Conjugation assays were performed to investigate the transfer of antibiotic resistance genes from A. baumannii clinical isolates to the environmental isolates (Fig 1A ). A total of ten XDR-AB and four NDM-AB isolates were used as the donors. Overnight cultures of the donor and recipient cells were adjusted in 0.85% NaCl until a density corresponding to a McFarland value of 0.5 using a densitometer (SiaBiosan, Riga, Latvia). Afterwards, the donor and recipient cells were mixed at a ratio of 1:3 in Luria-Bertini (LB) broth and incubated for 4 h at 37°C. Transconjugants were recovered on MHA plates containing the following components: 300 μg/ml sodium azide; 50 μg/ml ticarcillin or 300 μg/ml sodium azide; 20 μg/ml tetracycline or 300 μg/ml sodium azide; and 20 μg/ml kanamycin. For the controls, the donors and recipients were each inoculated in LB broth and incubated for 4 h at 37°C, and the number of recipient cells (cfu) was calculated. The colonies that grew on the selective media were collected for the detection of antibiotic resistance genes, integrons, and resistance plasmid groups. Antibiotic susceptibility patterns and the MICs of ticarcillin, kanamycin, and tetracycline were determined to confirm the transfer of antibiotic resistance within all the transconjugants. Conjugation frequencies (CF) were calculated as follows:
Free full text: Click here
