Identification of the infective dose of recovered multi-drug resistant nontyphoidal Salmonella spp. and the intestinal histomorphometric changes in broiler chicken

Abstract

The study is aimed to determine the ID₅₀ of the two recovered Salmonella isolates from various broiler farms in Wayanad district, Kerala. The isolates were confirmed as Salmonella Typhimurium through cultural and molecular characterisation. On antibiotic susceptibility testing both the isolates were found to be resistant to more than six classes of antibiotics. Vencobb 430Y chicks (n=24) were equally distributed into four groups (T1, T2, T3 and T4) with six birds in each group. All the birds tested negative for Salmonella on the fifth day. On the seventh day, the birds of treatment T2, T3 and T4 were orally inoculated with 10⁸,10⁹ and 10¹⁰ cfu/mL of MDR-S. Typhimurium. The birds were examined closely for clinical symptoms and changes in faecal matter consistency. The body weight of the birds was taken before infection and also on weekly basis post-infection. The clinical symptoms started showing from the fifth-day post-infection in T4 and the seventh day post-infection in T2 and T3. Fifty percentage of the birds from T4 exhibited progressive weakness with diarrhoea after the first-week post-infection without causing mortality. The body weight difference of birds from different treatment was non-significant during pre-infection and during the first and second week post-infection body weight was in the order T1>T2>T3>T4. The caecal Salmonella load was highest in T4 and it was found to increase with time. When the histomorphometry of the different segements of small intestine were compared, a significantly lower villi-to-crypt ratio was exhibited by T4, indicating impaired intestinal function. The ID₅₀ of recoveredS. Typhimurium was established as 10¹⁰ cfu/mL based on the clinical findings, faecal matter consistency pattern, body weight variations and intestinal histomorphometry parameters.