From St. Andrews: “MRSA emerged years before methicillin was even discovered”

U St Andrews bloc

University of St Andrews

20 July 2017
Christine Tudhope
01334 467 320
07526 624 243 or
christine.tudhope@st-andrews.ac.uk

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Methicillin resistant Staphylococcus aureus (MRSA) emerged long before the introduction of the antibiotic methicillin into clinical practice, according to researchers at the University of St Andrews.

A new study, in collaboration with the Wellcome Trust Sanger Institute and the University of Dundee, suggests the widespread use of earlier antibiotics such as penicillin rather than of methicillin itself allowed Methicillin resistant Staphylococcus aureus (MRSA) to emerge.

The findings, published in the open access journal Genome Biology, found that S. aureus acquired the gene that confers methicillin resistance (mecA) as early as the mid-1940s, fourteen years before the first use of methicillin.

Professor Matthew Holden, molecular microbiologist at the University of St Andrews, the corresponding author said:

“Our study provides important lessons for future efforts to combat antibiotic resistance. It shows that new drugs which are introduced to circumvent known resistance mechanisms, as methicillin was in 1959, can be rendered ineffective by unrecognized, pre-existing adaptations in the bacterial population. These adaptations happen because, in response to exposure to earlier antibiotics, resistant bacterial strains are selected instead of non-resistant ones as bacteria evolve.”

The mecA gene confers resistance by producing a protein called PBP2a, which decreases the binding efficiency of antibiotics used against S. aureus to the bacterial cell wall. The introduction of penicillin in the 1940s led to the selection of S. aureus strains that carried the methicillin resistance gene.

Dr Catriona Harkins, clinical lecturer in dermatology at the University of Dundee, the first author of the study said:

“Within a year of methicillin being first introduced to circumvent penicillin resistance, strains of S. aureus were found that were already resistant to methicillin. In the years that followed resistance spread rapidly in and outside of the UK. Five decades on from the appearance of the first MRSA, multiple MRSA lineages have emerged which have acquired different variants of the resistance gene.”

To uncover the origins of the very first MRSA and to trace its evolutionary history, the researchers sequenced the genomes of a unique collection of 209 historic S. aureus isolates. The oldest of these isolates were identified over 50 years ago by the S. aureus reference laboratory of Public Health England and have been stored ever since in their original freeze-dried state. The researchers also found genes in these isolates that confer resistance to numerous other antibiotics, as well as genes associated with decreased susceptibility to disinfectants.

Professor Holden said:

“S. aureus has proven to be particularly adept at developing resistance in the face of new antibiotic challenges, rendering many antibiotics ineffective. This remains one of the many challenges in tackling the growing problem of antimicrobial resistance. In order to ensure that future antibiotics retain their effectiveness for as long as possible, it is essential that effective surveillance mechanisms are combined with the use of genome sequencing to scan for the emergence and spread of resistance.”

Science paper:
Methicillin-resistant Staphylococcus aureus emerged long before the introduction of methicillin into clinical practice.

See the full article here .

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St Andrews is made up from a variety of institutions, including three constituent colleges (United College, St Mary’s College, and St Leonard’s College) and 18 academic schools organised into four faculties. The university occupies historic and modern buildings located throughout the town. The academic year is divided into two terms, Martinmas and Candlemas. In term time, over one-third of the town’s population is either a staff member or student of the university. The student body is notably diverse: over 120 nationalities are represented with over 45% of its intake from countries outside the UK; about one-eighth of the students are from the rest of the EU and the remaining third are from overseas — 15% from North America alone. The university’s sport teams compete in BUCS competitions, and the student body is known for preserving ancient traditions such as Raisin Weekend, May Dip, and the wearing of distinctive academic dress.

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