Sensitivity of multidrug-resistant Salmonella typhimurium DT104 to organicacids and thermal inactivation in liquid egg products

A mixture of four Salmonella typhimurium DT104 strains and a mixture of fou r S. typhimurium non-DT104 strains were examined for their ability to grow in tryptic soy broth (TSB) acidified with acetic, lactic, citric, or malic acids at pH 5.4, 4.4 and 3.7 Significantly (P < 0.05) higher numbers of S, typhimurium DT104 cells were detected at pH 4.4 and 4.0 in TSB acidified wi th acetic acid and at pH 4.4 and 3.7 in TSB acidified with lactic acid comp ared to non-DT104 cells. Acid-shocked and non-shocked (control) cells were plated on TSA (pH 7.3) acidified with lactic acid at pH 5.4, 4.4, and 4.0 a nd on TSA (pH 7.0 +/- 0.2) containing 0.5, 2.5, and 5% sodium chloride. Pop ulations of acid-shocked S. typhimurium DT104 and non DTI04 cells recovered on acidified or salt-supplemented TSA were significantly ( P < 0.05) lower than those of non-shocked cells. A significantly lower number of acid-shoc ked non-DT cells recovered on TSA at pH 5.4, compared to acid-shocked DT104 cells, suggests that DT104 cells may be more resistant to acid shock and s ubsequent exposure to acid pH D values and z values of acid-shocked or non- shocked cells of DT104 and non-DT104 strains in liquid whole egg (WE) egg y olk (EY) egg white (EW) whole egg + 10% salt (WES) and egg yolk + 10% salt (EYS) were determined. Differences in thermal sensitivity of the two types of cells were few. Rates of thermal inactivation of S, typhimurium DT104 ce lls indicate that the USDA pasteurization process would eliminate >8 log(10 ) cfu ml(-1) of EW heated at 57 degrees C and > 11 log(10) cfu ml(-1) of WE , EY, WES, or EYS heated at 61 degrees C. D values of acid-shocked DT104 an d non-DT104 cells heated in liquid egg products were significantly (P < 0.0 5) lower than those of respective non-shocked cells. (C) 2000 Academic Pres s.