Antimicrobial Efficacy of Phyto-L, Thiosulfonate from Allium spp. Containing Supplement, against Escherichia Coli Strains from Rabbits

SIMPLE SUMMARY: The aim of this study was to evaluate the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Phyto-L (Pro Tech s.r.l.), a commercial product containing organosulfur compounds (OSCs) such as propyl propane thiosulfonate (PTSO) from Allium spp., on 108 enteropathogenic E. coli (EPEC) strains responsible for colibacillosis in rabbits. Bacterial suspensions with a charge of 10(8) CFU/mL were tested with different concentrations (20, 10, 5, 2.5, 1.25, 0.6, 0.3, and 0.15 μL/mL) of Phyto-L. To evaluate MBC values, bacterial suspensions corresponding to the MIC and above the MIC were plated on Tryptic Soy agar (TSA) without Phyto-L. The MICs of the tested strains corresponded to 1.25 μL/mL (37/108-34.3%), 2.5 μL/mL (70/108-64.8%), and 5 μL/mL (1/108-0.9%). The MBCs were 1.25 μL/mL (15/108-13.9%), 2.5 μL/mL (46/108-42.6%), 5 μL/mL (9/108-8.3%), 10 μL/mL (20/108-18.5%), 20 μL/mL (8/108-7.4%), and higher than 20 μL/mL (10/108-9.3%). Based on the results obtained, Phyto-L has antibacterial activity on EPEC strains. Therefore, in field applications, Phyto-L should be useful in limiting the E. coli load in the rabbit gut, preventing the occurrence of colibacillosis. Moreover, considering that 10(4)–10(5) CFU/g of feces is the charge of E. coli normally present in the intestinal contents of rabbits under physiological conditions, it is possible that lower dosages than those found in this study may be effective in preventing the disease in rabbit farms. ABSTRACT: Colibacillosis, caused by enteropathogenic Escherichia coli (EPEC), is one of the most common diseases in rabbit farms, resulting in economic losses due to mortality and decrease in production. Until recently, antimicrobials were used to both treat and prevent disease on livestock farms, leading to the possible risk of antimicrobial resistance (AMR) and the selection of multidrug-resistant (MDR) bacteria. Therefore, interest in alternative control methods, such as the use of natural substances, has increased in the scientific community. The aim of this study was to evaluate the antimicrobial efficacy of Phyto-L (Pro Tech s.r.l.), a product containing organosulfur compounds (OSCs) such as propyl propane thiosulfonate (PTSO) from Allium spp., against 108 strains of E. coli isolated from rabbits with colibacillosis from 19 farms. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Phyto-L were assessed. Bacterial suspensions with a charge of 10(8) CFU/mL, corresponding to those found in the rabbit gut under pathologic conditions, were tested with different concentrations from 20 to 0.15 μL/mL of Phyto-L. For each strain, the MIC and concentrations above the MIC were plated on Tryptic Soy agar (TSA) without Phyto-L to assess the MBCs. MIC and MBC values ranged from 1.25 to 5 μL/mL and 1.25 to 20 μL/mL, respectively, depending on the strain tested. The data showed an interesting antibacterial activity of Phyto-L against EPEC strains. Therefore, this product could be effective in preventing colibacillosis in field application, especially considering that 10(4)–10(5) CFU/g of feces is the amount of E. coli usually found in the gut contents of rabbits under physiological condition.