The role of immune evasion cluster (IEC) encoded proteins in Staphylococcus aureus (S. aureus) nasal colonisation

Staphylococcus aureus (S. aureus) permanently colonises the nose of about 20%
of the healthy human population. Colonisation is a risk factor for subsequent
infection. Still, little is known about the mechanisms defining S. aureus
carriage. Recently a key role for Clumping factor B (ClfB), a S. aureus cell
wall protein, was demonstrated. A role for the immune evasion cluster (IEC) is
proposed in this study. The IEC is carried by
beta-hemolysin-converting-bacteriophages and is found predominantly in human S.
aureus isolates. The IEC is formed by genes encoding four human specific innate
immune evasion molecules, namely SCIN (Staphylococcal Complement INhibitor),
CHIPS (Chemotaxis Inhibitory Protein S. aureus), SAK (Staphylokinase) and SEA
(Staphylococcal Enterotoxin A). Therefore, it is hypothesised that S. aureus
with an IEC is able to persist longer in the human nose than S. aureus without
an IEC.

This study aims to define the role of the IEC in S. aureus colonisation.

Experimental study.
Week 1 Pre-study blood samples are collected. Nasal culture is obtained
and questionnaire is filled in.
Week 2 Nasal cultures is repeated in order to differentiate between
persistent, intermittent and non-carriers.
Week 3 Decolonisation treatment is started for all volunteers (nasal
mupirocin twice daily for five days in combination with once daily washing with
chloorhexidin containing soap [Hibiscrub®, Regent Medical, United Kingdom]). If
a side effect of mupirocin is noted (allergic reaction or itching), the
volunteer can no longer participate in this study.
Week 9 Five weeks after mupirocin and chloorhexidin treatment, nostrils
are cultured again to assess colonisation status. If eradication of S. aureus
was not successful, mupirocin treatment is repeated. The participant can
participate in the study only if eradication is successful after one or two
treatments.
Week 10 Artificial inoculation is performed. Both the S. aureus strains
with and without IEC are cultured separately to log phase in TSB. An inoculum
is prepared immediately prior to inoculation. In both the left and right
nostril 1.10exp7 colony forming units (cfu*s) are applied. In each individual
volunteer, either the S. aureus with or without bacteriophage is installed. The
latter is blinded and at random. Inoculation will take place under medical
supervision. Participants receive hygienic advice. After inoculation, medical
check up and culture of both nostrils separately is performed at day 1, 2, 3,
4, 7, 14, 21 and 28 to count the mean number of cfu*s between the strain with
respectively without IEC.
Week 14 End of study. Medical check-up all participants. A nasal,
pharyngeal and rectal swab is obtained. All participants who still carry the
inoculation strain are treated with mupirocin and are swabbed again after one
week. A second blood sample is drawn.

14 volunteers are inoculated with S. aureus strain 8325-4 with IEC (1.10exp7
colony forming units per nostril)
14 volunteers are inoculated with S. aureus strain 8325-4 without IEC (1.10exp7
colony forming units per nostril)

The burden associated with participation is multiple visits to the Erasmus MC.

There are no risks associated with filling in the questionnaire and taking a
nasal swab. The risk associated with the collection of blood is a hematoma and
pain near the injection site. The risk associated with using mupirocin are its
side effects: ichting and irritation. These side effects are rare, however. The
risk of inoculation with S. aureus is a (skin)infection with S. aureus.
However, a large proportion of healthy individuals carry S. aureus, without any
problems. Also, the strain that is used has little virulence. Moreover, in our
previous inoculation studies there were no important infections seen.