Another important issue to consider is the clinical settings of reinfection by different CMV strains, a reminder that vaccine design should aim for cross-protection against infection by multiple epidemic CMV strains.
Analysis of the rstR gene carried by the recent epidemic strains showed that, unlike the O139 strains of 1993, which carried multiple copies of an El Tor type CTXET prophage, the new O139 strains carry at least one copy of the Calcutta type CTXCalc prophage in addition to the CTXET prophage.
A 25-loci Multiple Locus VNTR Analysis (MLVA MLVAA was initially performed to define genetic relationships, followed by an investigation of genetic diversity between epidemic strains through Single Nucleotide Repeat (SNR) analysis.
Experiments are ongoing to determine which of these amino acid variants are responsible for the neurovirulence difference between the pre-epidemic and epidemic strains.
These methods generally target toxins or their associated toxin genes and are unable to discriminate epidemic strains from non-epidemic strains14, 25,26,27.
Identification of these epidemic strains may assist in determining relatedness of strains and recognizing transmission of C. difficile within healthcare facilities.
Compared with the pre-epidemic strains from Asian lineage, the epidemic strains isolated after 2012 have undergone an A188V mutation in the NS1 gene11 that enabled the protein to suppress IFN-β induction.
These mutations in tcdC have been proposed as a possible explanation for the increased virulence of the epidemic strains.
It is likely that the environment is the source of epidemic strains.
Additionally, the Burkholderia epidemic strain marker (BCESM) is part of the cci pathogenicity island and may be involved in person-to-person transmission of epidemic strains [27], [28].
