DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03173

Antimicrobial resistance, heavy metal resistance, and integron content in bacteria isolated from a South African tilapia aquaculture system

Hafizah Y. Chenia*, Anelet Jacobs

*Email: cheniah@ukzn.ac.za

ABSTRACT: Antibacterial compounds and metals co-select for antibiotic resistance when bacteria harbour resistance genes towards both types of compounds, facilitating the proliferation and evolution of antibiotic and heavy metal resistance. Antimicrobial and heavy metal resistance indices of 42 Gram-negative bacteria from a tilapia aquaculture system were determined to identify possible correlations between these phenotypes. Agar dilution assays were carried out to determine susceptibility to cadmium, copper, lead, mercury, chromate, and zinc, while susceptibility to 21 antimicrobial agents was investigated by disk diffusion assays. Presence of merA, the mercury resistance gene, was determined by dot-blot hybridizations and PCR. Association of mercury resistance with integrons and transposon Tn21 was also investigated by PCR. Isolates displayed a high frequency of antimicrobial (erythromycin – 100%, ampicillin – 85%, trimethoprim – 78%) and heavy metal (Zn2+ - 95% and Cd2+ – 91%) resistance. No correlation was established between heavy metal and multiple antibiotic resistance indices. Significant positive correlations were observed between heavy metal resistance profiles, indices, Cu2+ and Cr3+ resistance with erythromycin resistance. Significant positive correlations were observed between merA (24%)/Tn21 (24%) presence and heavy metal resistance profiles and indices, however, significant negative correlations were obtained between integron-associated qacE∆1 (43%) and sulI (26%) gene presence and heavy metal resistance indices. Heavy metal and antibiotics co-select for resistance, with fish-associated, resistant bacteria demonstrating simultaneous heavy metal resistance. Thus, care should be taken when using anti-fouling heavy metals of feed additives in aquaculture facilities.