Detection and Prevalence of Listeria in U.S. Produce Packinghouses and Fresh-Cut Facilities

Abstract

Listeria monocytogenes (LM) contamination of produce can often be traced back to the environment of packinghouses and fresh-cut facilities. As there is limited information on the detection, prevalence, and distribution of this pathogen in produce operations, environmental “routine sampling” plans for LM and other Listeria spp. were developed and implemented in three packinghouses and five fresh-cut facilities in the US. For “routine sampling”, a total of 2,014 sponge samples were collected over 6 - 8 separate samplings per operation, performed over one year; vector and pre-production samples (n=156) were also collected as needed to follow up on positive findings. In addition, a single “validation sampling” visit by an outside expert was used to evaluate the routine sampling. Among the 2,014 routine sponge samples collected, 35 and 30 were positive for LM and Listeria species other than LM (“LS”), respectively. LM prevalence varied from 0.8% to 5.8% for packinghouses and <0.4% to 1.6% for fresh-cut facilities. Among the 394 validation sponge samples, 23 and 13 were positive for LM and LS, respectively. Validation sampling found statistically significantly higher LM prevalence compared to routine sampling for 3/8 operations. For all samples collected, up to eight isolates per sample were characterized by sequencing of sigB, which allowed for classification into sigB allelic types. Among the 97 samples with more than one Listeria isolate characterized, 28 had more than one sigB allelic type present, including 18 sponges that were positive for LM and another Listeria spp and 13 sponges that were positive for more than one LM subtype. This indicates that collection of multiple isolates is necessary to capture Listeria diversity present in produce operations. Additionally, 17/77 sponges that were positive for LM were positive at only one enrichment time (i.e., 24 or 48h), indicating that LM testing after two different enrichment times provides enhanced sensitivity.

Adaptation to a Commercial Quaternary Ammonium Compound Sanitizer Leads to Cross-Resistance to Select Antibiotics in Listeria monocytogenes Isolated From Fresh Produce Environments

“…Listeria monocytogenes is well adapted to agricultural environments, where it proliferates in decaying plant matter in the soil ( Linke et al, 2014 ; Liao et al, 2021 ). It is also frequently recovered from diverse food processing environments ( Gray et al, 2006 ; Freitag et al, 2009 ; Cherifi et al, 2018 ; Kim et al, 2018 ; Hurley et al, 2019 ; Sullivan and Wiedmann, 2020 ). Listeria monocytogenes prevalence in these environments presents a particular concern to processors of minimally processed ready-to-eat (RTE) products, such as fresh produce, that are prone to contamination during handling and processing ( Gallagher et al, 2003 ; Farber et al, 2020 ).…”

A Systematic Review of Listeria Species and Listeria monocytogenes Prevalence, Persistence, and Diversity throughout the Fresh Produce Supply Chain

“…A study in three packinghouses and five fresh-cut facilities on both the East and West coasts of the U.S. environmentally sampled zones 2 and 3 for Listeria. Zone 2 consisted of areas that are in close proximity to food or FCS, while zone 3 included areas in the processing and packing area that are not adjacent to FCS [ 56 ]. Listeria spp.…”

“…Listeria spp. and Lm were found in zones 2 and 3 in packinghouses and only in zone 3 for fresh-cut facilities [ 56 ].…”

Prevalence of Listeria Species on Food Contact Surfaces in Washington State Apple Packinghouses

“…Moreover, repeated isolation of Listeria spp. has been shown on fans over brush beds in produce packinghouses ( 20 ) and on freezer fans in meat facilities ( 43 ). These devices represent potential niches for L. monocytogenes ( 44 ) and are recommended to be scheduled into daily cleaning and sanitation programs ( 7 ).…”