Antibiotic Resistance: An Unexpected Chronology

Researchers from the Institut Pasteur have shed light on the rise of ampicillin resistance back in the 60s. Through the genome sampling of historical Salmonella strains, they proved that antibiotic resistance can be traced back prior to the release of ampicillin on the UK market. As such, their discovery suggests that low doses of penicillin routinely fed to livestock in the 1950s in North America and Europe may have encouraged antibiotic-resistant bacteria to evolve and spread. These results will be published in The Lancet Infectious Diseases on Wednesday, November 29th.

Antibiotic resistance kills around 25,000 people a year in Europe, and this is predicted to rise to over 10 million people worldwide by 2050. Many bacteria that cause serious infections humans like Salmonella, have already developed resistance to common antibiotics.

Ampicillin, one of the most commonly used antibiotics today and the first broad-spectrum penicillin for the treatment of infections due to Enterobacteria(1), was released on European markets at the start of the sixties, notably on the UK market in 1961. Shortly after (in 1962-1964), the first outbreaks of disease in humans caused by ampicillin-resistant strains of the common zoonotic (which cause disease that can be spread between animals and humans) bacterium, Salmonella Typhimurium, were identified in this country.

This short timeline prompted the researchers at the Institut Pasteur to investigate the emergence of ampicillin resistance. They found that bacteria that can pass on genes resistant to ampicillin emerged several years before the widespread use of this antibiotic in humans.

In this study, they tested 288 historical samples of S. Typhimurium bacteria collected from humans, animals, and food and feed in Europe, Asia, Africa, and America between 1911 and 1969. Samples were tested for antibiotic susceptibility and were analysed by whole genome sequencing, in order to identify the mechanisms of resistance to ampicillin.

Hence, molecular analysis suggests that the ampicillin resistance gene (blaTEM-1) emerged in Salmonella, several years before the antibiotic was released onto the pharmaceutical market. The findings also indicate that a possible cause was the common practice of adding low doses of narrow-spectrum penicillin G (also known as benzylpenicillin) to animal feed in the 1950s and 60s.

“Our findings suggest that antibiotic residues in farming environments such as soil, waste water, and manure may have a…

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