Preface

Staphylococci is a bacterial genus with high pathogenic potential for both humans and animals, especially dairy animals. In this broad group of bacteria, 85 species and 30 subspecies have currently been reported, generally divided into two large groups: coagulase positive (CPS) and coagulase negative (CNS) staphylococci.

Within the coagulase positive group is *Staphylococcus aureus,* which is the main pathogen for humans and livestock and companion animals; the main coagulase negative strain is *S. epidermidis*. However, other species have caused infections and should not be ignored. A high percentage of people carry this microorganism in different parts of the body, mainly in the nose; data increasingly points to a high percentage of carriers also in the pharynx.

*S. aureus* can colonize and behave as a commensal; the colonization process is a fundamental part of the life cycle of the bacteria. Under certain circumstances, including environmental, bacterial and host factors, they can produce a wide variety of infections ranging from mild to fatal. The severity of *S. aureus* infections is mainly due to the existence of antibiotic-resistant strains, especially methicillin-resistant *S. aureus* (MRSA) strains, which appeared within a few years of the introduction of methicillin replacing penicillin, to which there was already a high percentage of resistant strains, for the treatment of this bacterium.

At first these strains were only found in hospital environments, mainly causing nosocomial infections, and were called hospital-acquired MRSA (HA-MRSA) strains. However, since the 1990s they have moved into the community, causing infections in people who had not been in a hospital environment. The WHO issued a global alert for the prevention and combat of the new strains, which became known as community-acquired MRSA (CA-MRSA). These strains, however, have managed to return to hospitals, now causing new infections in hospitals as well.

Years after the appearance of CA-MRSA strains, MRSA strains were found in livestock workers, giving rise to the group of MRSA strains acquired from livestock (LA-MRSA). This indicates that *S. aureus* strains present in animals can be passed to humans and vice versa.

All of this speaks to the ongoing evolutionary dynamics of staphylococci, especially *S. aureus*.

What is it that makes this microorganism so pathogenic and able to adapt to changes in the host and the environment? How can we determine the presence of staphylococci and their virulence factors? What new treatments are there to combat this microorganism? These are some of the questions that this book seeks to answer.

The first section brings together several chapters referring to colonization by *Staphylococcus aureus* and the factors involved in the process. The second section concerns the epidemiology and pathogenesis of *S. aureus*. The third section is related to the diagnosis of the bacteria and its virulence factors. The last section explores new compounds with antibacterial activity against staphylococci.

In the first section, "*Staphylococcus aureus* and Methicillin Resistant *Staphylococcus aureus* (MRSA) Carriage and Infections", reviews *S. aureus* and MRSA strains in relation to their carriage in humans, their pathogenesis, their resistance to antibiotics, the diseases they cause and their treatment. "Multidrug-Resistant *Staphylococcus aureus as* Coloniser in Healthy Individuals" analyzes the relationship between colonization by *S. aureus* and the possibility of causing disease in carriers through carrying a bacterium that can be dangerous due to its pathogenic properties and their resistance to antibiotics.

The second section contains two chapters on the epidemiology and pathogenesis of *S. aureus*. The colonization of *S. aureus,* the initial process through which this microorganism can produce a disease or persist for a long time in the host is described in "Main Factors of *Staphylococcus aureus* Associated with the Interaction to the Cells for Their Colonization and Persistence". This chapter also discusses the molecules involved in the adhesion of the bacteria to the host cells and their regulation mechanism, as well as biofilm formation, an important part of the colonization process. The evolution of the *S. aureus* strains produces variations in the colonization of the population, leading to changes at the epidemiological level. An example case is described in "The Molecular Epidemiological Study of MRSA in Mexico". Such epidemiological studies contribute to the understanding and development of possible control measures for this microorganism.

Section three consists of two chapters related to diagnosis, an important part of the fight against staphylococci and an essential process in the detection and control of infections they cause. "Recent Progress in the Diagnosis of *Staphylococcus* in Clinical Settings" reviews different methods to detect these microorganisms, from conventional microbiological methods, through molecular methods to the advanced technique of surface-enhanced Raman spectroscopy (SERS). The significance of staphylococcal infections for the livestock sector, especially dairy animals, is covered in "Occurrence of Mastitis in Dairy Herds and the Detection of Virulence Factors in Staphylococci", which describes coagulase negative and methicillin-resistant staphylococcal mastitis infections.

The ability of staphylococci to resist multiple antibiotics enhances their pathogenic capacity, which is why new substances that can eliminate these bacteria are needed. The search for new compounds with antibacterial activity against staphylococci is presented in Section four. The use of silver and copper nanoparticles as an alternative to combat staphylococci is discussed in "The Ability of Some Inorganic Nanoparticles to Inhibit Some *Staphylococcus* spp.". The second chapter of this section, "Potential Use of African Botanicals and Other Compounds in the Treatment of Methicillin-Resistant *Staphylococcus aureus* Infections", analyzes the use of various active substances from medicinal plants that have shown antibacterial action against staphylococci and especially against MRSA strains.

We hope readers will enjoy this book and find information and recent advances relevant to the study of colonization, diagnosis, and treatment of staphylococci, and especially of *S. aureus* and MRSA strains.

## **Dr. Jaime Bustos-Martínez**

Department of Health Care, Autonomous Metropolitan University-Xochimilco, Mexico City, Mexico

### **Dr. Juan José Valdez-Alarcón**

Multidisciplinary Center for Studies in Biotechnology, Faculty of Veterinary Medicine and Zootechnics, Universidad Michoacana de San Nicolás de Hidalgo, Michoacán, Mexico
