ANTI-SALMONELLA ACTIVITY AND PROBIOTIC POTENTIAL OF LACTIC ACID BACTERIA ISOLATED FROM HEALTHY CATTLE FAECES

Abstract

Salmonella is an important cause of foodborne zoonosis with significant public and animal health burden.Current interventions targeted at mitigatingSalmonella carriage in livestock include antibiotic use, which selects for antibiotic resistance. The use of Lactic Acid Bacteria (LAB) as probiotics is a possible alternative intervention against the carriage of zoonotic enterobacteria.This study was undertaken to characterise the anti-Salmonella and probiotic potential of LAB in cattle against enterobacteria.

Salmonella entericaand LAB were cultured from 138 and 40 faecal samples of cattle, respectively, from University of Ibadan Teaching and Research farm. The Salmonella strains were identified with MALDI-TOF-MS and biochemical profiling system, while LAB were identified by partial sequencing of 16S rRNA gene. The antimicrobial activities of LAB Cell-Free Supernatant (CFS) and viable cells against S. entericaserovarTyphimuriumATCC 14028 andselected Salmonella from cattle were evaluated by cup diffusion and agar overlay methods,respectively. The Salmonella kill rate was determined by co-culture with selected LAB and LAB bacteriocin production was tested by ammonium sulphate precipitation. Organic acid production was quantified by HPLC, whilethe MICs of selected antibiotics toS.entericaand LAB were determined by automated antimicrobial susceptibility testing and gradient MIC strips, respectively. The ability of selected LAB strains to withstand simulated gastric conditions (consecutive pH 3 and 7% bile) and haemolysison bovine blood agar was determined. The potential of selected LAB (approximately 8.6 x 1010 cfu/day for 30 days) to inhibit enterobacteria in vivoin calves (weight= 50 ± 10 kg, n= 6) was evaluated using qPCR with three untreated calves as controls. The effect of freeze drying and 3 months room temperature storage of selected LAB was determined by bacterial viable count.Data were analysed bydescriptive statistics andStudent’s t- test at α0.05. Thirty twoS. entericaisolates were identified with a prevalence of 23.2%.A total of 88 LAB belonging to four genera and 15 species were identified; Lactobacillus (11) was the predominant genus, while Streptococcus infantarius (26) was the most abundant species. The inhibition of CFS against the tested pathogens was ≤ 20.0 mm, while viable cells inhibition was ≤ 22.0 mm. Complete inhibition of S.entericawas observed after 16 hours of co-incubation with LAB and no LAB produced bacteriocin. The organic acid with the highest concentrationwas lactic acid (67.9 ± 1.5 mg/mL) produced by Lactobacillus salivariusC86. All the Salmonella and LAB evaluated were susceptible to all the antibiotics tested.Lactobacillus amylovorus C94 and L.salivarius C86demonstrated the highest resistance to gastric conditions with a final 2 log10 reduction and were not haemolytic. The antibacterial activity of L.amylovorus C94 and L.salivarius C86 against enterobacteriainvivo were significant compared with the control (p=0.01). Lactobacillus amylovorus C94 and L. salivarius C86 both survived freeze drying with a reduction of 1 log10 viability per month. Lactobacillus amylovorus C94 and Lactobacillus salivarius C86 demonstrated antimicrobial activity against Salmonella entericastrains and reduced enterobacteria carriage in calves. They are therefore promising probiotic candidates