Microbiology-Vibrio Cholera Antibiotics



Antibiotic Susceptibility of Non-Cholera Vibrios Isolated from Farmed and Wild Marine Fish

(Argyrosomus japonicus), Implications for Public Health

Justine Fri, 1

Roland Ndip Ndip, 2

Henry Akum Njom, 1

and Anna Maria Clarke 1

This study aimed to evaluate the antibiogram and antibiotic resistance genes (ARGs) of Vibrio isolates recovered from a marine fish (Argyrosomus japonicas) and water samples from two commercial dusky kob aquaculture farms and the Kariega estuary, South Africa, and to evaluate these findings for their public health implications.

A total of 277 molecularly confirmed Vibrio isolates consisting of 126 Vibrio fluvialis, 45 Vibrio vulnificus, 30 Vibrio parahaemolyticus, and 76 vibrios belonging to species of the genus other than Vibrio cholera were subjected to susceptibility testing to 15 antibiotics by the disc diffusion method.

Multiple antibiotic resistance index ( MARI) was used to determine the antibiotic resistance-associated health risk, while polymerase chain reaction was used to evaluate the presence of 14 ARGs for nonsusceptible strains. Highest resistances were recorded to amoxicillin (76.2%), ampicillin (67.5%), erythromycin (38.3%), and doxycycline (35.0%), while susceptibilities were highest to gentamicin (100%), followed by norfloxacin (97.8%), florfenicol (90.3%), tetracycline (87.7%), and chloramphenicol (87.4%).

We recorded a 58.5% multidrug resistance (resistance to ‡2 antimicrobial classes). MARI did not vary significantly between sites ( p > 0.05); however, values of >0.2 were recorded in 40% (108/277) of all strains tested. ARG markers, amps, blaOXA, tetA, tetM, dfr1, sul1, sul2, ermB, nptII, strA, and SXT integrase, were detected in one or more strains with ermB (82.5%), sul2 (53.8%), strA (44%), dfr1 (42.3%), and tetM (38.3%) being the most abundant. Healthy marine finfish (dusky kob) and their environment can serve as reservoirs for antibiotic-resistant vibrios and ARGs, which could be disseminated to humans and other susceptible bacteria and this, therefore, becomes a public health concern.

Keywords: Vibrio, marine fish, antibiotic drug resistance, antibiotic-resistant genes, public health


Antimicrobials are widely used for the prevention and treatment of bacterial diseases in food animals.1 They are among the most widely administered drugs approved for animal health and management. Global estimates indicate higher volumes of antimicrobials used in food-producing animals, exceeding those used in humans.

2 Most

animal feeds are supplemented with various concentrations of antimicrobials ranging from subtherapeutic to full doses. Moreover, almost all the classes of antibiotics used in the treatment of human infections are also used in food animals, including the newest classes of drugs such as third- and fourth-generation cephalosporins, fluoroquinolones, glycopeptides, and streptogramins.


In aquaculture, the control of antibiotic usage varies widely from country to country.

3 Most developed countries either have

registered antibiotics for bacterial disease control, with well-defined regulations regarding their usage, or no longer permit the registration of products for nontherapeutic purposes such as growth promoters.

4,5 However, about 90% of aquaculture in-

industries are located in developing countries with weaker control strategies. Although antibiotics play an important role in the prevention and treatment of bacterial diseases both in humans and food animals, the indiscriminate use of these anti- microbials has led to the emergence of antibiotic-resistant bacteria and antibiotic resistance genes (ARGs) in the environment.

Members of the genus Vibrio are abundant in the marine environment and may contaminate edible fish. Vibrio cholerae, Vibrio parahaemolyticus, Vibrio Vulnificus, and Vibrio fluvialis are the most significant human pathogens of the genus that may cause mild to potentially fatal foodborne illnesses, especially from consumption of contaminated seafood.

6–8 The acquisition

of ARGs by these pathogenic bacteria is of concern as these may

1 Microbial Pathogenicity and Molecular Epidemiology Research Group ( MPM), Department of Biochemistry and Microbiology,

University of Fort Hare, Alice, South Africa. 2 Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon.

MICROBIAL DRUG RESISTANCE Volume 24, Number 9, 2018 ª Mary Ann Liebert, Inc. DOI: 10.1089/mdr.2017.0276


cause treatment failure and difficulties in human disease management. Previous studies have reported antibiotic resistance or resistance genes in vibrios isolated from shrimps

9,10 and other

seafood. 11,12

These pathogenic bacteria with acquired ARGs may serve as reservoirs of resistance genes to susceptible bacteria. The accumulation of antibiotic residues in edible fish tissues may also alter human intestinal flora and cause food poisoning or allergies.

13 Some of these residues may be detected from several months 14 up to a few years posttreatment with antimicrobials.

15 The World Health Organization considers the emergence of drug-resistant bacteria, particularly multidrug-resistant strains, to have critical consequences for human medicine.

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