Swedish researchers have identified a new vaccine candidate against pneumococci bacteria that can cause pneumonia, sepsis and meningitis.

The vaccine molecules comprise nano-sized membrane vesicles produced by the bacteria and provide protection in an experimental model, according to the study published in the journal PNAS.

Researchers at Karolinska Institutet examined the possibility of developing a vaccine based on nano-sized membrane vesicles that pneumococcal bacteria naturally produce from their cell membrane in order to communicate with their surroundings and affect other cells. These vesicles contain proteins that help the bacteria to evade the host immune system.

The team isolated such vesicles, called membrane particles, from cultivated pneumococcal bacteria. They found that immunisation with these membrane vesicles protected experimental subjects from getting severe infections with pneumococci.

Moreover, the subjects developed protection not only against the pneumococcal strain/type from which the particles were isolated but also against other pneumococcal strains/types. The researchers also identified two proteins in the membrane particles, MalX and PrsA, both of which are essential for the main protective effect.

"Our vaccine candidate - membrane particles containing both these proteins - provide protection regardless of pneumococcal type," said Birgitta Henriques-Normark, Professor at the Department of Microbiology, Tumor and Cell Biology, at the Karolinska Institutet.

"The results suggest that membrane particles can be used as a platform for producing vaccines against pneumococcal infections and perhaps other bacterial infections, and this is something we are now working on," Henriques-Normark added.

The pneumococcus (also known as Streptococcus pneumoniae) is the most common cause of ear and sinus infection, but also a major contributor to more severe diseases such as pneumonia, sepsis (blood poisoning) and meningitis. Pneumococcal infections mainly affect children below the age of two and the elderly and claim almost two million lives globally every year.

The researchers noted that since childhood vaccination was introduced, the incidence of severe pneumococcal infections in infants has decreased, but the effect has not been observed in adults.

"There is an urgent need for new vaccine strategies to protect the elderly from pneumococcal infections," Henriques-Normark said. "The number of severe pneumococcal infections in adults has not decreased significantly and most of the infections are now caused by pneumococcal bacteria that today's vaccines do not protect against."