All presumptive positive Salmonella isolates were subcultured onto nutrient agar plates (CM0309; Oxoid Ltd., England, UK) and incubated at 37 °C for 16–18 h. Isolates were first confirmed by their reaction in the Minibact-E biochemical tests (SSI, Denmark) and then by slide agglutination using polyvalent antisera (Poly A-E+Vi from SSI, Denmark). Specific serovars were established by serotyping at the WHO National Salmonella and Shigella Center, Institute of Health, Bangkok, Thailand [31 ].
Phage typing was done for S. Typhimurium (28 isolates) and S. Enteritidis (43 isolates) according to the scheme defined by the PHLS Colindale London at the OIE-National reference laboratory for Salmonella, Istituto Zooprofilattico Sperimentale delle Venezie, Italy [32 (link)]. Strains showing a typing pattern that did not conform to any recognized phage type was designated “reacted but did not conform” (RDNC) while those that did not show any phage type pattern at all were designated “non-typable” (NT).
Phage typing was done for S. Typhimurium (28 isolates) and S. Enteritidis (43 isolates) according to the scheme defined by the PHLS Colindale London at the OIE-National reference laboratory for Salmonella, Istituto Zooprofilattico Sperimentale delle Venezie, Italy [32 (link)]. Strains showing a typing pattern that did not conform to any recognized phage type was designated “reacted but did not conform” (RDNC) while those that did not show any phage type pattern at all were designated “non-typable” (NT).