The invention provides methods and compositions for detecting and diagnosing sexually transmitted infections using a string of epitopes (SOE) specific for detection of causative microorganisms. The antigenic epitopes may be single epitope sequences a plurality of epitope sequences joined by repeats of glycine (-GG-) and/or lysine (-KK-) to form a series of epitopes (SOE), or nucleotide sequences encoding one or more SOEs and host cells harboring said SOE nucleotide sequences. SOEs specific for highly immunogenic regions of proteins from Trichomonas, Treponema and Neisseria species are provided. SOEs to detect the presence of trichomonas species comprise regions from Trichomonas-sptciric aldolase, GAPDH, α-enolase and α-actinin proteins. Pharmaceutical compositions comprising SOEs can also be used as vaccines or to elicit an immune response to specific microorganisms.