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Listeria monocytogenes is a ubiquitous gram-positive, rod-shaped, widespread in nature, facultative intracellular human and animal pathogen that causes infections collectively termed listeriosis. L. monocytogenes EGD encodes a total of 133 surface proteins, the abundance of which, as well as the variety of anchoring systems, probably reflects the ability of this bacterium to survive in diverse environments and to interact with many kinds of eukaryotic cells. The group of surface proteins also includes proteins with murein hydrolase activity-autolysins. To date, five L. monocytogenes autolysins have been identified: p60, P45, Ami, MurA and Auto. These enzymes are involved in numerous cellular processes including cell growth, cell wall turnover, peptidoglycan maturation, cell division and separation, formation of flagella, sporulation, chemotaxis and biofilm formation, genetic competence, protein secretion, the lytic action of some antibiotics and pathogenicity. We have recently identified a putative sixth listerial peptidoglycan-degrading enzyme, which has surprisingly been identified as FlaA, a flagellar protein of L. monocytogenes.
This review summarizes current data on resistance among Salmonella spp. isolates of food origin from countries in different regions of the world. The mechanisms of resistance to different groups of antimicrobial compounds are also considered. Among strains resistant to quinolones and/or fluoroquinolones the most prevalent mechanism is amino acid substitutions in quinolone resistance-determining region (QRDR) of genes gyrA, parC but mechanism of growing importance is plasmid-mediated quinolone resistance (PMQR) associated with genes qnrA, qnrB, qnrC, qnrD, qnrS but frequency of their detection is different. Resistance to sulfonamides is mostly associated with genes sul1 and sul2, while resistance to trimethoprim is associated with various variants of dhfr ( dfr) genes. Taking into account Salmonella spp. strains isolated from food, resistance to β-lactams is commonly associated with β-lactamases encoding by blaTEM genes. However strains ESBL and AmpC – positive are also detected. Resistance to aminoglicosides is commonly result of enzymatic inactivation. Three types of aminoglycoside modifying enzyme are: acetyltransferases (AAC), adenyltransferases (ANT) and phosphotransferases (APH). Resistance to tetracyclines among Salmonella spp. isolated from food is most commonly associated with active efflux. Among numerous genetic determinants encoding efflux pumps tetA, tetB, tetC, tetD, tetE and tetG are reported predominatingly. One of the most common mechanisms of resistance against chloramphenicol is its inactivation by chloramphenicol acetyltrasferases (CATs), but resistance to this compound can be also mediated by chloramphenicol efflux pumps encoded by the genes cmlA and floR. It is important to monitor resistance of Salmonella isolated from food, because the globalization of trade, leading to the long-distance movement of goods, animals and food products, encourages the spread of resistant pathogens around the world.
In this preliminary report we show that a 29 kDa surface protein of Listeria monocytogenes EGD removed from cells with 4 M LiCl has peptidoglycan (murein) hydrolyzing activity, as revealed by zymographic analysis using Bacillus subtilis murein and heat-killed Micrococcus luteus cells casted in the gel. Following two-dimensional electrophoresis, the protein was electroblotted to PVDF membrane and its identity (FlaA) was revealed by sequencing. Peptidoglycan hydrolysing activity of FlaA purified by FPLC on Mono-S Sepharose against labelled Escherichia coli murein was demonstrated.
Listeria monocytogenes is an opportunistic pathogen that causes infections collectively termed listeriosis, which are related to the ingestion of food contaminated with these gram-positive rods. The pathogenicity of L. monocytogenes is detennined by the following virulence factors: listeriolysin O, protein ActA, two phospholipases C, internalins (InlA and InlB), protein CwhA and a metalloprotease. The bacterium is a model organism in studies on the pathogenesis of intracellular parasites. It is able to penetrate, multiply and propagate in various types of eukaryotic cells and is also able to overcome the three main barriers encountered in the host: the intestinal barrier, the blood-brain barrier and the placenta. Based on L. monocytogenes genome sequence analysis 133 surface proteins have been identified. In particular, the large number of proteins covalently bound to murein sets L. monocytogenes apart from other gram-positive bacteria. The ability of this pathogen to multiply in various environments as well as the possibility of its interaction with many kinds of eukaryotic cells is, in fact, made possible by the large number of surface proteins.
The present study collected bacterial samples from water and bottom sediments from fish farms located in a nature reserve area in Poland with no recorded history of antibiotic use. The aim of the study was to determine the initial states of tetracycline, streptomycin, and erythromycin resistance before a potential increase of intensive aquaculture and application of antimicrobial agents in that region. With this in mind, the diversity and antibiotic resistance phenotypes and genotypes of isolates from the bottom sediments and water in five of the 13 fish ponds in Raszyn were evaluated. A total of 58 (sediment, n = 24; water, n = 34) non-repetitive and non-susceptible isolates were affiliated to 14 genera. Among the sediment isolates, Pseudomonas spp. and Bacillus spp. were isolated most frequently, and from the water, Stenotrophomonas spp. and Pseudomonas spp. Phenotypically resistant isolates selected by disk diffusion were further screened by polymerase chain reaction (PCR) and amplicon sequencing. The isolates derived from the water showed a greater percentage of phenotypically resistant isolates to each of the three antibiotics. The most common tetracycline resistant genes detected in isolates from both the water and sediment were tet(A), tet(T), tet(W), and tet(34). On the other hand, the genes tet(X), tet(H), tet(M), and tet(BP) were the most frequent among sedimentary isolates, while tet(B), tet(C), tet(D), and tet(32) were prevalent in aquatic isolates. The most prevalent streptomycin resistance genes among the aquatic isolates were aac(6’)-I, str(A), and str(B). The erythromycin resistance genes detected in all isolates included msr(A), erm(X), erm(V), erm(F), and erm(E).
Cells of a mutant of Listeria monocytogenes lacking functional PBP5, an enzyme with DD-carboxypeptidase activity, make thicker cells walls. In this study we show that the muropeptide profile of the mutant, obtained after HPLC analysis of a muramidase digest of cell wall murein, differs from that for the wild type strain. The main differences embrace strongly reduced disaccharide-tripeptide content, strongly increased amounts of pentapeptide-containing muropeptides and a shift in profile from less cross-linked muropeptides (monomers, dimers) towards more highly cross-linked ones.
The susceptibility of 96 strains of Listeria monocytogenes isolated from food to antibiotics and disinfectants currently used in human therapy, veterinary, medicine and food industry was determined by a standard operating procedure - broth dilution method. Antimicrobial agents included the β-lactams ampicillin and penicillin, the lantibiotic nisin, and the disinfectants benzalkonium chloride and chlorhexidine gluconate. Among the studied strains we found 13 strains with 8-fold, 7 strains with 16-fold and 2 strains with 32-fold decreased susceptibility to ampicillin, as determined by MIC, compared to wild type reference strain. Interestingly, the mentioned strains were isolated from frozen vegetables and soups, none of the isolates from dairy products showed any elevated resistance to the studied antimicrobial agents. The occurrence in food products of strains with increased resistance to ampicillin is disquieting, especially since β-lactams are the most frequent antibiotic of choice in the therapy of infections caused by the pathogen.
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