A rapid and reliable alternative to ISO 21528-1:2004 for detection of Enterobacteriaceae.
Current legislation in Europe uses the Enterobacteriaceae as a parameter in process hygiene criteria for various food products and refers to the corresponding ISO standard (ISO 21528-1:2004) as mandatory analytical method for this purpose. The ISO procedure includes an enrichment step in EE ("Enterobacteriaceae Enrichment") broth, but it has been reported recently that some isolates of Enterobacteriaceae do not grow well or will even die off in this broth, which could lead to false negative results. To determine if this trait is common among the Enterobacteriaceae, a collection of 95 strains was screened for growth in EE broth. Inhibition was observed with 9 strains (7 Cronobacter sakazakii, 1 Cronobacter malonaticus and 1 Enterobacter amnigenus). Factors affecting cell death were found to be related mainly to the inclusion of bile salts and dyes in this medium. In a second step, an alternative method omitting the EE broth was evaluated using 326 samples, comprising 8 different food matrices and environmental samples from the corresponding manufacturing sites. Positive results were obtained for 235 samples using the ISO standard method and 232 samples using the alternative shortened method. No significant difference was found between the results for the two methods. It is proposed that the standard method for detection of Enterobacteriaceae is revised accordingly.
Quality and Safety Department, Nestlé Research Centre, Vers-chez-les-Blanc, CH-1000 Lausanne, Switzerland. han.joosten@rdls.nestle.com
Han
H
Joosten
John
J
Marugg
Roger
R
Stephan
Adrianne
A
Klijn
Tim
T
Jackson
Carol
C
Iversen
D001431:Bacteriological Techniques; D015169:Colony Count, Microbial / Q000379:methods*; D003257:Consumer Product Safety; D003470:Culture Media / Q000737:chemistry; D004755:Enterobacteriaceae / Q000254:growth & development / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D006801:Humans; D006920:Hygiene; D012680:Sensitivity and Specificity; D013997:Time Factors
D003470:Culture Media