Interactions of organic acids with Staphylococcus aureus and MRSA strains from swine mandibular lymph node tissue, commercial pork sausage meat and feces

Authors: Beier, Ross; Andrews, Kathleen - Kate; Poole, Toni; Harvey, Roger; Crippen, Tawni - Tc; Anderson, Robin; Nisbet, David

Submitted to: International Journal of Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2020
Publication Date: 11/19/2020
Citation: Beier, R.C., Andrews, K., Poole, T.L., Harvey, R.B., Crippen, T.L., Anderson, R.C., Nisbet, D.J. 2020. Interactions of organic acids with Staphylococcus aureus and MRSA strains from swine mandibular lymph node tissue, commercial pork sausage meat and feces. International Journal of Microbiology and Biotechnology. 5(4):165-183. https://doi.org/10.11648/j.ijmb.20200504.12.
DOI: https://doi.org/10.11648/j.ijmb.20200504.12

Interpretive Summary: Staphylococcus aureus is a Gram-positive bacterium causing infections affecting human health. S. aureus is a major cause of both hospital and community acquired diseases of the skin, of endocarditis, meningitis, and sepsis, and is involved in the toxic shock syndrome. Methicillin-resistant S. aureus (MRSA) is a worldwide health concern and occurs in food animals. Improved strategies are needed to ensure disinfection of MRSA. S. aureus commonly colonizes pigs, and pig herds are known to be reservoirs for MRSA. In this study S. aureus strains were isolated from swine feces, mandibular lymph node tissue, and commercial pork sausage matter. Strains were tested for methicillin-resistance, and how they react to six organic acids. We observed an internal tissue contamination of 8.2% by MRSA bacteria; this data suggests that the prevalence of MRSA in final pork products may not only be from surface contamination, but from S. aureus invasion of swine tissue. The pH was determined at the points where the S. aureus strains were inhibited by organic acids. We were able to calculate the molar undissociated and dissociated organic concentrations at the points of inhibition of the bacteria. The inhibition of S. aureus did not correlate with pH or the undissociated organic concentrations, but it did correlate with the dissociated organic acid concentrations. A concentration range of 14.94 to 21.05 mM for four dissociated organic acids, acetic, butyric, formic, and propionic was successful in disinfecting the 164 strains of S. aureus tested. Therefore, a dissociated OA concentration of 21 mM of any one of these OAs would be expected to disinfect S. aureus.

Technical Abstract: Staphylococcus aureus is a Gram-positive bacterium affecting human health, and a major cause of skin infections. Methicillin-resistant S. aureus (MRSA) is a worldwide health concern and occurs in food animals. mproved strategies are needed to ensure disinfection of MRSA. A total of 164 S. aureus strains were isolated from swine feces, mandibular lymph node tissue, and commercial pork sausage matter. Strains were tested for methicillin-resistance, and susceptibility to six organic acids (OAs) citric, L-lactic, butyric, acetic, propionic, and formic acid was performed. We show 8.2% intracellular S. aureus contamination in swine lymph node tissue; the prevalence of MRSA in final pork products may not be surface contamination. The pH was determined at the minimum inhibitory concentrations (MICs) of the S. aureus strains. The Henderson-Hasselbalch equation was used to calculate the molar undissociated and dissociated OA concentrations. Inhibition of S. aureus did not correlate with pH or the undissociated OA concentrations, but it did correlate with the dissociated OA concentrations. A dissociated OA concentration of 21 mM was successful in disinfecting the S. aureus strains tested. Studies must be conducted in vivo to confirm this concentration value. Acetic, butyric, formic, and propionic were the most effective OAs tested against S. aureus.