CHAPTER ONE

INTRODUCTION 

Staphylococcus aureus a member of staphylococcaceae is considered as an opportunistic pathogen for the different mammals including livestock as well as humans (Lowy1998, projan and novick, 1995). It has been reported that staphylococcus aureus is resistance against varies antibiotics present in the market (Lowy, 1998; walsh and bowe, 2002). this bacterial strain word widely known for causing many of the severe and deadly disease like osteomyelitis bacteremia , endocarditic, meningitis, scalded skin syndrome, toxic shock syndrome, food poisoning, etc( Lowy, 1998; drekema et al ., 2001 ). It is the primary cause of lower respiratory tract infections surgical site infection (Richard, et al., 1993) and the second leading of nosocomial  bacteremia (wisplinghoff et al ., 2004) pneumonia, and cardiovascular infections (Richard et al., 1993). Beside these disease, it is also found on the skin of the human beings and causing major problems like pimples, sour throat, hair follicle infection, acne, and sties (a sty is an inflammation of a gland in the eyelid). It is also causes boils, which are deeper pus-filled abscesses of the skin and underlying tissue (freeman-cook and freeman-cook, 2006 Carleton et al., 2004; king et al., 2006). In common with other facultative aerobes, staphylococcus aureus can grow in the absence of oxygen either by fermentation or by using an alternative terminal electron acceptor, such as nitrate.

    Various studies suggest that oxygen play a role in the pathogenesis of staphylococcus aureus, in both is capacity to produce virulence factors and its ability to persist and grow in different and often hostile environment niches (Chan and foster, in 1998; clement and foster, ohisen et al., 1997; Ross and onderdonk, 2000). The bacteria contain or can produce a variety virulence factor like adhesion, colonization, exoenzyme and exotoxins, capsule etc.These virulence factors help the bacteria to attack to the host cell, it can bind to protein such as fibronectin, laminin, vitronectin, and collagen, which form the extra cellular matrix of epithelia and endothelia surfaces (Gillaspy et al., 1990; freeman-cook, 2006). The resistance to antibiotics emerged and spread rapidly among strains of staphylococcus aureus, about 90% of staphylococcus aureus strains are currently resistant to penicillin and derivatives. To combat this problem, new derivatives of penicillin were introduced (Lowry, 2003; freeman-cook, 2006).

    Today, around 50% of all staphylococcus infections are multidrug resistant (resistant to penicillin, methicillin, tetracycline, and erythromycin). One antibiotic stood for years as a drug that did not cause resistant bacteria to emerge. It often thought of as “last resort “, the name implies exactly how it has been used. Thus, the battle between human and bacteria continues (Freeman- cook et al., 2006). The computational approach has been use to investigate novel drug targets in other pathogenic organisms such as pseudomonas aeruginosa (sakharkar et al., 2004; perumal et al., 2007) and in helicobacter pylori (outla et al., 2006). As most currently known, antibacterial are essentially inhibitors of certain bacterial enzymes. In this study, we have adopted a strategy for comparative pathway analysis to find out some potential target against staphylococcus aureus. Only those enzymes which show unique properties than the host were selected as the target.

         Staphylococcus aureus is a vanguard for both nosocomial and community- acquired infection. It is the primary cause of surgical infection and lower respiratory tract infections, (Richard et al., 1993) and the second leading cause of cardiovascular infections, and pneumonia (Richards et al., 1999). Because of evolved resistance to antimicrobial drugs such as penicillin newer narrow-spectrum β-lactamase-resistant penicillin antimicrobial drugs (e.g. methicillin, oxacillin) infection with staphylococcus aureus are especially difficult to treat and this resistance appeared soon after they were introduced into clinical practice respectively in 1940s and 1960s (Lowy et al., 2003 ). Initially resistance to penicillin was restrained to small number of hospitalized patients, but as use of penicillin increased, resistance spread first to other hospitals and then into the community (chambers at el., 2001). Greater than 80% of community and hospital- acquired staphylococcus aureus isolated were resistant to penicillin by the late 1960s (Lowy et al., 2003). Current report suggests that the spread and evolution of methicillin-resistant staphylococcus aureus (MRSA) seems be following identical wavelike emergence pattern (Chamber et al., 2001). In many US hospitals, MRSA is now endemic and epidemic along term care facilities and communities (Straus Baugh et al., 1960). National nosomial infections surveillance system's data suggest that the proportion of staphylococcus aureus isolate that are resistant to methicillin has increased to 59.5%-64.4%, in intensive care unit (klevens et al ., 2006). Accurate national estimate of incidence are needed for understanding the magnitude of the problem. Nevertheless, national studies examine the effect of staphylococcus aureus or MRSA on the healthcare system are greater than 5years old (Kuehnert et al., 2005). Noskin et al., estimated that there were 290,000 staphylococcus aureus related hospitalization for 1999-2000 and reported that125, 969 (43.2%) were likely resistant to methicillin (Kuehnert et al., 2005). The infections caused by this pathogen range from mild infections such as skin infections, poisoning to life threatening infections such as pneumonia, sepsis, osteomyelitis and infection endocarditic. Methicillin- resistant staphylococcus aureus is considered as super bug which was first reported in 1961 and now-a-days cause mortality rate of 39% while MRSA cause 24% death [laupland et al .., 2008].