Current Trends in Foodborne Human Listeriosis

Abstract

Human listeriosis results from the ingestion of foods contaminated with Listeria monocytogenes (Lm). About 1600 listeriosis cases are reported every year in the USA with >95% hospitalization and 15-20% death. The proportions of persons with listeriosis hospitalized and who die are very similar in Europe with slightly higher rates in Scandinavian countries. The occurrence of disease requires adaptation, survival, and usually growth of Lm in foods before consumption by members of the susceptible population. Despite concerted efforts by the food safety community, the disease incidence has not changed significantly since 2001 and remains higher than the Healthy People 2020 target of 0.2 cases per 100,000 individuals. In recent years, human listeriosis cases have been reported to involve non-typical foods, e.g. celery, cantaloupe, caramel apple, frozen vegetables and ice cream. In some outbreaks, a few infected individuals were considered outside the realm of the standard vulnerable population group. Our recent work with the outbreak associated with ice cream samples, indicated that a low-level contamination in a food that does not support growth can cause listeriosis in highly susceptible populations. Separately, using a combination of polymerase chain reaction (PCR)-based serotyping and whole genome sequencing (WGS)-based analyses; we have discovered that a genetic variant of the serotype 4b strain, called 4bV, was responsible for 3-4 recent outbreaks in the USA. Three of the four products associated with these outbreaks were grown in a small geographical region of the USA while the fourth was never linked to a specific grower, but rather a processing facility. These 4bV strains contain a 6.3kb DNA fragment normally associated with lineage II Lm strains. The significance of this DNA fragment in the serotype 4b background is currently being investigated. This article reviews current listeriosis outbreaks with an emphasis on the expansions in food niche, case demography and genotypes of Lm. The discussion raises important questions about Lm adaptation in different foods and environments and the role of certain genotypes in such adaptation and disease outcome.

Investigation of a Multistate Outbreak of Listeria monocytogenes Infections Linked to Frozen Vegetables Produced at Individually Quick-Frozen Vegetable Manufacturing Facilities

“…The only product samples available for enumeration during this investigation indicated results below the detectable limits of the analysis (<0.3 MPN/g); there is insufficient information to indicate whether this finding reflects the dose consumed by those who became ill (which may be suggestive of low infective dose causing illness), as only two samples were enumerated, and consumers may have held products under conditions in which bacterial growth could have occurred. Recent research has demonstrated that low‐level contamination in food that may not support growth can still cause listeriosis in highly susceptible populations ( Datta & Burall, 2018 ). A recent review of available literature related to L. monocytogenes prevalence in frozen vegetables noted that few studies reported enumeration of L. monocytogenes in frozen vegetables and, in most of the cases, the numbers were below the limit of enumeration of the plate count procedure applied in each of the studies ( Koutsoumanis et al, 2020 ; Willis et al, 2020 ).…”

Evaluation of Antiphytoviral and Antibacterial Activity of Essential Oil and Hydrosol Extracts from Five Veronica Species

“…In this study, Listeria monocytogenes was the most sensitive bacterium to EO fractions from the five Veronica species (Table 5). This emerging foodborne pathogen, which has been associated with outbreaks worldwide and mortality rates as high as 20% [58], was successfully inhibited at concentrations ranging from 0.32 to 6.13 mg/mL, with V. chamaedrys, V. serpyllifolia, and V. arvensis active at concentrations below 1 mg/mL. On the other hand, S. aureus was the least sensitive among the Gram-positive bacteria with MIC values ranging from 4.89 to 42.89 mg/mL.…”

Developing Recombinant Antibodies by Phage Display Against Infectious Diseases and Toxins for Diagnostics and Therapy

“…This bacterial infection, listeriosis, can cause severe illness, including meningitis and sepsis when reaching the systemic circulation. As of today, 13 different L. monocytogenes serotypes have been discovered, of which type 4b, 1/2a and 1/2b have shown to be the most virulent ( Datta and Burall, 2018 ). Contaminated food also contains non-pathogenic Listeria species, making the diagnosis more difficult.…”