A review of microbial injury and recovery methods in food.

The existence of injured microorganisms in food and their recovery during culturing procedures is critical. Microbial injury is characterized by the capability of a microorganism to return to normalcy during a resuscitation process in which the damaged essential components are repaired. Injury of microorganisms can be induced by sublethal heat, freezing, freeze-drying, drying, irradiation, high hydrostatic pressure, aerosolization, dyes, sodium azide, salts, heavy metals, antibiotics, essential oils, sanitizing compounds, and other chemicals or natural antimicrobial compounds. Injured microorganisms present a potential threat in food safety since they may repair themselves under suitable conditions. Detection of injured microorganisms can be important to practical interpretations of data in food microbiology. This review provides an overview of microbial injury in food and discusses the development of recovery methods for detecting injured foodborne microorganisms.

Evaluation of a 5'-nuclease (TaqMan) assay with the thin agar layer oxyrase method for the detection of Yersinia enterocolitica in ground pork samples.

A 5'-nuclease (TaqMan) assay was evaluated for its capability to recover and detect stressed Yersinia enterocolitica. Sensitivity studies of a 5'-nuclease assay for detecting Y. enterocolitica 0:8 in a pure culture system and spiked ground pork samples demonstrated that the assay has reliable sensitivity with a detection limit of 3 to 4 log CFU/ml or CFU/g. The PCR 5'-nuclease (TaqMan) assay was evaluated with the Thin Agar Layer Oxyrase method (TALO, overlaying 14 ml of Trypticase soy agar with a 1:30 dilution of "Oxyrase for Agar" onto a prepoured pathogen-specific, selective medium), and it was compared against the selective medium cefsulodin-irgasan-novobiocin (CIN) for recovering and detecting Y. enterocolitica from inoculated nonfrozen and frozen (-15 degrees C, 2 days) ground pork samples. The TALO method showed more sensitivity (detection limit, 2 log CFU/ml), and it has greater recovery capability (0.5 to 1 log CFU/ml) than CIN (P < 0.05). The 5'-nuclease assay provided rapid detection processing (5 versus 24 h after an 18-h enrichment). The sensitivity per PCR was calculated to as low as 0 to 1 log CFU per PCR reaction; however, in the method's current developmental stage, target pathogens should be enriched to 3 to 4 log CFU/ml or CFU/g to show consistent results. In a survey of 100 ground pork samples using TALO, CIN, and PCR methods, no Y. enterocolitica was recovered. A combined cultivation and an automated PCR TaqMan could be used as a presumptive screening test for detecting Y. enterocolitica in food samples.