engleski

Abundance of carbapenem-resistant bacteria in wastewater treatment plant

The carbapenem resistance in Gram-negative bacteria, which is usually associated with resistance to several other classes of antibiotics, has become a global problem of this century in hospital settings. Reports regarding the occurrence of viable carbapenem- resistant bacterial population (CRBP) outside medical institutions are globally scarce. The aim of this study was to quantify the numbers of viable CRBP through the secondary type of municipal wastewater treatment process (WWTP). The study was performed at the WWTP of the Croatian capital city of Zagreb, on 20 sampling occasions from September 2015 to June 2016. The CRBP was enumerated on CHROMagar Acinetobacter supplemented with CR102, which allows the growth of carbapenem-resistant isolates after incubation at 37C/72 h. The CRBP were found in influent, effluent, fresh activated sludge, anaerobically digested sludge, but not in lime- treated stabilized sludge of pH 12. Similar abundance (p>0.05) of CRBP was detected in influent and fresh activated sludge (median value 4.0 log CFU/mL) and significant decrease (p<0.05) was evidenced in effluent (1.8 log CFU/mL) and anaerobically digested sludge (3.2 log CFU/g). Average elimination of CRBP in secondary treated water averaged 51%. Although its moderate elimination in WWTP, significant numbers of CRBP are released through the treated water in natural recipient. The elimination of CRBP in WWTP is a result of incorporation of these bacteria in flocs of activated sludge. Anaerobic mesophilic digestion of surplus activated sludge reduces the abundance of CRBP, but only alkaline disinfection by lime treatment was certain to prevent spreading of CRBP in the environment.

carbapenem ; antibiotic resistant ; wastewater treatment plant ; bacteria

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