Microbial endogenous response to acute inhibitory impact of antibiotics

Enhanced endogenous respiration was observed as the significant/main response of the aerobic microbial culture under pulse exposure to antibiotics: sulfamethoxazole, tetracycline and erythromycin. Peptone mixture and acetate were selected as organic substrates to compare the effect of complex and simple substrates. Experiments were conducted with microbial cultures acclimated to different sludge ages of 10 and 2 days, to visualize the effect of culture history. Evaluation relied on modeling of oxygen uptake rate profiles, reflecting the effect of all biochemical reactions associated with substrate utilization. Model calibration exhibited significant increase in values of endogenous respiration rate coefficient with all antibiotic doses. Enhancement of endogenous respiration was different with antibiotic type and initial dose. Results showed that both peptone mixture and acetate cultures harbored resistance genes against the tested antibiotics, which suggests that biomass spends cellular maintenance energy for activating the required antibiotic resistance mechanisms to survive, supporting higher endogenous decay rates.

[Formula: see text]: maximum growth rate for X_H (day^-1); K_S: half saturation constant for growth of X_H (mg COD/L); b_H: endogenous decay rate for X_H (day^-1); k_h: maximum hydrolysis rate for S_H1 (day^-1); K_X: hydrolysis half saturation constant for S_H1(mg COD/L); k_hx: maximum hydrolysis rate for X_S1 (day^-1); K_XX: hydrolysis half saturation constant for X_S1 (mg COD/L); k_STO: maximum storage rate of PHA by X_H (day^-1); [Formula: see text]: maximum growth rate on PHA for X_H (day^-1); K_STO: half saturation constant for storage of PHA by X_H (mg COD/L); X_H1: initial active biomass (mg COD/L).