Research on Decade of MRSA Samples in Irish Hospitals May Help Prepare for Potential Emergence of New MRSA Strains

Posted on: 15 April 2014

Scientists in the School of Dental Science, Trinity College Dublin, the National MRSA Reference Laboratory (NMRSARL) at St. James’s Hospital and Alere Technologies, Germany, have recently published findings that provide new intelligence on the pool of MRSA strains circulating in Irish hospitals over the last decade from which the next dominant MRSA hospital strains of the future may come. The information gathered will assist the researchers in identifying emerging new MRSA strains at an early stage so that clinicians can be well prepared in preventing the spread of the next dominant strain which arises.

Methicillin-resistant Staphylococcus aureus, most commonly known as MRSA, is a major cause of hospital-acquired infection in many countries worldwide. MRSA has been endemic in Irish hospitals for nearly 40 years, during which time particular MRSA strains have dominated for periods of several years and have then been replaced by different MRSA strains. The ST22-MRSA-IV strain has dominated in Irish hospitals since 2002 and since then has accounted for 70-80% of life-threatening MRSA bloodstream infections each year.

The pattern from the last 40 years suggests that the ST22-MRSA-IV strain may be replaced at any time by another strain which would then become the dominant strain in Irish hospitals. However, little was known about the properties of other MRSA strains responsible for infections in Irish hospitals since the rise to predominance of the ST22 strain making pre-planning and advance control measures very difficult.

The microbiologists from the Oral Biosciences Microbiology Unit in the School of Dental Science, Trinity studied a large sample of MRSA that occurred sporadically in patients with bloodstream infections in Irish hospitals between 2000-2012. The researchers revealed that the sporadic MRSA consisted of a myriad of MRSA strains, numerous sub-types and variants. Many of the sporadic MRSA were more resistant to drugs and carried genes that made them particularly virulent and aided their spread between different MRSA samples, which in turn, created further new variants which are more difficult to treat effectively with antibiotics.

Commenting on the significance of the findings, corresponding author on the study Professor David Coleman, Professor and Chair of Oral and Applied Microbiology, School of Dental Science, Trinity said: “This study reveals the presence of a very large number of different MRSA strains in Irish hospitals that sporadically cause infection. Given the history of dominant MRSA strain replacement in Irish hospitals over the last 40 years, any one of these strains may become predominant. Understanding the detailed characteristics of the pool of sporadic MRSA present in Irish hospitals and ongoing surveillance will permit the early identification of emerging new MRSA strains so that appropriate control measures can be put in place to prevent their spread.”

The extensive genetic diversity found among the Irish sporadic MRSA investigated is similar to that previously identified among a large collection of MRSA strains from around the world, indicating that Irish sporadic MRSA is a microcosm of worldwide MRSA and that many have been imported into Ireland from different countries.

The paper has just been published in leading international journal Antimicrobial Agents and Chemotherapy and is available in full here: http://aac.asm.org/content/58/4/1907.full

Co-authors on the study are: Peter Kinnevey BA, PhD, Derek Sullivan BA, PhD and David Coleman, PhD, ScD from the Dublin Dental University Hospital; Anna Shore BSc, PhD and Grainne Brennan BSc, MSc from the Dublin Dental University Hospital and The National MRSA Reference Laboratory; and Stefan Monecke, PhD and Ralf Ehricht, PhD from Alere Technologies, Dresden, Germany.

ENDS