Are reactive oxygen species (ROS) the main mechanism by which copper ion treatment degrades the DNA of Mycobacterium avium subsp. paratuberculosis suspended in milk?

Abstract

Abstract Aim: the aim of the present study is to show what is the effect of copper ions, and ROS generated in response to oxidative stress, on the damage to MAP DNA when exposed to a copper ion challenge in cow's milk. Methods and Results: spiked milk with different MAP bacterial loads was supplemented with blocking agents. These were either the copper chelators EDTA and BCS or the reactive oxygen species (ROS) quenchers D-mannitol, gallic acid and quercetin. DNA protection, MAP viability and ROS production generated after exposure to a copper challenge were then measured. In a bacterial load of 104 cells mL-1, both copper chelators and all ROS quenchers offered significant protection to MAP DNA. In a concentration of 102 cells mL-1, only D-mannitol and a mix of quenchers significantly protected the viability of the bacteria, and only at a concentration of 106 cells mL-1 was there a lower production of ROS when supplementing milk with gallic acid, quercetin and mix of quenchers. Conclusion: based on these findings, it may be concluded that MAP DNA damage can be attributed to the combined effect of the direct copper ions and ROS generated. Nevertheless, taking into account the antioxidant environment that milk provides, the direct effect of copper could play a prominent role.