Abstract
Contact of aquatic microbiocenoses with antibiotics present in the environment can cause the former to develop resistance to antimicrobial drugs. Therefore, the search for methods to detect antibiotics and drug-resistant microorganisms in the environment is important. The presented paper proposes a simple procedure to assess environmental exposure to antibiotics and the presence of non-susceptible microorganisms. Medium solutions with selected antibiotics and a microbial growth indicator were applied to test plates, and were inoculated with water samples from various ecosystems. After incubation, the susceptibility of the microorganisms to antibiotics was determined and presented in chronic microbial toxic concentration (MTC) values. It was confirmed that the presented procedure enables the assessment of the antibiotic susceptibility and adaptation potential of unselected microorganisms from different aquatic ecosystems. However, the MTC values depend on the inoculum volume, the density and seasonal activity of the microorganisms, the method of inoculum preparation, and the incubation time of the test plate. The described procedure may be practically applied as a screening test to identify the presence of drug-resistant microorganisms. Additionally, it may also be suitable as a method to assess environmental exposure to antibiotics. However, prior standardisation is required before implementing this procedure in quantitative studies.