Staphylococcus aureus is a common bacteria (a type of germ) in the nose and on the skin of people and animals.
MRSA, which is a short form of “methicillin-resistant Staphylococcus aureus,” is a specific “staph” bacteria. MRSA is often resistant to (is not killed by) several types of antibiotic treatments. Most S. aureus is methicillin-susceptible (killed by methicillin and most other common treatments). One out of every three people (33%) is estimated to carry staph in their nose, usually without any illness. About two in 100 (2%) carry MRSA
Now researchers have found out that staph is not the original driving factor in the evolution of methicillin-resistant Staphylococcus aureus (MRSA) as previously thought. Still, rather it was the widespread use of antibiotics such as penicillin before the introduction of methicillin.
The adaptations happen because, in response to exposure to earlier antibiotics, resistant bacterial strains are selected instead of non-resistant ones as bacteria evolve.
Staphylococcus aureus acquired the mecA gene, which confers methicillin resistance by producing a protein called penicillin-binding protein 2a (PBP2a) as early as the mid-1940s, about 14 years before the first use of methicillin.
The introduction of penicillin in the 1940s led to the selection of Staphylococcus aureus strains that carried this gene.
When Methicillin was introduced to avoid the penicillin resistance, strains of Staphylococcus aureus were found that were already resistant to methicillin. And in the years that followed, resistance spread rapidly. Now, after coming a long way, we can see multiple MRSA lineages that have emerged and acquired different variants of the resistance gene.
To uncover the origins of the very first MRSA and to trace its evolutionary history, the research team sequenced the genomes of a unique collection of 209 of the earliest MRSA isolates recovered in Europe between 1960 and 1989.
They also found genes in these isolates that confer resistance to numerous other antibiotics, as well as genes associated with decreased susceptibility to disinfectants.
Staphylococcus aureus has proven to develop resistance in the face of new antibiotic challenges, rendering many antibiotics ineffective. This is one of the many challenges in tackling the growing problem of antimicrobial resistance.
To ensure that future antibiotics retain their effectiveness for as long as possible, effective surveillance mechanisms are combined with the use of genome sequencing to scan for the emergence and spread of resistance.