Antibiotic-resistant phenotypes and genotypes of Laribacter hongkongensis isolated from different hosts

  Objective  To examine phenotype and genotype distribution of antibiotic-resistant Laribacter hongkongensis (LH) strains isolated from different hosts.

  Methods  Totally 117 LH strains were isolated from intestinal tracts of fresh water fish and frogs in Guangdong province from January 2015 to August 2016, and 5 strains from human faces. Kirby-Bauer (K-B) disk diffusion method was used to test the susceptibility to 13 antibiotics of the strains. Detections of 9 antibiotic-resistant genes were performed for 122 LH strains with PCR amplification. Chi-square test was adopted to analyze differences in antibiotic resistance of the strains.

  Results  Of the 122 LH strains, 86.89% were resistant to rifampin, 78.6% to cefalotin, 48.7% to ampicillin, 78.6 % to sulfamethoxazole, 18.9% to erythromycin, 18.0% to tetracycline, and 14.5% to ciprofloxacin, respectively, with an overall multiple antibiotic-resistant rate of 57.4%. Among the 22 tetracycline-resistant LH strains, the detection rates of tetA and tetR resistance-related genes were 72.7% and 68.2 %; for the 36 sulfa-resistant LH strains, the detection rates of sul1 and sul2 resistance-related genes were 86.1% and 50.0%. The ampicillin-, cefalotin-, erythromycin-, and rifampicin-resistant rate were significantly higher among LH strains isolated from fresh water fish than among those from frogs (P < 0.05 for all); while the tetracycline-, ciprofloxacin-, sulfamethoxazole-, and streptomycin-resistant rate of the LH strains from frogs were significantly higher than those of the strains from fish (P < 0.05 for all). Significantly higher carrying rates of antibiotic resistance-related genes, including sul1, sul2, tetA, tetR, aac (6′) -ib, and ereA, were observed among the LH strains isolated from frogs than among those from fish (all P < 0.05）. Of the 5 LH strains from human, only one was multiple antibiotic-resistant.

  Conclusion  The antibiotic-resistant stains are highly prevalent for LH isolated from freshwater products in Guangdong province and the antibiotic resistance is different for the LH strains isolated from various hosts. Carrying tetA, tetR, sul1, and sul2 genes may play a main role for the LH strains′ sulfonamides and tetracyclines resistance.