Management of milking wastewater as a significant control point of microbial pollution in the environment.

Abstract

Introduction and objective: Milking wastewater (MW) is an under-recognised reservoir of antibiotic resistant bacteria (ARB) and antimicrobial resistance genes (ARGs). The aim of the study is to evaluate MW as a point source pollutant for the presence of ARB and ARGs, to develop a treatment plant, and to address current legislation.

Material and methods: Milking wastewater was analysed for the total number of bacteria, Enterococcus spp., Staphylococcus spp., Enterobacterales, and Clostridium perfringens. Microbial identification by MALDI-TOF MS was followed by antimicrobial susceptibility testing and detection of ARGs. Wastewater samples were also tested for the antimicrobials presence using immunochromatographic tests. An on-site two-chamber MW treatment plant was designed with consideration of its cost-effectiveness and profitability. The system incorporated filtration through a mixture of fine sand and 10% kaolin, or a fine sand filter bed, yielding hydraulic conductivity coefficients of 5.13 × 10-6 m/s and 5.36 × 10-5 m/s, respectively. The treated effluent was considered suitable for activities not requiring tap water quality.

Results: Escherichia coli and Enterococcus spp. were identified as ARB. PCR confirmed the presence of ARGs conferring resistance to β-lactams (cphA, bla_GES1-9,11, bla_TEM1,2) and chloramphenicol (cfr). Milkling wastewater samples also tested positive for chloramphenicol.

Conclusions: To mitigate environmental contamination, regulations should be established for the release of bioactive substances, with penalties imposed for non-compliance with recommended safety measures.