Survey for psychrotrophic bacterial pathogens in minimally processed lettuce

Abstract

A total of 120 minimally processed, cut and packaged lettuce samples were purchased from retail supermarkets or provided by a salad production facility over an 8‐month period. The samples were tested for total aerobic plate counts and for the presence of potentially pathogenic species belonging to the genera of Listeria, Aeromonas and Yersinia. The aerobic plate counts ranged from 103 to 109 colony forming units (cfu) g−1. Most samples (76%) contained between 105 and 107 cfu g−1 total aerobic bacteria. Listeria monocytogenes was isolated from three samples, Aeromonas hydrophila or Aeromonas caviae from 66 samples, and Yersinia enterocolitica from 71 samples. The pathogenic potential of Y. enterocolitica isolates was determined by screening for an array of biochemical, serological and genetic traits (heat‐stable enterotoxin gene, the attachment and invasion gene locus, the invasin gene locus and the virulence plasmid). The Y. enterocolitica isolates lacked many of the phenotypic and genetic markers associated with virulence in primary pathogenic strains. As the roles of the reputed virulence factors of Aeromonas spp. in human infection are uncertain, the pathogenic potential of the Aeromonas isolates in lettuce remains unclear.

Growth of Listeria monocytogenes on shredded, ready-to-eat iceberg lettuce

“…Vegetables have been reported to be contaminated by L. monocytogenes (De Simó n, Tarragó, & Ferrer, 1992;Francis, Thomas, & O'Beirne, 1999;Szabo, Scurrah, & Burrows, 2000). Unfortunately, it has been demonstrated that industrial process rendering RTE vegetables like sanitized washing, do not guarantee the total elimination of the pathogen when present (Nguyen-The & Carlin, 1994;Szabo et al, 2000).…”

The involvement of tetA and tetE tetracycline resistance genes in plasmid and chromosomal resistance of Aeromonas in Brazilian strains

“…For that reason, some Aeromonas species have been classified as emerging pathogens (Szabo et al 2000, Edberg et al 2007.…”

Biocontrole de Listeria monocytogenes por Pediococcus acidilactici em couve minimamente processada

“…Utilizou-se o ágar MRS com 0,2 e 20% (p/v) do produto, mas pode proporcionar oportunidade para o crescimento de espécies psicrotróficas anaeróbias facultativas (FRANCIS;O'BEIRNE, 2001;THOMAS;O'BEIRNE, 2000). Considerando que a maioria desses alimentos é consumida sem nenhum tratamento térmico, uma das principais preocupações é com relação a bactérias patogênicas capazes de crescerem em temperatura de refrigeração (FARBER, 1991;SCHUENZEL;HARRISON, 2002;SZABO;SCURRAHAND;BURROWS, 2000). Dentre os patógenos que podem ser encontrados em produtos vegetais frescos destacam-se Aeromonas hydrophila, Clostridium botulinum, Listeria monocytogenes, Yersinia enterocolitica, Salmonella spp., Escherichia coli O157:H7 e Campylobacter jejuni (DHOKANE et al, 2006;SCHUENZEL;HARRISON, 2002;SZABO;SCURRAHAND;BURROWS;.…”