Tracing Listeria monocytogenes contamination in artisanal cheese to the processing environments in cheese producers in southern Chile

Artisanal cheese from southern Chile is made primarily by rural families who raise dairy cows and produce cheese as a way to add value to their milk. The most common cheese produced is chanco, a semi-hard cheese that is typically sold in unauthorized markets. The methods of chanco production do not always follow good manufacturing practices; however, the presence of Listeria monocytogenes contamination in this cheese has not been previously documented. To better understand production practices and L. monocytogenes contamination, 39 cheese producers were surveyed with regard to infrastructure, cleaning and sanitation, pest control, personal hygiene, training, raw materials, and manufacturing. During four sampling trips in 2016 (March, May, August, and November), 546 samples were collected (468 cheese samples and 78 milk samples). For producers that tested positive for L. monocytogenes, environmental monitoring was also conducted, for which 130 additional samples were collected. Presumptive L. monocytogenes isolates (N = 94) were further characterized and subtyped using standard techniques and qPCR-based species/subtype verification; a subset of 52 isolates were also subtyped by Pulsed Field Gel Electrophoresis (PFGE). L. monocytogenes was found in 19 cheeses (4.1%) from five producers (12.8%). The most frequent serotypes were 1/2b (48.9%), group 4B (4b, 4d, 4e) (45.7%), and serotype 1/2a (5.4%). Although no milk samples tested positive for L. monocytogenes, all cheese samples from two producers tested positive during two of the samplings. Distinct PFGE types were recovered from each facility, demonstrating persistence of certain subtypes of the pathogen that ultimately caused end-product contamination. Environmental monitoring of the five positive producers revealed a prevalence of L. monocytogenes ranging from 0 to 30%, with food contact surfaces having the highest incidence of this organism. The findings of this study contribute to the understanding of L. monocytogenes incidence in artisanal cheese in the region of southern Chile.