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An Anonymous Coward writes:

Dr. Lowe, from In the Pipeline, writes about the origins of MRSA (Methicillin-resistant Staphylococcus aureus), a type of multi-drug resistant bacteria that is responsible for approximately 11,000 deaths in the US:

OK, everyone recognizes the problem that we face with drug-resistant bacteria. MRSA (methicillin-resistant Staphylococcus aureus) is the most well-known variety, and it’s bad news. Penicillin was introduced in the 1940s, and methicillin was brought to market in 1959, largely because so many infections were becoming resistant to penicillin by then. The first methicillin-resistant strains were noted in the early 1960s, which would seem to make the story pretty clear.

But it isn’t. [...] MRSA bacteria actually predate the introduction of methicillin. So does that mean that they aren’t a product of antibiotic use? Not at all – it’s just that the antibiotic that brought them on was penicillin, not methicillin.

From the primary research:

It therefore appears that the first MRSA clone emerged, and developed resistance to two of the earliest antibiotics—streptomycin and penicillin—almost immediately after the S. aureus population would have been first exposed to them.

At the time of its discovery, the incidence of MRSA in the general population is likely to have been very low. This is demonstrated by the fact that screening of over 5000 samples at Public Health England yielded only three methicillin-resistant isolates. Therefore, it is likely that when methicillin was introduced to circumvent penicillin resistance in S. aureus, it did not select for emergence of MRSA at that time, but instead provided the selective pressure, which drove the nosocomial spread of a pre-existing variant, at a time when infection control measures in UK hospitals were limited.

Nosocomial spread: hospital-acquired infection or spread of infections within a hospital.

Blog Post: http://blogs.sciencemag.org/pipeline/archives/2017/08/07/where-mrsa-came-from [sciencemag.org]
Scientific Paper: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5517843/ [nih.gov]
MRSA: https://en.wikipedia.org/wiki/Methicillin-resistant_Staphylococcus_aureus [wikipedia.org]

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