engleski

In vitro effect of subMICs of antibiotics on the antigenic structure of Pseudomonas aeruginosa strains isolated from patients with cystic fibrosis

Objectives: Pseudomonas aeruginosa is the leading pathogen responsible for morbidity and mortality in patients with cystic fibrosis (CF), and is the primary reason for the reduced survival age. Different molecules are responsible for P. aeruginosa virulence, including lipopolysaccharide (LPS) as a cellular component. Suppresion or modulation of P. aeruginosa virulence factors may be an alternative strategy for treatment of lung infections in CF. The aim of this study was to examine the influence of subminimal inhibitory concentrations (subMICs) of ceftazidime and ciprofloxacin on the LPS structure of P. aeruginosa strains isolated from patients with CF. Methods: A total of 20 strains isolated from sputa of patients with CF were used. Serotyping based on the detection of heat stable LPS bacterial surface antigens (O-antigens) was performed as slide agglutination tests using O-specific polyclonal sera and a suspension of live bacterial isolate to be examined, according to the International Antigenic Typing System. Serotyping was performed before and after exposure of strains to 1/2, 1/4, 1/8, 1/16, and 1/32 MIC of antibiotics. Results: The slide agglutination test with polyclonal diagnostic sera showed that only nine strains were typable, while six strains were polyagglutinable, three strains were non-typable, and two strains were auto-agglutinable. After the exposure of strains in exponential phase of their growth to subMICs of antibiotics, a significant difference in typeability of the strains were observed. Treatment with subMICs of ceftazidime and ciprofloxacin resulted in the alteration of polysaccharide structure of typable strains. Out of nine monoagglutinable strains, seven strains have become auto-agglutinable after exposure to 1/2, 1/4, 1/8 and 1/16 MIC of ceftazidime, while two strains have become polyagglutinable, suggesting the loss of most of the O-antigenic determinants of the LPS. The polyagglutinability was observed more frequently after exposure of those strains to 1/2, 1/4 and 1/8 MIC of ciprofloxacin (five out of nine strains). The non-typable strains have become auto-agglutinab le or polyagglutinable, depending on the concentration of antibiotic. Conclusion: The results of this study have shown that the antigenic structure of P. aeruginosa strains isolated from sputa of patients with CF was significantly changed after in vitro exposure to subMICs of ceftazidime and ciprofloxacin, due to the loss of O-antigenic determinants.

Pseudomonas aeruginosa ; cystic fibrosis ; antibiotics ; subinhibitory concentrations ; lipopolysaccharide

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