Mesophilic Aeromonads in Wild and Aquacultured Freshwater Fish

Abstract

Numbers and species of motile Aeromonas were determined in freshly caught freshwater fish, in the surrounding environment, and also during iced chilled storage of fish specimens. Although no significant differences were observed in water samples, initial levels for skin, gill, and intestines were significantly lower in farmed rainbow trout (Oncorhynchus mykiss) than in wild brown trout (Salmo trutta) and pike (Esox lucius). During storage of wild specimens, naturally occurring aeromonads grew fairly well on the surfaces of skin and body cavity. Of 171 strains assigned to the genus Aeromonas, 88% were identified to phenospecies and putative genospecies level by using comprehensive biochemical schemes. The isolates were allocated to putative hybridization groups (HGs) 1 and 3 Aeromonas hydrophila (29%); putative HG 8 Aeromonas veronii biovar sobria (19%); putative HG 2 Aeromonas bestiarum (18%); putative HG 9 Aeromonas jandaei (16%); putative HGs 4 and 5a Aeromonas caviae (2%); putative HG 12 Aeromonas schubertii (2%); and putative HG 11 (unnamed, 0.6%). The remaining 20 isolates (12%) resembled A. schubertii but could not be allocated to currently recognized phenospecies or to putative HGs. Although cultured rainbow trout yielded strains of putative HGs 1, 4, and 8, which appear to be of major clinical importance, most isolates assigned to putative HGs 1 and 8 were recovered from pike. Differences among HGs found in wild animals could be related to their origin (unpolluted rivers for brown trout and urban rivers for pike). The recovery of these aeromonads species was not related to sampling site. The initial levels of motile aeromonads, their behavior during storage, and the strong potential spoilage activity of most isolates confirm that these bacteria can contribute to deterioration of iced wild freshwater fish. Although adequate cooking would inactivate motile aeromonads, the high incidence of isolates belonging to gastroenteritis-associated HGs should be regarded as a potential health concern, particularly for susceptible populations when there is a possibility of cross-contamination.

Effect of Chilling on Microbiological, Biochemical and Sensory Attributes of Whole Aquacultured Rainbow Trout (Oncorhynchus mykiss Walbaum, 1792)

“…Epizootic Ulcerative syndrome caused by A. sobria resulted in great damage to fish farms in Bangladesh and India [48]. Gonzalez et al [49] noticed the strong potential spoilage activity of aeromonads in wild and aquacultured iced freshwater fish. A. hydrophila, A. veronii biovar veronii and A. veronii biovar sobria are the strains more often associated with gastroenteritis in humans and the enteropathogenic potential of these strains were comparatively high when grown at low temperatures than at 37oC [50,51].…”

Major foodborne pathogens in fish and fish products: a review

“…It is generally accepted that bacteria found on fish skin are the same as those found in the contaminated water, including such genera and species as Aeromonas spp. (Aeromonas hydrophila, A. bestiarum, A. caviae, A. jandaei, A. schubertii, A. veronii), Flexibacter spp., Proteus spp., Providencia spp., Psychrobacter spp., Moraxella spp., Pseudomona fluorescens, Acinetobacter johnsonii, Alcaligenes piechaudii, Enterobacter aerogenes, Escherichia coli, Micrococcus luteus, and Vibrio fluvialis (Christensen 1977;Allen et al 1983;Youssef et al 1992;Diler et al 2000;Gonzalez et al 2000Gonzalez et al , 2001Zmyslowska et al 2001).…”

The Bacterial Microflora of Fish

“…The bacteria from the surface of freshwater fish have been reported to include Acinetobacter johnsonii [58], aeromonads (notably Aeromonas hydrophila, A. bestiarum, A. caviae, A. jandaei, A. schubertii, and A. veronii biovar sobria [59]), Alcaligenes piechaudii, Enterobacter aerogenes, Escherichia coli, Flavobacterium [25], Flexibacter spp., Micrococcus luteus, Moraxella spp., Pseudomonas fluorescens, psychrobacters [58], and Vibrio fluvialis [23,56,60]. To some extent, the presence of aeromonads reflected whether or not the water in which the fish occurred was polluted or clean [59].…”

“…To some extent, the presence of aeromonads reflected whether or not the water in which the fish occurred was polluted or clean [59].…”