Pathogenicity of food and clinical Listeria monocytogenes isolates in a mouse bioassay

Cadmium ingestion exacerbates Salmonella infection, with a loss of goblet cells through activation of Notch signaling pathways by ROS in the intestine

Whether cadmium ingestion affects the susceptibility to infection and the detailed mechanism have not been investigated. We aimed to evaluate the effects of cadmium on the intestinal mucosal barrier and Salmonella infection. We found that oral administration of cadmium caused damage to the intestinal mucosal barrier, with body weight loss, an increase in inflammation, significantly reduced Muc2 expression and goblet cell loss in the intestine. The effect of cadmium on secretory cell differentiation was further demonstrated to be regulated by the overactivation of the Notch signaling pathway by increased production of ROS both in mice and in intestinal organoids. The damage of cadmium to the intestinal barrier, and goblet cell and Paneth cells loss, dramatically increased susceptibility to enteropathogensinfection at a low dose (102 CFU), with a high death ratio, body weight loss and severe intestinal inflammation. However, enteropathogens susceptibility and intestinal barrier damage enhanced by cadmium was alleviated by inhibiting ROS production and Notch pathway activation, with reversion of goblet cell loss. This study indicated cadmium didn't only affect the integrity of intestinal barrier and epithelial differentiation, but also increased the risk of enteropathogenic infection from food contamination or environmental pollution, which signals an alarm for public health.

Retrospective Study of Listeria Monocytogenes Isolated in the Territory of Inner Eurasia from 1947 to 1999

Listeriosis is one of the most significant humans and animals foodborne infectious diseases. Here, we characterized 48 Listeria monocytogenes strains isolated in the territory of inner Eurasia during the second half of the 20th century. A total of 23 strains (52.3%) were susceptible to the nine antibiotics tested, 30.43%, 15.22%, and 8.7% were resistant penicillin G, ampicillin, and enrofloxacin, respectively. We applied the multilocus sequence typing (MLST) scheme to determine the phylogenetic positions of the strains. All but one strain belonged to the II phylogenetic lineage, and the majority of the strains belonged to one of the previously described clonal complexes (СCs). More than 60% of the strains belonged to the clonal complex CC7 that prevailed among all sources, including cattle (58%), small ruminants (64%), rodents (71%), and humans (50%). Further, CC7, CC101, and CC124 were found among human isolates. The MLST scheme was supplemented with virulence gene analysis. In total, eight inlA, six inlB, and six inlC allelic variants were found, and all but one strain carried one of the two inlE alleles. Most strains (62.5%) belonged to the same multivirulence locus sequence typing (MvLST) type, which includes CC7, inlA allele 4, inlB allele 14, inlC allele 6, and inlE allele 8.

The pathogenic potential of different pulsed-field gel electrophoresis types of Listeria monocytogenes strains isolated from food in Northeast Bosnia and Herzegovina

Listeria monocytogenes is often present in meat and meat products that are sold in the area of northeast Bosnia and Herzegovina. The major objective of this study was to examine the virulence of L. monocytogenes strains isolated from these types of food in that geographic area. Polymerase chain reaction was used to detect eight genes responsible for virulence of this pathogen, namely, prfA, inlA, inlB, hly, plcA, plcB, actA, and mpl. All examined isolates were confirmed to possess the eight virulence genes. Ten different pulsed-field gel electrophoresis (PFGE) macrorestriction profiles were recognized among 19 L. monocytogenes strains after restriction with two different endonucleases (ApaI and AscI). The pathogenicity of three different PFGE types of L. monocytogenes was confirmed through in vivo tests, which were performed on female white mice (Pasteur strain), and it ranged from 3.55 × 10(8) LD50 to 1.58 × 10(10) LD50. All of the three different PFGE types of L. monocytogenes were regarded as moderately virulent in relation to the reference strain L. monocytogenes Scott A. This result might be one of the reasons for the absence of reported listeriosis in northeast Bosnia and Herzegovina, despite the high degree of food contamination with this pathogen.

Low genetic diversity and epidemiological significance of Listeria monocytogenes isolated from wild animals in the far east of Russia

The causative agent of listeriosis, a serious disease of humans and animals, Listeria monocytogenes is a ubiquitous bacterium that inhabits both anthropogenic and pristine environments. We report L. monocytogenes isolation from wild animals, humans, food and the environment of a far eastern region of Russia. In total, 654 samples of internal organs of small rodents belonging to the Muridae and Cricetidae families, and 986 samples of the liver and muscles of mollusks and fish were examined to obtain 7 and 14 independent L. monocytogenes isolates, respectively. The wild animal isolates were compared with human (n=9), food (n=8) and environmental (n=3) isolates obtained in the same region. Twenty of the 21 wild animal isolates belonged to the serovar 4b. The serovars 4b, 1/2a, 1/2b, and 4b, 1/2a, 1/2b, 1/2c were found between human and food isolates, respectively. All isolates were characterized into molecular subtypes by DNA sequencing of the 618 bp internal fragment of the house keeping gene prs and 621 bp internal fragment of the virulence gene inlB. Sequence analysis revealed 4 and 13 alleles for prs and inlB fragments, respectively. Distinct prs and inlB alleles clustered into two groups consistently with established phylogenetic lineages. Among isolates of every lineage, the nucleotide diversity of the prs fragment was low; the nucleotide diversity of the inlB fragment was low among wild animal isolates and higher among human isolates. All rodent isolates and 10 of 14 marine organism isolates carried the same allele of the inlB fragment, which was also found among environmental (two of three), food (two of eight) and human (two of nine) isolates.

Virulence of Listeria monocytogenes isolates from humans and smoked salmon, peeled shrimp, and their processing environments

The virulence of 82 Listeria monocytogenes isolates from human cases and cold-smoked salmon, cooked peeled shrimp, and their production environments was assessed using the plaque-forming assay and a subcutaneous inoculation test in mice. These isolates were previously typed using serotyping and pulsed-field gel electrophoresis. The isolates from food-production environments were collected in several surveys over the period of 5 years. Sixty-eight (99.8%) of 69 isolates tested from food and food-processing environments were considered virulent while only one was avirulent. All clinical isolates (13) were highly virulent. The isolates were from raw materials, final products, and the production environment. This stresses the importance of hygiene in the processing environment as well as among personnel to avoid contamination of the final product.

Comparison of Listeria monocytogenes virulence in a mouse model

Listeriosis results from exposure to the foodborne pathogen Listeria monocytogenes. Although many different strains of L. monocytogenes are isolated from food, no definitive tests currently predict which isolates are most virulent. The objectives of this study were to address two major data gaps for risk assessors, variability among L. monocytogenes strains in pathogenicity and virulence. Strains used in our monkey clinical trial or additional food isolates were evaluated for their virulence and infectivity in mice. All strains were equally pathogenic to immunocompromised mice, causing deaths to 50% of the population 3 days after exposure to doses ranging from 2 to 3 log CFU. Doses resulting in 50% deaths on the fifth day after administration were 1 to 2 log lower than those on the third day, indicating that the full course of pathogenicity exceeds the 3-day endpoint in immunocompromised mice. Three strains were chosen for further testing for their virulence and infectivity in liver and spleen in normal (immunocompetent) mice. Virulence was not significantly different (P > 0.05) among the three strains, all resulting in deaths to 50% of mice at 5 to 7 log CFU by 5 days after administration. All strains were equally infective in liver or spleen, with higher numbers of L. monocytogenes directly correlated with higher doses of administration. In addition, there was no preference of organs by any strains. The lack of strain differences may reflect the limitation of the mouse model and suggests the importance of using various models to evaluate the pathogenicity and virulence of L. monocytogenes strains.

Cellular lipid fatty acid pattern heterogeneity between reference and recent food isolates of Listeria monocytogenes as a response to cold stress

Cells of four reference strains (Scott A, LO 28, CNL 895807 and ATCC 19115) and of five recent food isolates (A00M011, A00M018, A00M087, A00M092 and A00M123) of Listeria monocytogenes were grown until late exponential phase in Brain Heart Broth at two different temperatures (37 degrees C and 4 degrees C). Our results show that significant differences exist between the cellular lipid fatty acid profile of reference and recent food isolates. Like the reference strains, and in keeping with previous reports on the cellular lipid fatty acid profile of L. monocytogenes, the recent food isolates were characterised by the presence of ai15:0, i15:0 and ai17:0. In addition, the fatty acid ai13:0 was observed in all of the recent food isolates grown at 4 degrees C, whereas only two reference strains, Scott A and LO 28, showed ai13:0 in their cellular lipid fatty acid profile at 4 degrees C. When grown at 4 degrees C, the recent food isolates showed a mean aiC15/aiC17 ratio of 66, while reference strains were characterised by significantly lower ratios, ranging between 4.3 (ATCC 19115) and 28.9 (Scott A). These results showed that all of the recent food isolates, Scott A and LO28 strains use chain length and anteiso-branching (ai15:0) as their major response to cold temperature adaptation. However, the cold adaptation response of reference strains CNL 895807 and ATCC 19115 appears to be different.

Molecular and experimental virulence of Listeria monocytogenes strains isolated from cases with invasive listeriosis and febrile gastroenteritis

We analyzed 27 Listeria monocytogenes strains of serotypes 1/2b and 4b, from invasive and gastroenteric listeriosis, for molecular and experimental virulence. Molecular virulence was tested by PCR for the presence of 8 major virulence-associated genes and genetic polymorphisms through restriction enzyme analysis; genomic DNA typing using pulsed-field gel electrophoresis was also performed. Experimental virulence was evaluated through intra-peritoneal and intra-gastric mouse virulence assays. Our results showed no significant differences in the virulence-related molecular properties of the strains analyzed. All strains were equally pathogenic following intra-peritoneal inoculation of mice. In mice inoculated intra-gastric with 4 representative strains of the 2 types of listeriosis, there were no significant differences in the bacterial count when comparing invasive and gastroenteric strains, suggesting that the strains were comparable in terms of mean oral infectivity.

Incidence of Listeria monocytogenes in raw seafood products in Japanese retail stores

The incidence of Listeria monocytogenes in raw fish, shellfish, and fish roe was investigated in seafood products collected from randomly selected retail stores in and around Tokyo, Japan. Of the 10 samples of 208 examined found positive for L. monocytogenes by mini-VIDAS LMO, seven were fish roe (cod, salmon) and three were minced tuna. Three serotypes (1/2a, 1/2b, 3b) were detected among the isolated strains; serotype 1/2a was predominant (8 of 10).