What Antibiotic Threat Do the Heavy Metals Contaminated Sites of Mine Hide?

Abstract

The environment contaminated by antibiotics and heavy metals as a consequence of human activities is of great concern nowadays. Many pieces of research proved that the environment could act as a reservoir of antibiotic resistance determinants allowing them to spread among different bacterial species via the process called horizontal gene transfer. The result is antibiotic resistance even in pathogen microorganisms. Heavy metals act as important factors in this process because of their potential to select antibiotic resistant bacteria thanks to linkage among antibiotic resistance genes and heavy metals resistance genes. Thus, this experiment was conducted to screen the antibiotic tolerance profile of bacteria obtained from heavy metal contaminated environment of mine, dump and the contaminated soil near the entry of mine. Several samples were collected from the only active gold mine in Slovakia in Hodruša – Hámre. The presence of cultivable bacteria was proved via cultivation approaches with subsequent MALDI – TOF MS (Matrix – Assisted Laser Desorption/Ionisation Time of Flight Mass Spectrometry) identification of selected isolates. Representative bacterial isolates were screened for their antibiotic tolerance against chosen antibiotics (ampicillin (AMP), chloramphenicol (CHLOR), tetracycline (TET) and kanamycine (KAN)) with the aim to define their minimal inhibitory concentration (MIC). The cultivable bacteria from studied environments were dominated by Gram-negative protebacteria of Pseudomonas and Rhizobium genera. Among more than 150 isolates the resistance to ampicillin (MIC>100μg/ml – 49% isolates), kanamycine (MIC>100μg/ml - 18% isolates), and chloramphenicol (MIC>20μg/ml – 16% isolates) dominated. The resistance to tetracycline (MIC>20μg/ml) was detected in less than 1% of isolates. Overall counts of antibiotic resistance and multi-resistance were alarmingly high taking in account that industrial environments with no known antibiotic exposure were analysed. Our data indicate that heavy metals contaminated environment could influence the occurrence and the spread of antibiotic resistance. Possibly, metal contaminated environment act as a reservoir of antibiotic resistant bacteria.