VirB4- and VirD4-like ATPases, components of a putative type 4C secretion system in Clostridioides difficile

The type 4 secretion system (T4SS) represents a bacterial nanomachine capable of trans-cell wall transportation of proteins and DNA and which has attracted intense interest due to its roles in the pathogenesis of infectious diseases. During the current investigation we uncovered three distinct gene clusters in Clostridioides difficile strain 630 coding for proteins structurally related to components of the VirB4/D4 type 4C secretion system from Streptococcus suis strain 05ZYH33 and located within sequences of conjugative transposons (CTn). Phylogenic analysis shows that VirB4- and VirD4-like proteins of CTn4 locus, on one hand, and those of CTn2 and CTn5 loci, on the other hand, fit into separate clades, suggesting specific roles of identified secretion system variants in physiology of C. difficile. Our further study on VirB4- and VirD4-like products coded by CTn4 revealed that both proteins possess Mg2+-dependent ATPase activity, form oligomers (most probably, hexamers) in water solutions, and rely on potassium but not sodium ions for the highest catalytic rate. VirD4 binds nonspecifically to DNA and RNA. Its DNA binding activity strongly decreased with the W241A variant. Mutations in the nucleotide sequences coding for presumable Walker A and Walker B motifs decreased stability of the oligomers and significantly but not completely attenuated enzymatic activity of VirB4. In VirD4, substitutions of amino acid residues in the peptides reminiscent of Walker structural motifs resulted neither in attenuation of enzymatic activity of the protein nor influenced the oligomerization state of the ATPase.

Mobile Genetic Elements in Vancomycin-Resistant Enterococcus faecium Population

Horizontal gene transfer constitutes a key driving force in bacterial evolution. The ability to acquire mobile genetic elements encoding antimicrobial resistance has contributed to the emergence of Enterococcus faecium as one of the main human nosocomial opportunistic pathogens. The deep analysis of the vancomycin-resistant E. faecium (VREfm) population’s mobilome, as the architecture and evolution of the core genome enables to observe VREfm plasticity and power of adaptation in animals, plants, environment and food. The persistence of VREfm is facilitated by the exchange of plasmids, phages and conjugative transposons that have allowed them to achieve a rapid adaptation to changes in environmental conditions. They can acquire resistance determinants from several species and transfer resistance genes to other potentially pathogenic bacteria such as methicillin-resistant Staphylococcus aureus strains.

Two perspectives of Listeria monocytogenes hazards in dairy products: the prevalence and the antibiotic resistance

Listeria monocytogenes is among the most food-borne pathogens. It has the ability to grow over a range of temperature, including refrigeration temperature. Foods kept in refrigerator more than the prescribed period of time create an opportunity for the occurrence of Listeria monocytogenes. As this review shows, the prevalence of L. monocytogenes has more likely evident in pasteurized milk than other dairy products, such as raw milk. Inadequate temperature and faults in technology during pasteurization can be the disposing factors for the presence of the organism in dairy products. The organism, on the other hand, has been found to be resistant to those commonly known antibiotics that have human and veterinary importance, namely, ampicillin, Tetracycline, and chloramphenicol, streptomycin, erytromycin, penicillin G., and others. Resistance ability of the organism can be mediated by different natural and acquired resistance mechanisms, such as self-transferrable plasmids, mobilizable plasmids, and conjugative transposons. The emergence and spread of antibiotic resistance of L. monocytogenes has serious public health and economic impacts at large. This paper has reviewed the prevalence and the antibiotic resistance of L. monocytogenes isolates of dairy products and the strategic mechanisms of the organism develop resistance against the antibiotics.

Genomic study of the Type IVC secretion system in Clostridium difficile: understanding C. difficile evolution via horizontal gene transfer

Clostridium difficile, the etiological agent of Clostridium difficile infection (CDI), is a gram-positive, spore-forming bacillus that is responsible for ∼20% of antibiotic-related cases of diarrhea and nearly all cases of pseudomembranous colitis. Previous data have shown that a substantial proportion (11%) of the C. difficile genome consists of mobile genetic elements, including seven conjugative transposons. However, the mechanism underlying the formation of a mosaic genome in C. difficile is unknown. The type-IV secretion system (T4SS) is the only secretion system known to transfer DNA segments among bacteria. We searched genome databases to identify a candidate T4SS in C. difficile that could transfer DNA among different C. difficile strains. All T4SS gene clusters in C. difficile are located within genomic islands (GIs), which have variable lengths and structures and are all conjugative transposons. During the horizontal-transfer process of T4SS GIs within the C. difficile population, the excision sites were altered, resulting in different short-tandem repeat sequences among the T4SS GIs, as well as different chromosomal insertion sites and additional regions in the GIs.

Characterization Of Tetracycline Resistance Of Salmonella Enterica Subspecies Enterica Serovar Infantis Isolated From Poultry In The Northern Part Of Serbia

Resistance to tetracycline was studied inSalmonellaInfantis isolated from 28 poultry farms in the Northern part of Serbia (The Autonomous Province of Vojvodina). A total of 18 isolates were resistant to nalidixic acid (NAL) and tetracycline (TET). The minimal inhibitory concentration (MIC) to TET, ranged from 1-256 mg/L. Namely, 13 isolates exhibited MIC to TET at 256 mg/L, in four of the isolates, the MIC was 128 mg/L and one isolate had MIC 64 mg/L. Ten isolates were exhibiting a MIC of 1mg/L. It was evident thatSalmonellaInfantis had also spread to breeders and layers. In this work, we detected thetetAgene and the correspondingtetRgene (encoding the repressor protein) as well as the truncated transposon Tn1721,which are responsible for the resistance to TET. The presence of the non conjugative transposons from the conjugative plasmid has facilitated the spread of resistance to TET inSalmonella. It was concluded that higher biosecurity practice in poultry farming presents the best option to eliminate infections caused bySalmonellaspp. from poultry flocks in Serbia. A rational use of antimicrobials is necessary to prevent any further spread ofSalmonellaInfantis resistant clones.

Resistance Determinants and Their Association with Different Transposons in the Antibiotic-ResistantStreptococcus pneumoniae

Multiple resistance ofStreptococcus pneumoniaeis generally associated with their unique recombination-mediated genetic plasticity and possessing the mobile genetic elements. The aim of our study was to detect antibiotic resistance determinants and conjugative transposons in 138 antibiotic-resistant pneumococcal strains isolated from nasopharynx of healthy young children from Lublin, Poland. These strains resistant to tetracycline and/or to chloramphenicol/erythromycin/clindamycin were tested by PCR using the specific genes as markers. The presence of Tn916family transposons, carryingtet(M) andint/xisTn916, was observed in all of the tested strains. Tn916was detected in 16 strains resistant only to tetracycline. Tn6002and Tn3872-related element were found among 99erm(B)-carrying strains (83.8% and 3.0%, resp.). Eight strains harbouringmef(E) anderm(B) genes were detected, suggesting the presence of Tn2010and Tn2017transposons. Among 101 chloramphenicol-resistant strains, two variants of Tn5252-related transposon were distinguished depending on the presence ofint/xis5252genes specific forcatgene-containing Tn5252(75.2% of strains) orintSp23FST81gene, specific forcat-containing ICESp23FST81 element (24.8% of strains). In 6 strains Tn916-like and Tn5252-like elements formed a Tn5253-like structure. Besides clonal dissemination of resistant strains of pneumococci in the population, horizontal transfer of conjugative transposons is an important factor of the high prevalence of antibiotic resistance.