Antimicrobial Drug Resistance in Fish Pathogens

Abstract

Major concerns surround the use of antimicrobial agents in farm-raised fish, including the potential impacts these uses may have on the development of antimicrobial-resistant pathogens in fish and the aquatic environment. Currently, some antimicrobial agents commonly used in aquaculture are only partially effective against select fish pathogens due to the emergence of resistant bacteria. Although reports of ineffectiveness in aquaculture due to resistant pathogens are scarce in the literature, some have reported mass mortalities in larvae caused by resistant to trimethoprim-sulfamethoxazole, chloramphenicol, erythromycin, and streptomycin. Genetic determinants of antimicrobial resistance have been described in aquaculture environments and are commonly found on mobile genetic elements which are recognized as the primary source of antimicrobial resistance for important fish pathogens. Indeed, resistance genes have been found on transferable plasmids and integrons in pathogenic bacterial species in the genera ,, ,, and . Class 1 integrons and IncA/C plasmids have been widely identified in important fish pathogens ( spp., spp., spp., spp., and spp.) and are thought to play a major role in the transmission of antimicrobial resistance determinants in the aquatic environment. The identification of plasmids in terrestrial pathogens ( serotypes, , and others) which have considerable homology to plasmid backbone DNA from aquatic pathogens suggests that the plasmid profiles of fish pathogens are extremely plastic and mobile and constitute a considerable reservoir for antimicrobial resistance genes for pathogens in diverse environments.

Edwardsiella piscicida: A versatile emerging pathogen of fish

“…Fish reared in aquaculture are often kept under crowded and stressful conditions and require prophylactic and therapeutic use of antimicrobials to control disease outbreaks [44]. The use of antibiotics in aquaculture introduces a selective pressure on the microbial flora in aquatic environments and often promotes antibiotic resistance [46]. Resistant bacteria can thus multiply after the suppression of sensitive bacteria.…”

Agelasines B, D and antimicrobial extract of a marine sponge Agelas sp. from Tahuna Bay, Sangihe Islands, Indonesia

“…Of these, Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter spp and Enterococcus faecium (VRE) were classified as critical priority and S. aureus (MRSA and VRSA) as high priority group (WHO 2017). Similarly, there is an alarming increase in resistance of fish pathogens such as Aeromonas hydrophila, Edwardsiella tarda and Aeromonas salmonicida against the commercial antibiotics, which were recently reported to be partially effective against the fish pathogens (Miller and Harbottle 2018). Moreover, the ability of fish pathogens such as Aeromonas spp., Edwardsiella spp.…”

“…and Vibrio spp. to transfer antibiotic-resistant genes to other fish pathogens exacerbates the current antibiotic resistance crisis (Miller and Harbottle 2018). Together, these facts strongly suggest a desperate need for new antibiotics to combat these deadly infectious bacteria (Tommasi et al 2015).…”

Rearing background and exposure environment together explain higher survival of aquaculture fish during a bacterial outbreak

“…Consequently, infections reduce economic profitability of the industry by impairing growth, and increasing morbidity and mortality of hosts. Infections are prevented and treated with chemicals, antibiotics and vaccinations (Brown & Gratzek, 1980;McEwen & Fedorka-Cray, 2002), which is expensive and can result in secondary problems such as increased pathogen resistance to drugs (Durso & Cook, 2014;Levy & Marshall, 2004;Martinez, 2009) and spill-over of chemical residues into the environment (Guardabassi, Dalsgaard, Raffatellu, & Olsen, 2000;Martinez, 2009;Sorum, 2006). Thus, ecologically sustainable methods for preventing diseases in production environments are constantly being explored.…”