Hello everybody,

I wanted to isolate phages against Micrococcus luteus from human nose swabs. I tested nose and mouth swabs in a spot assay on M. luteus for phages and the results were clear spots for both. The swabs were diluted in sterile saline only.

Then I cultivated 10ml M. luteus in TSB media to OD600 of 0.5 and added 100µl filtered swab material to the culture and added 100µl of saline to another culture as negative control.

I incubated both at 37°C shaking. The next day the M luteus with swab sample was clear and the negative was opaque, at OD600 of 2.0.

For me, this is a sign of lysed bacteria probably due to phages lysing them.

So, I took 1 ml of the whole culture (not centrifuged) and filtered it through 0.2µm and added it to a new culture, incubated overnight shaken at 37°C. I also tested the filtrate in a new spot test.

The spot test as well as the culture did not show any signs of lysis or spots.

So, I think there might be something other lysing agents in human samples, like lysozyme or something. Or the phages are inactivated fast or go temperent... Does anyone have an idea, what this result could mean?