Assessment of Chlorine Tolerant Escherichia coli Recovered from Wastewater Effluents

Abstract

TPS 931: Water and foodborne chemicals, Exhibition Hall, Ground floor, August 28, 2019, 3:00 PM - 4:30 PM Background: A serious concern for public health is the increasing tolerance of bacterial pathogens including E. coli to chlorine at the recommended dose of 0.5 mg/l. This study assessed chlorine tolerance of E. coli recovered from wastewater effleunts in the Eastern Cape Province, South Africa. Methods: Secondary effluent samples were collected from the clarifier of two wastewater treatment plants and E. coli was isolated following standard procedures and confirmed using PCR assay. The bacterial survival (n=20) at the recommended chlorine dosage (0.5 ml), lethal dose (n=3) and inactivation kinetics (n=3) at lethal doses were examined. Bacterial isolates (n=3) with the highest chlorine tolerance were confirmed using the 16S rRNA gene sequence. Nucleotide sequences were subjected to the Basic Local Alignment Search tools (BLAST) search, NCBI GenBank. Results: Presumptive isolates were identified as E. coli (n=20). The nucleotide sequences of the three isolates with the highest chlorine tolerance were deposited in GenBank as E. coli SAMRC-1 (accession number KX874327), E. coli SAMRC-2 (accession number KX874328) and E. coli SAMRC-3 (accession number KX874329), respectively. At the recommended free chlorine of 0.5 mg/l, E. coli isolates (n = 20) at initial cell density of 8.35 – 8.75 log were reduced to 3.88 – 6.0 log with chlorine residuals of 0.14 – 0.44 mg/l in 30 min. Higher chlorine doses (0.75 – 1.5mg/l) further reduced bacteria (n=3) to greater than 7.3 log showing a marked reduction in the viability of E. coli isolates while a high rate of bacterial kill (R2 = 0.9 – 0.98) was achieved over time (10 min interval at 30 min exposure) at chlorine dose of 1.5 mg/l. Conclusions: Poor removal efficiency of E. coli at chlorine dose of 0.5 mg/l demonstrated chlorine tolerance while higher chlorine doses showed the potential to check chlorine tolerance of bacteria.