Abstract
Pseudomonas aeruginosa (P. aeruginosa) possesses a plethora of virulence determinants, including the production of biofilm, pigments, exotoxins, proteases, flagella, and secretion systems. The aim of our present study was to establish the relationship between biofilm-forming capacity, the expression of some important virulence factors, and the multidrug-resistant (MDR) phenotype in P. aeruginosa. A total of three hundred and two (n = 302) isolates were included in this study. Antimicrobial susceptibility testing and phenotypic detection of resistance determinants were carried out; based on these results, isolates were grouped into distinct resistotypes and multiple antibiotic resistance (MAR) indices were calculated. The capacity of isolates to produce biofilm was assessed using a crystal violet microtiter-plate based method. Motility (swimming, swarming, and twitching) and pigment-production (pyoverdine and pyocyanin) were also measured. Pearson correlation coefficients (r) were calculated to determine for antimicrobial resistance, biofilm-formation, and expression of other virulence factors. Resistance rates were the highest for ceftazidime (56.95%; n = 172), levofloxacin (54.97%; n = 166), and ciprofloxacin (54.64%; n = 159), while lowest for colistin (1.66%; n = 5); 44.04% (n = 133) of isolates were classified as MDR. 19.87% (n = 60), 20.86% (n = 63) and 59.27% (n = 179) were classified as weak, moderate, and strong biofilm producers, respectively. With the exception of pyocyanin production (0.371 ± 0.193 vs. non-MDR: 0.319 ± 0.191; p = 0.018), MDR and non-MDR isolates did not show significant differences in expression of virulence factors. Additionally, no relevant correlations were seen between the rate of biofilm formation, pigment production, or motility. Data on interplay between the presence and mechanisms of drug resistance with those of biofilm formation and virulence is crucial to address chronic bacterial infections and to provide strategies for their management.
Highlights
No relevant correlations were seen between the rate of biofilm formation, pigment production, or motility
Pseudomonas aeruginosa (P. aeruginosa) is a motile, non-fermenting Gram-negative bacillus with non-fastidious growth requirements, which is ubiquitous in various aquatic environments, in addition to being commonly involved in healthcare-associated infections (HAIs) [1,2]
The antimicrobial resistance levels of the P. aeruginosa isolates included in the study were the following: CAZ 56.95% (n = 172), LEV 54.97% (n = 166), CIP 52.64% (n = 159), FEP 49.34% (n = 149), GEN 33.77% (n = 102), AMI 25.82% (n = 78), MER 23.17% (n = 70), IMI 21.19% (n = 64), and COL 1.66% (n = 5; minimum inhibitory concentrations (MICs) > 2 mg/L); overall, 44.04% (n = 133)
Summary
Pseudomonas aeruginosa (P. aeruginosa) is a motile, non-fermenting Gram-negative bacillus with non-fastidious growth requirements, which is ubiquitous in various aquatic environments, in addition to being commonly involved in healthcare-associated infections (HAIs) [1,2]. P. aeruginosa is considered as an opportunistic pathogen (8–20% of hospitalized individuals are colonized), as it is more commonly found in patients affected by invasive surgical interventions, immunosuppression (associated with malignancies and their treatment, HIV infection), or other underlying diseases (e.g., diabetes) [3,4,5]. This microorganism has been associated with a wide variety of hard-to-treat infections, such as ventilator-associated pneumonia (VAP), sepsis, skin and soft tissue infections (linked to burn injuries or pressure ulcers), bone and joint infections, otitis externa, and keratitis [6,7]; in addition, multisite infections are fairly common. In addition to persister (or small colony variant; SCV) formation, the chemical composition of biofilms inhibits the diffusion of antimicrobials (acting as a pharmacokinetic barrier to these drugs) and disinfectants/biocides [15]
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