[Pseudomonas aeruginosa virulence factors as a therapeutic target in multidrug-resistant strains].

Pseudomonas aeruginosa (PSAE) is known for its ability to form biofilm and produce other virulence factors associated with a resistant phenotype. Multidrug-resistant (MDR) PSAE strains represent a serious problem in healthcare and are the focus of an increasing number of studies dealing with the therapy of infections caused by these bacteria. Nowadays, a number of studies focus on the presence of virulence factors rather than on the mechanisms of resistance to the antibiotics used, as it is the study of virulence factors that makes it possible to expand the possibilities of effective and efficient therapy. This review describes the virulence factors produced by the one of the five PSAE secretion systems that have the potential to become targets for so-called antivirulence therapy, have been described. These are mainly alkaline protease, elastase B, exotoxins A, S and Y and pyocyanin. In addition to specific virulence factors, recent studies have focused on the components of the PSAE secretion systems that mediate the transport of toxins and lytic enzymes out of the bacterial cell. Inhibition of specific molecules for type 2 and 3 secretion systems may prevent secretion of virulence factors into the extracellular space and host cells, which would have a significant impact on reducing PSAE virulence.

[Resistance of bacterial pathogens isolated from the lower respiratory tract and their clonality in intensive care patients in a post-COVID-19 period].

OBJECTIVES: The period of the COVID-19 pandemic had a significant impact on the healthcare system, including its effect on compliance with the established procedures of a rational antibiotic policy, especially in the context of nosocomial pneumonia, where it was very difficult to distinguish a possible bacterial superinfection from a severe inflammatory reaction caused by the SARS-CoV-2 virus. The aim of the present study was to analyze the antimicrobial resistance of bacterial pathogens isolated from the lower respiratory tract and their clonality in intensive care patients in 2022 and to compare it with the previous COVID-19 period. MATERIAL AND METHODS: Bacterial strains isolated from the lower respiratory tract (LRT) of patients hospitalized at the Department of Anaesthesiology, Resuscitation and Intensive Care, Olomouc University Hospital (DARIC) over a three-year period (January 1, 2020 - December 31, 2022) were included in the study. The susceptibility to antibiotics was determined by the standard microdilution method according to the EUCAST criteria, and selected isolates were compared using pulsed-field gel electrophoresis (PFGE). RESULTS: The resistance of the most common bacterial pathogens isolated from the LRT of patients hospitalized at DARIC did not change significantly during the COVID-19 (2020-2021) and post-COVID-19 (2022) periods, with the exception of Serratia marcescens and Enterococcus faecium species. These two showed an increase in the number of strains during the COVID-19 pandemic, as well as a significant increase in the proportion of resistant strains. In the case of Serratia marcescens, there was a subsequent decrease in the number of isolates and their resistance in 2022. For Enterococcus faecium, the total number of isolates also decreased significantly, but the frequency of vancomycin-resistant isolates (VRE) continued to increase. During the COVID-19 pandemic, increased VRE detection can be linked to proven clonal spread, but significant clonality was no longer confirmed in 2022. Comparison of similarity by PFGE in other bacterial species also did not reveal significant horizontal transmission between patients in the post-COVID-19 period, as most isolates (85%) showed a unique restriction profile. CONCLUSIONS: The results indicate that the frequency and antimicrobial resistance of the majority of the most common bacterial pathogens from the LRT of patients hospitalized at DARIC in the post-pandemic period remain comparable to the time before and during the COVID-19 pandemic outbreak. An exception is Enterococcus faecium, which showed an increase in vancomycin resistance in both the COVID-19 and the post-COVID-19 periods.

Clinical microbiology and its role in current medicine.

The characteristics of current clinical microbiology and its role in modern medicine are presented. The article defines the main objectives of microbiological examination, principles of antibiotic and diagnostic stewardship. The main emphasis is placed on the correct interpretation of microbiological results.

[Digitalization in clinical microbiology].

Reflections on digitalization in clinical microbiology are presented. The advantages and limitations of digital processing of microbiological data for individuals and the human population are considered.

[Impact of the COVID-19 pandemic on antimicrobial resistance].

OBJECTIVES: The COVID-19 pandemic has had a major impact on the healthcare system, which has been forced to manage large numbers of patients, including those with respiratory insufficiency and in need of oxygen therapy. Due to concerns about bacterial co-infection, antibiotic therapy was administered to many patients. The aim of the present study was to compare antimicrobial resistance in intensive care patients in the pre-pandemic and pandemic periods. MATERIAL AND METHODS: Patients hospitalized at the Department of Anesthesiology, Resuscitation and Intensive Care Medicine of the University Hospital Olomouc in the pre-COVID-19 period (2018-2019) and during the pandemic (2020-2021) were enrolled in the study. Clinical samples from the lower respiratory tract were routinely collected twice a week, with one strain of a given species first isolated from each patient being included in the study. RESULTS: While several bacterial species (Escherichia coli, Proteus mirabilis and Haemophilus influenzae) were found to occur less frequently, an increased occurrence was documented for Enterococcus faecium, Serratia marcescens and Klebsiella variicola. Overall, however, it can be concluded that there was no major change in the frequency of bacterial pathogens isolated from the lower respiratory tract during the COVID-19 period. Similarly, with only a few exceptions, antimicrobial resistance did not change significantly. More significant increases in resistance to piperacillin/tazobactam, cefotaxime, ciprofloxacin and gentamicin have been demonstrated for Serratia marcescens. However, a decrease in the resistance of Pseudomonas aeruginosa and Burkholderia cepacia complex to meropenem was also observed. CONCLUSIONS: There was no significant change in the frequency of bacterial pathogens and their resistance to antibiotics during the COVID-19 pandemic. However, there was an increase or decrease in the percentage of some species and in their resistance.

[Acute care treatment of COVID-19 pneumonia with acute respiratory failure].

Treatment of COVID-19 patients and their extreme numbers represented an unprecedented challenge for the intensive care system in healthcare facilities throughout the Czech Republic, a country particularly affected by the new coronavirus SARS-CoV-2 pandemic. A steep increase in the need for intensive care placed an excess burden on bed and staff capacity. For a severe and critical course of COVID-19, bilateral pneumonia with acute hypoxemic respiratory failure is pathognomonic. In the intensive care setting, COVID-19 therapy is primarily symptomatic, supporting failing respiratory function to gain time needed to restore it and to repair the lungs. The aggressiveness and comprehensiveness of respiratory support depend on the severity of failure, ranging from simple oxygen therapy, to non-invasive support and mechanical ventilation, to extracorporeal support. By contrast, specific COVID-19 therapy is directly targeted against SARS-CoV-2 or modulates the organism's response to the virus. Primary, virus-induced lung injury may be secondarily complicated by coinfection or superinfection, most commonly bacterial, increasing the severity and lethality of the disease. Therefore, anti-infective therapy is crucial for the prognosis and outlook of intensive care COVID-19 patients. Among nosocomial infections complicating COVID-19, ventilator-associated pneumonia (developing in mechanically ventilated patients) is particularly important and challenging, and so are issues related to bacterial resistance and rational antibiotic therapy.

[Enterococcal infections and their treatment options].

AIM: The study aimed to characterize enterococcal infections at the University Hospital Olomouc and to define antibiotic treatment options. MATERIAL AND METHODS: The data was obtained from the ENVIS LIMS laboratory information system. Between 1 January 2015 and 31 December 2019, clinically relevant enterococci in the hospital and their resistance to antibiotics were retrospectively evaluated. Until mid-2016, criteria defined by Facklam and Collins and biochemical properties determined with the Encoccus test were used for identification. Subsequently, all enterococci were identified using the MALDI-TOF MS system. The susceptibility to antibiotics was determined using a standard microdilution method according to the EUCAST criteria. RESULTS: A total of 8 239 clinically relevant enterococci were isolated over the 5-year period. The most frequently isolated species were Enterococcus faecalis and Enterococcus faecium, which accounted for more than 90% in the period 2017-2019. Enterococci were most frequently isolated from urine (35 %), surgical wounds (17 %) and urethral/vaginal swabs (17 %). Clinically relevant enterococci were most commonly isolated from patients with oncological diagnoses (22%), those with urinary and genital diseases (15%) and respiratory diseases (9%). Enterococcus faecalis strains showed very low resistance to the antibiotics tested. Enterococcus faecium was shown to have 24 % proportion of vancomycin-resistant strains (VRE). CONCLUSION: Primary antibiotics suitable for treating infections with the etiological role of Enterococcus faecalis include aminopenicillins, in case of severe infections in combination with aminoglycosides, in particular gentamicin. For Enterococcus faecium strains, glycopeptides must be chosen. To treat VRE, linezolid or tigecycline are indicated.

[Bacterial complications in surgical management of esophageal cancer].

One of the most common cancers is esophageal carcinoma. The basic therapeutic approach is esophagectomy, one of the most extensive procedures in general surgery, potentially leading to serious postoperative complications, in particular respiratory complications. The objective was clinical and microbiological characterization of patients after the surgical removal of the esophagus for carcinoma. In 2020, a total of 14 patients underwent the surgery. Respiratory complications occurred in 57 % of them, with pneumonia leading to respiratory failure and acute respiratory distress syndrome being noted in 21 %. The identified bacterial pathogens were strains of Acinetobacter johnsonii, Enterobacter cloacae, Serratia marcescens, Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Enterococcus faecium. In one case, the patient's condition was complicated by fungal infection caused by Candida krusei. The study results warrant the need for close collaboration between the physician caring for a particular patient and a microbiologist that must be continuous and based on daily assessment of both microbiology test results and the patient's clinical condition.

Antibiotic treatment issues in patients with COVID-19.

The COVID-19 pandemic may increase the current threat of antimicrobial resistance and exacerbate another, rather silent, pandemic posed by the increasing frequency of multidrug-resistant bacterial pathogens and the associated potential for loss of effective antibiotics. Antibiotic treatment has often been used in patients hospitalized for COVID-19 due to concerns about possible bacterial co-infection, as confirmed by previous experience with viral respiratory infections such as H1N1 influenza, SARS and MERS. Concerns or unknowns related to the COVID-19 pandemic have also affected physicians behavior, including the use of antibiotics. However, the high rate of antibiotic use in patients, especially those with mild to moderate COVID-19 disease, is inconsistent with the actual incidence of bacterial co-infections and/or secondary respiratory infections. Thus, it is clear that a careful assessment of the role of antibiotic treatment in patients hospitalized for COVID-19 is required. According to the current WHO recommendation, the application of antibiotics is especially suitable for patients with severe/critical degree of respiratory insufficiency requiring intensive oxygen therapy, artificial lung ventilation or support by extracorporeal membrane oxygenation.

[Bacteremia pathogens in the University Hospital Olomouc].

OBJECTIVES: To provide an overview of the most common bacterial species isolated from blood cultures in the University Hospital Olomouc in the years 2015-2019 and their antibiotic resistance patterns. MATERIAL AND METHODS: The data were obtained from the laboratory information management system ENVIS LIMS. The results were analyzed retrospectively for the period from January 1, 2015 to December 31, 2019. Among positive blood cultures, the prevalence of bacterial species was assessed and the most frequent species were evaluated for resistance to selected antibiotics. Each sample was processed using standard microbiology methods with the MALDI-TOF MS system. Susceptibility to antibiotics was tested with the microdilution method according to the EUCAST recommendations. RESULTS: Over the study period, a total of 3 400 isolates from blood cultures were included. Coagulase-negative staphylococci were the most prevalent (37 %), followed by Escherichia coli (16 %), Klebsiella pneumoniae (9 %), Staphylococcus aureus (7 %), Streptococcus spp. (5 %), Pseudomonas aeruginosa (4 %), Enterobacter cloacae (2 %), Enterococcus faecalis (2 %) and Enterococcus faecium (2 %). Resistance of E. coli to 3rd generation cephalosporins, piperacillin/tazobactam, gentamicin and fluoroquinolones ranged from 7 % to 33 %. A high percentage of Klebsiella pneumoniae strains (33 %-65 %) was resistant to the above antibiotics. The prevalence of methicillin-resistant Staphylococcus aureus reached 3-7 %. Pseudomonas aeruginosa exhibited resistance to piperacillin/tazobactam, ceftazidime, cefepime, meropenem, ciprofloxacin and gentamicin ranging from 3 % to 46 %. CONCLUSION: Knowing the prevalence of bacterial species from blood cultures and their antimicrobial resistance patterns is important for empirical antibiotic therapy in case of an existing infection. It is advisable to conduct such epidemiological studies as part of antibiotic stewardship.

[Direct identification of bacteria in blood cultures by MALDI-TOF MS].

BACKGROUND: Early and causal administration of antibiotics in patients with a positive blood culture is an essential prerequisite for successful treatment of infection. However, isolation and subsequent identification of bacteria in a blood culture by classical (culture) methods may last several days. MALDI-TOF MS is a method allowing rapid identification of bacteria, not only cultures from culture media, but also directly in clinical specimens. METHODS: The study included samples of positive blood cultures taken from patients in the University Hospital Olomouc between 2016 and 2018 and examined at the Department of Microbiology of the Faculty of Medicine, Palacký University Olomouc. Positive blood culture samples were processed using an in-house method involving the removal of blood cells by low-speed centrifugation. Subsequently, a pellet obtained by high-speed centrifugation and sample washing was tested by MALDI-TOF MS. RESULTS: A total of 110 positive blood cultures were examined using the method of direct identification. At a species level, more Gram-negative bacteria (88 %) than Gram-positive bacteria (79 %) were correctly identified, with higher identification score values being obtained for the former. Identification score values of 2.0 or higher were found in 62 % of blood cultures containing Gram-negative bacteria and 17 % of blood cultures containing Gram-positive bacteria. Identification score values ranging from 1.7 to 2.0 were found in 21 % of Gram-negative blood cultures and 33 % of blood cultures containing Gram-positive bacteria. CONCLUSION: Direct identification of microorganisms from positive blood cultures using MALDI-TOF MS enables more rapid diagnosis. By reducing the time required to obtain the result of pathogen identification, it may positively affect the antibiotic treatment of patients.

Gut microbiota metabolizes nabumetone in vitro: Consequences for its bioavailability in vivo in the rodents with altered gut microbiome.

1. The underlying microbial metabolic activity toward xenobiotics is among the least explored factors contributing to the inter-individual variability in drug response. 2. Here, we analyzed the effect of microbiota on a non-steroidal anti-inflammatory drug nabumetone. 3. First, we cultivated the drug with the selected gut commensal and probiotic bacteria under both aerobic and anaerobic conditions and analyzed its metabolites by high-performance liquid chromatography (HPLC) with UV detection. To analyze the effect of microbiota on nabumetone pharmacokinetics in vivo, we administered a single oral dose of nabumetone to rodents with intentionally altered gut microbiome - either rats treated for three days with the antibiotic imipenem or to germ-free mice. Plasma levels of its main active metabolite 6 methoxy-2-naphthylacetic acid (6-MNA) were analyzed at pre-specified time intervals using HPLC with UV/fluorescence detection. 4. We found that nabumetone is metabolized by bacteria to its non-active metabolites and that this effect is stronger under anaerobic conditions. Although in vivo, none of the pharmacokinetic parameters of 6-MNA was significantly altered, there was a clear trend towards an increase of the AUC, Cmax and t1/2 in rats with reduced microbiota and germ-free mice.

[Effect of previous antibiotic therapy on the epidemiology of ventilator-associated pneumonia].

OBJECTIVES: Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in intensive care patients. The aim of the study was to evaluate the effect of previous antibiotic therapy on the incidence of VAP, mortality and spectrum of bacterial pathogens. MATERIAL AND METHODS: The retrospective, observational study comprised patients over 18 years of age meeting the clinical criteria of VAP. Controls were patients requiring mechanical ventilation for more than 48 hours with no signs of VAP. Each group was divided into two arms according to previous antibiotic therapy. Tracheal aspirates and oropharyngeal swabs were taken from all patients. Cultured isolates were identified using standard microbiological techniques. Antimicrobial susceptibility testing was performed according to the European Committee on Antimicrobial Susceptibility Testing guidelines. In both groups, 28-day mortality, 90-day mortality and multidrug-resistant (MDR) bacterial pathogen frequency were evaluated. RESULTS: The study included 49 patients (32 patients with previous antibiotic therapy, 17 antimicrobial-naive patients). The proportion of individuals with previous antibiotic therapy was significantly lower in VAP patients (34%) than among controls group (66%; p = 0.02). The VAP criteria were met by 23 patients (11 with previous antibiotic therapy, 12 without the therapy). The Enterobacteriaceae including extended-spectrum beta-lactamase-producing strains and Pseudomonas aeruginosa were the most common pathogens isolated. MDR pathogens were statistically significantly more frequent in patients with previous antibiotic therapy (77% vs. 33%; p = 0.047). In patients with previous antibiotic therapy, 28-day mortality was lower (18%; n = 2) than in antimicrobial-naïve patients (33%, n = 4; p = 0.640). The difference was more pronounced in 90-day mortality, albeit with low statistical significance (18%, n = 2 vs. 58%, n = 7; p = 0.089). CONCLUSIONS: Previous antibiotic therapy was associated with a lower incidence of VAP and a higher frequency of MDR bacterial pathogens. VAP antibiotic therapy modified according to knowledge of previous antibiotic therapy and cultured isolates was correlated with lower 28-day and 90-day mortality rates.

[Vancomycin-resistant enterococci].

The review describes important bacterial pathogens, namely enterococci, focusing on their resistance to glycopeptides. Presented are the basic phenotypes and genotypes of vancomycin-resistant enterococci and options for antibiotic therapy of infections with their etio-logical role. At the same time, their prevalence in the Czech Republic is characterized based on data from the EARS-Net and studies available in the literature. Finally, potential approaches to preventing the spread of these dangerous multidrug-resistant bacteria are defined.

[Hospital-acquired pneumonia in the light of current recommendations - is there a space for improving patient care?]

Hospital-acquired pneumonia (HAP) is an infection of the lung parenchyma. It is the second most frequent nosocomial infection and the leading cause of death from infection in critically ill patients. Hospital-acquired and, particularly, ventilator-associated pneumonia prolong the hospital stay and increase treatment costs. The clinical signs of pneumonia are rather non-specific, with limited possibilities to distinguish the lung condition from other nosological entities. The yield, effectiveness and cost of new rapid diagnostic procedures as well as early biochemical markers specific for pneumonia have not been sufficiently verified and clinical translation of technological innovations is slow. In bedside clinical practice, the diagnosis continues to be based on clinical examination together with imaging methods, most frequently X-ray. The spectrum of etiologic agents changes, with an increase in the prevalence of multidrug-resistant (MDR) bacterial pathogens. Initial antibiotic therapy, particularly in critically ill ventilated patients, needs to include broad-spectrum agents due to the risk of the presence of MDR bacteria. The likelihood of successful treatment may be increased by regular updates of recommendations for adequate initial antibiotherapy with regard to the epidemiological situation and knowledge of bacterial resistance to antimicrobials in a particular hospital and region. As part of the current valid guidelines, recommendation were newly translated; however, their level of evidence is often very low and the strength of recommendation is mostly weak or moderate. Their benefit to everyday practice is questionable. The article points to changes brought about by the recent European guidelines published in fall 2017 and summarizes current issues concerning HAP pathogens in intensive care units in the Czech Republic.

Detection of Prosthetic Joint Infection Based on Magnetically Assisted Surface Enhanced Raman Spectroscopy.

Accurate and rapid diagnosis of prosthetic joint infection (PJI) is vital for rational and effective therapeutic management of this condition. Several diagnostic strategies have been developed for discriminating between infected and noninfected cases. However, none of them can reliably diagnose the whole spectrum of clinical presentations of PJI. Here, we report a new method for PJI detection based on magnetically assisted surface enhanced Raman spectroscopy (MA-SERS) using streptavidin-modified magnetic nanoparticles (MNP@Strep) whose surface is functionalized with suitable biotinylated antibodies and then coated with silver nanoparticles by self-assembly. The high efficiency of this approach is demonstrated by the diagnosis of infections caused by two bacterial species commonly associated with PJI, namely, Staphylococcus aureus and Streptococcus pyogenes. The method's performance was verified with model samples of bacterial lysates and with four real-matrix samples of knee joint fluid spiked with live pathogenic bacterial cells. This procedure is operationally simple, versatile, inexpensive, and quick to perform, making it a potentially attractive alternative to established diagnostic techniques based on Koch's culturing or colony counting methods.

[Effect of silver nanoparticles on anaerobic bacteria].

OBJECTIVE: The aim was to evaluate the antibacterial effect of silver nanoparticles on anaerobic bacteria. MATERIAL AND METHODS: The microdilution method was used to determine the minimum inhibitory concentrations (MICs) of 28 nm silver nanoparticles, both unstabilized and stabilized by casein, gelatin and polyacrylic acid. The following anaerobic bacteria were tested: Bacteroides fragilis, Bacteroides thetaiotaomicron, Eggerthella lenta, Propionibacterium acnes, Clostridium perfringens, Clostridium difficile and Fusobacterium varium. RESULTS: Unstabilized silver nanoparticles exhibited antibacterial activity at concentrations ranging from 13 to 34 mg/L. A more significant effect with MIC values between 1 and 13 mg/L was shown for silver nanoparticles stabilized by casein. CONCLUSION: Unstabilized silver nanoparticles are active against anaerobic bacteria at concentrations proved to be cytotoxic to eukaryotic cells of human fibroblasts and multicellular organisms. Silver nanoparticles stabilized by casein appear to be more suitable for further research.

Occurrence of bacteria producing broad-spectrum beta-lactamases and qnr genes in hospital and urban wastewater samples.

The aims were to investigate the level of antibiotic-resistant bacteria in hospital and urban wastewater and to determine the similarity of isolates obtained from wastewater and hospitalized patients. Wastewater samples were collected in September 2013 and 2014. After identification using MALDI-TOF MS, beta-lactamase production was determined by relevant phenotypic tests. Genes responsible for the production of single beta-lactamase groups and Qnr proteins were established. The epidemiological relationship of the isolates from wastewater and hospitalized patients was determined by PFGE. A total of 51 isolates of enterobacteria were obtained. Overall, 45.1% of them produced broad-spectrum beta-lactamases. Genes encoding TEM, SHV, CTX-M, CIT, DHA and EBC types of enzymes and Qnr proteins were detected. No broad-spectrum beta-lactamase production was confirmed in the urban wastewater treatment plant. The most important finding was the detection of two identical isolates of K. pneumoniae in 2013, one from a patient's urinary catheter and the other from a wastewater sample.

[Interpretation of bacterial susceptibility/resistance to antibiotics].

Bacterial resistance may be defined from a microbiological, clinical and pharmacological perspective. Microbiological resistance refers to the presence of genetic information coding for the relevant mechanism of resistance of a bacterium to a particular antibiotic. In case of clinical interpretation, breakpoints are of key importance as their role is to distinguish bacterial pathogens in which successful therapy is highly probable from isolates with a high likelihood of failure. However, it is questionable whether this approach is suitable for all patients, particularly those receiving intensive care for life-threatening infections. A pharmacodynamic/pharmacokinetic definition of resistance may be understood as comprehensive since it allows consideration of all parameters, especially the patient's clinical condition, site of infection, minimum inhibitory concentration of a specific antimicrobial agent and its concentration in the relevant tissue. In that case, determination of bacterial susceptibility or resistance is more personalized and allows more targeted antibiotic therapy.

[Antibiotic therapy of hospital-acquired pneumonia and its pharmacoeconomics].

BACKGROUND: Important hospital-acquired infections include pneumonia, mainly because of the increasing resistance of bacterial pathogens to antimicrobials and the associated potential failure of antibiotic therapy. The present study aimed at determining the most frequent etiological agents of hospital-acquired pneumonia (HAP) and assessing the relationship between 30-day mortality and adequacy of antibiotic therapy. Based on the obtained information, optimal patterns of antibiotic therapy were to be defined, including a pharmacoeconomic perspective. METHODS: In patients with clinically confirmed HAP, bacterial etiological agents were identified, their susceptibility to antimicrobials was determined and statistical methods were used to assess the relationship between adequacy of antibiotic therapy and 30-day mortality. RESULTS: The study comprised 68 patients with clinically confirmed HAP. The most common etiological agents were strains of Pseudomonas aeruginosa (30.8 %), Klebsiella pneumoniae (23.1 %) and Burkholderia cepacia complex (15.4 %). Gram-negative bacteria accounted for 86.5 % of all bacterial pathogens. The overall mortality reached 42.5 %. In the subgroup of patients with inadequate antibiotic therapy, 30-day mortality was significantly higher (83.3 %) than in the subgroup with adequate therapy (30.0 %; p = 0.002). The risk for 30-day mortality was 2.78 times higher in case of inadequate antibiotic therapy (95%CI: 1.52-5.07). The proportion of Pseudomonas aeruginosa strains was significantly higher in the subgroup of patients with inadequate antibiotic therapy than in those with adequate therapy (67 % vs. 27 %; p = 0.032). CONCLUSION: Results of the present study suggest a significant relationship between mortality of patients with HAP and ineffective antibiotic therapy due to resistance of the bacterial pathogen. Thus, it is clear that initial antibiotic therapy must be based on qualified assumption of sufficient activity against the most common bacterial pathogens and results of surveillance of bacterial resistance in the relevant epidemiological unit. At the same time, however, it must be stressed that it is impossible to cover all potential variants of the etiological agents and their resistance phenotypes.