The explosive progress over the past decade in the fields of genomics, bioinformatics and
mass spectrometry has resulted in an increased capability to investigate and compare the
global protein expression of cells, tissues and organisms. The main focus of this study was
on characterising the protein expression profiles of different serovars of Salmonella
enterica and different serotypeso f Streptococcusp neumoniae in an attempt to identify
protein factors associatedw ith host specificity and virulence.
A novel approach for typing of bacterial isolates using SELDI TOF MS was developed. A
thorough investigation on the effect of different factors on the quality of the SELDI profile
was carried out, and the potential of several software programmes to perform cluster
analysis of the SELDI data was assessedB. oth cytosolic and membrane-associatepdr oteins
were separatedb y 2D GE, and detailed referencem aps of the proteins expressedu nder
standardisedc. onditions were created.I n the caseo f Salmonella, it containedm ore than 300
proteins. The comparativea nalysisa t the subspeciesle vel revealedt hat, in many cases,t he
variation in the expression patterns was greater between strains with the same serospecificity
than betweens erotypes/serovarss, uggestingt hat the serological properties of
bacteria do not correlate with differential protein synthesis. However, in the case of
Salmonella, where the serovars have different host specificity, the high resolution 2D gel
maps revealed several serovar-specific proteins, including enzymes involved in the
catabolismo f various substrates,o r in the processo f cell detoxification. Changesi n the
expression patterns of the serovars in different growth conditions, such as pH or oxygen
availability, were mostly universal amongst the serovars, although a few serovar-specific
proteins were also present.
The findings revealed parts of the proteome that alter their expression when the
microorganism are subjected to unfavourable conditions such as while colonising the host,
amongst other parts that remain stable. Overall, the results demonstrated the importance of
analysing many different isolates when performing protein expression studies in highly
variable microbial populations.
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