Salmonella Typhi Increasingly Resistant to Antibiotics

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Typhoid fever may be rare in developed countries, but this ancient threat, which has been around for thousands of years, is still a huge danger in our modern world. The bacterium that causes typhoid fever, Salmonella enterica serovar Typhi (S Typhi), is developing broad drug resistance and rapidly replacing non-resistant strains, according to new research.

Salmonella Typhi Increasingly Resistant to Antibiotics 1

Currently antibiotics are the only way to effectively treat typhoid fever caused by the bacterium Salmonella enterica serovar Typhi (S Typhi). But over the past three decades, the bacterium’s resistance to oral antibiotics has been growing and spreading. Researchers sequencing the genomes of 3,489 S Typhi strains from 2014 to 2019 in Nepal, Bangladesh, Pakistan and India found a recent increase in drug-resistant (XDR) Typhi.

XDR Typhi is not only resistant to first-class antibiotics such as ampicillin, chloramphenicol and trimethoprim/sulfamethoxazole, but is also becoming resistant to newer antibiotics such as fluoroquinolones and third-generation cephalosporins. Worse, these strains are spreading rapidly globally.

Although most cases of XDR Typhi come from South Asia, researchers have identified nearly 200 cases of international spread since 1990. Worse still, these strains are spreading rapidly globally. Although most cases of XDR Typhi come from South Asia, researchers have identified nearly 200 cases of international spread since 1990.

Most strains have been exported to Southeast Asia as well as East and Southern Africa, but typhoid superbugs have also been found in the United Kingdom, the United States and Canada. “The rate at which highly resistant strains of S. Typhi have emerged and spread in recent years is a real cause for concern and underscores the urgent need to expand prevention measures, particularly in countries at highest risk,” says infectious disease expert Jason Andrews. Scientists have been warning about drug-resistant typhoid for years, but the new research is the largest genome analysis of the bacterium to date. In 2016, the first XDR typhoid strain was identified in Pakistan. By 2019, it had become the dominant genotype in the country.

Historically, most XDR typhoid strains have fought third-generation antimicrobials such as quinolones, cephalosporins and macrolides. But by the early 2000s, mutations conferring resistance to quinolones accounted for more than 85 percent of all cases in Bangladesh, India, Pakistan, Nepal and Singapore. At the same time, cephalosporin resistance was coming into play.

Today there are very few oral antibiotics left that work: macrolides, azithromycin. And these drugs may not last much longer.To prevent this from happening, health experts argue that countries should expand access to typhoid vaccines and invest in research into new antibiotics. A recent study in India, for example, estimates that vaccinating children in urban areas with typhoid vaccine could prevent 36 percent of typhoid cases and deaths.

Pakistan is currently leading the way on this front. It is the first country in the world to offer routine immunization for typhoid. Millions of children were vaccinated last year and health experts argue that more countries should follow suit.


The research was published in The Lancet Microbe.

Ali Esen

Istanbul University, Department of Mathematics. Interested in science and technology.

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