Representative images of the standardisation process for the detection of C. trachomatis, N. gonorrhoeae, M. hominis and U. urealyticum by 16S rDNA gene amplification. Lanes MWM: 100-bp marker (Invitrogen™, Carlsbad, CA). The sizes (bp) are indicated on the left. The PCR products were electrophoresed on a 1.8% (wt/vol) agarose gel, stained with ethidium bromide and photographed under UV light. A. Lanes 1-4: Single PCR detection of M. hominis, C. trachomatis, N. gonorrhoeae and U. urealyticum. B. Lanes 1-2: Duplex PCR for the simultaneous detection of M. hominis and N. gonorrhoeae; lane 3: negative control (no template). C. Lanes 1-6: Triplex PCR for the simultaneous detection of M. hominis, N. gonorrhoeae and U. urealyticum; lane 7: negative control. D. Lanes 1-4: Quadruplex PCR for the simultaneous detection of M. hominis, N. gonorrhoeae, U. urealyticum and C. trachomatis; lane 5: negative control. Panels B, C and D also show the effects of the target DNA concentration on the multiplex amplifications; the best yield is shown in lanes 2, 6 and 4 using 100 ng of DNA template.