Demonstration of antigenic and specific outer membrane protein(s) of Acinetobacter baumannii
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Date
2009-06
Authors
A.H.M. Shafiqul Islam
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Abstract
Acinetobacter baumannii has been recognized as an emerging nosocomial pathogen and
is very often multi-resistant to antibiotics. It has also been identified as an important
cause of morbidity and mortality in hospitals, especially among immunocompromised
patients. Early diagnosis of infection caused by A. baumannii is the major strategy for
controlling the nosocomial infection caused by this pathogen. Current identification of
this bacteria is by conventional culture method and biochemical tests, which takes about
2 to 7 days to produce results. Hence, there is a need for a new rapid, sensitive, specific
and economical test that would allow rapid management of A. baumannii infections.
Development of a specific and sensitive diagnostic test requires a biomarker, which does
not cross react with other bacteria and is specific only to A. baumannii. This formed the
aim of this study; to detect the presence of a specific and antigenic biomarker for A.
haumannii from the OMPs, which can be used for the development of a rapid and
specific diagnostic test. Protein profiles of OMP lysates from the ATCC strain and
clinical isolates of A. baumannii were demonstrated using the technique of SDS-PAGE
and the protein profiles were compared. The protein profiles of the clinical isolates were
90% identical to that of the ATCC strain. Following this, the protein
electrophoretograms were subjected to \\'estern blot analysis using serum from patients
infected with A. haumannii and non-A. baumannii. The Western blot analysis revealed a
34.4 kDa antigen which was immunogenic when probed IgA, IgM and IgG of A.
baumannii sera but did not cross react with sera from other nosocomial infections and
normal controls. This was confirmed by repeated testing.
Studies were also done to asses the effect of temperature on the expression of the OMPs.
The OMPs profile expressed at 41°C showed few proteins were over-expressed (17.3,
22.4 and 60.5 kDa) while some proteins were down-regulated, suggesting that elevated
body temperature during A. baumannii infection influences the expression of the
bacterial proteins for survival of this bacterium.
Further characterization ofthe 34.4 kDa protein demonstrated that it was associated with
both OMPs and SAPs of A. baumannii and is not a glycoprotein. The 34.4 kDa antigen
was present in all the clinical isolates of A. baumannii. The expression of this protein
was enhanced in most cases suggesting that tl iis protein could also be related to the
virulence of the bacteria. To date, no previous report is available with reference to this
specific protein for A. baumannii. The results are encouraging in that the 34.4 kDa
protein identified is specific for A. baumannii and can be used as a biomarker for
development of a diagnostic test which would be faster and more specific than the
current techniques of diagnosis. However, further studies need to be done to measure the
antibody level against this specific protein, the sensitivity and specificity of the protein
and the retention time of the antibody detectable in the serum of the infected patients.
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Keywords
Acinetobacter baumannii , Multi-resistant to antibiotics.