Pseudomonas aeruginosais one of the leading nosocomial pathogens worldwide. Nosocomial infections caused by this organism are often hard to treat because of both the intrinsic resistance of the species (it has constitutive expression of AmpCβ-lactamase and efflux pumps, combined with a low permeability of the outer membrane), and its remarkable ability to acquire further resistance mechanisms to multiple groups of antimicrobial agents, includingβ-lactams, aminoglycosides and fluoroquinolones.P. aeruginosarepresents a phenomenon of bacterial resistance, since practically all known mechanisms of antimicrobial resistance can be seen in it: derepression of chromosomal AmpC cephalosporinase; production of plasmid or integron-mediatedβ-lactamases from different molecular classes (carbenicillinases and extended-spectrumβ-lactamases belonging to class A, class D oxacillinases and class B carbapenem-hydrolysing enzymes); diminished outer membrane permeability (loss of OprD proteins); overexpression of active efflux systems with wide substrate profiles; synthesis of aminoglycoside-modifying enzymes (phosphoryltransferases, acetyltransferases and adenylyltransferases); and structural alterations of topoisomerases II and IV determining quinolone resistance. Worryingly, these mechanisms are often present simultaneously, thereby conferring multiresistant phenotypes. This review describes the known resistance mechanisms inP. aeruginosato the most frequently administrated antipseudomonal antibiotics:β-lactams, aminoglycosides and fluoroquinolones.

To evaluate the prevalence of some virulence genes among 510 clinical Enterococcus spp. isolates and to assess the association of those genes with the species, infection site, and patient group (inpatients/outpatients). Adhesins genes (aggregation substances agg and asa1 of Enterococcus faecalis and Enterococcus faecium, respectively), enterococcal surface protein (esp), endocarditis-specific antigen A (efaA), collagen-binding proteins (ace/acm)); invasins (hyaluronidase (hyl) and gelatinase (gelE)); cytotoxines (activation of cytolysin (cylA) in E. faecalis); and modulators of the host immunity and inflammation (enhanced expression pheromone (eep) in E. faecalis) were detected by polymerase chain reaction. The overall prevalence was: esp - 44.3%, agg/asa1 - 38.4%, ace/acm - 64.3%, efaA - 85.9%, eep - 69.4%, gelE - 64.3%, hyl - 25.1%, and cylA - 47.1%. E. faecalis isolates had significantly higher frequency of adhesin genes (esp and agg/asa1) and gelatinase in comparison to E. faecium. Multiple virulence genes in E. faecalis were significantly more prevalent than in E. faecium isolates. Domination of E. faecium with or without only one gene compared to the isolates of E. faecalis were found. Enterococcus spp. isolates obtained from outpatients compared to inpatients isolates had significantly higher frequency of agg/asa1, eep, gelE and cylA. Some adhesins genes (esp, agg/asa1 and efaA) had higher prevalence among the non-invasive Enterococcus spp. isolates compared to those causing invasive bacteremia, while ace/acm revealed higher dissemination in isolates causing invasive infections compared to non-invasive isolates. Most E. faecalis attaches to abiotic surfaces in hospital environment, which correlates with higher prevalence of gene encoding for virulence factors involved in biofilm formation, such as enterococcal surface protein, aggregation substance, and gelatinase. The intestinal tract is an important reservoir for opportunistic enterococcal pathogens and allows them to access infectious sites through different virulence factors, demonstrated in outpatient isolates in this study.

The aim of this study was to evaluate the prevalence of some virulence genes among 202 Pseudomonas aeruginosa isolates from cystic fibrosis (CF) patients (n=42) and non-CF in-patients (n=160) and to analyze the values according to the patient groups, infection localization and antimicrobial resistance. The following frequencies in all studied strains were established: algD (encoding GDP-mannose 6-dehydrogenase AlgD) - 91.1%, pilB (type IV fimbrial biogenesis protein PilB) - 23.8%, nan1 (neuraminidase) - 21.3%, lasB (elastase LasB) - 100%, plcH (haemolytic phospholipase C precursor) - 91.6%, exoS (exoenzyme S) - 62.4%, and exoU (exoenzyme U) - 30.2%. The prevalence of nan1 was significantly higher (P<0.01) in CF isolates (38.1%) than that in non-CF isolates (16.9%). The nan1-positive CF strains were cultured from 16 patients with recurrent lung exacerbations. This study revealed a statistically significant difference (P<0.01) between the portion of multidrug-resistant (MDR) nosocomial P. aeruginosa strains containing a large number (≥5) of virulence genes (38.1%) and the respective part of non-MDR isolates (17.6%). Moreover, pilB, exoU and nan1 manifested a higher spread (P<0.001) among MDR than in non-MDR strains (respectively, 39.1% vs. 13.2%; 40.2% vs. 17.7% and 26.1% vs. 4.4%). In conclusion, the dissemination of nan1 in CF isolates was moderate and correlated with the lower proportion of patients with lung exacerbations. The molecular-genetic detection of this gene may be used as an indirect measure of CF pulmonary disease evolution. Simultaneous determination of virulence factors and antimicrobial resistance is the contemporary approach for examination of the microbiological aspects of infections caused by P. aeruginosa.

Cystic fibrosis (CF) is a life-limiting autosomal recessive disorder affecting a large number of individuals in Europe. The disease arises from mutations in the CFTR gene encoding the cystic fibrosis transmembrane conductance regulator, a chloride ion channel crucial for maintaining epithelial ion and fluid homeostasis. Dysfunctional CFTR disrupts mucociliary clearance, particularly in the respiratory tract, resulting in persistent bacterial colonization, chronic inflammation, and progressive pulmonary damage—ultimately leading to respiratory failure, the principal cause of mortality in CF patients. Early diagnosis and advances in therapy have substantially improved both survival and quality of life. A hallmark of CF pathology is the establishment of polymicrobial infections within the thickened airway mucus. Pseudomonas aeruginosa is the dominant pathogen in chronic CF lung infections and demonstrates a remarkable capacity for adaptation via biofilm formation, metabolic reprogramming, and immune evasion. Biofilms confer increased tolerance to antimicrobial agents and facilitate long-term persistence in hypoxic, nutrient-limited microenvironments. P. aeruginosa exhibits a wide range of virulence factors, including exotoxins (e.g., ExoU, ExoS), pigments (pyoverdine, pyochelin), and motility structures (flagella and pili), which contribute to tissue invasion, immune modulation, and host damage. During chronic colonization, P. aeruginosa undergoes significant genotypic and phenotypic changes, such as mucoid conversion, downregulation of acute virulence pathways, and emergence of hypermutator phenotypes that facilitate rapid adaptation. Persistent cells, a specialized subpopulation characterized by metabolic dormancy and antibiotic tolerance, further complicate eradication efforts. The dynamic interplay between host environment and microbial evolution underlies the heterogeneity of CF lung infections and presents significant challenges for treatment. Elucidating the molecular mechanisms driving persistence, hypermutability, and biofilm resilience is critical for the development of effective therapeutic strategies targeting chronic P. aeruginosa infections in CF.