The resistance of bacterial strains of Klebsiella pneumoniae and Enterobacter cloacae isolated from urine samples to β-lactam antibiotics Research background: Strains of K. pneumoniae and E. cloacae show different types of resistance to β-lactam antibiotics Research objectives: 1. to determine the frequency of different types of resistance of bacterial strains K. pneumoniae and E. cloacae to β-lactam antibiotics in the urine samples of the patients from the area of Brod-Posavina County by disk diffusion, determinig of MIK or with the help of phenotyping 2. to assess whether there is a difference in the frequency of resistance among hospital patients and outpatients. Study Plan: A cross-sectional study. Examinees and methods: In this study, 100 urine samples of hospital patients and outpatients, who applied to the Department for clinical microbiology of the Institute of Public Health of Brod-Posavina County in Slavonski Brod, were microbiologibcally processed. Bacterial strains of K. pneumoniae or E. cloacae were detected in the samples. All samples were tested for resistance to cefoxitin by disc diffusion method and by Double disk test for ESBL production, while production of AmpC β-lactamases and carbapenemases was detected by phenotyping. Results: The results show that among the bacterial strains Klebsiella pneumoniae and Enterobacter cloacae, a high frequency of resistance to cefoxitin, as well as the production of ESBLs and AmpC β-lactamase is present. The production of carbapemanases has not been determined. Conclusion: Worldwide, including Croatia, there is increasing resistance to bacterial strains of K. pneumoniae and E. cloacae to β-lactam antibiotics. Thereby, the increase in resistance was also registered in Brod-Posavina County. Among these strains, a high resistance to cefoxitin, high frequency of ESBL and AmpC β-lactamases production was detected, while the production of carbapenemases has not been determined. It was found that there is statistically significant difference in resistance to cefoxitin and in production of AmpC β-lactamases in bacterial strains of K. pneumoniae and E. cloacae between hospital patients and outpatients.