Luis Lopez


Education: Bachelor of Science in animal sciences and industry (May 2020)

McNair Project: Determination of minimum inhibitory concentration (mic) of sodium bisulfate, phosphoric acid and organic acids against three commonly reported salmonella serotypes ((s. Typhimurium (atcc 14028), s. Heidelberg (atcc 8326) and s. Enteritidis (atcc 4931)) in fat used to coat pet food (2019)

Mentor: Greg Aldrich, Ph.D.

Using animal by-products in pet food adds value for material that would otherwise be considered “unusable” by humans. By-products like rendered fat are coated onto companion animal diets after the process kill-step. However, they may harbor pathogens like Salmonella spp., which could contaminate the final product. The purpose of this project was to determine the minimum inhibitory concentration (MIC) of Sodium Bisulfate against 3 commonly reported Salmonellaserotypes in fat used to coat pet food. These included S. Typhimurium (ATCC 14028), S. Heidelberg (ATCC 8326) and S. Enteritidis (ATCC 4931). The MIC of SBS against individual serotypes and a cocktail of the serotypes were evaluated using a broth microdilution method (Cockerill, 2012). A single colony of each of three Salmonella serotypes ((S. Typhimurium (ATCC 14028), S. Heidelberg (ATCC 8326) and S. Enteritidis (ATCC 4931)) were inoculated in 10 ml of tryptic soy broth (TSB) and incubated at 37ºC for 24 hr. The culture was then centrifuged at 5,000 rpm for 10 min and the bacterial pellet was re-suspended in fresh TSB. A volume of 200 μL of antimicrobial solution consisting of twice the desired final concentration was dispensed in the first well of a 96-microtiter plate (triplicate wells) and 100 μL of sterile water in the remaining wells. A serial two-fold dilution of the antimicrobial was performed. One hundred microliters of bacterial culture containing ~ 6 logs CFU/mL (in TSB) was added to each well to make a final volume of 200 μL. A positive control consisted of Salmonella inoculum only (no antimicrobial) and a negative control consisted of TSB without Salmonella. The microtiter plate was incubated at 37ºC for 24 hr. The MIC for S. Enteritidis, S. Heidelberg, and S. Typhimurium was (0.313%) each and the same (0.313%) for the ‘cocktail’. Based on this MIC study and a previous study from this lab (Dhakal et al), the addition of SBS at low levels could yield a promising result for mitigation a multiple Salmonella spp. when applied to in fat used to coat pet food.