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5 Discussion

S. aureus causes apart from minor skin infections severe life-threatening invasive diseases

like pneumonia, endocarditis and sepsis in healthy and especially in immunocompromised

patients. The rapid emergence of S. aureus strains resistant to Methicillin (MRSA) and

many other available antibiotics further aggravates the situation, reﬂected by the drastic

increase in both nosocomially and community acquired MRSA related infections and the

therewith increased mortality rates (Corriere and Decker, 2008). Thus, highlighting the

pressing need for alternative strategies to prevent and treat S. aureus infections.

5.1 Characterisation of the bacteriostatic effect mediated by S. aureus

speciﬁc IgGs

As passive immunisation is appropriate for short term usage, an antibody-based therapy is

highly desirable for the prevention and treatment of S. aureus infections. The major risk fac-

tor for S. aureus infection is for example a post-surgical infection by either an endogenous

or nosocomial S. aureus strain (Perl et al., 2002; Kluytmans et al., 1997; Wertheim et al.,

2005). But, since only few surgeries are scheduled well in advance, a strategy based on

active immunisation would most likely not be appropriate. Moreover, passive immunisation

is also applicable in immunocompromised patients, not able to trigger a sufﬁcient humoral

response.

Furthermore, the combination of antibodies with different functionalities, e.g. neutralisa-

tion of toxins or adhesion to host cell tissue, opsonisation and subsequent phagocytosis by

professional phagocytes, would further increase the beneﬁcial aspects of passive immuni-

sation. In this respect the observation that most likely the immunoglobulin fraction of human

serum caused bacteriostasis of S. aureus (Ehrenkranz et al., 1971), could be indicative of

a so far uncharacterised direct function mediated by S. aureus speciﬁc antibodies.

For this reason, after reproducing the results obtained with human serum, we employed

an intravenous immunoglobulin (IVIG) preparation as source of S. aureus speciﬁc IgGs in

order to analyse whether these mediate inhibition of staphylococcal growth. In fact IVIG ex-

hibited a bacteriostatic effect on S. aureus, and additional control experiments revealed that

this inhibition of growth is solely due to IgG. Moreover, IgGs responsible for bacteriostasis

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Crosley CRSH268MW2 Bedienungsanleitung Seite 56