#07-200

Complete

Date Full Report Received

07/29/2009

Date Abstract Report Received

07/29/2009

Investigation

Institution:
Primary Investigator:

Multidrug-resistant (MDR) Salmonella has been implicated in several infections and outbreaks worldwide; they have been linked to the consumption of contaminated products involving pork as well. Despite the interventions of HACCP in abattoirs, Salmonella is still isolated from carcasses, and retailers (NARMS, 2005). The objective of this study was to compare the relative efficacy of organic acids and sanitizers against multiple drug-resistant (MDR) serovars of Salmonella and non-resistant Salmonella in order to gain more information on the potential effectiveness of intervening chemical treatments in pork slaughter and processing. The study also determined if exposure of normal and MDR Salmonella to organic acids affects sensitivity to sanitizers. Observed changes in Salmonella isolates which either had or did not have the qacE∆1 gene were compared.

This research was conducted in four steps. First, MDR-Salmonella were exposed to two different organic acids (lactic and acetic acid) with samples withdrawn at different times to determine survival due to acid exposure. Bacteria were first pre-adapted to acid conditions, since it has been found that acid adapted bacteria are more resistant to further treatments. The second stage of the project was performed by exposing the MDR-Salmonella to three different quaternary ammonium compounds (QACs), two pure compounds (benzalkonium chloride, cetylpyridinium chloride) and one commercial compound (S.S.4) to determine survival due to exposure to these sanitizers. Samples were taken at different exposure times and neutralized in DE neutralizing buffer before enumerating by plating. The third phase of the project involved the possibility of organic acids conferring cross-protection against further treatment with quaternary ammonium compounds. This objective was developed using the same strains and QACs from the previous objectives. Strains were pre-adjusted to acid conditions in the same way that it was done in the first objective of the project and subsequently treated with QACs. Samples were withdrawn after 10 minutes of treatment and neutralized in DE buffer and plated in order to determine the survival rates. The last part of the research involved the susceptibility of MDR and non-MDR Salmonella in biofilms to treatment with quaternary ammonium compounds. Briefly, planktonic and biofilm cells were prepared according to the procedure of Ren and Frank (1993) with slight modifications and subsequently treated with QACs. Survival rates were determined.

Acid adapted and non-adapted Salmonella were both sensitive to the organic acid treatments; however, the acid adapted Salmonella were more resistant than the non-adapted when challenged with lactic and acetic acid 2%. It is known, acid adaptation can induce cross-protection to subsequent treatments such as organic acids, heat, osmotic pressure and oxidizers (Davidson and Taylor, 2007; Greenacre et al., 2006; Foster 1991). However, acid adaptation did not appear to induce cross-protection to further quaternary ammonium compounds treatment.

Quaternary ammonium compounds were more effective after 600 sec at 200 ppm. There was no significant difference in response to QACs between MDR and non-MDR Salmonella. MDR and non-MDR Salmonella in biofilms were more resistant to QACs treatment than planktonic cells, but the response to QAC treatments did not vary for MDR or non-MDR cells when in biofilms.

According to our findings we concluded that treatments that are available in food processing plants are equally effective against MDR and non-MDR Salmonella.

Contact information: Dr. Mark Harrison, phone number: 706-542-1088, e-mail address: mahfst@uga.edu. Department of Food Science and Technology, University of Georgia, Athens, USA 30605.