UK MRSA Investigation Network

A bacterium called Staphylococcus aureus is often part of our normal body flora and is harmless for the majority of people, but may sometimes cause infection that ranges in severity from trivial (e.g. boils) to severe (e.g. infection of the heart valves or bones). Staphylococcus aureus is also the leading cause of infections that occur in people after admission to hospital for reasons other than infection. Some strains of Staphylococcus aureus have acquired resistance to an antibiotic (methicillin) that is otherwise the treatment of choice for infection caused by this organism. These methicillin-resistant Staphylococcus aureus (MRSA) are most often found in the hospital setting. Becoming a carrier of MRSA is the forerunner to infection, and development of carriage in a given patient occurs after transmission of the organism from another patient. Hospital infection control aims to prevent spread of these bacteria but can sometimes fail. One way to reveal how bacteria spread and pinpoint where preventive strategies require strengthening is to perform bacterial typing to determine if MRSA affecting two patients are highly related (suggesting that it passed from one person to another) or different. However, this is not straightforward since two particular strains of MRSA have become so successful that they are almost always the culprits (they are called EMRSA-15 and EMRSA-16). Two patients carrying or infected with one of these strains could have acquired it from each other or may have acquired it independently of each other, and current laboratory typing tools are unable to tell the two situations apart. We believe that it is now possible to develop a new generation of typing tools that distinguish between two strains based on the identification of single letter DNA changes in the bacterial genome. The objective of our study is to focus on MRSA strains that are important in the UK. We will undertake whole genome sequencing of numerous isolates each of EMRSA-15 and -16 obtained from across the country. The data generated will be examined to define those genetic differences that would prove most useful for defining clusters within the group. This will form the basis for the development of a new generation of typing technique that we aim to translate into the clinical setting where it will provide the capability to study the spread of MRSA transmission in the UK and beyond in such a way that has previously proved impossible.