ARS | Publication request: The Prevalence of Listeria monocytogenes in Queso Fresco in Sinaloa, Mexico

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 10, 2008
Publication Date: August 4, 2008
Citation: Chaidez, C., Martinez, C., Soto, M., Duarte, N., Call, J.E., Porto Fett, A.C., O Connor, C., Luchansky, J.B. 2008. The Prevalence of Listeria monocytogenes in Queso Fresco in Sinaloa, Mexico. Meeting Abstract. P2-16. Page 82.

Technical Abstract: Introduction: The association of Listeria monocytogenes (Lm) outbreaks with Latin-style soft cheese has been well documented. The presence of Lm in fresh cheese, such as “Queso fresco” (QF), is a major public health concern in North, Central, and South America due to the popularity of this style of cheese. Since prevalence of Lm in QF and subsequent illnesses have been poorly documented, more information is needed to identify the niches of Lm in the food supply. Purpose: The focus of this study was to identify the prevalence and types of Lm in QF in the northwestern Mexican state of Sinaloa. Methods: We obtained a sample of QF from 75 independent merchants within Culiacan, the capital of Sinaloa, between the months of January and August of 2007. Lm was enriched in TSB and subsequently plated on Palcam Agar and Listeria Chromoagar. Isolates were verified as Lm using API, PFGE, and ribotyping. Results: Sixteen isolates of Lm were retained in 7 of the 75 QF samples (9% sample prevalence; 1 to 5 isolates per positive sample). The results from PFGE molecular subtyping indicates there were three different pulsotypes found within these isolates; the majority (14 of 16 isolates) displayed pulsotype I, whereas pulsotypes II and III contained one isolate each. Significance: The predominance of pulsotype I strains of Lm in QF samples obtained from Culiacan suggests two possibilities: 1.) there is a common/point source of contamination for pulsotype I strains, and/or 2.) pulsotype I strains of Lm thrive in the raw milk and/or processing plant environment in this region of Mexico. Also, the relatively high prevalence of Lm in QF argues for additional research to definitively identify the source(s) of contamination, quantify levels and types of strains, and develop cost effective interventions.