻ strains were higher than those in tdh⁺ strains. A total of 14 strains of V. parahaemolyticus (9 tdh⁺ strains, 5 tdh⁻ strains) were screened for six point mutations of drug-resistance genes, all of which were rrs gene mutations encoding 16S rRNA.

  Conclusion  The drug resistance of tdh⁻ V. parahaemolyticus strains was more serious than that of tdh⁺ V. parahaemolyticus strains; the rrs gene mutation of 16S rRNA was one of the main resistance mechanisms of V. parahaemolyticus to aminoglycosamines except for resistance genes: aph(3'')-Ib, aac(3)-Ⅱ, aac(6’) –I and aph(3'')-Id. bla_CARB gene can be used to predict the ampicillin resistance phenotype of V. parahaemolyticus, bur there was no clear relationship between other antibiotic resistance phenotypes and the corresponding resistance genes