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MRSA epidemics in US, South America share common ancestor
Two epidemics of community-associated MRSA, both linked to the USA300 clone and its Latin American variant, appeared to derive from sister clades with a common ancestor, according to recent data.
Researchers collected 51 isolates of USA300 strains and the USA300 Latin American variant (USA300-LV) from parallel MRSA epidemics in South America and the United States. USA300-LV MRSA isolates were collected from a surveillance study conducted at tertiary care hospitals in Colombia, Ecuador and Venezuela between 2006 and 2007. Also identified for analysis were the first two strains of USA300-LV identified in South America in 2005. US300 strains were collected from several states between 1999 and 2012.
All MRSA isolates were identified, and genomic DNA from the isolates were prepared and sequenced. The researchers determined genetic relationships between USA300 and USA300-LV through phylogenetic analysis.
In the initial assessment, the researchers found a close relationship between isolates belonging to USA300-LV and USA300. They identified two specific sister clades segregated by geographic location, and the parallel epidemics shared a common ancestor in about 1975 (HPD 95%, 1932-1993), with origins in 1989 (HPD 95%, 1971-1999) in North American epidemics and 1985 (HPD 95%, 1962-1997) in South American epidemics.
According to the credibility intervals on these dates, the two clades occurred before the first reports of USA300 in North America, and they indicate that members of the USA300 clade have existed in the Western Hemisphere since the 1930s. The two clades deviated from each other before the USA300 epidemic in North America, and the researchers said the South American epidemic does not appear to contribute to the spread of the US epidemic.
The investigators said these findings suggest that tracking the relationships between South American and North American MRSA epidemics may be useful in better understanding and inhibiting their durability and transmission.
“Our identification of highly virulent and closely related MRSA clades ... suggests either convergent acquisition of traits that enhanced virulence or significant adaptations that occurred in their common ancestor,” the researchers wrote. “Therefore, understanding the common attributes of [South American epidemic] and [North American epidemic] strains could help to uncover the molecular determinants of the rapid dissemination of these lineages.” – by Jen Byrne
Disclosure : Planet reports receiving lecture fees, research support and consulting fees from Pfizer. Please see the full study for a list of all other authors’ relevant financial disclosures.