You will all be familiar with the acronym MRSA (Methicillin Resistant Staphylococcus aureus), but you probably won’t be so familar with the methicillin part, unless you are even older than me.

Methicillin was the first semi-synthetic beta-lactam and was manufactured by Beecham and released commercially in 1959. This antibiotic was a marked improvement on the original penicillins such as Penicillin G (benzylpenicillin). Scientists had discovered that by making the side chain of the beta-lactam ring bulkier, the “steric hindrance” produced made the antibiotic more stable to penicillinases. At that time at least 50% already of all Staph aureus isolates produced penicillinase and were thus resistant to straightforward penicillin.

However a major problem with methicillin is that it is poorly absorbed when given orally and it is broken down rapidly by acid in the stomach. In 1961, Beecham released newer penicillinase stable beta-lactams called oxacillin and cloxacillin (flucloxacillin was first used commercially in the early seventies). These newer antibiotics were much more stable when given orally.

And as with all antibiotics, it did not take long before resistance to methicillin in the human population became prevalent. The first Staphylococcus aureus isolate resistant to methicillin (MRSA) was described in 1961 in the UK.

Clinical use of methicillin tapered off during the 1980s and as far as I am aware the antibiotic is no longer available commercially, but the name Methicillin Reistant Staphylococcus aureus continues to this day.

Maybe we should change the name of MRSA to BRSA… The mechanism of resistance in MRSA (mecA gene encoding for altered PBP2a) confers resistance to not just methicillin, but all beta-lactams. For me, the acronym BRSA makes it clear what antibiotics can be excluded for starters in treatment of an MRSA infection.

Michael

p.s. The taxonomical establishment have since changed the name of methicillin to meticillin, for reasons which are best known to themselves….