Abstract

Salmonella is a leading cause of foodborne illness globally, and its detection in contaminated samples is often hampered by competing microorganisms. Novobiocin (NV), an antibiotic supplement, is known to selectively inhibit Gram-positive bacteria, potentially enhancing Salmonella recovery in culture-based diagnostics. However, the optimal point of its addition in the isolation protocol remains unclear. This study systematically evaluated the effect of novobiocin addition at different stages of the Salmonella isolation process. Using a modified ISO 6579-1 (2017) protocol, 30 known Salmonella-positive faecal samples were processed through five experimental groups in a completely randomized design. The groups tested NV addition in pre-enrichment (Buffered Peptone Water, BPW), enrichment (Muller-Kauffmann Tetrathionate, MKTT; Rappaport-Vassiliadis, RV), and plating (Xylose Lysine Deoxycholate, XLD) media, both with and without NV. Isolation rates were compared using multinomial logistic regression. The addition of novobiocin significantly improved Salmonella isolation rates (p=0.03). The highest isolation rate (100%) was achieved in the group using BPW followed by enrichment in MKTT supplemented with NV. This was superior to enrichment in RV with NV (90%). The addition of NV directly to the selective agar (XLD) did not yield a significant improvement in isolation rates compared to XLD without NV. Novobiocin significantly enhances Salmonella isolation when incorporated into selective enrichment broths, particularly MKTT. To improve diagnostic sensitivity for both motile and non-motile strains, a modification of the standard protocol is recommended: the parallel use of MKTT+NV and RV+NV during the enrichment step, rather than a single broth.

Key words: Culture, Diagnostic sensitivity, Enrichment, Isolation, Novobiocin, Salmonella