Aeromonas species in fish, fish-eggs, shrimp and freshwater

Mesophilic aeromonads in wild and aquacultured freshwater fish

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.

Prevalence, species differentiation, haemolytic activity, and antibiotic susceptibility of aeromonads in untreated well water

The use of untreated water for drinking and other activities have been associated with intestinal and extraintestinal infections in humans due to Aeromonas species. In the present study aeromonads were isolated from 48.7% of 1,000 water samples obtained from wells and other miscellaneous sources. Aeromonas species were detected in 45% of samples tested in spring, 34.5% in summer, 48% in autumn and 60% of samples tested in winter. Speciation of 382 strains resulted in 225 (59%) being A. hydrophila, 103 (27%) A. caviae, 42 (11%) A. sobria and 11 (3%) atypical aeromonads. Of 171 Aeromonas strains tested for their haemolytic activity, 53%, 49%, 40% and 37% were positive in this assay using human, horse, sheep and camel erythrocytes respectively. The results obtained indicate that potentially enteropathogenic Aeromonas species are commonly present in untreated drinking water obtained from wells in Libya (this may also apply to other neighbouring countries) which may pose a health problem to users of such water supplies. In addition, ceftriaxone and ciprofloxacin are suitable drugs that can be used in the treatment of Aeromonas-associated infections, particularly in the immunocompromised, resulting from contact with untreated sources of water.

The role of seafood in bacterial foodborne diseases

Pathogenic bacteria, when present in marine seafood and in fresh cultured products, are usually found at fairly low levels, and where these products are adequately cooked, food safety hazards are insignificant. A few bacteria associated with faecal contamination of seafood continue to pose a large-scale health threat through seafood.

The cytotoxic enterotoxin of Aeromonas hydrophila induces proinflammatory cytokine production and activates arachidonic acid metabolism in macrophages

An aerolysin-related cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses multiple biological activities, which include its ability to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. The role of Act in the virulence of the organism has been demonstrated. In this study, we evaluated the potential of Act to induce production of proinflammatory cytokines associated with Act-induced tissue injury and Act's capacity to activate in macrophages arachidonic acid (AA) metabolism that leads to production of eicosanoids (e.g., prostaglandin E(2) [PGE(2)]). Our data indicated that Act stimulated the production of tumor necrosis factor alpha and upregulated the expression of genes encoding interleukin-1beta (IL-1beta) and IL-6 in the murine macrophage cell line RAW264.7. Act also activated transcription of the gene encoding inducible nitric oxide synthase. Act evoked the production of PGE(2) coupled to the cyclooxygenase-2 (COX-2) pathway. AA is a substrate for PGE(2), and Act produced AA from phospholipids by inducing group V secretory phospholipase A(2). We also demonstrated that Act increased cyclic AMP (cAMP) production in macrophages. cAMP, along with PGE(2), could potentiate fluid secretion in animal models because of infiltration and activation of macrophages resulting from Act-induced tissue injury. After Act treatment of RAW cells, we detected an increased translocation of NF-kappaB and cAMP-responsive element binding protein (CREB) to the nucleus using gel shift assays. Act also upregulated production of antiapoptotic protein Bcl-2 in macrophages, suggesting a protective role for Bcl-2 against cell death induced by proinflammatory cytokines. The increased expression of genes encoding the proinflammatory cytokines, COX-2, and Bcl-2 appeared correlated with the activation of NF-kappaB and CREB. This is the first report of the detailed mechanisms of action of Act from A. hydrophila.

Enterotoxins in Aeromonas-associated gastroenteritis

Aeromonas species produce an array of virulence factors, and the pathogenesis of Aeromonas infections is therefore complex and multifactorial. Aeromonas-associated gastroenteritis is especially a problem in young children. The potential involvement of enterotoxins in the pathogenesis of Aeromonas infections is discussed.

Molecular approaches to measuring microbial marine pollution

Developments in the rapid detection of pathogens (PCR and its variations) and molecular typing of strains isolated from the ecosystem illustrate the stimulation of research due to the recent foodborne and waterborne disease outbreaks.