Aerobic Exercise Induces Alternative Splicing of Neurexins in Frontal Cortex.

Aerobic exercise (AE) is known to produce beneficial effects on brain health by improving plasticity, connectivity, and cognitive functions, but the underlying molecular mechanisms are still limited. Neurexins (Nrxns) are a family of presynaptic cell adhesion molecules that are important in synapsis formation and maturation. In vertebrates, three-neurexin genes (NRXN1, NRXN2, and NRXN3) have been identified, each encoding for α and ß neurexins, from two independent promoters. Moreover, each Nrxns gene (1-3) has several alternative exons and produces many splice variants that bind to a large variety of postsynaptic ligands, playing a role in trans-synaptic specification, strength, and plasticity. In this study, we investigated the impact of a continuous progressive (CP) AE program on alternative splicing (AS) of Nrxns on two brain regions: frontal cortex (FC) and hippocampus. We showed that exercise promoted Nrxns1-3 AS at splice site 4 (SS4) both in α and ß isoforms, inducing a switch from exon-excluded isoforms (SS4-) to exon-included isoforms (SS4+) in FC but not in hippocampus. Additionally, we showed that the same AE program enhanced the expression level of other genes correlated with synaptic function and plasticity only in FC. Altogether, our findings demonstrated the positive effect of CP AE on FC in inducing molecular changes underlying synaptic plasticity and suggested that FC is possibly a more sensitive structure than hippocampus to show molecular changes.

Characterization of novel conjugative multiresistance plasmids carrying cfr from linezolid-resistant Staphylococcus epidermidis clinical isolates from Italy.

OBJECTIVES: The objective of this study was to investigate the genetic environment of the cfr gene from two linezolid-resistant clinical isolates of Staphylococcus epidermidis from Italy. METHODS: The two strains (SP1 and SP2) were phenotypically and genotypically characterized. Transferability of cfr was assessed by electrotransformation and conjugation. The genetic contexts of cfr were investigated by PCR mapping, sequencing and comparative sequence analyses. RESULTS: SP1 and SP2 belonged to ST23 and ST83, respectively. In both strains, the cfr gene was located on a plasmid, which could be transferred to Staphylococcus aureus by transformation and conjugation. In isolate SP1, linezolid resistance mediated by mutations in 23S rRNA and the L3 ribosomal protein was also detected. pSP01, the cfr-carrying plasmid from strain SP1, had a larger number of additional resistance genes and was sequenced (76 991 bp). It disclosed a distinctive mosaic structure, with four cargo regions interpolated into a backbone 95% identical to that of S. aureus plasmid pPR9. Besides cfr, resistance genes distributed in the cargo regions included blaZ, lsa(B), msr(A) and aad, and a gene cluster for resistance to heavy metals. A closely related cfr plasmid (pSP01.1, ∼ 49 kb), differing from pSP01 by the lack of a large cargo region with some resistance genes, was detected in strain SP2. CONCLUSIONS: The conjugative multiresistance plasmid pSP01 is the first cfr-carrying plasmid to be sequenced in Italy. This is the first time cfr has been found: (i) in association with blaZ, msr(A) and heavy metal resistance genes; and (ii) in an S. epidermidis strain (SP2) belonging to ST83.

Genetic determinants and elements associated with antibiotic resistance in viridans group streptococci.

OBJECTIVES: To investigate the distribution of erythromycin, tetracycline and chloramphenicol resistance mechanisms and determinants and the relevant genetic environments and elements in viridans group streptococci (VGS). METHODS: A total of 263 VGS collected from routine throat swabs in 2010-12 and identified to the species level were studied. Antibiotic resistance determinants and the relevant genetic contexts and elements were determined using amplification and sequencing assays and restriction analysis. RESULTS: The investigation provided original information on the distribution of resistance mechanisms, determinants and genetic elements in VGS. Erythromycin-resistant isolates totalled 148 (56.3%; 37 belonging to the cMLS phenotype and 111 belonging to the M phenotype); there were 72 (27.4%) and 7 (2.7%) tetracycline- and chloramphenicol-resistant isolates, respectively. A number of variants of known genetic contexts and elements carrying determinants of resistance to these antibiotics were detected, including the mega element, Φ10394.4, Tn2009, Tn2010, the IQ element, Tn917, Tn3872, Tn6002, Tn916, Tn5801, a tet(O) fragment from ICE2096-RD.2 and ICESp23FST81. CONCLUSIONS: These findings shed new light on the distribution of antibiotic resistance mechanisms and determinants and their genetic environments in VGS, for which very few such data are currently available. The high frequency and broad variety of such elements supports the notion that VGS may be important reservoirs of resistance genes for the more pathogenic streptococci. The high rates of macrolide resistance confirm the persistence of a marked prevalence of resistant VGS in Europe, where macrolide resistance is, conversely, declining among the major streptococcal pathogens.

Transduction of the Streptococcus pyogenes bacteriophage Φm46.1, carrying resistance genes mef(A) and tet(O), to other Streptococcus species.

Φm46.1 - Streptococcus pyogenes bacteriophage carrying mef(A) and tet(O), respectively, encoding resistance to macrolides (M phenotype) and tetracycline - is widespread in S. pyogenes but has not been reported outside this species. Φm46.1 is transferable in vitro among S. pyogenes isolates, but no information is available about its transferability to other Streptococcus species. We thus investigated Φm46.1 for its ability to be transduced in vitro to recipients of different Streptococcus species. Transductants were obtained from recipients of Streptococcus agalactiae, Streptococcus gordonii, and Streptococcus suis. Retransfer was always achieved, and from S. suis to S. pyogenes occurred at a much greater frequency than in the opposite direction. In transductants Φm46.1 retained its functional properties, such as inducibility with mitomycin C, presence both as a prophage and as a free circular form, and transferability. The transductants shared the same Φm46.1 chromosomal integration site as the donor, at the 3' end of a conserved RNA uracil methyltransferase (rum) gene, which is an integration hotspot for a variety of genetic elements. No transfer occurred to recipients of Streptococcus pneumoniae, Streptococcus oralis, and Streptococcus salivarius, even though rum-like genes were also detected in the sequenced genomes of these species. A largely overlapping 18-bp critical sequence, where the site-specific recombination process presumably takes place, was identified in the rum genes of all recipients, including those of the species yielding no transductants. Growth assays to evaluate the fitness cost of Φm46.1 acquisition disclosed a negligible impact on S. pyogenes, S. agalactiae, and S. gordonii transductants and a noticeable fitness advantage in S. suis. The S. suis transductant also displayed marked overexpression of the autolysin-encoding gene atl.

ICESp1116, the genetic element responsible for erm(B)-mediated, inducible resistance to erythromycin in Streptococcus pyogenes.

ICESp1116, responsible for erm(B)-mediated, inducible erythromycin resistance in Streptococcus pyogenes, was comprehensively characterized, and its chromosomal integration site was determined. It displayed a unique mosaic organization consisting of a scaffold, related to TnGallo1 from Streptococcus gallolyticus, with two inserted fragments separated by IS1216. One fragment, containing erm(B), displayed high-level identity to a portion of the S. pyogenes plasmid pSM19035; the other, containing a truncated tet(M) gene, displayed high-level identity to the right-hand portion of Clostridium difficile Tn5397.

ICESp2905, the erm(TR)-tet(O) element of Streptococcus pyogenes, is formed by two independent integrative and conjugative elements.

In ICESp2905, a widespread erm(TR)- and tet(O)-carrying genetic element of Streptococcus pyogenes, the two resistance determinants are contained in separate fragments inserted into a scaffold of clostridial origin. ICESp2905 (∼65.6 kb) was transferable not only in its regular form but also in a defective form lacking the erm(TR) fragment (ICESp2906, ∼53.0 kb). The erm(TR) fragment was also an independent integrative and conjugative element (ICE) (ICESp2907, ∼12.6 kb). ICESp2905 thus results from one ICE (ICESp2907) being integrated into another (ICESp2906).

Two distinct genetic elements are responsible for erm(TR)-mediated erythromycin resistance in tetracycline-susceptible and tetracycline-resistant strains of Streptococcus pyogenes.

In Streptococcus pyogenes, inducible erythromycin (ERY) resistance is due to posttranscriptional methylation of an adenine residue in 23S rRNA that can be encoded either by the erm(B) gene or by the more recently described erm(TR) gene. Two erm(TR)-carrying genetic elements, showing extensive DNA identities, have thus far been sequenced: ICE10750-RD.2 (∼49 kb) and Tn1806 (∼54 kb), from tetracycline (TET)-susceptible strains of S. pyogenes and Streptococcus pneumoniae, respectively. However, TET resistance, commonly mediated by the tet(O) gene, is widespread in erm(TR)-positive S. pyogenes. In this study, 23 S. pyogenes clinical strains with erm(TR)-mediated ERY resistance-3 TET susceptible and 20 TET resistant-were investigated. Two erm(TR)-carrying elements sharing only a short, high-identity erm(TR)-containing core sequence were comprehensively characterized: ICESp1108 (45,456 bp) from the TET-susceptible strain C1 and ICESp2905 (65,575 bp) from the TET-resistant strain iB21. While ICESp1108 exhibited extensive identities to ICE10750-RD.2 and Tn1806, ICESp2905 showed a previously unreported genetic organization resulting from the insertion of separate erm(TR)- and tet(O)-containing fragments in a scaffold of clostridial origin. Transferability by conjugation of the erm(TR) elements from the same strains used in this study had been demonstrated in earlier investigations. Unlike ICE10750-RD.2 and Tn1806, which are integrated into an hsdM chromosomal gene, both ICESp1108 and ICESp2905 shared the chromosomal integration site at the 3' end of the conserved rum gene, which is an integration hot spot for several mobile streptococcal elements. By using PCR-mapping assays, erm(TR)-carrying elements closely resembling ICESp1108 and ICESp2905 were shown in the other TET-susceptible and TET-resistant test strains, respectively.