London, Jan 12 : Researchers have, for the first time, analysed the impact of antibiotic use on the rise of treatment-resistant bacteria over the last 20 years in the UK and Norway, saying that while the increase in drug use has amplified the spread of superbugs, it is not the only trigger. Researchers from the Wellcome Sanger Institute, the University of Oslo, the University of Cambridge, and collaborators, conducted a high-resolution genetic comparison of bacteria. They compared over 700 new blood samples with nearly 5,000 previously sequenced bacterial samples to answer questions about what factors influence the spread of antibiotic-resistant Escherichia coli (E. coli). The study, published in the Lancet Microbe, showed that greater antibiotic use does drive an increase in treatment-resistant bacteria in some instances. However, researchers confirmed that this varies depending on the type of broad-spectrum antibiotic used. They also found that the success of antibiotic-resistance genes depends on the genetic makeup of the bacteria carrying them. Dr Anna Pontinen from the University of Oslo, and visiting scientist at the Wellcome Sanger Institute, said that the study allowed them to start to answer some of the long-standing questions about what causes multidrug-resistant bacteria in a population. This study is the first time it has been possible to directly compare the success of the different strains of E. coli between two countries ' Norway and the UK ' and explain differences based on country-wide antibiotic usage levels. By analysing data that spanned almost 20 years, they found that the use of antibiotics was linked to increased resistance in some instances, depending on the type of antibiotic. One class of antibiotics, non-penicillin beta-lactams, were used three to five times more, on average, per person in the UK compared to Norway. This has led to a higher incidence of infections by a certain multi-drug resistant E. coli strain. However, the UK also uses the antibiotic trimethoprim more often, but analysis did not uncover higher levels of resistance in the UK when comparing the common E. coli strains found in both countries. The study found that the survival of MDR bacteria depended on what strains of E. coli were in the surrounding environment. Due to this and other selective pressures in an area, researchers concluded that it is not possible to assume that the widespread use of one type of antibiotic will have the same effect on antibiotic-resistant bacteria spread in different countries. "Our study suggests that antibiotics are modulating factors in the success of antibiotic-resistant E. coli, instead of the only cause," said Professor Julian Parkhill, co-author from the University of Cambridge. /IANS