P. aeruginosa is a widespread soil and water germ, which is found predominantly in damp environments. Since the gram-negative, oxidase-positive rod-shaped bacterium can survive and grow even in the presence of the minutest of traces of organic substances, it is an important nosocomial infection (hospital germ). P. aeruginosa can, as a pathogen, trigger a broad spectrum of symptoms. These include pneumonia, infections from burns and blood poisoning. Alongside acute infections, chronic airway infections also occur in pre-diseased people, for instance in patients with cystic fibrosis (CF), bronchiectasis or chronic obstructive pulmonary disease (COPD). This pathogen is particularly dangerous in that it has the ability to develop resistance against existing antibiotics.

During the past 40 years, particularly in Germany, but also in other European countries, Asia, Australia and North America, more than 6,000 P. aeruginosa isolates have been collected. A team of researchers at BREATH has now genotyped more than 2,800 of these isolates and at the same time studied the second and third most frequent clones in the P. aeruginosa population – ST235 and ST253. ST253 strains are typical Pseudomonas germs, whilst infections with the ST235 pathogens are accompanied by a very high level of mortality. The ST253 strains occurred equally frequently in acute and chronic infections, whilst ST235 was the most frequent clone in acute infections. In those affected by CF and COPD, the ST253 strain has been established as a chronic invasion of the airways for years or even decades, whilst ST235 on the other hand led to only single or short-term colonization. In immunocompetent patients, infections with ST235 strains led to severe eye and urinary tract infections. The ST235 clone was also the most frequent cause of life-threatening burn infections and ventilation-induced pneumonia in intensive care units. 

Studying the clones showed that variations in P. aeruginosa may occur which indicate rare features, genomic mobility and pathogenicity that differ greatly from previous knowledge of this bacterium. The studies on the PAO1 and PA14 strains generated findings on the basic metabolism and regulatory processes of P. aeruginosa, but the results of these studies show that after a short while, clones like ST235 can occur with various specific characteristics. Since some of these clones exhibit higher rates of mortality and stronger resistance against antibiotic therapies, the knowledge provided by the study must be taken into consideration, particularly for those pre-diseased.

The original publication ca be found here: Phenotypic and Genomic Comparison of the Two Most Common ExoU-Positive Pseudomonas aeruginosa Clones, PA14 and ST235.

Text: BREATH/ AB

Photo: MHH/ Figiel