**4. Treatment of bacterial STIs and resistance to antibiotics**

Since its introduction against syphilis, in 1943, penicillin has remained the treatment for this disease, at all stages, and until now, no forms of resistance have been reported [6].

With respect to *C. trachomatis*, infections unresponsive to tetracycline or doxycycline have been reported, but pathogenic strains of this bacterium showing stable resistance to tetracycline have not yet been isolated from humans [17]. However, in the case of chlamydiosis, it is very likely that the infections will reappear even if adequate treatment has been used. This fact is due to reinfection or relapse, if the bacteria deviate to persistent phenotypes, resistant to antibiotics [18].

The three classes of antibiotics used in the treatment of *Ureaplasma* spp. are quinolones, tetracyclines, and macrolides, tetracycline being the most frequently used drug in the treatment of *U. urealyticum* infections [19]. In bacteria, tetracycline resistance is encoded by several genetic determinants, of which *TetM* is the only tetracycline resistance determinant reported so far in mycoplasmas. Using NAATs, both the presence of mycoplasmas and their resistance to this antibiotic can be determined from a single biological product sample [20].

The biggest problems with antibiotic resistance occur with *N. gonorrhoeae*. Being a bacterium capable of incorporating and changing DNA, as well as transferring modified DNA sequences, *N. gonorrhoeae* is known as a bacterium that readily develops mutations. This fact is important both for the development of antibiotic resistance and also has an important role in developing the diagnosis using NAATs, considering that the sensitivity of a certain molecular test can be decreased if the target is a genetically modified region. In recent years, *N. gonorrhoeae* has become less sensitive to several antibiotics, such as sulfonamides, penicillin, tetracyclines, fluoroquinolones, and even cephalosporins, thus defending multiresistant strains to antibiotics and therefore the appropriate treatment is sometimes difficult to apply. In many countries, dual antimicrobial therapy (ceftriaxone plus azithromycin) is the recommended first-line empiric treatment [21]. Due to the phenomenon of resistance, lately, natural products are increasingly being sought as possible alternative treatments for gonorrhea [22].

Resistance of microorganisms to antibiotics is a very dynamic phenomenon, which highlights the need to update prevalence and susceptibility data in different geographical areas. The use of molecular tests for surveillance of antimicrobial resistance in sexually transmitted bacteria would provide a significant advantage in terms of public health and the treatment of these diseases [23].
