Evidence of Virulent Multi-Drug Resistant and Biofilm-Forming Listeria Species Isolated from Various Sources in South Africa

Antimicrobial resistance and prevalence of Listeria species from raw milk and dairy products in Burdur, Turkey

OBJECTIVES

Worldwide, but especially in emerging nations, concerns about food safety pose a serious obstacle to societal and economic progress. This research aimed to examine the prevalence of Listeria spp. in raw milk and dairy products in Burdur, as well as the presence of genes associated with biofilm formation and antibiotic resistance in the isolates.

METHODS

A total of 185 samples, including raw milk, curd, cream, butter, yogurt and cheese, were randomly collected in Burdur. The enrichment and isolation methods specified by the United States Department of Agriculture was used to identify Listeria species in milk and dairy product samples. Culture-positive strains were identified as Listeria genus and as species by PCR. Antibiotic susceptibility of the isolates was evaluated against 14 antibiotics using the disc diffusion technique (EUCAST).

RESULTS

Of them, 2.2% (4/185) were positive for Listeria spp. Listeria species were isolated from cheese and yogurt samples. Two of them were Listeria innocua 1.1% (2/185), one was Listeria ivanovii 0.5% (1/185) and the other was Listeria welshimeri 0.5% (1/185). As a result of multiplex PCR of the biofilm genotypic marker luxS and flaA genes, the flaA gene was detected in three of four isolates, the luxS gene was detected in one isolate, and these two genes were not found in one isolate. Although all isolates were resistant to gentamicin and rifampicin, they also showed multidrug resistance.

CONCLUSION

This study revealed that the diversity of prevalence of Listeria spp. in Burdur requires microbial risk assessment in the milk and dairy products value chain and the need to focus on the problem of multiple antibiotic resistance.

Taxonomy, ecology, and relevance to food safety of the genus Listeria with a particular consideration of new Listeria species described between 2010 and 2022

Since 2010, the genus Listeria has had the addition of 22 new species that more than tripled the number of species identified until 2010. Sixteen of these 22 new species are distantly related to the type species, Listeria monocytogenes, and several of these present phenotypes that distinguish them from classical Listeria species (L. monocytogenes, Listeria innocua, Listeria ivanovii, Listeria seeligeri, Listeria welshimeri, and Listeria grayi). These 22 newly described species also show that Listeria is more genetically diverse than previously estimated. While future studies and surveys are needed to clarify the distribution of these species, at least some of these species may not be widely spread, while other species may be frequently found spread to human-related settings (e.g., farms and processing facilities), and others may be adapted to specific environmental habitats. Here, we review the taxonomic, phylogenetic, and ecological characteristics of these new Listeria species identified since 2010 and re-iterate the suggestion of re-classification of some species into three new genera: Murraya, Mesolisteria, and Paenilisteria. We also provide a review of current detection issues and the relevance to food safety related to the identification of these new species. For example, several new non-pathogenic species could be misidentified as the pathogen L. monocytogenes, based on methods that do not target L. monocytogenes-specific virulence genes/factors, leading to unnecessary product recalls. Moreover, eight species in the proposed new genus Mesolisteria are not good indicators of environmental conditions that could allow L. monocytogenes to grow since Mesolisteria species are unable to grow at low temperatures.

Bowiea volubilis: From "Climbing Onion" to Therapeutic Treasure-Exploring Human Health Applications

Bowiea volubilis subsp. volubilis is primarily used to address human respiratory infections, coughs, and colds due to its diverse pharmaceutical properties. Notably, the plant contains alkaloids that exhibit notable antifungal, antibacterial, and cytotoxic properties. Additionally, the presence of saponins, with recognized antioxidant and anticancer attributes, further contributes to its medicinal potential. Steroid compounds inherent to the plant have been associated with anti-inflammatory and anticancer activities. Moreover, the bulb of B. volubilis has been associated as a source of various cardiac glycosides. Despite these therapeutic prospects, B. volubilis remains inedible due to the presence of naturally occurring toxic substances that pose risks to both animals and humans. The review focuses on a comprehensive exploration concerning B. volubilis ethnobotanical applications, phytochemical properties, and diverse biological activities in relation to in vitro and in vivo applications for promoting human health and disease prevention. The aim of the study is to comprehensively investigate the phytochemical composition, bioactive compounds, and potential medicinal properties of Bowiea volubilis, with the ultimate goal of uncovering its therapeutic applications for human health. This review also highlights an evident gap in research, i.e., insufficient evidence-based research on toxicity data. This void in knowledge presents a promising avenue for future investigations, opening doors to expanded inquiries into the properties and potential applications of B. volubilis in the context of human diseases.

Comparison of prevalence, characterization, antimicrobial resistance and pathogenicity of foodborne Listeria monocytogenes in recent 5 years in Japan

This study investigated the prevalence, serotype, antimicrobial resistance (AMR), virulence potential, and biofilm formation of Listeria monocytogenes isolated in 2022 in Japan and compared their profiles with those of isolates in 2012 and 2017. A total of 85 chicken samples were randomly collected from different supermarkets in Fukuoka in 2022. L. monocytogenes were isolated by conventional method and characterized by MALDI-TOF MS. Among 85 samples tested in 2022, 9 (10.6%) were positive for L. monocytogenes and 17 strains were isolated from the positive samples. The isolates were serotyped as 1/2b (41.2%), 3a (29.4%), 3b (23.5%) and 1/2a (5.9%). Antimicrobial susceptibility tests of the 2022 isolates showed susceptibility to majority of the antibiotics, except cefoxitin, oxacillin, and fosfomycin. Compared to the previous surveillance results, the prevalence of L. monocytogenes in 2022 (10.6%) was significantly lower (p < 0.05) than those of the isolates in 2017 (24%) and 2012 (52.9%). The distribution of serotypes 1/2a and 1/2b decreased over time, and serotype 4b was not detected in the 2022 isolates. The proportion of multidrug resistant strains in 2022 (16.7%) was significantly lower than those in 2012 (46.7%) and 2017 (82.6%). Moreover, a total of 36 isolates (12 isolates/ year) were used to detect the virulence genes (hlyA, plcA, clpC, and inlA) and biofilm-forming capacity. Most of the isolates from different years harboured four virulence genes. The biofilm formation of the 2022 isolates was significantly weaker (p < 0.05) than those of the 2012 and 2017 isolates. Thus, despite the low rates of contamination in chicken meat and AMR of the isolates, virulent L. monocytogenes contamination in food should still be acknowledged.

Foodborne Pathogen Biofilms: Development, Detection, Control, and Antimicrobial Resistance

Bacteria can grow either as planktonic cells or as communities within biofilms [...].

Multidrug-Resistant Biofilms (MDR): Main Mechanisms of Tolerance and Resistance in the Food Supply Chain

Biofilms are mono- or multispecies microbial communities enclosed in an extracellular matrix (EPS). They have high potential for dissemination and are difficult to remove. In addition, biofilms formed by multidrug-resistant strains (MDRs) are even more aggravated if we consider antimicrobial resistance (AMR) as an important public health issue. Quorum sensing (QS) and horizontal gene transfer (HGT) are mechanisms that significantly contribute to the recalcitrance (resistance and tolerance) of biofilms, making them more robust and resistant to conventional sanitation methods. These mechanisms coordinate different strategies involved in AMR, such as activation of a quiescent state of the cells, moderate increase in the expression of the efflux pump, decrease in the membrane potential, antimicrobial inactivation, and modification of the antimicrobial target and the architecture of the EPS matrix itself. There are few studies investigating the impact of the use of inhibitors on the mechanisms of recalcitrance and its impact on the microbiome. Therefore, more studies to elucidate the effect and applications of these methods in the food production chain and the possible combination with antimicrobials to establish new strategies to control MDR biofilms are needed.