Salmonella responsible for serious infections are gradually becoming less sensitive to several antibiotics used to combat them.
Researchers analyzed the genetic makeup of 7,691 Salmonella samples from 77 countries. These bacteria were collected between 1954 and 2024. All were associated with so-called invasive infections. In such cases, the bacteria leave the intestine and normally reach sterile areas, particularly the bloodstream.
A colorized scanning electron micrograph showing Salmonella Typhimurium, in red, in contact with cultured human cells.
Credit: Rocky Mountain Laboratories, NIAID, NIH. Public domain.
To understand their resistance, the team searched their DNA for genes capable of protecting the bacteria against certain drugs. They also compared these genetic data with the results of laboratory tests. This approach makes it possible to track the emergence and spread of resistance over several decades.
The results concern several important treatments. About 7.39% of the samples showed resistance or reduced susceptibility to ciprofloxacin. For third-generation cephalosporins, this proportion reached 7.91%. Fosfomycin resistance concerned 4.23% of the samples, compared with 0.79% for azithromycin.
This study primarily serves to identify global trends in the bacteria that were analyzed.
However, several trends are increasing over time. The researchers observed a worldwide rise in resistance to azithromycin. They also found more resistance or reduced susceptibility to ciprofloxacin and several cephalosporins. Some genetic mechanisms can therefore spread across different bacterial lineages.
In practical terms, a resistant bacterium can continue multiplying despite an antibiotic that should normally kill it or stop its growth. Doctors then have fewer effective treatments available. This situation becomes particularly important during an invasive infection, which requires more extensive care.
The global map nevertheless remains very incomplete. The available data are significantly scarcer in several regions of Africa and South America. The authors therefore call for increased sequencing and data sharing in regions that are still poorly monitored.
This genetic surveillance can also detect the arrival of a new resistance mechanism in a region more quickly.