Assessment of physico-chemical properties of sewage sludge and unlocking its prospect as a powerhouse of antibiotic-resistant bacteria

Abstract

Sewage sludge is a reservoir of pharmaceutically active ingredients (Antibiotics), antibiotic resistant genes and antibiotic-resistant bacteria; a potential risk to mankind and environment. Thus, sewage treatment and disposal offer re-invigoration of water resources aiming to minimise adversities associated with antibiotic pollution. This study unravels the physico-chemical aspects of sewage sludge and its valorisation using bio-remediation). Assessment of physico-chemical parameters were conclusive of the fact that sludge samples were enriched with inorganic components (Chloride, Phosphate and Sulphate) and organic constituents (Total carbon, total solids). Sludge samples were found to be contaminated with heavy metals Cr (12.69 mg/Kg), As (1.23 mg/Kg), Se (0.86 mg/Kg), Hg (1.49 mg/Kg) and Pb (30.32mg/Kg), with non-adherence to prescribed limits (Haryana State Pollution Control Board).  With a known history of antibiotic persistence in sludge, screening for bacterial isolates capable of utilizing Cephalosporin (Cefixime:200mg) as their sole source of carbon and energy was carried out. 5 isolates exhibiting fastidious growth were characterised as Bacillus sp., Escherichia sp., Pseudomonas sp., Streptococcus sp. and Enterobacter sp.  Noteworthy is the fact, isolates exhibited a broad range of tolerance as reflected by Minimum Inhibitory Concentration (MIC). This was carried out by Agar dilution method using cefixime (10-100mg/l). 0.03, 0.05, 0.07, 0.06 and 0.09% w/v were the respective Minimum Inhibitory Concentration (MIC) range. The isolate with maximum tolerance to cefixime was subjected to 16S rDNA sequencing and characterised as Enterobacter SCef1