Reduction of antibiotic-resistant-E. coli, -K. pneumoniae, -A. baumannii in aged-sludge of membrane bioreactor treating hospital wastewater.

A pilot-scale of membrane bioreactor (MBR) had functioned without sludge withdrawal for six months, proposed to minimize antibiotic-resistant bacteria (ARB) dissemination from hospital wastewater. With this proposal, an aging sludge in MBR has concerned as preserved-severe multidrug-resistant microorganisms. Thus, this study aims to investigate resistance alteration of ARB in the aging-sludge compared to that in the wastewater. Escherichia coli (EC), Klebsiella pneumoniae (KP), and Acinetobacter baumannii (AB) were antimicrobial-resistant indicators. In wastewater, AB showed the highest concentration followed by KP and EC, respectively, while an inverse order of those species showed in MBR-aging sludge. 60-isolates of each species per sample were tested on 8-antibiotics (AMAB) and 19-antibiotics (AMEC&AMKP) to evaluate antimicrobial resistance (AM) potency. The results show that high ARB variation of 0 to 100% population among those ARB had shown in the wastewater, while a significant reduction of those ARB population in MBR-aged-sludge had appeared surprisingly (P < 0.05). For example, the AMEC population of sludge to influent was <0.5 as of ESBL, Cefoperazone, Cefquinome, Imipenem, Gentamicin, Enrofloxacin, and Marbofloxacin. Among the three species studied, AB showed the highest antibiotic-resistant reduction of 8 antibiotics (100%), followed by KP (17 antibiotics, 99.44%) and EC (16 antibiotics, 88.89%), respectively. High dissolved oxygen levels and prolonged sludge age were possibly contributing to the reduction of those ARB in the MBR. This study gives a new point of view on potential ARB population reduction via the appropriate MBR operation.