Page 59 - ii_3_2020

//Aquaculture 57

little or no damage to the host. Hence, all antibiotics are AMR occurs naturally through microbial adaptation to
antimicrobials but not all antimicrobials are antibiotics. the environment, exacerbated by the inappropriate and
excessive use of antimicrobials. It may exist in combination
Some of the important bacterial diseases for fishery species with present and past use of antibiotics, probiotics, prebiotics
and most frequently used antibiotics in aquaculture are and other treatment, singly or combined. These systems
outlined in Tables 1 and 2 (Reantaso 2018 ). have been designated as “hotspots for AMR genes” where
3
significant genetic exchange and recombination can occur.
Table 1: Main bacterial diseases in aquaculture Various factors are involved in this process such as lack of
Gram-negative bacteria Gram-positive bacteria regulation and oversight of use, poor therapy adherence,
Vibriosis (V. anguillarum, V. harveyi clade, Mycobacteriosis non-therapeutic use, over the counter (OTC) or online sales
V. parahaemolyticus, Aliivibrio salmonicida (Mycobcaterium and availability of counterfeit or poor-quality antimicrobials.
(V. salmonicida), V. vulnificus, Photobacterium fortuitum, M. marinum, AMR may also happen through horizontal gene transfer (HGT)
damselae. Nocardia asteroids, N.
crassostreae(ostreae), and mutation events that allow genetic exchange within
N. seriolae microbial populations, a process which has been ongoing
Aeromonasis ( Motile Aeromonas spp.: Streptococcosis since ancient times.
Aeromonas caviae, A. hydropila, A. sobria, (Streptococcus
A. veronii, A. jaondei, A. salmonicida) agalactiae, S. iniae, The consequences of AMR include the failure to successfully
Lactococcus garvieae, treat infections leading to increased mortality, more severe or
Aerococcus viridans)
Edwardsiellosis ( Edwardsiella anguillarum, Renibacteriosis prolonged illness, production losses and reduced livelihood
E. ictaluri, E. piscicida, E. tarda, Yersinia (Renibacterium and food security. Microorganisms that develop AMR are
ruckeri) salmoninarum) sometimes referred to as ‘superbugs’. It has been estimated
Pseudomonasis: Pseudomonas anguilliseptica, that 90 percent of bacteria originating in seawater are
P. fluroscens) resistant to one or more antibiotics and up to 20 percent of
Flavobacteriosis (Flavobacterium the bacteria are resistant to at least five.
branchiophilum, F. columnare, F. psychphilum,
Tenacibaculum maritinum)
Sources of antimicrobials in
Infection with Intracellular Bacteria Infection with
(Piscirickettssia salmonis, Hepatobacter Anaerobic Bacteria aquaculture
penaei, Francisella noatunensis, Chlamydia (Clostridium botulinum,
spp.) Enterobacterium Antibiotics enter aquatic environments through various
catenabacterium)
means. The application of organic manure e.g. cow dung,
poultry litter and piggery wastes in integrated farms is
Table 2: Frequently used antibiotics in aquaculture
common in many Asian countries, where the inorganic
Type Generic Name
nutrients support the growth of photosynthetic organisms
Tetracyclines Oxytetracycline, Doxycycline eaten by aquatic animals. This practice in turn often leads to
Quinolones Oxolinic acid, flumequine, enrofloxacine (and other higher occurrence of antimicrobial resistant bacteria which
fluroquinolone) might later have an impact on fish quality and shelf life as well
Phenicols Florfenicol, Chloramphenicol and Thiamphenicol as consumers’ health. Another source is through animal feed,
Anti-folates Trimethoprim/Sulfamethoxazole, trimethoprim, which often contains antimicrobials which had been added to
sulfonamides promote growth or prevent and treat diseases. Meanwhile,
β-lactums Amoxicillin the direct medication of fish in aquaculture also leads to
Macrolides Erythromycine, Josamycin, Neomycin(for Gram+Ve an increase in the level of antimicrobial resistance among
Bacteria) bacteria in the fish intestine.
Nitrofurans Nitrofurantin
Once bacteria have acquired AMR genes, they may exist in
Antimicrobial resistance (AMR) occurs when bacteria the environment for a long time. Bacterial strains carrying
and other microbes such as parasites, viruses and fungi resistance determinants in commercial seafood products
develop resistance to drugs used to treat the infections they include disease-causing pathogenic bacteria in humans,
cause. AMR, together with antimicrobial use (AMU) were thereby increasing the risk of spreading AMR from aquaculture
4
identified in the first Joint FAO/OIE/WHO Expert Meeting on to consumer. Some studies have found that 70-80 percent of
Antimicrobial Use (AMU) and Antimicrobial Resistance (AMR) the antibiotics given to fish are excreted into the water and
in Aquaculture as being major hazards. can further alter the microbial communities present.

INFOFISH International 3/2020 ● www.infofish.org
Credit: CNA