Microbiological analysis of skin lesions of cod (Gadus morhua) from the southern part of the Baltic Sea

Abstract

Introduction: Since the middle of the 1980s, severe skin disorders have been observed in Baltic cod (Gadus morhua) eachyear. Available data on the spectrum of bacteria isolated from the clinical cases being limited, and evaluation of the microbialbackground of fish skin lesions being useful, a bacteriological examination has been undertaken. Material and Methods: A totalof 1,381 cod were caught during two voyages of the Baltica research vessel in the Polish exclusive economic zone of the southernBaltic Sea. After an examination which found lesions in 164 of the fish, a microbiological analysis was performed to isolate bacteriafrom them. The collected strains were phenotyped and genotyped, and their antimicrobial resistance was analysed by minimuminhibitory concentration (MIC) techniques. Results: Bacteriological examinations provided 850 isolates. The dominantmicroorganisms were mesophilic Aeromonas spp., Pseudomonas spp. and Shewanella baltica. Opportunistic bacteria potentiallyhazardous to human health were also isolated, e.g. Alcaligenes faecalis, Staphylococcus epidermidis, Stenotrophomonasmaltophilia and Vibrio sp. The MIC analysis determined the highest number of bacteria to resist sulphamethoxazole and amoxicillinand clavulanic acid. Conclusion: Most of the collected bacteria were opportunistic pathogens for fish, widespread in the aquaticenvironment, and potentially threatening to humans.