Diversity of E. Coli Create a Complex View of Bloodstream Infections in Superbugs Study

New data from a study conducted by the Wellcome Trust Sanger Institute suggests that drug-resistant “superbugs” are not necessarily out-competing other strains. The UK-based study is the first large-scale genetic study of Escherichia coli (E. coli). The study was conducted by using samples of E. coli collected from patients with long-term bloodstream infections of more than 10 years, both antibiotic-susceptible and antibiotic-resistant strains.

Results from the study, published in Genome Research, indicate that bloodstream infections were caused by over 200 different strains of E. coli. The bacteria are commonly found in human digestive tracts and are the predominant source of infections in the blood stream. New strains of E. coli were found to emerge over time, but rather than continuously rising, the strains tapered off reaching a balance with other strains.

The researchers in this study chose to use a collection of 1509 E. coli, predominately collected by the British Society of Antimicrobial Chemotherapy Bacteremia Surveillance program, to shift away from only studying drug-resistant strains, like the superbug strain ST131. From the data, it was discovered that ST131 surfaced in England in 2002, quickly balancing with other strains. Simultaneously, strain ST69, a non-drug-resistant strain evolved and quickly leveled off with other strains.

Dr. Sharon Peacock, MRCP, PhD, a professor of clinical microbiology at the London School of Hygiene & Tropical Medicine said in a press release, “The reason for this equilibrium may relate to the fact that all bacteria are constantly competing with others to survive in places where they are carried, such as the gut."

Despite the detection of 228 different strains of E. coli in the collection, 5 strains dominated more than half of the total population. The most popular strain, ST73, which is an antibiotic-susceptible strain, followed by the multidrug-resistant strain ST131. From this information, the researchers determined that the various types of genes each strain carried were a predisposition to their overall success. Some of the strongest genes endowed the bacterium to either survive in digestive tracts, or eliminate adversaries by cutting off their resources or killing them.

In addition to E. coli, methicillin-resistant Staphylococcus aureus (MRSA) also causes hospital-acquired infections and is transmitted from person to person. MRSA is multidrug-resistant, but lacks the diversity of E. coli, with only 1 principle strain active at a given time. To avoid MRSA, it has been proven beneficial to limit the number of hospital transmissions. This provides possible future areas of study for reducing blood infections caused by E. coli.