Impact of pooling powdered infant formula samples on bacterial evolution and Cronobacter detection.
Enterobacter sakazakii has been identified as the causative agent of serious neonatal infections, associated with high mortality rates. In most cases, powdered infant formula (PIF) has been identified as the source of infection. Recently, strains commonly referred to as E. sakazakii were proposed for classification in a new genus, Cronobacter. The standardised method for detection of Cronobacter in PIF (ISO/TS 22964; IDF/RM 210) involves pre-enrichment in buffered peptone water (BPW), followed by selective enrichment and plating onto ESIA chromogenic agar. For greater convenience and to reduce analysis cost, the common practice in the food industry is to pool samples at a constant dilution rate, in order to perform a single pre-enrichment and subsequent analysis. The consequences on the sensitivity of Cronobacter detection are not evident. We evaluated the impact of pooling on the growth of Cronobacter and PIF background microflora in samples undergoing pre-enrichment culturing in BPW. Growth of the pathogen was monitored by direct plating onto selective agar or by using a recently developed sensitive enumeration method, based on membrane filtration followed by transfer of the filter onto the selective agar. The evolution of the total bacterial population of the PIF was monitored from a qualitative and quantitative point, using molecular or classical microbiological methods. Results showed that pooling had a negative impact on the maximum population of Cronobacter attained, whereas no clear effect was observed on the onset of growth. This observation suggests strong bacterial interactions with the PIF background microflora, confirmed by a generally higher background microflora growth potential in PIF samples from various origins. These important findings suggest that, in some cases, the practice of pooling samples may affect the performance of the detection method.
Agence française de sécurité sanitaire des aliments, Afssa Laboratoire d'Etudes et de Recherches sur la Qualité des Aliments et des Procédés agro-alimentaires, Afssa LERQAP, 23 Avenue du Général de Gaulle, 94706 Maisons Alfort cedex, France.
Rabeb Bennour
RB
Miled
Sandra
S
Neves
Nicolas
N
Baudouin
Bertrand
B
Lombard
Véronique
V
Deperrois
Pierre
P
Colin
Nathalie Gnanou
NG
Besse
D001419:Bacteria / Q000254:growth & development; D015373:Bacterial Typing Techniques / Q000379:methods*; D015169:Colony Count, Microbial; D044083:Cronobacter sakazakii / Q000254:growth & development*; D004755:Enterobacteriaceae / Q000254:growth & development*; D005516:Food Microbiology; D006801:Humans; D007223:Infant; D041943:Infant Formula / Q000592:standards; D056265:Microbial Interactions