**6. Genotyping**

long time periods, whereas intermittent carriers may carry different strains over time [31, 33, 35]. Furthermore, the load of SA is higher in persistent carriers, which results in increased dispersal and a higher risk of infection [24, 29]. Nasal carriers who are also persistent carriers

Approaches that use high-throughput nasal swab data can also be applied to help in our understanding of the bacterial spread. While many studies have focused on nasal swab data, it is still unknown whether nasal SA colonization alone can trigger an SA outbreak. By achieving a deeper understanding of the repercussions of carrying nasal SA, this should help to refine and optimize strategies for risk control among athletes, thereby reducing SA infections.

The skin is the largest organ of the human body, representing more than 10% of the body mass [38]. In athletes who participate in contact and collision sports, the risk of transmission of SA has been shown to be particularly high [39–41]. It has been hypothesized that "skin-toskin contact" might be the main cause of SA transmission in athletes, with the physical contact inducing SA dissemination in these athletes [1]. The average area of the skin surface of a

[43], the skin of an athlete is usually soaked in sweat, which provides a moist and nourishing environment that is suitable for SA growth. Therefore, skin sweat has been considered to be a

Recent evidence suggests that nasal SA has a high propensity to colonize the skin surface [45]. This idea is supported by the finding that colonization often simultaneously disappears from other body sites if an intranasal topical antibiotic is used to temporarily eliminate the SA nasal carriage [46]. Furthermore, cutaneous investigations that examined sweat glands, sebaceous glands, and hair follicles have reported that these areas are likely to be associated with their own unique microbiota [47]. Sebaceous glands secrete lipid-rich sebum, with this hydrophobic coating able to protect and lubricate the hair and skin. In general, sebum serves as an antibacterial coating and acts as a molecular defense mechanism [48]. However, the relationship between exercise-induced sweating and SA transmission in physical contact sports

It has been reported that the nasal cavity is the primary reservoir for SA and that these carriers are an established risk factor for transmission. Two factors may be involved in the SA transmission in an athletic setting. First, nasal carriers also carry the organism on their hands. Thus, not only are contaminated hands considered to be a likely source for causing the transmission, the hands actually serve in many cases as the primary vectors for transmitting the nasal SA. Second, SA can also live on the skin, which makes it easy to transmit from one person to another via sweat. This route is considered to be the major mode of transmission. The reason for the presence of a higher density of SA on the skin surface is due to the sweat that occurs

[42]. Although a dry, salty, low-pH skin surface discourages SA growth

are reported to have higher SA loads and disperse more SA [21, 36, 37].

**5. Skin surface of** *S. aureus* **in athletes**

key point of transmission during physical contact [44].

human adult is 2 m2

38 Frontiers in Frontiers in Staphylococcus Aureus *Staphylococcus aureus*

among athletes remains unclear.

during exercise in nasal carriers [11].

Although there is a low risk of the SA infection in team sports, early detection and an awareness of possible pathways of SA transmission could play a huge part in reducing social and economic impacts if an outbreak was to occur in a particular type of sports. Studies that have examined team sports have reported on the importance of early detection in the prevention of the spread of SA [1]. When there is an SA outbreak among a sports team, the first goal should be to identify all of the carriers, which includes both players and the coaching staff. However, it can be difficult to directly obtain such information at the present. Since the SA isolation test is the most reliable and sensitive method that can be used in these identifications, the use of these tests is essential for accurate surveillance of SA outbreaks. However, it should be noted that these tests also isolate many nonspecific SA from the anterior nares of the nose or the wound. Thus, the lack of SA specificity could hinder the surveillance. At present, both mannitol salt agar with egg yolk and Baird-Parker agar media are specifically used for SA isolation. Since these media require a large amount of time for the preparation, this raises the labor costs. In addition, the mannitol salt agar with egg yolk and Baird-Parker media exhibit weak reactivity against other different bacteria, and thus, this test requires appropriate proficiency in the discerning of the colony. Therefore, a reliable method that can be readily adopted by general diagnostic laboratories will need to be developed in order to improve the diagnostic ability of these tests. The examination methodology used is central to the SA surveillance.

Recently, molecular typing methods have greatly improved our understanding of SA transmission, provided powerful tools for tracing the transmission of individual strains and revealed methicillin-resistant SA (MRSA) strains [17]. Since there is a lack of data on the prevalence of SA transmission among athletes, this has prevented effective surveillance, thereby leading to the failure of preventing infections. In the infection control field, our understanding of SA transmission is limited by the methods used to determine the relatedness of microorganisms in the context of time and space. Conventional typing methods, such as phage typing, multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) [54], spa typing [55, 56], and multi-locus enzyme electrophoresis (MLEE) [57], have all been successfully used to describe the global population structure of SA. In addition, this methodology has been used to provide a framework for the description of the major lineages associated with healthcare-associated infections in different countries and to monitor their emergence, dispersal, and decline in different settings [58]. However, when attempting to investigate the finer details of infection outbreaks, these conventional typing methods have serious limitations [59]. Phage-open reading frame typing (POT) has been developed as a genotyping tool based on multiplex polymerase chain reaction (PCR) [60]. These POT methods have been applied to investigate nosocomial MRSA outbreaks, with the discriminatory power of the method shown to be excellent [61, 62]. Although strategies that use molecular genotyping have been able to successfully detect the presence of SA colonization within a few hours, at the present time, they cannot help in predicting the carrier state. In addition, these methods are expensive as compared to that for standard cultures.

## **Acknowledgements**

This paper is a revised and enhanced version of the authors' recent publication [11]. This study was funded by the Ministry of Education, Culture, Sports, Science and Technology, grant number (KAKENHI24700748), Grant-in-Aid for Young Scientists (B).
