Detection and recovery rates achieved using direct plate and enrichment/immunomagnetic separation methods for Escherichia coli O157:H7 in minced beef and on bovine hide

Abstract

Aims: To assess the detection and recovery rates achieved with commonly used cultural methods for the enumeration and recovery of Escherichia coli O157:H7 from minced beef and bovine hide. Methods and Results: Minced beef and bovine hide were inoculated with varying concentrations (log 10 1AE58-2AE58 CFU g)1 and log 10 2AE42-4AE49 CFU 100 cm 2 respectively) of E. coli O157:H7 and recovered using a direct plate method or an enrichment/immunomagnetic separation (IMS) method and then plated onto SMAC or SMAC-CT in both cases. The direct plate method detected the pathogen consistently from minced beef samples with an average recovery of 69AE2-91AE2%. From faecal material on the bovine hide the recovery of the pathogen ranged from 1AE80 to 64AE5% with fresh faeces depending on the inocula while from dried faeces on hide the results ranged from no recovery at all to 25AE1%. Enrichment/IMS recovered E. coli O157:H7 at all inocula levels tested in minced beef while the pathogen was only detected consistently at an average inocula level of log 10 2AE73 CFU 100 cm 2 from fresh faeces and log 10 4AE49 CFU 100 cm 2 from dried faeces on bovine hide. Conclusions: The direct count enumeration method for E. coli O157:H7 underestimated the numbers of pathogens present. The enrichment/IMS procedure consistently detected the pathogen from minced beef but did not always detect E. coli O157:H7 from faeces on bovine hide. Significance and Impact of the Study: Overall this study highlights that any microbial data, used in either predictive microbiology or risk assessment, must take account of the sensitivity and associated performance of the methods employed, in order to make an accurate reflection of the true microbiology of the examined sample.

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Comparison of IMS Platforms for Detecting and Recovering Escherichia coli O157 and Shigella flexneri in Foods

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Improving microbial safety in the beef production chain

“…Factors which may influence prevalence include the sampling site choice (Reid et al, 2002;Kalchayanand et al, 2009), feeding systems and season (Rhoades et al, 2009). The concentration of E. coli O157 on the hides is typically around 100 CFU/cm 2 (Arthur et al, 2004;O'Brien et al, 2005).…”