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.
OBJECTIVE
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.


RESULTS
Minced beef and bovine hide were inoculated with varying concentrations (log(10) 1.58-2.58 CFU g(-1) and log(10) 2.42-4.49 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 69.2-91.2%. From faecal material on the bovine hide the recovery of the pathogen ranged from 1.80 to 64.5% with fresh faeces depending on the inocula while from dried faeces on hide the results ranged from no recovery at all to 25.1%. 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) 2.73 CFU 100 cm(2) from fresh faeces and log(10) 4.49 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.


CONCLUSIONS
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.
O'Brien
S B
SB
The National Food Centre, Teagasc, Ashtown, Dublin, Ireland.
Duffy
G
G
Daly
D
D
Sheridan
J J
JJ
Blair
I S
IS
McDowell
D A
DA
D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial / Q000379:methods; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D005516:Food Microbiology; D018189:Immunomagnetic Separation; D008461:Meat Products / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D015203:Reproducibility of Results; D018570:Risk Assessment; D012867:Skin / Q000382:microbiology*