Trypticase soya agar

In this study, 354 S. Typhimurium isolates were collected between 2002 and 2017 and are listed in Table S1 in the supplemental material. Twenty-eight isolates were collected between 2002 and 2008 in Lwiro in the South Kivu province of the DRC. A total of 326 isolates were collected between 2007 and 2017 in the provinces of Kongo-Central (n = 181), Kinshasa (n = 33), Sud-Ubangi (n = 58), Tshopo (n = 49), Sankuru (n = 1), Maniema (n = 1), Bas-Uele (n = 2), and Mai-Ndombe (n = 1).
All isolates were stored in tubes of Trypticase soya agar (Oxoid, Basingstoke, UK) and shipped to the ITM for confirmation and further identification. At the ITM in Belgium, isolates biochemically confirmed as Salmonella spp. were serotyped using commercial antisera (Sifin, Berlin, Germany) according to the Kauffmann-White scheme (49 ), including O:5 reactivity. A representative selection of the isolates (10%) was sent to the National Reference Centre Sciensano in Belgium for confirmation of serotype.

A bacteriological examination was performed following Shukla and Mishra [28 ]. Under strict aseptic conditions, visceral organ samples (liver, heart, lung, and unabsorbed yolk sac) were collected from diseased and freshly deceased broiler chicks, as well as the yolk sac of dead in-shell chicks. All samples were pre-enriched in 9 mL buffer peptone water (PBW) (Oxoid Ltd, Hampshire, England) and incubated aerobically at 37 °C for 24 h. A loopful of inoculated broth was streaked onto the surface of Cetrimide and MacConkey’s agar (Oxoid Ltd, Hampshire, England) and incubated aerobically for 24–48 h at 37 °C. Suspected colonies appeared as large, transparent (non-lactose fermenter) on MacConkey’s agar, and yellowish green pigmentation with a fruity smell on Cetrimide agar were selected and purified on Trypticase Soya Agar (TSA) (Oxoid Ltd, Hampshire, England). Purified colonies were examined morphologically by gram’s staining and characterized biochemically using catalase, oxidase, indole, methyl red, voges-proskauer, citrate utilization, nitrate reduction, and glucose fermentation tests [29 ]. For the further identification, all suspected strains were preserved in 70% glycerol at − 20 °C.