Use of Enterococcus faecium as a Surrogate for Salmonella enterica during Extrusion of a Balanced Carbohydrate-Protein Meal

Abstract

Multiple outbreaks of salmonellosis have been associated with the consumption of low-moisture products, including extruded products. Therefore, there is a need for a nonpathogenic, surrogate microorganism that can be used to validate extrusion processes for Salmonella. The objective of this research was to determine if Enterococcus faecium NRRL B-2354 is an adequate surrogate organism for Salmonella during extrusion. Extrusions at different temperatures were done in material contaminated with both organisms. Results indicated that the minimum temperature needed to achieve a 5-log reduction of E. faecium was 73.7°C. Above 80.3°C, the enumeration of E. faecium showed counts below the detectable levels (<10 CFU g(- 1)). Salmonella was reduced by 5 log at 60.6°C, and above 68.0°C the levels of this organism in the product were below the detection limit of the method. The data show that E. faecium is inactivated at higher temperatures than Salmonella, indicating that its use as a surrogate would provide an appropriate margin of error in extrusion processes designed to eliminate this pathogen. Attempting to minimize risk, the industry could validate different formulations, in combination with thermal treatments, using E. faecium as a safer alternative for those validation studies.

Salmonella Inactivation During Extrusion of an Oat Flour Model Food

“…Similar results were also observed by Himathongkham and others () and Bianchini and others () for inactivation of the pathogen, Salmonella Enteritidis, and Enterococcus faecium , a common surrogate test organism for Salmonella , during extrusion of feed. However, Bianchini and others () reported that the Salmonella population in a balanced carbohydrate–protein meal typical of an extruded pet food formula at 28% moisture was reduced by 5 log CFU/g at just 60.6 °C, which conflicts with the findings of our study and a study by Walsh and Funke () that demonstrated a 1‐log reduction of Staphylococcus aureus during low‐temperature extrusion (35 to 55 °C) of spaghetti at an initial moisture content of 31.5%. Our results also differ with those obtained by Ukuku and others () who demonstrated that corn meal and whey protein isolate extruded at 55 °C with a w of 0.98 to 0.99 (35.5% to 42.1% moisture content) resulted in greater than 5‐log and 4‐log reductions of Escherichia coli , respectively, and Quéguiner and others () who found that temperatures over 130 °C were necessary to achieve a greater than 4‐log reduction of Streptococcus thermophiles in whey powder having a very low initial moisture content (4% to 5%).…”

Evaluation of a Biological Pathogen Decontamination Protocol for Animal Feed Mills

“…faecium has been used as a surrogate for Salmonella in various thermal lethality studies, including dry heating of peanuts, moist-air heating of almonds, thermal inactivation in liquid products, and extrusion (1,2,10,18,19). E. faecium was used for the present study because it is easy to recover from contaminated surfaces and feed using selective and differential media.…”

Development of a Dry Inoculation Method for Thermal Challenge Studies in Low-Moisture Foods by Using Talc as a Carrier for Salmonella and a Surrogate (Enterococcus faecium)

“…E. faecium NRRL B-2354 has been established as a surrogate for Salmonella for the validation of thermal processes to ensure a 4-to 5-log reduction of Salmonella in almonds (1,5, 27f this organism is also regarded as a suitable surrogate for foodbome pathogens in thermal processing of other nuts, dairy products, juices, and meat, and it has been extensively used in validation studies for different low-moisture food products, including almonds, walnuts, peanut butter, extruded products (i.e. carbohydrate-protein meal), and others (1,3,4,6,29,32,34). Ma et al (29) demonstrated that the heat resistance of E. faecium NRRL B-2354 was consistently and significantly greater (17.7 times) than that of Salmonella in ground beef, raising the concern that the surrogate may overly exceed the heat resistance of the target pathogen; therefore, its use in thermal process validation may result in overprocessing and higher energy costs (29).…”