A Study on experimental infection of Salmonella enterica serotype Kentucky in Backyard Chicken

Abstract

Salmonella is a widely-reported zoonotic bacterial pathogen and poultry is one its major reservoir and source to infect humans. There are >2500 serovars of Salmonella and all motile serovars are zoonotic. S. Kentucky is of one of the motile serovars which has recently been identified from poultry and humans in Bangladesh and the human isolates from non-typhoidal clinical cases were genetically closely related to those from poultry. However, its pathogenic potentials and shedding probability and duration from infected/colonized chickens have never been reported. To assess its pathogenic potentials and shedding probability 22 backyard chickens were infected orally, each with 106cfu, which were then observed for 23 days to see clinical signs, gross and histo-pathological changes, survivability, shedding of the organism in faeces and evidence of colonization in different internal organs, by organism isolation and identification. Novobiocin added Modified Semisolid Rappaport Vasiliadis (MSRV) and Brilliant Green Agar (BGA) were used for the organism isolation and identification following standard procedures. Polymerase chain reaction (PCR) using universal primers for Salmonella was also applied on some representative samples to identify the presence of Salmonella. Four chickens, 2 on day 2 post infection (DPI 2) and the other 2 on DPI 15 were sacrificed and the internal organs were examined bacteriologically and histo-pathologically using standard procedures. The results showed that the zoonotic S. Kentucky strain of human non-typhoidal clinical case origin could cause reduced feed intake, watery or pasty fecal droppings, catarrhal enteritis and typhlitis in backyard chickens. No noticeable histopathological changes were seen in any internal organs after DPI 2, but spleen had reactive changes in prolonged course of infection. The probability of S. Kentucky shedding was 77% (95% CI 54-90%) on DPI 2, 41% (95% CI 21-60%) on DPI 12 and 13% (95% CI 3-31%) on DPI 21. The survival probability of the infected chickens was 50% (95% CI 28-68%) on DPI 6, 32% (95% CI 14-51%) on DPI 15 and 14% (95% CI 3-31%) on DPI 23.