Abstract
Background: The extended-spectrum beta-lactamase (ESBL) Klebsiella pneumoniae is one of the leading causes of health-associated infections (HAIs), whose antibiotic treatments have been severely reduced. Moreover, HAI bacteria may harbor pathogenic factors such as siderophores, enzymes, or capsules, which increase the virulence of these strains. Thus, new therapies, such as antimicrobial photodynamic inactivation (aPDI), are needed. Method: A collection of 118 clinical isolates of K. pneumoniae was characterized by susceptibility and virulence through the determination of the minimum inhibitory concentration (MIC) of amikacin (Amk), cefotaxime (Cfx), ceftazidime (Cfz), imipenem (Imp), meropenem (Mer), and piperacillin–tazobactam (Pip–Taz); and, by PCR, the frequency of the virulence genes K2, magA, rmpA, entB, ybtS, and allS. Susceptibility to innate immunity, such as human serum, macrophages, and polymorphonuclear cells, was tested. All the strains were tested for sensitivity to the photosensitizer PSIR-3 (4 µg/mL) in a 17 µW/cm2 for 30 min aPDI. Results: A significantly higher frequency of virulence genes in ESBL than non-ESBL bacteria was observed. The isolates of the genotype K2+, ybtS+, and allS+ display enhanced virulence, since they showed higher resistance to human serum, as well as to phagocytosis. All strains are susceptible to the aPDI with PSIR-3 decreasing viability in 3log10. The combined treatment with Cfx improved the aPDI to 6log10 for the ESBL strains. The combined treatment is synergistic, as it showed a fractional inhibitory concentration (FIC) index value of 0.15. Conclusions: The aPDI effectively inhibits clinical isolates of K. pneumoniae, including the riskier strains of ESBL-producing bacteria and the K2+, ybtS+, and allS+ genotype. The aPDI with PSIR-3 is synergistic with Cfx.
Highlights
Klebsiella pneumoniae is one of the major health-associated infection (HAIs) producers worldwide, including pneumonia, urinary tract, and bloodstream infections [1,2]
This work seeks to demonstrate the capacity of antimicrobial photodynamic inactivation (aPDI) to inhibiting the growth of clinical isolates of K. pneumoniae, which are diverse in antimicrobial susceptibility, genotype, and virulence
Phenotypic and genotypic characterization was conducted to determine the frequency of genes encoding virulence factors, the minimum inhibitory concentration (MIC) values determined for various antibiotics, and susceptibility to innate immune components
Summary
Klebsiella pneumoniae is one of the major health-associated infection (HAIs) producers worldwide, including pneumonia, urinary tract, and bloodstream infections [1,2]. HAI-producing K. pneumoniae strains progressively accumulate more multiple-drugs resistance (MDR), including extended-spectrum β-lactamases (ESBL) and carbapenemases, such as KPC [3,4,5]. Treatment options for infections caused by MDR strains of K. pneumoniae are severely reduced to colistin and tigecycline [6,7,8]. The high MDR shown by strains of K. pneumoniae does not fully explain its notable success as one of the most important agents of HAIs, suggesting the participation of other factors [9]. An increasing number of authors suggest that increased bacterial survival during infections is related to virulence factors [1,3,9,10,11,12,13,14].
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