Culture-based study on the development of antibiotic resistance in a biological wastewater system treating stepwise increasing doses of streptomycin

AMB Express

Table 2 Activities of nine antibiotics against bacterial isolates harvested from stepwise increased STM exposures

Antibiotics	Antibiotic range (µg mL⁻¹)	Prevalence of antibiotic resistance (%)^a
Antibiotics	Antibiotic range (µg mL⁻¹)	0 mg L⁻¹, STM	0.1 mg L⁻¹, STM	1 mg L⁻¹, STM	5 mg L⁻¹, STM	25 mg L⁻¹, STM	50 mg L⁻¹, STM
AZ	0.016–256	0	38.4	38.4	30.8	23.0	23.0
TZ	0.016–256	7.7	23.0	38.4	23.0	15.4	15.4
EF	0.002–32	0	0	0	0	0	0
ETP	0.064–1024	0	0	7.7	7.7	7.7	7.7
SX	0.002–32	7.7	15.4	30.8	30.8	23.0	0
TC	0.016–256	0	23.0	30.8	30.8	30.8	15.4
TGC	0.016–256	0	0	0	0	0	0
TM	0.016–256	7.7	7.7	7.7	15.4	15.4	30.8
Sm	1–1024	15.4	53.8	69.2	69.2	53.8	53.8

AZ azithromycin, TZ ceftazidime, EF enrofloxacin, ETP ertapenem, SX sulfamethoxazole, TC tetracycline, TGC tigecycline, TM tobramycin, STM streptomycin
^aA total of 40 different bacterial strains (78 bacterial isolates, i.e. 13 isolates from each Sm stage) were used for MIC assay and the percentage of antibacterial resistance was calculated by the number of resistant strains among the total stains