Aeromonas Isolates from Fish and Patients in Tainan City, Taiwan: Genotypic and Phenotypic Characteristics

Abstract

The present study aimed to isolate Aeromonas from fish sold in the markets as well as in sushi and seafood shops and compare their virulence factors and antimicrobial characteristics with those of clinical isolates. Among the 128 fish isolates and 47 clinical isolates, Aeromonas caviae, A. dhakensis, and A. veronii were the principal species. A. dhakensis isolates carried at least 5 virulence genes, more than other Aeromonas species. The predominant genotype of virulence genes was hlyA lip alt col ela in both A. dhakensis and A. hydrophila isolates, alt col ela in A. caviae isolates, and act in A. veronii isolates. A. dhakensis, A. hydrophila, and A. veronii isolates more often exhibited hemolytic and proteolytic activity and showed greater virulence than A. caviae isolates in Caenorhabditis elegans and the C2C12 cell line. However, the link between the genotypes and phenotypes of the studied virulence genes in Aeromonas species was not evident. Among the four major clinical Aeromonas species, nearly all (99.0%) A. dhakensis, A. hydrophila, and A. veronii isolates harbored bla_CphA, which encodes a carbapenemase, but only a minority (6.7%, 7/104) were nonsusceptible to carbapenem. Regarding AmpC β-lactamase genes, bla_AQU-1 was exclusively found in A. dhakensis isolates, and bla_MOX3 was found only in A. caviae isolates, but only 7.6% (n = 6) of the 79 Aeromonas isolates carrying bla_AQU-1 or bla_MOX3 exhibited a cefotaxime resistance phenotype. In conclusion, fish Aeromonas isolates carry a variety of combinations of virulence and β-lactamase resistance genes and exhibit virulence phenotypes and antimicrobial resistance profiles similar to those of clinical isolates.IMPORTANCEAeromonas species can cause severe infections in immunocompromised individuals upon exposure to virulent pathogens in the environment, but the characteristics of environmental Aeromonas species remain unclear. Our study showed that several pathogenic Aeromonas species possessing virulence traits and antimicrobial resistance similar to those of Aeromonas isolates causing clinical diseases were present in fish intended for human consumption in Tainan City, Taiwan.

Keywords: Aeromonas; antimicrobial susceptibility; virulence factors; β-lactam.

FIG 1

Distribution of Aeromonas species in clinical samples and in fish obtained from markets and from sushi and seafood shops.

FIG 2

Twenty-four-hour survival rates of Caenorhabditis elegans worms infected by the major genotypes of fish and human isolates of four Aeromonas species, Aeromonas dhakensis (AD), Aeromonas hydrophila (AH), Aeromonas veronii (AV), and Aeromonas caviae (AC), in the liquid toxicity assay. ***, P < 0.0001 compared with A. caviae. F, fish isolates; A2, clinical isolates. Symbols for genotypes: ◇, hlyA lip alt col ela; ❖, lip col ela; ★, act; ☆, hlyA lip ascF-ascG alt col ela; ✷, hlyA lip alt col ela; ▲, act hlyA aerA lip ascF-ascG alt ast col ela; ※, hlyA lip ascF-ascG alt ast col ela.

FIG 3

Cytotoxicity of Aeromonas dhakensis (AD), Aeromonas hydrophila (AH), Aeromonas veronii (AV), and Aeromonas caviae (AC) isolates to the C2C12 mouse fibroblast cell line, expressed as the proportion of the level of LDH release induced by the Aeromonas isolates compared with the level of LDH release induced by lysis solution (the value for the positive control was 100%). F, fish isolates; A2, clinical isolates; PC, positive control; NC, negative control. Symbols for genotypes: ◇, hlyA lip alt col ela; ❖, lip col ela; ★, act; ☆, hlyA lip ascF-ascG alt col ela; ✷, hlyA lip alt col ela; ▲, act hlyA aerA lip ascF-ascG alt ast col ela; ※, hlyA lip ascF-ascG alt ast col ela.