Occurrence and genetic characterization of Listeria spp. in minimally processed vegetables commercialized in Porto Alegre, Brazil

Sylvia Elisa Frizzo Verdin,Dariane Castro Pereira,Gertrudes Corção,Silvia Regina Pavan Da Silva,Aline Modelski Schatkoski

doi:10.22456/1679-9216.15965

Sylvia Elisa Frizzo Verdin, Dariane Castro Pereira + Show 3 more

Open Access

https://doi.org/10.22456/1679-9216.15965

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Abstract

Minimally processed vegetables go through many steps before they are refrigerated, selection, washing, peeling, cutting, disinfection and finally packaging. However, if no care is taken at the origin of the raw materials and in the process ing stages, there is a chance of finding pathogenic bacteria, such as Listeria monocytogenes, which are able to grow at low temperatures. The aim of this research was to verify the occurrence of Listeria sp. in minimally processed vegetables sold in Porto Alegre, Brazil, and the genetic relationship among the isolates. Minimally processed salads were sampled monthly from local supermarkets and analyzed by inoculation on Listeria Enrichment Broth and subsequent seeding on two selective media, Palcam and Modified Oxford Agar. The typical colonies were identified to species level and their intergenic region 16S-23S rDNA were amplified in order to verify the genetic variability. Species of Listeria were found in 23 of the 52 processed salad samples analyzed and L. monocytogenes was found in seven. The presence of L. monocytogenes in the samples is a health concern, as these salads are eaten without further treatment by the consumer. The amplification of the intergenic region 16S-23S rDNA, showed a great genetic diversity among the isolates, with 43 different patterns, proving the usefulness of this technique in epidemiologic studies.

Highlights

The increasing demand for fresh fruit and vegetables, has encouraged the consumption of minimally processed foods [22,23]
When present in minimally processed vegetables, Listeria isolates may be able to survive if no inhibition mechanism is prompted during storage [12], since this bacteria grows at ordinary refrigeration temperatures and in modified atmosphere [5,21]
In the samples analyzed in the present study Listeria species were isolated in 23 of the 52 samples of minimally processed salad products analyzed

Summary

Introduction

The increasing demand for fresh fruit and vegetables, has encouraged the consumption of minimally processed foods [22,23]. When present in minimally processed vegetables, Listeria isolates may be able to survive if no inhibition mechanism is prompted during storage [12], since this bacteria grows at ordinary refrigeration temperatures and in modified atmosphere [5,21]. Since these readyto-eat products are quite popular, the investigation of the occurrence of L. monocytogenes in leafy vegetables, especially of the kind used in salad preparations, is important. The amplification of the 16S – 23S rDNA spacer regions, whether cleaved or not with restriction enzymes, has been used in many studies [1,3,6,26]

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