<i>Salmonella</i>Contamination Associated with Bacterial Soft Rot of Fresh Fruits and Vegetables in the Marketplace

Abstract

Wash water from 66% of 401 samples of fresh fruits and vegetables collected in the marketplace and affected by bacterial soft rot were positive for suspected strains of Salmonella, i.e., black, hydrogen sulfide-positive colonies on Salmonella-Shigella agar incubated for 24 h at 37°C. By comparison, 30% of 402 healthy samples were positive. Incidence of suspected Salmonella in broth enrichment cultures was 59% in 533 soft rotted samples and 33% in 781 healthy samples. Thirty percent of 166 representative strains of suspected Salmonella, selected at random from 20 different commodities, were confirmed to be Salmonella by physiological and serological tests. Adjusting incidence values accordingly, Salmonella contamination was potentially present in at least 18 to 20% of soft rotted samples and in 9 to 10% of healthy samples. Wash water from 120 paired healthy and soft rotted fruits and vegetables contained an average of 1.0 × 10⁵ and 3.7 × 10⁶ CFU/ml, respectively, of suspected Salmonella-a ratio of 1:37. Average concentrations of suspected Salmonella in enrichment cultures of healthy and soft rotted samples were 7.5 × 10⁷ and 2.7 × 10⁹ CFU/ml, respectively, also in the ratio of 1:37. Fresh potato, carrot, and pepper disks coinoculated with the soft rot bacterium Erwinia carotovora and with Salmonella typhimurium, and incubated for up to 72 h at room temperature, contained approximately 10 times the concentration of S. typhimurium as did disks inoculated with Salmonella alone. Disks coinoculated with Pseudomonas viridiflava and S. typhimurium contained approximately three times the Salmonella populations as disks inoculated with Salmonella alone.