In this study the prevalence of Salmonella spp. was 23% (Table 1). All of the isolates (51) were investigated for serotyping which explored S. Weltevreden (47 isolates) from 10 samples (from extensive and intensive farms) and S. Agona from one sample of intensive farm. The occurrence of S. Weltevreden in different farms (intensive and extensive) located in different three provinces in the Mekong Delta, Vietnam was surprising. The fingerprinting (PFGE analysis) revealed high similarity suggesting clonal relationship and illustrating high dissemination of S. Weltevreden in extensive and intensive shrimp farms located in epidemiological unrelated areas. Three isolates of S. Agona were recovered from one intensive farm (Table 2). Previous studies revealed that occurrences of S. Weltevreden in seafood and associated with human disease in particular in the Southeast Asian countries e.g. Thailand. However, it was striking that the most common serotypes reported in human and animals i.e. S. Typhimurium and S. Enteritidis were not identified from shrimp in this study.
The prevalence of Salmonella spp. in shrimp was found to be little higher than other studies (Elizabeth et al. 2008). However, the predominance of S. Weltevreden in shrimp observed in this study was in agreement with other studies (Elizabeth et al. 2008). S. Weltevreden has been frequently isolated from seafood and its involvement in human diseases has been reported in the Southeast Asian countries. This has been identified as predominant serovar in Thailand (Bangtrakulonoth et al. 2004), in Malaysia (Yasin et al. 1995) and Vietnam (Phan et al., 2005). S. Weltevreden has been identified as causal agent of acute enteritidis (Ashok et al., 2005) and its pathogenic properties i...
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...gs which suggest that the serovars in this study did not originated from fecal contamination of human and livestock where drugs used for therapy and as growth promoter in farm animal production which did not really reflected in the resistance profiles of the isolates tested.
Since the Salmonella spp. are not the part of normal flora of seafood rather part of normal gut flora of human and worm blooded animals, its occurrence in seafood indicating fecal pollution in the pond environment. But the source of Salmonella spp. based on the occurrence pattern of S. Weltevreden in intensive and extensive shrimp farm in widely distributed areas and its resistance profile was unclear in this study. Therefore, it is needed to conduct further study to characterize this S. Weltevreden strains, including its ecology and survival in shrimp environments as well as source or origin.