According to a new study led by UC San Diego scientists, Methicillin-resistant Staphylococcus aureus (MRSA) bacteria exposed to cigarette smoke becomes more resistant to threat from the immune system. According to senior author of the study and pulmonologist at UCSD and the Veterans Affairs San Diego Healthcare System, Laura E. Crotty Alexander, smoke stresses out invasive bacteria and far more difficult to kill.

He said, “We already know that smoking cigarettes harms human respiratory and immune cells, and now we've shown that, on the flipside, smoke can also stress out invasive bacteria and make them more aggressive”.

Cigarette smoke causes MRSA to alter its cell walls to repel toxic substances. Thus, the smoke leads the bacteria to strengthen its defense which in turn boosts survival against reactive oxygen species, which macrophages generate in order to kill pathogens.

The researchers tested the bacteria's vulnerability to individual mechanisms that macrophages typically utilize to kill bacteria. They exposed immune cells to two different batches of MRSA, one normal and one treated with cigarette smoke extract. They discovered that the bigger the dose of smoke, the bigger the effect.

The study published in the journal Infection and Immunity stated that MRSA exposed to the smoke extract were four times more resistant to macrophage killing than non-exposed MRSA.

Crotty's team also found that smoke-exposed MRSA became more resistant to killing by antimicrobial peptides. These are small protein pieces the immune system uses to poke holes in bacterial cells and trigger inflammation.

The worst thing that scientists discovered was that the increased resistance continued for 24 hours after exposure.

This suggested that it could be inherited. Under ideal conditions MRSA divides about every 30 minutes. At that rate, a single MRSA cell could generate nearly 17 million descendents in 12 hours.