Isolation of Salmonella from Flies in the Mekong Delta, Vietnam

From July 2004 to April 2005, total of 494 flies, including 128 houseflies (Musca domestica) and 366 blowflies (Genus Calliphora), were captured at 6 pig farms, at a slaughterhouse and at 2 wet markets in the Mekong Delta, Vietnam to know the role of flies as a transmitter of Salmonella. Salmonella were isolated from 38 (7.7%) of the 494 flies samples. The isolation rates of Salmonella from flies captured at a slaughterhouse (15.5%) were significantly higher than that in pig farms (4.5%) and in wet markets (6.5%). The isolation rates of Salmonella from blowflies (9.8%) were higher than those houseflies (1.6%). From those 38 Salmonella-positive fly samples, 41 Salmonella strains were isolated and 14 serovars were identified. The predominant serovars were S. Typhimurium, S. Panama, S. Newport, S. Derby, S. Bareilly, S. Lexington and S. Anatum. Of the 41 Salmonella isolates examined, 38 (92.7%) showed resistance to at least one or following antibiotics ; SM, OTC, KM, NA, ABPC, SMX, CP, and GM. No isolates showed resistance to CEZ, CTRX and CPFX. Among the resistant isolates, 22 isolates were multi-drug resistance. Flies seem to play an important role, as an epidemiological link between humans and domestic animals in the Mekong Delta, Vietnam.