The potential ecological risk of co and cross-selection resistance between disinfectant and antibiotic in dairy farms

• Clean in place (CIP) system used dairy Wastewater disinfectant infectant resistance. • CIP induces antibiotic resistance genes (ARG) via co and cross-selection. • Disposal of CIP dairy wastewater ARG, thus poses threat to the environment. • Effective treatment of dairy wastewater is required to curb spread of ARG. The surge in antibiotic use in various industries has led to increased excretion of antibiotic resistance genes (ARG) to the environment, this poses threat to human and animal health. The dairy industry particularly dairy farms have been identified as one of the large contributors of antibiotic resistant bacteria (ARB) and ARG in the environment. The unregulated use of antibiotics and the use of disinfectants in the clean in place (CIP) process and heavy metal used for animal feed has been said to result in the induction of antibiotic resistance genes in pathogenic bacteria present in dairy wastewater (DWW). Disinfectant and heavy metals induce antibiotic resistance by inducing efflux pump genes which induce co-selection and cross-selection. There are several studies reporting cross and co-selection between heavy metals, disinfectants such as H 2 O 2 and antibiotics which induce ciprofloxacin and ampicillin resistance in Staphylococcus aureus, while Zn resistance genes(czrC) and methicillin resistance gene (mecA) select for Methicillin-resistant Staphylococcus aureus (MRSA). Controlling the spread of antimicrobial resistance in the environment requires a thorough understanding of their causes. Hence, this review aims to provide an overview of the role chemical materials present in DWW such as CIP chemicals, heavy metals in induction of antibiotic resistance through co- and cross-selection. Additionally, and their mechanism of co- and cross-selection resistance, their pathway to the environment and preventative measures are also discussed.