New, Targeted Test for Colistin-Resistant Enterobacter Species
The new assay accounts for “heteroresistance,” providing accurate colistin resistance results
A study conducted by a team of researchers from the German Center for Infection Research, Justus Liebig University Giessen Institute of Microbiology and Molecular Biology, and Research Center Borstel–Leibniz Lung Center has achieved a breakthrough in understanding the spread of antibiotic resistance in Enterobacter species, which cause many nosocomial infections that are difficult to treat.
Since some species are highly resistant to commonly used antibiotics, clinicians resort to the reserve antibiotic, colistin, or polymyxin E, to treat Enterobacter infections. But due to imprecise taxonomic classification and high error rate, currently used microbiological tests for colistin resistance are unable to detect and drive the prognosis accurately.
So, the researchers analyzed Enterobacter isolates collected at German university hospitals over a period of three years. Using mass spectrometry, the team detected species-specific variations in lipid A—the anchor structure of lipopolysaccharides (LPS) in the bacterial membrane—a crucial factor in colistin resistance. They also found that the expression of these inherent variations is complex and not just triggered by the presence of colistin.
“Our analyses revealed that these bacteria have a sensor on their surface that responds to the pH value, i.e., the acidity in the environment, and regulates accordingly, either up or down, the genes required for the expression of colistin resistance," said Trinad Chakraborty, professor, former director of the Institute of Medical Microbiology at Justus Liebig University Giessen, and senior author, in a recent press release.
Thus, differences in the pH of conventional tests can affect the extent of colistin resistance in various Enterobacter species, leading to inaccurate results.
These findings led the team to develop a new, robust assay that can identify actual levels of colistin resistance in Enterobacter isolates. Accurate colistin resistance results could further help clinicians avoid treatment failures when prescribing colistin, leading to targeted and cost-effective treatment options for nosocomial infections.