Molecular epidemiology of pseudomonas aeruginosa clinical isolates from Portuguese Central Hospital

Catheter-related infections caused by Pseudomonas aeruginosa: virulence factors involved and their relationships

The nosocomial pathogen Pseudomonas aeruginosa is equipped with a large arsenal of cell-associated and secreted virulence factors which enhance its invasive potential. The complex relationships among virulence determinants have hitherto not been fully elucidated. In the present study, 175 catheter-related isolates were observed for the presence of selected virulence factors, namely extracellular enzymes and siderophore production, biofilm formation, resistance to antibiotics, and motility. A high percentage of the strains produced most of the tested virulence factors. A positive correlation was identified between the production of several exoproducts, and also between the formation of both types of biofilm. An opposite trend was observed between the two types of biofilm and the production of siderophores. Whereas the relationship between the submerged biofilm production (i.e. the biofilm formed on the solid surface below the water level) and the siderophore secretion was negative, the production of air-liquid interface (A-L) biofilm (i.e. the biofilm floating on the surface of the cultivation medium) and the siderophore secretion were positively correlated. All correlations were statistically significant at the level P = 0.05 with the correlation coefficient γ ≥ 0.50. Our results suggest that: (1) the co-production of the lytic enzymes and siderophores can play an important role in the pathogenesis of the catheter-related infections and should be taken into account when the virulence potential is assessed; (2) biofilm-positive strains are capable of forming both submerged and non-attached A-L biofilms; and (3) the different micro-environment in the submerged biofilm and A-L biofilm layers have opposite consequences for the production of other virulence factors.

Pseudomonas aeruginosa serotypes in nosocomial pneumonia: prevalence and clinical outcomes

INTRODUCTION

Pseudomonas aeruginosa frequently causes nosocomial pneumonia and is associated with poor outcome. The purpose of this study was to assess the prevalence and clinical outcome of nosocomial pneumonia caused by serotype-specific P. aeruginosa in critically ill patients under appropriate antimicrobial therapy management.

METHODS

A retrospective, non-interventional epidemiological multicenter cohort study involving 143 patients with confirmed nosocomial pneumonia caused by P. aeruginosa. Patients were analyzed for a period of 30 days from time of nosocomial pneumonia onset. Fourteen patients fulfilling the same criteria from a phase IIa studyconducted at the same time/centers were included in the prevalence calculations but not in the clinical outcome analysis.

RESULTS

The prevalence of serotypes was: O6 (29%), O11 (23%), O10 (10%), O2 (9%), and O1 (8%). Serotypes with a prevalence of less than 5% were found in 13% of patients, 8% were classified as not typeable. Across all serotypes, 19% mortality, 70% clinical resolution, 11% clinical continuation, and 5% clinical recurrence were recorded. Age and higher APACHE II (Acute Physiology and Chronic Health Evaluation II) were predictive risk factors associated with probability of death and lower clinical resolution for P. aeruginosa nosocomial pneumonia. Mortality tends to be higher with O1 (40%) and lower with O2 (0%); clinical resolution tends to be better with O2 (82%) compared to other serotypes. Persisting pneumonia with O6 and O11 was, respectively, 8% and 21%; clinical resolution with O6 and O11 was, respectively, 75% and 57%.

CONCLUSIONS

In P. aeruginosa nosocomial pneumonia, the most prevalent serotypes were O6 and O11. Further studies including larger group sizes are needed to correlate clinical outcome with virulence factors of P. aeruginosa in patients with nosocomial pneumonia caused by various serotypes; and to compare O6 and O11, the two serotypes most frequently encountered in critically ill patients.