Cronobacter Support
05-18-2009, 03:18 PM
1st International Conference on Cronobacter Poster Abstract 40
Impact of sample pooling on Enterobacter sakazakii growth and detection
Enterobacter sakazakii has been identified as the causative agent of serious neonatal infections, associated with high mortality rate. In most cases, the source of infection has been powdered infant formula (PIF). The standardised method for detection of E. sakazakii from PIF (ISO/TDS 22964; IDG/DRM 210) involves preenrichment in buffered peptone water (BPW), followed by selective enrichment and plating on chromogenic agar ESIA. In order to reduce analysis cost and heaviness, common practice in industries consist in pooling samples at constant dilution rate, in order to realise single first enrichment. Consequences on E. sakazakii growth and detection are not established. In order to evaluate pooling impact on enrichment, growth curves for 3 E. sakazakii strains were determined at various initial contamination levels and powder quantity, in first age PIF decimally diluted in BPW and incubated for 24 hours at 37°C. Growth of the pathogen was monitored by direct plating on ESIA agar or using a recently developed sensitive enumeration method, based on membrane filtration followed by transfer of the filter on the selective agar. Results showed that pooling had a negative impact on E. sakazakii maximal population attained, whereas no clear effect was observed on growth beginning. Variance analysis revealed a significant impact of powder quantity but no effect of initial contamination level on maximal population attained. A mean comparison student t-test revealed a significant impact of powder quantity for a same pathogen concentration, and no impact of bacterial concentration for a same powder quantity. The impact of pooling on the behaviour of E. sakazakii undergoing enrichment culturing in BPW, mainly for maximal population attained, suggests strong bacterial interactions with the PIF background microflora. This may affect detection method performances. Impact of background flora on pooling results should be confirmed with further studies, in order to better explain this phenomenon.
Nathalie Gnanou-Besse, Rabeb Beennour Miled, Nicolas Baudouin, Pierre Colin
Agence française de sécurité sanitaire des aliments Laboratoire d’Etudes et de Recherches sur la Qualité des Aliments et sur les Procédés agro-alimentaires (AFSSA) LERQAP, 23 avenue du Général de Gaulle , 94706 Maisons Alfort cedex, France.
Impact of sample pooling on Enterobacter sakazakii growth and detection
Enterobacter sakazakii has been identified as the causative agent of serious neonatal infections, associated with high mortality rate. In most cases, the source of infection has been powdered infant formula (PIF). The standardised method for detection of E. sakazakii from PIF (ISO/TDS 22964; IDG/DRM 210) involves preenrichment in buffered peptone water (BPW), followed by selective enrichment and plating on chromogenic agar ESIA. In order to reduce analysis cost and heaviness, common practice in industries consist in pooling samples at constant dilution rate, in order to realise single first enrichment. Consequences on E. sakazakii growth and detection are not established. In order to evaluate pooling impact on enrichment, growth curves for 3 E. sakazakii strains were determined at various initial contamination levels and powder quantity, in first age PIF decimally diluted in BPW and incubated for 24 hours at 37°C. Growth of the pathogen was monitored by direct plating on ESIA agar or using a recently developed sensitive enumeration method, based on membrane filtration followed by transfer of the filter on the selective agar. Results showed that pooling had a negative impact on E. sakazakii maximal population attained, whereas no clear effect was observed on growth beginning. Variance analysis revealed a significant impact of powder quantity but no effect of initial contamination level on maximal population attained. A mean comparison student t-test revealed a significant impact of powder quantity for a same pathogen concentration, and no impact of bacterial concentration for a same powder quantity. The impact of pooling on the behaviour of E. sakazakii undergoing enrichment culturing in BPW, mainly for maximal population attained, suggests strong bacterial interactions with the PIF background microflora. This may affect detection method performances. Impact of background flora on pooling results should be confirmed with further studies, in order to better explain this phenomenon.
Nathalie Gnanou-Besse, Rabeb Beennour Miled, Nicolas Baudouin, Pierre Colin
Agence française de sécurité sanitaire des aliments Laboratoire d’Etudes et de Recherches sur la Qualité des Aliments et sur les Procédés agro-alimentaires (AFSSA) LERQAP, 23 avenue du Général de Gaulle , 94706 Maisons Alfort cedex, France.