Potential virulence determinants of Salmonella serovars from poultry and human sources in Spain

A total of 173 Salmonella strains of different serovars isolated during 1992 from poultry and human sources in Zaragoza (NE Spain) were investigated for potential virulence factors. Parameters studied included production of aerobactin, enterobactin, colicin (including colicin V) and hemolysin, serum resistance against serum from man, sheep, cattle and chicken, binding of Congo red and crystal violet, auto-agglutination and calcium dependency at 37 degrees C and double colony morphology. Preliminary studies showed tests with completely negative results (colicins and hemolysin production, double colony morphology, auto-agglutination and calcium dependency at 37 degrees C) and tests with completely positive results (enterobactin production and binding of Congo red). The tests with variability of results were production of aerobactin, serum resistance and crystal violet binding. Aerobactin production was detected in 80% of Salmonella strains of clinical human origin and in 30% of Salmonella strains isolated from healthy slaughtered chickens. Sixty-five per cent of patient isolates were human serum resistant, 73% were ovine serum resistant, 85% were bovine serum resistant and 98% were chicken serum resistant. The percentages of poultry isolates serum resistant were 61, 86, 60 and 89% in human, ovine, bovine and chicken serum, respectively. Crystal violet binding was detected in 22.5% of Salmonella isolates from human origin and in 32.3% of Salmonella strains from poultry origin. This study can form a marker for the prevalence of strains with various characteristics (production of aerobactin, serum resistance and crystal violet binding) for comparison in future epidemiological studies. Furthermore, the data of this work suggested that strains causing enteric salmonellosis in man are partially identical to strains isolated from carrier broilers.