**1. Introduction**

Sexually transmitted infections (STIs) are some of the most common infections worldwide. Newer sexually transmitted pathogens have been recognized and functionally described since 1980, with over 30 such infectious products currently known, which may be bacteria, viruses, or parasites. Today, conditions exist in developing countries that lead to an ever-increasing rate of STIs. Factors that influence this growth are: population explosion, especially in age groups that include teenagers and young people, population migration to urban areas, wars, or poverty. In these countries, in addition to human immunodeficiency virus (HIV) infection, three sexually transmitted bacterial infections (gonorrhea, chlamydia, and syphilis) can be considered among the first to affect the health of the population and reproductive life.

The most common sexually transmitted infection worldwide is chlamydia, with approximately 146 million infections each year. But while trends in increasing numbers of *Chlamydia* spp. infections appear to have stabilized in recent years, gonorrhea rates have increased, especially among men. The 2013 report on STIs in Europe shows that, in the countries of the European Union and the European Economic Area, STIs differ by age group: young adults between 15 and 25 had only 14% of syphilis cases but had nearly 39% of gonorrhea and 67% of chlamydia cases [1].

The Centers for Diseases Control and Prevention's (CDC) estimates that the prevalence and cost of STIs in the United States indicate that 20% of the population in this region (about one in five people) had an STI in 2018, infections that have cost that year almost 16 billion dollars in direct medical costs from the budget of the American health system [2].

No STI can be viewed and treated as an isolated infection because multiple infections are very common and the presence of an STI denotes high-risk sexual behavior that may be associated with other infections, which may be more serious. STIs can be classified based on both cause and clinical manifestations. Some of the pathogens can also be transmitted non-sexually, but for each of them, sexual transmission is clinically and epidemiologically important.

Many STIs are caused by bacterial infectious agents. In general, most STIs caused by bacteria are treatable, but if they go undiagnosed or are diagnosed too late, they can seriously affect the health of infected people. Thus, early detection and treatment can reduce the spread of bacterial STIs in the population.

Bacterial vaginosis is known to be highly implicated in female infertility and is probably a major cause of unexplained infertility. Screening and treatment of bacterial vaginitis during infertility treatment has greatly decreased its rate [3].
