Negative control
In the laboratory, the medium with nasal secretion was pipetted into micro-screw tubes (Sarstedt; Nrnbrecht, Germany) and kept frozen at -80C until further processing. The NucleoSpin Food Kit (Macherey-Nagel; Dren, Germany) and protocols from Macherey-Nagel were used for DNA extraction. DNA-extracts amplification of the variable V3 and V4 regions of the bacterial 16S-rRNA gene was performed in 25 PCR-cycles with the primer pair 357F/800R.