Characterization of Listeria monocytogenes isolated from wildlife in central New York

Genomic Characterization of Listeria monocytogenes and Other Listeria Species Isolated from Sea Turtles

Listeria monocytogenes is a ubiquitous pathogen found both in the environment and food. It can cause listeriosis in a wide range of animals as well as in humans. Investigations on presence, spread and virulence are still limited to terrestrial and human environments. Embracing the One Health Approach, investigating the presence and spread of L. monocytogenes in marine ecosystems and among wildlife, would provide us with useful information for human health. This study investigated the presence of L. monocytogenes and Listeria spp. in two species of sea turtles common in the Mediterranean Sea (Caretta caretta and Chelonia mydas). A total of one hundred and sixty-four carcasses of sea turtles (C. caretta n = 161 and C. mydas n = 3) stranded along the Abruzzo, Molise, Campania, and Calabria coasts, were collected. Brain and fecal samples were taken, enriched, and cultured for the detection of Listeria spp. From the specimens collected, strains of L. monocytogenes (brain n = 1, brain and feces n = 1, multiorgan n = 1 and feces n = 1), L. innocua (feces n = 1 and brain n = 1), and L. ivanovii (brain n = 1) were isolated. Typical colonies were isolated for Whole Genome Sequencing (WGS). Virulence genes, disinfectants/metal resistance, and antimicrobial resistance were also investigated. L. monocytogenes, L. innocua, and L. ivanovii were detected in C. caretta, whilst only L. monocytogenes and L. innocua in C. mydas. Notable among the results is the lack of significant differences in gene distribution between human and sea turtle strains. Furthermore, potentially pathogenic strains of L. monocytogenes were found in sea turtles.

Study of Zoonotic Pathogens in Alien Population of Veiled Chameleons (Chamaeleo calyptratus) in the Canary Islands (Spain)

Veiled chameleons (Chamaeleo calyptratus) are native to the Arabian Peninsula that have been introduced as pets in many regions around the world, such as the Canary Islands (Spain). In this work, the gastrointestinal content from veiled chameleons of Gran Canaria island (Canary Islands) has been analyzed to determine the presence of zoonotic bacteria. Forty animals were analyzed using different selective culture media and PCR. The most isolated bacteria were Yersinia enterocolitica (52.4%), followed by Salmonella spp. (40.0%), with positive isolates for Salmonella Tyhpi and Salmonella Typhimurium. Pseudomonas spp. was found in 32.5% of the chameleons. More than half were positive for Pseudomonas aeruginosa. Antibiotic-resistant Staphylococcus spp. was detected in six animals plus one isolate of non-resistant Staphylococcus hominis. Multiple mycobacteria species belonging to both tuberculous and non-tuberculous complexes were identified as well as Escherichia coli carrying the stx₁ and eae virulence genes with 12.5% and 7.5% prevalence, respectively. Listeria monocytogenes, Campylobacter spp., and Vibrio spp. were found in lower proportion (<5%). The results obtained indicate that veiled chameleons in Gran Canaria could be playing a role in the maintenance and dissemination of the pathogens detected, harming public health and biodiversity.

Genomic and pathogenicity islands of Listeria monocytogenes-overview of selected aspects

Listeria monocytogenes causes listeriosis, a disease characterized by a high mortality rate (up to 30%). Since the pathogen is highly tolerant to changing conditions (high and low temperature, wide pH range, low availability of nutrients), it is widespread in the environment, e.g., water, soil, or food. L. monocytogenes possess a number of genes that determine its high virulence potential, i.e., genes involved in the intracellular cycle (e.g., prfA, hly, plcA, plcB, inlA, inlB), response to stress conditions (e.g., sigB, gadA, caspD, clpB, lmo1138), biofilm formation (e.g., agr, luxS), or resistance to disinfectants (e.g., emrELm, bcrABC, mdrL). Some genes are organized into genomic and pathogenicity islands. The islands LIPI-1 and LIPI-3 contain genes related to the infectious life cycle and survival in the food processing environment, while LGI-1 and LGI-2 potentially ensure survival and durability in the production environment. Researchers constantly have been searching for new genes determining the virulence of L. monocytogenes. Understanding the virulence potential of L. monocytogenes is an important element of public health protection, as highly pathogenic strains may be associated with outbreaks and the severity of listeriosis. This review summarizes the selected aspects of L. monocytogenes genomic and pathogenicity islands, and the importance of whole genome sequencing for epidemiological purposes.

Loggerhead Sea Turtle as Possible Source of Transmission for Zoonotic Listeriosis in the Marine Environment

Listeria monocytogenes is an ubiquitous pathogen isolated from different host species including fish, crustaceans, and molluscs, but it is rarely a pathogenic microorganism to marine reptiles. In particular, only two cases of fatal disseminated listeriosis have been described in the loggerhead sea turtle (Caretta caretta). In this study, we describe a lethal case of L. monocytogenes infection in a loggerhead sea turtle. The turtle was found alive, stranded on a beach in North-eastern Italy, but perished soon after being rescued. The autoptic examination revealed that heart, lung, liver, spleen, and urinary bladder were disseminated with multiple, firm, 0.1-0.5 mm sized, nodular, white-green lesions. Microscopically, these lesions corresponded with heterophilic granulomas with Gram+ bacteria within the necrotic center. Furthermore, the Ziehl-Neelsen stain was negative for acid-fast organisms. Colonies isolated from heart and liver were tested through MALDI-TOF for species identification, revealing the presence of L. monocytogenes. Whole Genome Sequencing on L. monocytogenes isolates was performed and the subsequent in silico genotyping revealed the belonging to Sequence Type 6 (ST 6); the virulence profile was evaluated, showing the presence of pathogenicity islands commonly observed in ST 6. Our results further confirm that L. monocytogenes should be posed in differential diagnosis in case of nodular lesions of loggerhead sea turtles; thus, given the zoonotic potential of the microorganism, animals should be treated with particular caution. In addition, wildlife animals can play an active role as carriers of possibly pathogenetic and virulent strains and contribute to the distribution of L. monocytogenes in the environment.

In Vitro and In Vivo Virulence Study of Listeria monocytogenes Isolated from the Andalusian Outbreak in 2019

In 2019, the biggest listeriosis outbreak by Listeria monocytogenes (Lm) in the South of Spain was reported, resulting in the death of three patients from 207 confirmed cases. One strain, belonging to clonal complex 388 (Lm CC388), has been isolated. We aimed to determine the Lm CC388 virulence in comparison with other highly virulent clones such as Lm CC1 and Lm CC4, in vitro and in vivo. Four L. monocytogenes strains (Lm CC388, Lm CC1, Lm CC4 and ATCC 19115) were used. Attachment to human lung epithelial cells (A549 cells) by these strains was characterized by adherence and invasion assays. Their cytotoxicities to A549 cells were evaluated by determining the cells viability. Their hemolysis activity was determined also. A murine intravenous infection model using these was performed to determine the concentration of bacteria in tissues and blood. Lm CC388 interaction with A549 cells is non-significantly higher than that of ATCC 19115 and Lm CC1, and lower than that of Lm CC4. Lm CC388 cytotoxicity is higher than that of ATCC 19115 and Lm CC1, and lower than that of Lm CC4. Moreover, Lm CC388 hemolysis activity is lower than that of the Lm CC4 strain, and higher than that of Lm CC1. Finally, in the murine intravenous infection model by Lm CC388, higher bacterial loads in tissues and at similar levels of Lm CC4 were observed. Although a lower rate of mortality of patients during the listeriosis outbreak in Spain in 2019 has been reported, the Lm CC388 strain has shown a greater or similar pathogenicity level in vitro and in an animal model, like Lm CC1 and Lm CC4.

Asymptomatic Carriage of Listeria monocytogenes by Animals and Humans and Its Impact on the Food Chain

Humans and animals can become asymptomatic carriers of Listeria monocytogenes and introduce the pathogen into their environment with their feces. In turn, this environmental contamination can become the source of food- and feed-borne illnesses in humans and animals, with the food production chain representing a continuum between the farm environment and human populations that are susceptible to listeriosis. Here, we update a review from 2012 and summarize the current knowledge on the asymptomatic carrier statuses in humans and animals. The data on fecal shedding by species with an impact on the food chain are summarized, and the ways by which asymptomatic carriers contribute to the risk of listeriosis in humans and animals are reviewed.