Comparison of Enrichment Conditions for Rapid Detection of Low Numbers of Sublethally Injured Escherichia coli O157in Food

Abstract

A comparative study of lag phases and growth rates of healthy, stressed, and sublethally injured Escherichia coli O157 cells in 10 enrichment broths was performed. The evaluation of enrichment protocols was validated by different end point detection methods (two PCR and two combined capture-plate methods). Tryptic soy broth b [TSB (b)] provided the fastest growth (max = 1.00 1 0.06 h- ) but failed to recover oxidative-stressed E. coli O157. TSB (a), TSB-yeast extract medium, TSB supplemented with 8 mg/liter novobiocin plus 16 mg/liter vancomycin (TSB+), buffered peptone water (BPW), and BPW supplemented with 8 mg/liter vancomycin (BPW+V) enabled resuscitation of E. coli O157 cells independent from precultural conditions. Modified TSB plus 10 mg/liter novobiocin (mTSB+N), EC medium, EC reduced bile salts medium (ECred), TSB (b), and TSB supplemented with 8 mg/liter novobiocin plus 16 mg/liter vancomycin plus 2 mg/liter rifampin plus 1 mg/liter K-Telluriet plus 1.5 g/liter bile salts no. 3 (TSB++) all failed to recover E. coli O157 cells for at least one type of stress. The use of TSB (a), TSB+, BPW, and BPW+V was compared with that of mTSB+N (International Organization for Standardization reference broth) for reliable detection of low numbers of healthy, stressed, and sublethally injured E. coli O157 (approximately 10 CFU/10 g) from foods (sprouted seeds, fermented sausage, raw milk, and raw ground beef). When low numbers of healthy cells were inoculated, BPW, BPW+V, TSB, TSB+, and mTSB+N enabled growth until detectable numbers within 6 h of enrichment at 41.5 degrees C. Results showed that mTSB+N failed to recover to detectable numbers E. coli O157 cells sublethally injured by freeze and food stresses, in contrast to what was obtained with BPW and BPW+V. This study highlights that using mTSB+N for recovery of E. coli O157 from foods may yield false-negative results.

Mungo bean sprout microbiome and changes associated with culture based enrichment protocols used in detection of Gram-negative foodborne pathogens

“…Despite various efforts that have previously been undertaken to improve the current methods for detection of foodborne pathogens from sprouted seeds, there are various difficulties that still remain [19–22]. One drawback in particular is the lack of physiological traits that would allow the selective discrimination of target pathogens such as STEC and Salmonella from large amounts of sprout associated background flora predominated by non-target bacteria including enterobacteria species that outnumber these pathogens by several orders of magnitude.…”

Prevalence of Shiga toxin-producing Escherichia coli in food products of animal origin as determined by molecular methods

“…This allows resuscitation of sublethally injured cells without risking outgrowth by competing flora since E. coli is a fast grower (Jasson et al, 2009). In this study, we employed an overninght enrichment in BHI, which gave the possibility to detect also 1-10 cfu/g of sample.…”

Growth of Stressed Strains of Four Non-O157 Shiga Toxin-Producing Escherichia coli Serogroups in Five Enrichment Broths

“…Still, some authors state that shorter enrichment periods are more effective to detect positive samples, whereas others report to the contrary (13,14,30,33). Previous studies to compare enrichment media mostly monitored bacterial growth by using absorbance or optical density measurements (2,17,20). Although these optical density techniques are rapid and relatively easy to automate, they do have important drawbacks, i.e., the a relatively high detection limit and an underestimation of the lag phase.…”

“…Although the International Organization for Standardization/ Technical Specification specifies an enrichment period of 18 to 24 h, multiple studies have proven the advantageous effect of a shorter enrichment period. This may be owing to overgrowth of competing organisms and the release of PCRinhibiting organic components during overnight incubation (14,17,31).…”