Transcription and Translation Products of the Cytolysin Gene psm-mec on the Mobile Genetic Element SCCmec Regulate Staphylococcus aureus Virulence

The F region downstream of the mecI gene in the SCCmec element in hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) contains two bidirectionally overlapping open reading frames (ORFs), the fudoh ORF and the psm-mec ORF. The psm-mec ORF encodes a cytolysin, phenol-soluble modulin (PSM)-mec. Transformation of the F region into the Newman strain, which is a methicillin-sensitive S. aureus (MSSA) strain, or into the MW2 (USA400) and FRP3757 (USA300) strains, which are community-acquired MRSA (CA-MRSA) strains that lack the F region, attenuated their virulence in a mouse systemic infection model. Introducing the F region to these strains suppressed colony-spreading activity and PSMα production, and promoted biofilm formation. By producing mutations into the psm-mec ORF, we revealed that (i) both the transcription and translation products of the psm-mec ORF suppressed colony-spreading activity and promoted biofilm formation; and (ii) the transcription product of the psm-mec ORF, but not its translation product, decreased PSMα production. These findings suggest that both the psm-mec transcript, acting as a regulatory RNA, and the PSM-mec protein encoded by the gene on the mobile genetic element SCCmec regulate the virulence of Staphylococcus aureus

Origin and Molecular Evolution of the Determinant of Methicillin Resistance in Staphylococci ▿

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important multidrug-resistant pathogens around the world. MRSA is generated when methicillin-susceptible S. aureus (MSSA) exogenously acquires a methicillin resistance gene, mecA, carried by a mobile genetic element, staphylococcal cassette chromosome mec (SCCmec), which is speculated to be transmissible across staphylococcal species. However, the origin/reservoir of the mecA gene has remained unclear. Finding the origin/reservoir of the mecA gene is important for understanding the evolution of MRSA. Moreover, it may contribute to more effective control measures for MRSA. Here we report on one of the animal-related Staphylococcus species, S. fleurettii, as the highly probable origin of the mecA gene. The mecA gene of S. fleurettii was found on the chromosome linked with the essential genes for the growth of staphylococci and was not associated with SCCmec. The mecA locus of the S. fleurettii chromosome has a sequence practically identical to that of the mecA-containing region (∼12 kbp long) of SCCmec. Furthermore, by analyzing the corresponding gene loci (over 20 kbp in size) of S. sciuri and S. vitulinus, which evolved from a common ancestor with that of S. fleurettii, the speciation-related mecA gene homologues were identified, indicating that mecA of S. fleurettii descended from its ancestor and was not recently acquired. It is speculated that SCCmec came into form by adopting the S. fleurettii mecA gene and its surrounding chromosomal region. Our finding suggests that SCCmec was generated in Staphylococcus cells living in animals by acquiring the intrinsic mecA region of S. fleurettii, which is a commensal bacterium of animals

Staphylococcal Cassette Chromosome mec-Like Element in Macrococcus caseolyticus▿

Macrococcus is a bacterial genus that is closely related to Staphylococcus, which typically is isolated from animal skin and products. The genome analysis of multidrug-resistant Macrococcus caseolyticus strain JCSC5402, isolated from chicken, previously led to the identification of plasmid pMCCL2, which carries a transposon containing an unusual form of the Macrococcus mec gene complex (mecAm-mecR1m-mecIm-blaZm). In M. caseolyticus strain JCSC7096, this mec transposon containing the mec gene complex (designated Tn6045 in this study) was found integrated downstream of orfX on the chromosome. Tn6045 of JCSC7096 was bracketed by the direct repeat sequences (DR) specifically recognized by cassette chromosome recombinase (CCR). A non-mecA-containing staphylococcal cassette chromosome (SCC) element, designated SCC7096, was integrated next to the mec transposon and separated from the latter by a DR. Nested PCR experiments showed that the mec transposon not only was excised singly but also coexcised with SCC7096 from the chromosome at the DRs. The coexcised elements formed the extrachromosomal closed circular DNA of the SCCmec-like element. SCCmec is known to be the mobile element conveying methicillin (meticillin) resistance in staphylococci. However, its origin has been unknown. Our observation revealed a potential mechanism of the generation of a new SCCmec-like element in M. caseolyticus, a commensal bacterium of food animals

Enriched bovine IgG fraction prevents infections with Enterohaemorrhagic Escherichia coli

A bovine IgG‐enriched whey fraction contains antibodies against various bacterial antigens. We investigated the protective effects of a bovine whey fraction preparation against infections with Enterohaemorrhagic Escherichia coli O157:H7, Salmonella enterica serovar Enteritidis, and Mycobacterium avium in mouse models. After infection with these pathogens, the IgG‐enriched fraction or skim milk was given ad libitum at a 5% solution instead of water. The mice given the IgG‐enriched fraction were significantly resistant to orally challenged EHEC O157:H7 (LD50: 4.0 × 105 CFU/mouse) infections compared with the mice given skim milk (LD50: <1.5 × 102 CFU/mouse). The mice given the IgG‐enriched fraction were also significantly resistant to orally challenged S. Enteritidis (LD50: 5.0 × 106 CFU/mouse) infections compared with the mice given skim milk (LD50: <2.5 × 101 CFU/mouse). When the mice were nasally infected with M. avium, the numbers of the bacteria in lungs of mice given the IgG‐enriched fraction were significantly lower than those given skim milk 2 and 3 weeks after infection. These results strongly indicate that oral administration of the bovine IgG‐enriched whey fraction protects mice against food‐borne infection and also that it partially protects mice against respiratory tract infection

Staphylococcal Cassette Chromosome(SCC) : A Unique Gene Transfer System in Staphylococci

Bacterial Integrative Mobile Genetic Elements (Adam P.Roberts et al eds

Spread of GES-5 carbapenemase-producing Pseudomonas aeruginosa clinical isolates in Japan due to clonal expansion of ST235.

The first outbreak in Japan of GES-5 carbapenemase-producing Pseudomonas aeruginosa occurred in a long-term care facility in 2014. To assess the spread of GES-5 producing P. aeruginosa clinical isolates in medical settings in Japan, 1,476 carbapenem-resistant P. aeruginosa isolates obtained from 2012 to 2016 were characterized. Of these 1,476 isolates, 104 (7.0%) harbored blaGES-5. Southern blotting revealed that the blaGES-5 was located on the chromosome. The isolation rates of these GES-5 producers increased significantly every year, from 2.0% (6 of 295) in 2012 to 2.8% (8 of 283) in 2013 to 5.3% (16 of 303) in 2014 to 9.7% (29 of 300) in 2015 to 15.3% (45 of 295) in 2016. Of the 104 GES-5 producers, 102 belonged to clonal complex (CC) 235, including 99 belonging to ST235 and three belonging to ST2233). Whole genome sequence analysis revealed that CC235 P. aeruginosa harboring blaGES-5 spread in a clonal manner. These results indicate that these GES-5 producing CC235 P. aeruginosa clinical isolates have spread in medical settings throughout Japan