**3. Epidemiology of genitourinary staphylococcal infection**

Barring the role of a few bacteria such as *Chlamydia* whose impact on fertility has been well established, the significance of other bacteria in infertility is controversial. An epidemiological research revealed that the prevalence of bacterial vaginosis (BV) as 70.34% among infertile women. Previously, the categories of organisms with the potential to cause bacterial infection in female reproductive system have involved *Gardnerella vaginalis*, *Mobiluncus* sp., *Bacteroide* sp., *Prevotella* sp., and *Mycoplasma* sp. [12]. In general, Gram-positive bacteria were significantly higher in number than the Gram-negative bacteria. Series of epidemiological studies have revealed that *Staphylococcus* is among the top bacterium detected from reproductive organs and is closely related with infertility. For example, Momoh et al. [13] reported a prevalence rate of 38.7% *S. aureus* from high vaginal swab and endocervical swabs and a prevalence of 75% from semen cultures of infertile couples. Another investigation identified *S. aureus* as the most prevalent vaginal pathogen (57.33%) among local infertile women, followed by *Escheri‐ chia coli* (25.33%) [14].

Parallel to the situation in females, abnormal presence of *Staphylococcus* sp. has been increas‐ ingly evidenced in the genitourinary system of male patients with fertile problem. In a study of a total of 140 sperm samples collected from the University of Benin Teaching Hospital, *S. aureus* (28.3%) and *S. saprohyticus* (13.0%) were the most common pathogens found and have negative effects on sperm motility and morphology [15]. The commonest bacteria isolated from 160 men attending infertility clinics in South-eastern Nigeria were *Proteus* sp., *S. aureus*, and *E. coli*, and most of the detected strains were resistant to antibiotics assessed[16]. Besides the *S. aureus*, other staphylococci are also commonly found in infertile male patients. *S. epidermi‐ dis* was found to be one of the most common bacteria in 295 infertile males at the Hospital Juárez de México, and the bacteria profoundly affected the sperm motility, pH, morphology, and viscosity [17].

In healthy women of child-bearing age, the protective mucosa in the vagina is populated with microflora typically dominated by lactobacilli, and their dominance over pathogenic anae‐ robes is positively associated with vaginal health. Thanks to the biological antagonism provided by a healthy vaginal microbiota, opportunistic microorganisms are in very low numbers in normal vagina. It is proven that lactobacilli provide a constant acidic pH value and maintain the appropriate concentration of hydrogen peroxide in the genital environment. While under the condition of BV, the concentration of lactobacilli reduces but of some pathogenic bacteria, especially anaerobes or microaerophiles, increase [18]. BV represents the most common vaginal syndrome that affects fertile, premenopausal, and pregnant women, with an incidence rate ranging from 20% to 50% [19, 20]. BV is not caused by one specific pathogenic microorganism but rather by an imbalance of vaginal microbiota. *Staphylococcus* sp., as a kind of amphimicrobian, has been established as one of the specific pathogenic bacteria related to BV. BV is frequently disregarded because the symptoms are often absent or insig‐ nificant. However, this vaginal disorder has already become the most common lower genital tract disorder among women of reproductive age and the most prevalent cause of vaginal discharge and malodour.

Genitourinary MRSA carriage and infection are not rare. A retrospective study was previously conducted on 57 pregnant women positive for MRSA over a 4.5-year period. The data showed that skin and soft tissue infection accounted for 96% of cases and recurrent infection occurred in 58% of the women [21]. Vaginal colonization with *S. aureus* and MRSA was further valuated by Chen *et al.*, who reported that 507 *S. aureus* isolates (17.1%) were obtained from vaginal cultures of 2963 pregnant women, of which 14 (2.8%) were MRSA [22]. In addition, MRSA has become the predominant pathogen that causes the surgically managed infections in the genitourinary area. *S. aureus,* along with *E. coli*, *Streptococci,* and *Trichomonas vaginalis*, forms the abnormal vaginal flora that contributes to the onset of aerobic vaginitis. These pathogenic bacteria substantially alter the vaginal lactate concentration and increase the levels of inflam‐ matory cytokines such as IL-6, IL-1β and leukemia inhibitory factor (LIF) in the vaginal fluid. Two methicillin-sensitive stains of *S. aureus* (MNPE and CDC587) have been documented to induce the expression of IL-8 in human vaginal epithelial cells [23]. Alterations in vaginal microbiology have been associated with many pathological conditions such as endometritis, miscarriage, premature labor, and infertility [24]. Moreover, the flora and cytokines imbalance has implicated in the pathogenesis of pelvic inflammatory disease (PID) and cervicitis and is also a risk factor for urinary tract infection and sexually transmitted disease (STD) [25].
