Introduction and objective:
Klebsiella pneumoniae is an essential component of the human gut microflora. However, it can pose a threat by causing opportunistic infections, especially in hospitalised or immunocompromised patients. It is a serious problem for health medicine, primarily because of increasing resistance to previously used antibiotics. Infections with multidrug-resistant strains are difficult to treat, creating a challenge for clinicians. Also of growing concern is the increasing resistance to the drug of last resort – colistin (CL). The aim of the study is to determine the prevalence of resistance to CL among clinical K. pneumoniae strains.

Material and methods:
The study was conducted on 200 clinical strains of K. pneumoniae. Drug susceptibility, production of resistance mechanisms, and determination of the minimum inhibitory concentration of CL were evaluated.

Results:
Of all isolates, 73.0% produced carbapenemases, while the remainder produced an extended substrate spectrum – β-lactamases (ESBLs). All strains showed a diverse antibiotic resistance profile. Resistance to CL was noted among 14.5% of carbapenemase-producing strains, particularly MBL and OXA-48. ESBL-positive strains showed full susceptibility to CL.

Conclusions:
Although a low rate of CL resistance was observed, this was true for strains simultaneously producing carbapenemases. Such strains should be under special epidemiological surveillance due to their potential to cause epidemic outbreaks. Monitoring the prevalence of clinical CL-resistant strains would allow for more effective counteraction against pathogens in various fields, including medicine, agriculture, veterinary medicine and industry.