ARS | Publication request: RESUSCITATION OF ACID-INJURED SALMONELLA CELLS IN ENRICHMENT BROTH, APPLE JUICE, AND ON CUT SURFACES OF FRUITS

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: May 3, 2004
Publication Date: July 12, 2004
Citation: Liao, C., Fett, W.F. 2004. Resuscitation of acid-injured salmonella cells in enrichment broth, apple juice, and on cut surfaces of fruits [abstract]. Institutes of Food Technologists. p. 100.

Technical Abstract: We have recently demonstrated that upon exposure to 2.4% acetic acid (AA) for 5 min, 30-40% of surviving Salmonella cells on apple slices can be injured. Detection of low numbers of injured pathogens in foods requires an enrichment step to resuscitate the injured bacteria and to increase the sensitivity of the cultural or molecular methods. The objectives of this study were to identify liquid media most suitable for recovery of AA-injured Salmonella cells and to investigate the resuscitation patterns of injured Salmonella in apple juice and on cut surfaces of fruits. AA-injured Salmonella Mbandaka cells were prepared as stated above. Following incubation at 4, 20, or 35ºC, the changes in the populations of injured cells in inoculated phosphate buffered saline (PBS), buffered peptone water (BPW), pasteurized apple juice, and three enrichment broths including lactose broth (LB), universal pre-enrichment broth (UPB), and tetrathionate broth (TT) were determined. Recovery of injured cells on apple and cucumber slices were also investigated using the filter membrane method recently reported. Resuscitation of injured cells occurred in three non-selective media (UPB, BPW, and LB), but not in PBS, apple juice, and selective TT broth. A significantly higher degree of recovery occurred in UPB than in LB or BPW. Recovery of injured cells also occurred on cut surfaces of cucumber (pH 3.8), but not apple (pH 2.9-3.3), and at 20 or 35ºC but not at 4ºC. Acid-injured Salmonella cells can revive, proliferate, and represent a safety hazard in salad fruits such as cucumber when stored at elevated temperatures. To improve detection, pre-enrichment of the sample in UPB instead of LB or BPW is recommended. Direct enrichment of the sample in TT which may inhibit the resuscitation of injured cells should be avoided.