**3. Diagnosis of bacterial STIs**

The bacteria that cause STIs are very different from each other, so the methods of detecting bacterial STIs are very varied. Even for the same bacteria, there are different test methods. Substantial differences between testing methods and surveillance systems in different countries mean that many infections go undiagnosed and thus go unreported.

For example, the laboratory diagnosis of syphilis is based primarily on a series of serological tests: a positive screening test followed by a confirmatory test. Since antibodies can only be detected about 3 weeks after infection, the very early stage of the disease cannot be diagnosed serologically. Dark-field microscopy is used for epithelial lesions, and nucleic acid amplification tests (NAATs) have recently been introduced that can be used for direct detection of the causative pathogen [6].

Also, for the detection of *C. trachomatis*, immunoglobulin antibodies (IgG) persist in the body for years and therefore can be used as markers for infection [13], but the presence of antibodies does not indicate an infection present in the body at the time of detection, so these markers cannot be used in diagnosis.

Although bacterial cultures are considered by some to be the gold standard, some of the bacteria that cause STIs are very difficult to grow on culture media, and therefore most clinicians are unable to correctly assess the presence of one or another STI agent, if use these microbiological methods. For example, *M. genitalium* is difficult to grow on culture media because it has slow growth, strict nutrient requirements, and suitable culture media is not widely available [14]. On the other hand, due to the difficulties of sample collection, transfer, and storage, these methods show low sensitivity and are not suitable for screening, as some bacteria are fragile and difficult to transport.

New laboratory methods using the Polymerase Chain Reaction (PCR) technique allow rapid and targeted detection of STI pathogens, and the multiplex real-time PCR (RT-PCR) technique can be successfully used for the detection of multiple agents from a single sample STI, considering their association in many cases. These genetic tests allow establishing a diagnosis in a maximum of 2–3 days, with a sensitivity of up to 99%. In contrast, cell cultures provide a sensitivity of 85–95% in acute urethral infections with *N. gonorrhoeae* and less than 50% in chronic forms in women [15].

These multiplex RT-PCR kits are suitable for the routine detection of these STIs. They have proven to be cost-effective and rapid diagnostic tools with high reliability for the simultaneous detection of multiple pathogens present [16].
