Detection of Enterobacter sakazakii in South African food products

[摘要] It is estimated by the World Health Organisation (WHO) that thousands of millions ofcases of foodborne diseases occur world–wide every year. Enterobacter sakazakii isa member of the family Enterobacteriaceae and has been identified as an occasionalcontaminant of powdered infant formula milk (IFM). Enterobacter sakazakii is anopportunistic emerging pathogen and has the ability to cause a severe form ofneonatal meningitis. This organism was referred to as 'yellow pigmentedEnterobacter cloacae until 1980 after which it was renamed as E. sakazakii.The current method for the detection of E. sakazakii is very time consumingand includes pre–enrichment, enrichment in Enterobacteriaceae enrichment broth,subsequent plating on violet red bile glucose agar and subculturing on tryptone soyagar. In this study a polymerase chain reaction (PCR) method was developed for theidentification of the presence of E. sakazakii in infant food products. A part of the 16Sribosomal RNA (rRNA) gene from E. sakazakii was amplified using the primer pairEsak2 and Esak3.An internal amplification control (IAC) was constructed as part of the PCRdetection method. The 850 base pair (bp) E. sakazakii PCR product was digestedwith AluI and the two fragments containing the primer binding sites were ligated,resulting in a 240 bp IAC. During this study a positive band for both the target DNA(850 bp) and the IAC (240 bp) was simultaneously observed when the IAC wasadded to the PCR mixture at a concentration of 0.72 pg.ml-1.Four of 22 South African food products tested positive for the presence ofE. sakazakii, using both the PCR and recommended culturing methods. The PCRmethod was used successfully for the detection of E. sakazakii within three days andthus provides a possible alternative and improvement on the recommended currentculturing methods. Other microorganisms present in the products tested includedEscherichia coli, Klebsiella pneumoniae, Raoultella terrigena ('Klebsiella terrigena)and Chryseomonas luteola.Since E. sakazakii is usually present in low numbers in food products, it ispossible that these few cells are unevenly distributed in the products, making it important to take multiple samples when evaluating IFM and thereby ensuring thateven low numbers of this pathogen are detected.

[发布机构] Stellenbosch University