I’ve been meaning to get to a really interesting article titled “Killing niche competitors by remote-control bacteriophage induction.” So, let’s talk about your nose.
Two species that are found in the human nose are Staphylococcus aureus (methicillin resistant strains are called MRSA) and Streptococcus pneumoniae. Typically, only one species or the other is found: they usually don’t coexist in your schnozz. One mechanism that S. pneumoniae uses to displace S. aureus is to make hydrogen peroxide, but it’s unclear how this actually works, since hydrogen peroxide, at concentrations which are lethal to S. aureus, is also lethal to S. pneumoniae.
What this study found is that hydrogen peroxide, at levels usually produced by S. pneumoniae, kills those S. aureus strains that have a lysogenic phage–a bacterial virus that has incorporated itself into the S. aureus genome. Usually, the lysogenic phage acts like any other stretch of DNA, but when the S. aureus cell is stressed, as is the case when exposed to low levels of hydrogen peroxide, the phage becomes lytic: it turns the cell into a phage factory, kills the cell, and then the phage infects other cells (which, if also stressed, will be killed, and so on).
This gets interesting in several ways. First, many S. aureus have bacteriophage, so they’re susceptible to hydrogen peroxide. These bacteriophage, when existing as part of the bacterial genome, often encode proteins that help cause disease. This could result in a tradeoff between persistence in your schnozz and the ability to cause disease.
Second, other stress agents, such as the antibiotic ciprofloxacin, were shown in the study to induce this response. That means that these drugs are more effective against the lysogenic strains than the non-lysogenic ones.
It’s like a Mutual of Omaha special…in your nose.
Cited article: Laura Selva, David Viana, Gili Regev-Yochay, Krzysztof Trzcinski, Juan Manuel Corpa, íñigo Lasa, Richard P. Novick, and José R. Penadés. 2009. Killing niche competitors by remote-control bacteriophage induction
PNAS 106: 1234-1238. doi: 10.1073/pnas.0809600106