**1. Introduction**

Staphylococcus is normal resident bacterium that lives in nasal cavity, throat, skin and mucous membrane of humans as well as a variety of animals and birds [1]. Approximately 20% of healthy populations are persistent nasal carriers and 30% are intermittent carriers of *S. aureus*. Individuals who are colonized with *S. aureus* are at a great risk of infection and also serve as an important source of transferring *S. aureus* in the community and hospital settings [2].

Based on the Coagulase production, Staphylococci are classified into Coagulase negative staphylococci (CONS) and Coagulase positive staphylococci (COPS). Of these, CONS causing infections are mostly seen in immune-compromised patients [3]. COPS (eg. *S. aureus*) is a pathogen of great concern, because of its intrinsic virulence property, its ability to cause a variety of life-threatening infections (superficial skin infections to deep seated infections), and its capacity to adapt to different environmental conditions [4].

*S. aureus* is a major problem in animals. It causes mastitis or intramammary infections and is a cause of major financial losses in the dairy industry. In Poultry industry, *S. aureus* causes a variety of disease manifestations such as comb necrosis, bacterial chondronecrosis and also leads to leg weakness, lameness and septicemia [5].

In the modern world, antibiotics are used in treatment and prophylaxis of human and animal infection. They are also used in poultry industry to prevent bacterial infection and reduce the financial loss [6]. In some developing and underdeveloped countries, antibiotics are used as growth promoters in animal feed, especially in poultry industry to increase the yield of meat production. Due to irrational use of antibiotics, *S. aureus* has emerged to become increasingly antibiotic resistant. This leads to treatment failure and leaves us with limited choice of antibiotics to be used in future [7]. Resistant bacteria can be transmitted from animals to humans among poultry workers and other agricultural workers, who are in close contact

with these animals. It is documented that, after using the antibiotic, 'Avoparcin' as growth promoter in animal feed, there is emergence of glycopeptide- resistant Enterococcus. These resistant determinants are transferred to other gram positive bacteria such as MRSA via horizontal gene transfer method. These leads to development of resistance to Vancomycin, a drug of choice for the treatment of MRSA. Simarily, 'Tylosin' or Enrofloxacin (a derivative of fluoroquinolones) is used as a supplement in animal feeds. This has resulted in the development of Erythromycin and Ciprofloxacin- resistant Staphylococci [8].
