Essay Example on Methicillin resistant staphylococcus aureus is a gram positive Bacteria








INTRODUCTION Methicillin resistant staphylococcus aureus is a gram positive bacteria and an antibiotic resistant strain of staphylococcus aureus It has been found to be one of the reasons for nosocomial infections In 1972 it was from mastitic infected cattle MRSA was first isolated Animals and humans are mostly infected by these bacteria The infections include rashes osteomyelitis septicaemia and pneumonia This strain of S aureus has become a worldwide threat due to lack of treatment against this bacteria National nosocomial infection surveillance system shows that S aureus is the most common cause for nosocomial pneumonia and one of the causes for bloodstream infections in USA In USA the mortality rate of different diseases like AIDS MRSA infection hepatitis and tuberculosis were compared and interestingly it was found that the mortality rate was found to be more for MRSA infections The prevalence rate for MRSA infections in developed countries were found to be UK 44 Japan 60 70 USA 50 But 2011 reports shows that the mortality rate in USA has declined due to proper hospital care management The bacterium is resistant to β lactam antibiotics like penicillin methicillin erythromycin etc

Their resistance to antibiotics is due to the presence of mecA and mecC gene MecA gene plays a major role in the production of penicillin binding protein 2a PBP2a PBPs are membrane bound enzymes that helps in catalyzation of transpeptidase reaction which is needed for the cross linkage of peptidoglycan chains Due to low affinity of PBPs to β lactam antibiotics staphylococcus aureus can withstand high concentrations of these antibiotics In some MRSA strains the resistance is mainly influenced by a group of genes called blaz Another series of genes known as fem genes also plays an essential role in resistance to methicillin by cross linking peptidoglycan strands The recent studies shows that the MRSA were resistant towards methicillin 45 9 cefixame 44 co trimoxazole 28 erthyromycin 28 gentamycin 18 But 100 were sensitive to vancomycin glycopeptide The need fo the discovery of new antibiotics become important when vancomycin resistant MRSA was isolated in 1996 from Japan Linezolid is one of the synthetic antibiotics used recently for the treatment They act by destroying the bacterial growth by inhibiting the initiation process in protein synthesis Linezolid also helps in inhibiting virulence factor expression and reduces the amount of poison produced by gram positive pathogens Studies have shown that drugs against MRSA should be protein synthesis inhibitors with a gram positive spectrum eg quinupristin dalfopristin Studies have shown that MRSA has been acquired from hospital care workers who have poor handwashing techinques So these conditions can be minimised by improving hand washing techniques MRSA can be controlled by identifying their colonies or the persons who are infected by it Active Detection and Isolation ADI which include screening high risk patients for 

MRSA taking precaution for those who are MRSA positive adopting proper hand hygiene techniques can be used as a controlling technique for MRSA infections ANTIBIOTIC ACTION The discovery of penicillin by Alexander Fleming opened the door for other antibiotics to the world Antibiotic used to treat various diseases has specific site for its action In the recent world majority of diseases has been cured with the antibiotics this lead to the detailed study about this class of drugs They are classified on the basis of mechanism of action chemical structure or spectrum of activity They act by inhibiting cell growth leading to lysis of cell Classification on the basis of mechanism of action as follows CELL WALL GROWTH INHIBITORS The following class of drugs acts by this mechanism β lactam antibiotics glycopeptides bacitracin a β LACTAM ANTIBIOTICS Eg pencillins and cephalosporins Mechanism of action Major component of cell wall comprises of peptidoglycans 1 The peptidoglycans are made of N acetyl glucosamine and N acetyl muramic acid The n acetyl muramic acid unit contain peptide chains which are the site of crosslinking The S aureus contains pentapeptide chains of L Ala γ D Glu L Lys Gly 5 D Ala D Ala 2 These are produced within the cell but the cross linking takes place outside the cell The cross linking is done by a group of enzymes known as transpeptidases These classes of Enzymes are called Penicillin Binding Proteins PBP They are bifunctional enzymes having both transpeptidase domain and transglycosylase domain 

The transglycosylase domain of the enzyme helps in the extension of the sugar by the addition of new peptidioglycan units from N acetylglucosamine b 1 4 N acetylmuramyl pentapeptide pyrophosphoryl undecaprenol 1 The transpeptidases perform their activity by acylation using serine as their active site 3 The β lactam antibiotics act on these enzymes They form covalent pencilloyl complex which prevents the cross linking reactions and their by inhibiting the cell wall synthesis b GLYCOPEPTIDES Eg vancomycin Mechanism of action It targets D Ala D Ala terminal of cell wall peptidoglycan chain inhibiting the transpeptidase activity Thus they prevent the cross linking of peptidoglycans which results in poor cell wall synthesis The resistance can arise by increasing the thickness of cell wall Vancomycin binds to the D ala D ala terminal through five hydrogen bonds This results in high affinity of antibiotics to its target but production of D ala D lac lead to resistance against the site c BICITRACIN They interfere with dephosphorylation of C55 isoprenyl pyrophosphate which is a membrane carrier molecule that transports the building blocks of bacterial cell wall It also acts as a receptor in plasma membrane of bacteria

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