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This study was conducted to determine the prevalence and characteristics of pathogenic Escherichia (E.) coli strains from diarrheic calves in Vietnam. A total of 345 E. coli isolates obtained from 322 diarrheic calves were subjected to PCR and multiplex PCR for detection of the f5, f41, f17, eae, sta, lt, stx1, and stx2 genes. Of the 345 isolates, 108 (31.3%) carried at least one fimbrial gene. Of these 108 isolates, 50 carried genes for Shiga toxin and one possessed genes for both enterotoxin and Shiga toxin. The eae gene was found in 34 isolates (9.8%), 23 of which also carried stx genes. The Shiga toxin genes were detected in 177 isolates (51.3%) and the number of strains that carried stx1, stx2 and stx1/stx2 were 46, 73 and 58, respectively. Among 177 Shiga toxin-producing E. coli isolates, 89 carried the ehxA gene and 87 possessed the saa gene. Further characterization of the stx subtypes showed that among 104 stx1-positive isolates, 58 were the stx1c variant and 46 were the stx1 variant. Of the 131 stx2-positive strains, 48 were stx2, 48 were stx2c, 11 were stx2d, 17 were stx2g, and seven were stx2c/stx2g subtypes. The serogroups most prevalent among the 345 isolates were O15, O20, O103 and O157.

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A total of 480 cage-cultured fish were collected from 4 coastal provinces in central Vietnam to investigate the causative agent of nocardiosis. Fish displayed unique characteristics such as paleness and lethargy and exhibited haemorrhages and ulcers on the skin. Prominent white nodules varying in size were observed in the spleen, kidney, and liver. Furthermore, histopathological sections showed typical granulomatous lesions in these organs. Using the Ziehl-Neelsen staining method, isolated bacteria exhibited acid-fast, bead-like filament morphology when cultured in brain-heart infusion medium or Ogawa medium. Phylogenetic analysis of 16S rDNA confirmed that the isolated bacterium was Nocardia seriolae. This study demonstrates for the first time an outbreak of N. seriolae in snubnose pompano in central Vietnam.