Global C. difficile epidemic caused by two antibiotic resistant strains
Researchers have shown that the global epidemic of Clostridium difficile was caused by two-closely-related strains that became resistant to a frontline antibiotic.
The study highlights the ease and rapidity with which the hospital bacterium, C. difficile, can spread throughout the world, emphasising the interconnectedness of the global healthcare system.
Unlike many healthcare-associated bacteria, C. difficile 027/NAP1/BI produces highly resistant and infectious spores. These spores can promote the transmission of C. difficile and potentially facilitate its spread over great distances, even across continents.
“Between 2002 and 2006, we saw highly publicised outbreaks of C. difficile in hospitals across the UK, USA, Canada and Europe,” says Dr Miao He, first author from the Wellcome Trust Sanger Institute. “We used advanced DNA sequencing to determine the evolutionary history of this epidemic and the subsequent pattern of global spread.
“We found that this outbreak came from two separate epidemic strains or lineages of C. difficile, FQR1 and FQR2, both emerging from North America over a very short period and rapidly spreading between hospitals around the world.”
The team used the genetic history to map both epidemic strains of C. difficile using a global collection of samples from hospital patients between 1985 and 2010. They demonstrated that the two C. difficile strains acquired resistance separately to the antibiotic, fluoroquinolone. This key genetic change may have instigated the epidemics in the early 2000s.
“Up until the early 2000s, fluoroquinolone was an effective treatment for C. difficile infection,” says Professor Brendan Wren, author from the London School of Hygiene and Tropical Medicine. “We’ve seen that since these strains acquired resistance to this frontline antibiotic, not only is it now virtually useless against this organism, but resistance seems to have been a major factor in the continued evolution and persistence of these strains in hospitals and clinical settings.”
The team found that the first outbreak strain of C. difficile, FQR1, originated in the USA and spread across the country, with sporadic cases in Switzerland and South Korea. In contrast, the second strain, FQR2, originated in Canada and spread rapidly over a much wider area, spreading throughout North America, Australia and Europe.
The research showed that C. difficile in the UK was frequently caused by long-range transmission events before spreading extensively. They confirmed separate transmission events to Exeter, Ayrshire and Birmingham from North America and a transmission event from continental Europe to Maidstone. These events triggered large-scale C. difficile outbreaks in many hospitals across the UK in the mid-2000s.
“We have exposed the ease and rapidity with which these fluoroquinolone-resistant C. difficile strains have transmitted across the world,” said Dr Trevor Lawley, lead author from the Wellcome Trust Sanger Institute. “Our research highlights how the global healthcare system is interconnected and how we all need to work together when an outbreak such as this occurs.
“Our study heralds a new era of forensic microbiology for the transmission tracking of this major global pathogen and will now help us understand at the genetic level how and why this pathogen has become so aggressive and transmissible worldwide. This research will act as a database for clinical researchers to track the genomic changes in C. difficile outbreaks.”
(Image: Micrograph of Gram-positive C. difficile bacteria from a stool sample culture. Credit: Janice Haney Carr, Centers for Disease Control and Prevention)
Miao He, Fabio Miyajima, Paul Roberts et al. (2012). Emergence and global spread of epidemic healthcare-associated Clostridium difficile
Published in Nature Genetics online on 9 December. doi:10.1038/ng.2478