A Study on Comparison of Various Methods of Detection of Methicillin Resistant Staphylococcus Aureus.

Rajendran, T (2012) A Study on Comparison of Various Methods of Detection of Methicillin Resistant Staphylococcus Aureus. Masters thesis, Madurai Medical College, Madurai.


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INTRODUCTION: Infections have been one of the major causes of Morbidity and mortality worldwide among human population[49]. All Microorganisms namely Bacteria, Viruses,Parasites and Fungi cause variety Of infections affecting every organ system of the body. Respiratory Infections, Gastrointestinal,Central nervous system[54], Skin and Soft tissue Infections are some of them to be mentioned. Staphylococcus aureus , One of the earliest detected bacteria was discovered by Sir Alexander Ogston in1880 in Aberdeen, Scotland[22].S.aureus is responsible for a wide Range of infections most notable among which are Neonatal sepsis[85], Endocarditis[133] , Bacteremia[31], and Skin infections. S.aureus is an Important pathogen causing serious infections both in hospitals and Community. Discovery of antimicrobial agents is one of the Most important developments in modern medicine. The modern era of Chemotherapy began in 1935 after the discovery of Sulphonamides By German chemist Gerhard Domagk [39] which was marketed by Bayer by the trade name Prontosil. Sulphonamides were used for Treating Staphylococcal septicemia, puerperal sepsis and Meningococcal Infections successfully. This was followed by the discovery of newer Therapeutic agents by many people which contributed to the Antibiotic Revolution in the last century. Penicillin was discovered by Alexander Fleming in 1928[128] and it was therapeutically used by Howard Flory in 1940. Initially penicillin was used for the treatment of war Wounds in 1943. Streptomycin was discovered by an American Microbiologist Selman Walksman [19] in 1943. In 1948 Cephalosporin Was identified by Brotzu [40] and introduced for therapeutic use In 1964. This was followed by the discovery of Erythromycin By Mc Guire[41] in 1952, Tetracycline by Lioyd Conover[74] in 1955, Rifamycin by Sensi and Margalith [42] in 1957, Vancomycin by Edmund Kornfeld in 1958[18] , the first Quinolone, Nalidixic acid by George Lesher[131] in 1962, Minocycline in 1967[74] Tegicycline in 1990[74], Linezolid by E.I.Dupont de Nemours[77] in 2000, Daptomycin in 2003[76], Telithromycin in 2004[75] and a newer anti tuberculous drug TMC207 By Andries[43] et al in 2005. Within a very short period after it’s Discovery (1943), resistance to Penicillin was developed by many Microorganisms, Staphylococcus aureus being the earliest. ANTIMICROBIAL RESISTANCE: Microbial resistance to Antimicrobial agents can be Intrinsic or Extrinsic[8]. Intrinsic resistance results from the normal genetic structure Or Physiological state of the micro organism. Extrinsic resistance is Defined as the acquired ability of a pathogen to withstand an Antibiotic that kills off it’s sensitive counterparts. During the past Twenty five years, alarming number of bacterial strains have evolved With resistance to antimicrobial agents[79]. This resistant microbial Strains have become one of the major concerns of the Clinicians, Microbiologists and Public Health officials. Resistance to antimicrobial Agents developed by micro organisms has created a major problem in The treatment of not only serious and life threatening infections in Hospitals but also common infections at the Community level. . Those patients who are in the intensive care units and burns wards and Infants and elderly are particularly vulnerable[20] . Widespread misuse of antimicrobial agents is one Of the important factors for favouring the emergence of resistant Bacterial strains. Genetic variability is essential for the development of Microbial resistance which occurs through various mechanisms such as 1.Point mutation occurring in nucleoside base pair resulting in alteration Of enzyme substrate or the target site of antimicrobial agents.2.Largescale Rearrangements of the bacterial genome generated by Integrons, Transposons Or Insertion sequences. 3. Acquisition of foreign DNA by plasmids, Bacteriophages or transposable genetic elements[71] This inheritance of Foreign DNA contributes to organism’s genetic variability and it’s Capacity to respond to the selection pressures imposed by the Antimicrobial agents. Resistance to antimicrobial agents is also mediated By microbial enzymes such as Beta lactamase which inactivate the Therapeutic agents. Methicillin, a betalactam antibiotic variant of penicillin Class (2,6- dimethoxy phenyl penicillin) was introduced in 1959 by Beecham[27].It was used to treat infections caused by resistant strains Of S.aureus, but because of it’s toxicity such as aplastic anaemia [50] and Nephrotoxicity[73], Methicillin is no longer used for therapeutic purpose Nowadays. Very soon after it’s discovery, Methcillin Resistance to S.aureus (MRSA) was identified in 1961[122] and has been increasing Since that time. Methicillin resistance first appeared among nosocomial Isolates of S.aureus in England in 1961. Prevalence of MRSA in Hospital infections in England was 21% in 1975 which became 35% In 1991[13] . Now it is prevalent world wide and varies from place To place ranging from 2% to 70% except a few countries like Netherland where the prevalence of MRSA is <0.5% [127]. In India, the Prevalence of MRSA is estimated to be 30 to 70 percent[7] . Since MRSA strain can resist practically all available antibiotics, it has Risen to the level of public health threat in hospitals and in the Community eversince it’s identification. Health care Associated MRSA (HA- MRSA) is different from Community Acquired MRSA (CA- MRSA ) in epidemiological and molecular aspects. Methicillin Resistance in S.aureus is mediated by mec A gene which codes for A modified penicillin binding protein 2a [72] (PBP -2a). This resistance Can be constitutive or inducible. Mec A gene is carried on mobile Genetic elements, Staphylococcal Cassette Chromosome [27] (SCC mec). Atleast five different SCC mec types of varying genetic sequences And size have been described. Types 1 to 3 are found in healthcare Associated MRSA strains and tend to be larger and multidrug Resistant. Types 4 and 5 are associated with community associated MRSA and are smaller and more susceptible to antibiotics other Than Betalactam antibiotics. CA- MRSA also carries the gene for Panton Valentine Leucocidin along with SCC mec type IV element. P.V.L is a virulent factor which was described by Panton and Valentine [79] in 1932. The genes coding for PVL are luk S-PV and Luk F-PV. PVL +ve CA- MRSA strains are associated with severe Necrotising pneumonia with very high fatal outcome. Hospital acquired MRSA is commonly associated with Pneumonia and bacteremia. MRSA bacteremia is a serious condition Which carries the risk of fatality ranging from 23% to 54%. HA-MRSA Is commonly found among infants and elderly and presents with risk Factors such as longer hospital stay [121], urinary catheterization, Diabetes, prior antibiotics especially quinolones, acute renal failure [16]. CA MRSA infection is usually associated with various Risk factors such as weak immune system (as in hivinfection, cancer, Asthma, I.V drug abuse) and prolonged exposure to antibiotics [118]. People who spend time in confined places such as prisons [80], Military barracks[134], college students who live in dormitories, people Who spend time in coastal areas where MRSA is present, athletes And football players, people who are rearing livestock animals that Are infected by CA- MRSA are also at risk of getting infected With MRSA. It produces primarily skin and soft tissue Infections[92]. Recently it has been found to be associated with fatal Necrotizing pneumonia, necrotizing fasciitis [10 ], Meningitis and Brain Abscess [104], Bone and joints infections. A newer strain of CA- MRSA USA 300 was identified in 2001. Now it’s prevalence has been Documented worldwide [60]. This new Strain has caused infections In players [11] and military recruits. CA- MRSA USA 300 has been Reported to have caused nosocomial infections [91] also such as Bacteremia [106] and osteomyelitis [38] and prosthetic joint infections. Drug resistance in other bacteria such as Neisseria gonorrhoeae, Salmonella , Shigella, Mycobacterium tuberculosis And Streptococcus pneumoniae is mainly community acquired problem Whereas MRSA were identified as nosocomial pathogens [122].Commonest Site of carriage of MRSA is anterior nares [2] MRSA is resistant to Many antibiotics and it is very difficult to eradicate from patients as Well as carriers. The therapeutic options are limited and the spectrum of Resistance is worrying. The glycopeptide antibiotic Vancomycin [115] and The lipopeptide antibiotic Daptomycin [15] are used to treat severe MRSA infections. Unfortunately MRSA strains resistant to these Drugs have started emerging recently [47].

Item Type: Thesis (Masters)
Uncontrolled Keywords: Comparison ; Various Methods ; Detection ; Methicillin Resistant Staphylococcus Aureus.
Subjects: MEDICAL > Microbiology
Depositing User: Subramani R
Date Deposited: 19 Aug 2017 02:18
Last Modified: 19 Aug 2017 02:18
URI: http://repository-tnmgrmu.ac.in/id/eprint/1469

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