A genetic analysis of dangerous antibiotic-resistant bacteria in a Saudi hospital (King Abdulaziz Medical City) has uncovered new associations between resistance genes and bacterial strains, which are useful for monitoring infections.

A global spread of the multidrug-resistant Klebsiella pneumoniae (K. pneumonia) is a pressing healthcare concern. K. pneumoniae are bacteria that live in the intestines and faeces, and that are usually harmless unless they spread to other parts of the body through human contact. An infected person can develop severe infections in the lungs, bladder, brain, liver, eyes, blood or open wounds. The risk of infection is higher when a person is sick, which makes it especially difficult to control in hospitals, where patients have a weaker immune system. Another risk factor for contracting infection is long-term antibiotic use, a common problem throughout the world, but especially in the Arab world.

In Saudi Arabia, K. pneumoniae is one of the most challenging pathogens to control in hospital-acquired infections of the urinary tract, respiratory tract and bloodstream. It is becoming resistant to antibiotics, including carbapenems, which are considered last-line antibiotics against superbugs.

Researchers at King Abdulaziz Medical City collected 71 samples from patients in 2011-2012. All samples of the bacteria studied were resistant to more than three types of antibiotics, and genetic analysis revealed the genes responsible for such antibiotics resistance. Among the genes that provide resistance to carbapenems, the researchers identified OXA-48 as the most prevalent, present in 67.6 percent of the sample studied, followed by NDM-1, present in 12.7 percent of the isolates. Around 8.5 percent of the samples carried both genes, and 11.2 percent had neither of the two genes. Remarkably, none of the samples carried one of the most prevalent carbapenem-resistance genes in the US and other countries (K.pneumoniae carbapenemases).

Further analysis classified these bacteria samples into 18 genetic profiles, known as sequence types (STs), and showed new correlations between some resistance genes and some sequence types. For example, all samples belonging to the most abundant sequence type (ST-199) were positive for the OXA-48 gene, but not NDM-1. The study also showed that the samples belonging to the ST-152 are a rare subspecies of K. pneumoniae called ozaenae, and are frequent carriers of the NDM-1 gene. This the first report to describe the presence of NDM-1 gene in this subspecies.   

The researchers also identified the mobile pieces of DNA that allow bacteria to acquire and exchange antibiotic-resistance genes. By looking at the factors that aid bacterial growth and invasion, the scientists also found that the samples may not have been hypervirulent, (variants linked to more aggressive type of infection) supporting the idea that antibiotic resistance and hypervirulence are independent of each other.  

Since bacteria with certain genetic profiles are more prone to acquire multi-drug resistance, keeping track of correlations between resistance genes, the DNA responsible for acquiring and exchanging that gene, and strains could help monitor this phenomenon to combat superbugs. 

References