Occurrence and Virulence Characteristics of Aeromonas Species in Meat, Milk and Fish in India

Aeromonas-induced gastroenteritis is common in India. The incidence of Aeromonas in meat, milk and fish in Kolkata, India and their enterotoxic potentiality have been evaluated here. Aeromonas contamination was detected in all or most of the meat and fish with average load of 1.1 × 102, 3.5 × 103, 1.1 × 103, 2.1 × 103 and 1.6 × 104 cfu/g of red meats, chicken, Indian major carps, tilapia and shrimp, respectively; the levels were at least one order higher on fish skin and meat surface. Aeromonas was also detected in milk and ready-to-eat foods. About 59% of the isolates were β-hemolytic, and 66–92% of them produced phospholipase, caseinase and enterotoxicity. Fish and shrimp isolates produced significantly higher levels of gelatinase (102.73–120.6 U/mL), hemolysin (causing >80% erythrocyte lysis) and enteric fluid accumulation (0.86–0.89 mL/cm ileum length) compared with those from meat and milk indicating their serious pathogenic potentiality. Phenotypically, 43.2, 12.2 and 12.2% of β-hemolytic strains were identified as recognized human pathogenic species, viz. Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii bv. sobria, respectively, which also expressed higher levels of virulence factors than other Aeromonas species detected. The ubiquitous presence of enterotoxigenic Aeromonas in different raw as well as ready-to-eat foods poses serious threat to human health. Practical Applications Ubiquitous presence of enterotoxigenic Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii bv. sobria in raw and ready-to-eat meat, milk and fish poses a serious human health risk in Indian subcontinent. Heavy bacterial load, combined with higher expression of virulence factors by the isolates, makes fish and shellfish as the most potential sources of Aeromonas infection. Different Aeromonas spp. differed in quantitative expression of different virulence factors. Qualitative and quantitative expression studies showed low positive correlations among gelatinase, hemolysin and ileal enterotoxicity, suggesting requirement of studying multiple virulence factors for identifying the virulent strains. A higher distribution of the bacterium on meat or fish surface and in unhygienically processed or stored food items indicates that adoption of standard practices of cleaning and sanitation would substantially improve safety of food products.