Inquilinus

Question

Hello,
I am 27 years old, CF patient (F508 homozygous). Until today I have only been colonized chronically by Staphylococcus aureus (Pseudomonas was always negative). My FEV1 value is between 107-117%. For several weeks I have been taking Kaftrio now (Trikafta). This led to a broad improvement: I have no cough and no sputum anymore.
Two weeks ago I had an infection, the course seemed to be not the usual one to me. At first, I had only slight symptoms of a cold, then 3-4 days later I got heavy dark green sputum (which I was not used to have anymore since Kaftrio), as well as I got fever over 39°C. After the intake of a fever-suppressing drug, the fever went down to a moderate temperature and it went away in the course of the next day. The blood showed increased inflammatory values, e.g. the leucocytes were increased and the CRP value.
In spite of the down-going fever I got 2 antibiotics (amoxicillin/clavulanic acid 3 times a day for 7 days and clarithromycin 500mg two times a day for 5 days).
In the meantime I have no symptoms of a cold anymore, however I still have some amount of slight greenish sputum (I did not have this before this cold). My CRP value got back to normal.
In the acute phase of the infection my sputum was tested. Now I have the result; besides the chronic colonization with Staphylcoccus aureus a new germ has been found: Inquilinus.
This germ seems to be relatively rare, I found on this site an old remark about this germ, which was written in 2013. Therefore I would like to ask if there are any new findings. I read about a worsening of the pulmonary function due to this germ.
Now my question:
how do you judge the danger of this germ concerning a worsening of the lung function and would you say it should be treated? If yes, how urgent is the beginning of a treatment and it there any hope of success due to the multiresistancy of the germ?
Best regards,

Answer

Dear questioner,
Inquilinus a very rare bacterium, that can be found from time to time in patients with CF in the airways. In many cases, this finding of the germ has no consequences, especially if it is only a temporary colonization - that means the bacterium is there but does not cause any symptoms and can disappear again. Therefore it is recommenden to test the sputum samples regularly.
Sometimes however, Inquilinius can cause symptoms such as cough, increased sputum production or a worsening of the lung function. Especially in patients with chronic lung diseases, like CF or an impaired immune system, the germ can become problematic. The treatement can be difficult, as the germ is resistant against many antibiotics.
Some patients stay in a stable condition besides the permanent finding of the germ, however. It is important to be under regular medical control. In case the health condition is worsening or signs of an acute infection appear, an antibiotic treatment is necessary.
Please talk to your CF physician about the best way and decide together if an antibiotic treatment makes sense - this is dependent on your health status after the last infection.
Best regards,
Dr. med. Christina Smaczny und Prof. Dr. med. Michael Hogardt

20.01.2026