In Vitro Characterization of Probiotic Potential of Limosilactobacillus fermentum against Salmonella Gallinarum Causing Fowl Typhoid

Simple Summary Fowl typhoid is an infectious bacterial disease of poultry that causes significant economic losses in the poultry sector. Antimicrobial therapy, biosecurity practices and vaccination programs are used to prevent and treat fowl typhoid. Misuse of antibiotics generally results in emergence of multidrug resistance in Salmonella Gallinarum. Although vaccination reduces flock losses, disease is still prevailing in many developing countries including Pakistan. To develop an alternative to these approaches, the present study was designed to explore Lactobacillus spp. of poultry origin which can inhibit Salmonella Gallinarum in vitro. Twenty one lactobacilli isolated from poultry have antibacterial activity against Salmonella Gallinarum. These isolates were further selected for the characterization of in vitro probiotic properties. Out of 21, two Limosilactobacillus fermentum strains isolated in this study have the ability to survive physicochemical barriers of the gut such as tolerance to low pH, bile salts, auto-aggregation and co-aggregation activity with Salmonella Gallinarum, and caused significant reduction in growth of Salmonella Gallinarum. These isolates may be used for the development of anti-Salmonella Gallinarum probiotics after in vivo study in broilers. Abstract Fowl typhoid, a septicaemic disease of poultry, is caused by Salmonella Gallinarum and leads to severe economic losses. The aim of the present study was to isolate, select and characterize indigenous probiotic lactobacilli with anti-Salmonella Gallinarum activity. A total 55 lactobacilli were isolated from the caeca and ileum parts of healthy chickens and identified to species level by 16S rDNA sequencing. All the isolates were initially screened for antimicrobial activity and selected isolates were further subjected to in vitro evaluation of probiotic properties. Lactobacilli isolates (n = 21) showed varying levels of activity (08–18 mm) against Salmonella Gallinarum. These selected isolates also showed tolerance to acidic conditions (pH 3 and 4). Out of these 21 isolates, 13 showed growth (>0.5 OD at 600 nm) 0.3% bile salts. Moreover, these isolates also had the ability of auto-aggregation (20.05 ± 0.62%–50.70 ± 1.40%), and co-aggregation with Salmonella Gallinarum (5.22 ± 0.21%–42.07 ± 0.70%). Results revealed that lactobacilli had a higher level of resistance to vancomycin (100%), streptomycin (100%), ciprofloxacin (95%), gentamicin (90%), doxycycline (90%), oxytetracycline (85%), and bacitracin (80%), and a lower level of resistance to penicillin (33%), erythromycin (28%), chloramphenicol (23%), fusidic acid (23%) and amoxicillin (4%). The Limosilactobacillus fermentum PC-10 and PC-76 were sensitive to most of the antibiotics. The overall results revealed that two Limosilactobacillus fermentum strains (PC-10 and PC-76) fulfill the in vitro selection criteria of probiotics, i.e, tolerance to low pH, resistance to bile salts, auto-aggregation, co-aggregation with Salmonella Gallinarum, and absence of acquired antibiotic resistance. The Limosilactobacillus fermentum PC-10 and PC-76 also inhibited the (>5 log10) growth of Salmonella Gallinarum in co-culture assay. It is concluded that Limosilactobacillus fermentum PC-10 and PC-76 may be further investigated and developed as anti-Salmonella Gallinarum probiotics for poultry.