Abstract
Listeria monocytogenes is an important pathogen that has been implicated in foodborne illnesses and the recall of products such as fruit and vegetables. This study determines the prevalence of virulence-associated genes and serogroups and evaluates the effects of different growth media and environmental conditions on biofilm formation by L. monocytogenes. Eighteen L. monocytogenes isolates from Hass avocados sold at markets in Guadalajara, Mexico, were characterized by virulence-associated genes and serogroup detection with PCR. All isolates harbored 88.8% actA, 88.8% plcA, 83.3% mpl, 77.7% inlB, 77.7% hly, 66.6% prfA, 55.5% plcB, and 33.3% inlA. The results showed that 38.8% of isolates harbored virulence genes belonging to Listeria pathogenicity island 1 (LIPI-1). PCR revealed that the most prevalent serogroup was serogroup III (1/2b, 3b, and 7 (n = 18, 66.65%)), followed by serogroup IV (4b, 4d–4e (n = 5, 27.7%)) and serogroup I (1/2a–3a (n = 1, 5.5%)). The assessment of the ability to develop biofilms using a crystal violet staining method revealed that L. monocytogenes responded to supplement medium TSBA, 1/10 diluted TSBA, and TSB in comparison with 1/10 diluted TSB (p < 0.05) on polystyrene at 240 h (p < 0.05). In particular, the biofilm formation by L. monocytogenes (7.78 ± 0.03–8.82 ± 0.03 log10 CFU/cm2) was significantly different in terms of TSBA on polypropylene type B (PP) (p < 0.05). In addition, visualization by epifluorescence microscopy, scanning electron microscopy (SEM), and treatment (DNase I and proteinase K) revealed the metabolically active cells and extracellular polymeric substances of biofilms on PP. L. monocytogenes has the ability to develop biofilms that harbor virulence-associated genes, which represent a serious threat to human health and food safety.
Highlights
Listeria monocytogenes is a bacterium ubiquitous in the environment and is the causative agent of listeriosis, leading to septicemia, encephalitis, endocarditis, meningitis, abortions, and stillbirths [1,2]
38.8% of L. monocytogenes isolates were positive for the prfA, plcA, hly, mpl, actA, and plcB genes associated with Listeria pathogenicity island 1 (LIPI-1) (Table 2)
This could be relevant for food safety and public health, as it shows the diversity of serogroups of L. monocytogenes in Hass avocados
Summary
Listeria monocytogenes is a bacterium ubiquitous in the environment and is the causative agent of listeriosis, leading to septicemia, encephalitis, endocarditis, meningitis, abortions, and stillbirths [1,2]. The severity of the pathology is associated with several at-risk groups, such as those with a weak immune system, adults >65 years, pregnant women, and newborn babies [3,4]. Salmonella, and Shiga toxin-producing Escherichia coli (STEC) are the most common causes of hospitalizations (82%) and deaths (825) reported in outbreaks with a single confirmed etiology [5]. The FDA (2020–2021) issues recalls of vegetable products and fruits when they are associated with a potential risk of L. monocytogenes [7]. A recent sampling (May 2014 to November 2015) by the FDA demonstrated the prevalence of
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