Polyagglutinable Pseudomonas aeruginosa from cystic fibrosis patients. A survey

Abstract

Chronic Pseudomonas aeruginosa lung infection is responsible for most of the mortallity and morbility observed in cystic fibrosis patients. During the course of the disease, the bacteria change from being O-serogroup typable (monoagglutinable), non-mucoid, resistant to normal human serum and motile, to become O-serogroup non-typable (polyagglutinable), serum-sensitive and non-motile. In spite of high levels of antibodies produced by the patient, and intensive antibiotic therapy it is not possible to eradiate the polyagglutinable bacteria from the lungs of the patients. The bacteria will reappear and it is not fully understood if it is the same strain which reappears, or it is a super-infection with a new strain which takes place. A reliable and stable typing method is needed to clarify this question. In the present study, the conventional typing methods, such as serotyping, phage typing and pyocin typing were compared with the newer DNA typing methods, such as, restriction fragment length polymorphism (RFLP) in combination with pulsed field gel electrophoresis (PFGE) and typing with a specific DNA probe. Typability, reproducibility and discriminatory power using the different typing methods were investigated. The conventional typing methods have proved to be adequate when typing P. aeruginosa isolates from non cystic fibrosis sources, but because the majority of cystic fibrosis P. aeruginosa isolates are polyagglutinable or non typable, serotyping is not useful. Phage typing also lacks discriminatory power as it lumps up to 40% of the isolates in the same phage group. Pyocin typing has the disadvantage of low reproducibility. Most of the conventional typing methods are based on receptors on the bacterial surface, which on exposure to the environmental conditions in the lung, are likely to provoke phenotypic changes of the bacteria. The obvious advantage of the newer DNA typing methods is that these methods are based on internal properties of the bacteria, as part of the bacterial genome is investigated. The present study has revealed that for the time being, restriction fragment length polymorphism (RFLP) and pulsed field gel electrophoresis (PFGE) in combination with phage typing is the best method of typing P. aeruginosa isolates from cystic fibrosis patients for epidemiological purposes.