Preface

*Staphylococcus aureus* is the most ubiquitous microorganism in humans, animals, and the environment, existing as commensal as well as pathogenic bacterium. The pathogen is a major etiology of bovine mastitis that compromises economy and public health. Its greater prevalence in dairy farms results in culling of animals from the production system due to its contagious nature. Several preventive and therapeutic approaches have been applied to stop *S. aureus* from infecting animals. Inability to control this pathogen from spreading from animals to humans and back to animals may result in extensive resistance.

Due to the rise in antibiotic resistance, new strains and types of *S. aureus* are developing. These include methicillin-resistant *S. aureus* (MRSA) and its different types, which include hospital-acquired MRSA (HA-MRSA), livestock-acquired MRSA (LA-MRSA), and community-acquired MRSA (CA-MRSA). Moreover, newer strains have recently developed against the antibiotic vancomycin: vancomycinresistant *S. aureus* (VRSA) and vancomycin-intermediate *S. aureus* (VISA). Further isolates are expected to emerge against other antibiotics, including penicillin, cephalosporins, tetracycline, aminoglycosides, mupirocin, and macrolide. It is evident that resistance in *S. aureus* may spread both vertically (from parent to offspring) as well as horizontally (transformation, transduction, and conjugation) by modifying drug target, limited uptake, inactivation of drug, and active efflux.

Several anti-methicillin-resistant *S. aureus* drugs are now becoming ineffective. Food and food products are harboring resistant strains of *S. aureus*, which is a threat to the environment. In humans, skin infections are a typical representation of strains that take longer than normal to treat. In addition to antibiotics, several other methods are being used to combat *S. aureus*, such as vaccines and bacteriophages. The use of lytic bacteriophages and their byproducts is a promising alternative for bacterial control, since they infect and lyse the pathogen without the inconvenience of side effects as well as contribute to lower consumption of antimicrobials, reflected in the reduction of rates of antibiotic resistance.

This book highlights mechanisms of resistance in *S. aureus* against different antibiotics. The first section discusses the status of resistance and reasons for its increase. The second section discusses the pathogenesis of *S. aureus* in animals and humans, as well as possible solutions. The book summarizes insights into drug resistance in *S. aureus* and its impacts on animals and humans. It opens up new horizons for further research to better cope with *S. aureus* infection.

> **Amjad Aqib** Department of Medicine, Cholistan University of Veterinary and Animal Sciences, Bahawalpur, Pakistan

Section 1
