Antibiotics | Evolution of Urinary Tract Infection Pathogens and Antibiotic Resistance Trends: A Single-Center Study from Bulgaria (2017–2022)

This study systematically reviews the changes in pathogen spectrum and antibiotic resistance in urinary tract infections at a major Bulgarian hospital from 2017 to 2022, revealing a significant increase in ESBL- and carbapenem-resistant Enterobacteriaceae, particularly after the onset of the COVID-19 pandemic. The research provides regional resistance data for empirical clinical treatment and highlights the importance of continuous surveillance and rational antibiotic use.

 

Literature Overview
This paper, 'Urinary Tract Infections in a Single-Center Bulgarian Hospital: Trends in Etiology, Antibiotic Resistance, and the Impact of the COVID-19 Pandemic (2017–2022)', published in the journal Antibiotics, reviews and summarizes urine culture data from St. George University Hospital in Bulgaria, analyzing the annual distribution of UTI pathogens and changes in their antibiotic resistance. The study specifically examines the impact of the pandemic on the rise in resistance, including increased resistance to ESBL, carbapenems, and quinolones in Enterobacteriaceae, as well as the persistent presence of high-level aminoglycoside resistance in Enterococci.

Background Knowledge
Urinary tract infections (UTIs) are common clinical infections, particularly in community and hospital settings. Their causative agents primarily include Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), and Proteus mirabilis (P. mirabilis). In recent years, with antibiotic misuse and the impact of the pandemic, the emergence of multidrug-resistant (MDR) strains has increased significantly, posing challenges to clinical treatment. Resistance patterns are region-specific, making local epidemiological data crucial for empirical antibiotic selection and antimicrobial stewardship strategies. Based on data from the microbiology laboratory of Bulgaria’s largest tertiary hospital, this study systematically analyzes pathogen types, resistance trends, and their relationship with the pandemic, providing important reference for future treatment and infection control strategies.

 

 

Research Methods and Experiments
The study employed a retrospective, single-center epidemiological design, collecting urine culture samples from St. George University Hospital in Bulgaria between 2017 and 2022. A total of 74,417 urine samples were analyzed, with 10,177 pathogens isolated and identified. Urine screening was conducted using the HB&L UROQUATTRO system, and positive samples were cultured on blood agar, EMB, and chromogenic media. Pathogen identification was performed using biochemical tests, MALDI-TOF MS, and the Vitek 2 Compact system. Antimicrobial susceptibility testing included disk diffusion, MIC determination, microbroth dilution (for polymyxins), and the Vitek 2 Compact system. All results were interpreted according to EUCAST standards. Descriptive analysis, regression models, and interrupted time series analysis were used to assess trends in resistance over time, with a special focus on changes during the pandemic period.

Key Conclusions and Perspectives

• Between 2017 and 2022, Gram-negative bacteria accounted for approximately 73% of isolated urinary pathogens, with E. coli remaining the most common pathogen, though its proportion declined from 48.8% in 2017 to 33.5% in 2022.
• Antibiotic resistance in K. pneumoniae and P. mirabilis increased significantly after the pandemic, with ESBL production rising from 66% to 77% in K. pneumoniae and from 13.5% to 24% in P. mirabilis.
• Carbapenem resistance in K. pneumoniae increased to 40.6%, while in P. aeruginosa it was 24%. No carbapenem resistance was detected in E. coli.
• Polymyxin resistance increased in K. pneumoniae but not in E. coli or P. aeruginosa.
• High-level gentamicin resistance (HLAR) in Enterococci remained stable at around 70%, while vancomycin resistance in Enterococcus faecium increased from 4.6% to 8.9%.
• Interrupted time series analysis from 2020–2022 revealed a significant upward trend in resistance, particularly for ESBL and quinolone resistance.
• Isolation rates of Candida spp. increased from 2% in 2017 to 6% in 2022, potentially linked to the increased use of broad-spectrum antibiotics during the pandemic.

Research Significance and Prospects
The study underscores the importance of regional resistance monitoring, especially in light of rising multidrug-resistant Enterobacteriaceae and Enterococci. Future efforts should focus on strengthening local antimicrobial stewardship, optimizing empirical treatment strategies, and advancing the development of new antimicrobial agents and combination therapies. Additionally, further research should explore resistance gene transmission mechanisms and integrate patient clinical data to evaluate the association between treatment strategies and resistance patterns.

 

 

Conclusion
This study systematically analyzed the pathogen composition and antibiotic resistance trends in urinary tract infections at a large Bulgarian hospital, revealing the continued dominance of Gram-negative bacteria and a significant increase in ESBL and carbapenem-resistant strains during the pandemic. The findings suggest that clinicians should adjust empirical treatment protocols, reduce the use of broad-spectrum antibiotics, and enhance local resistance surveillance and antimicrobial stewardship. Future studies should integrate multicenter data and patient clinical information to more comprehensively assess resistance evolution and the effectiveness of treatment strategies.

 

Milena Yancheva Rupcheva, Kostadin Kostadinov, Yordan Kalchev, Marianna Murdjeva, and Michael M Petrov. Urinary Tract Infections in a Single-Center Bulgarian Hospital: Trends in Etiology, Antibiotic Resistance, and the Impact of the COVID-19 Pandemic (2017–2022). Antibiotics.