One hundred and seventy-five isolates of the pathogenic bacterium Listeria monocytogenes recovered from human clinical (blood and cerebrospinal fluid), animal, and environmental sources in Europe, North America, and elsewhere were analyzed electrophoretically for allelic variation at 16 genetic loci encoding metabolic enzymes. Forty-five distinctive allele profiles (electrophoretic types, ETs) were distinguished, among which mean genetic diversity per locus (H) was 0.424. Cluster analysis of a matrix of genetic distances between paired ETs revealed two primary phylogenetic divisions of the species separated at a distance of 0.54. ETs in division I were presented by strains of serotypes 4b, 1/2b, and 4a, whereas strains of ETs in division II were of serotypes 1/2a and 1/2c.Human and animal isolates did not represent distinctive subsets of ETs. The occurrence of linkage disequilibrium between enzyme loci and the widespread distribution of certain ETs indicate that the genetic structure ofL. monocytogenes is clonal. One clone, marked by ET 1, caused major epidemics of human disease in western Switzerland in the period -1987 and in Los Angeles County, California, in 1985, both of which were attributed to contamination of soft cheese. ET 1 is closely related to the clone (ET 7) that caused two large outbreaks of listeriosis in Massachusetts in 1979 and Bacteria of the genus Listeria are widely distributed in the environment and also occur in the intestinal tract of healthy animals and humans (1). Among the several species of the genus, only Listeria monocytogenes is commonly pathogenic for humans (2, 3), in which it causes serious invasive disease (septicemia, meningitis, and meningoencephalitis), primarily in the immunologically compromised host, the neonate, and the fetus (1,2 3818The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
To define the prevalence of antibiotic resistance in Listeria species pathogenic for humans and animals, 1100 isolates (60 from cases of listeriosis and 1040 from food and environment) collected worldwide were screened. Of the 61 tetracycline- and minocycline-resistant strains (37 Listeria monocytogenes), 57 harbored tet(M); 4 non-L. monocytogenes isolates contained tet(S). One Listeria innocua isolate was also resistant to streptomycin and contained the tet(M) and aad6 genes. An L. monocytogenes isolate was trimethoprim-resistant, a characteristic not reported previously in Listeria species, because of the presence of a yet-uncharacterized gene. Three clinical isolates of L. monocytogenes were resistant to low levels of streptomycin. Since the tet(M), tet(S), and aad6 genes are common in enterococci and streptococci, these data suggest transfer from the latter to Listeria species. Uniform susceptibility to tetracycline, minocycline, trimethoprim, and streptomycin cannot be assumed any longer for Listeria species.
An outbreak of gastroenteritis occurred in Italy among 39 persons who had attended a private supper. All guests were previously healthy, young, non-pregnant adults; 18 (46%) had symptoms, mostly gastrointestinal (78%), with a short incubation period. Four were hospitalized with acute febrile gastroenteritis, two of whom had blood cultures positive for Listeria monocytogenes. No other microorganisms were recovered from the hospitalized patients' specimens. Epidemiological investigation identified rice salad as the most likely vehicle of the food-borne outbreak. L. monocytogenes was isolated from three leftover foods, the kitchen freezer and blender. Isolates from the patients, the foods and the freezer were indistinguishable: serotype 1/2b, same phage type and multilocus enzyme electrophoretic type. Eight (36%) of 22 guests tested were found to have antibodies against L. monocytogenes, compared with none of 11 controls from the general population. This point source outbreak was probably caused by infection with L. monocytogenes. Unusual features included the high attack rate among immunocompetent adults and the predominance of gastrointestinal symptoms.
Expression of proteins involved in the adhesion of Listeria monocytogenes to mammalian cells or in the intracellular life cycle of this bacterium, including listeriolysin O (LLO),). Of the strains isolated from patients with non-pregnancy-related cases of listeriosis, bacteremia was predominantly associated with group Ami1 strains (OR ؍ 1.89; P ؍ 1 ؋ 10 ؊2 ) and central nervous system infections were associated with group ActA2 strains (OR ؍ 3.04; P ؍ 1 ؋ 10 ؊3 ) and group ActA3 strains (OR ؍ 3.91; P ؍ 1 ؋ 10 ؊3 ).Since the transmission of human listeriosis was first shown to be food borne in 1981, Listeria monocytogenes has been recognized as a major food-borne pathogen. The severity of listeriosis, which can cause abortions, bacteremia, and central nervous system infections (CNSI) and has a high mortality rate (20 to 30% [13,36]), makes it a serious public health problem. In addition, the fact that various foods have been implicated in outbreaks of listeriosis (37) and the increase in product recalls (48) have led to serious economic problems associated with this bacterium.Based on present knowledge, any strain of L. monocytogenes should be considered potentially pathogenic for humans. Nevertheless, a number of observations suggests that L. monocytogenes virulence is heterogeneous. Serotyping has revealed that strains are heterogeneously distributed; most major outbreaks of listeriosis (37) have been caused by strains belonging to serovar 4b, which has also been responsible for numerous sporadic cases (13, 36). However, a low percentage of food samples is contaminated with strains of this serovar (1, 25). Analysis of surface proteins, sequencing of virulence genes, and PCR-restriction enzyme analysis of virulence genes have revealed that differences are connected to the origin or typing characteristics of the strains (34,38,43,49,50,51). The tests used to study L. monocytogenes pathogenicity include tissue culture assays and tests in which laboratory animals are used (5,7,9,44,46). These methods also have revealed heterogeneity in the virulence of strains. For example, counts of viable bacteria in spleens revealed that virulence levels varied from less than 10 3 to 10 8 CFU (5). However, there was no clear correlation between strain characteristics and the degree of virulence. Therefore, there are currently no laboratory tests which can predict the danger associated with L. monocytogenes strains.The mechanisms by which L. monocytogenes invades a host have been studied in detail (21). Listeriolysin O (LLO) is a 58-to 60-kDa secreted protein which allows the bacterium to escape from a phagocytosis vacuole (8, 15). LLO is a toxin which acts only on cholesterol-containing membranes in which cholesterol is considered the receptor. Nonhemolytic mutants are always avirulent in mice (15). However, the level of in vitro hemolysin production is not directly proportional to the virulence of a strain (18). InlB, which is a 67-kDa surface and secreted protein, is sufficient for entry of the bacterium into cells...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.