Microbial Identification of Staphylococcus Aureus - Book Report/Review Example

?The interface between phenotypic and molecular methods of microbial identification of . Staphylococcus Aureus. INTRODUCTION: The Staphylococcus comes from the Greek staphyle, meaning a bunch of grapes, and kokkos, meaning berry and these bacteria may also be found as commensals. They are facultative anaerobic bacteria. Staphylococci are gram positive bacteria that are spherical in shape and are arranged in irregular grape like clusters. They have ability to grow on many type of media under aerobic atmosphere. It is usually present in normal flora of skin and mucous membrane of oral cavity .It is also a member of respiratory tract. It has been observed that it can ferment carbohydrates producing light yellow pigments. (John Ingraham 1995, pg.72) Sir Alexander Ogston was the first to discover staphylococcus aureus from a pus in knee joint during year 1880.It can hemolyze blood and can cause plasma coagulation. Staphylococcus is responsible for many infections in humans and it affects almost every person once in a lifetime as it is a major pathogen affecting humans. They do not form spores and live freely in environment and have ability to form colonies .It produces catalase which also is a key factor in distinguishing it from streptococci. It develops resistance against many antimicrobial agents due to which it has given rise to many therapeutical problems. On agar it produces a yellowish colored colony. DISEASE STATES: Staphylococcus infections are very common among humans .It severity can range from minor food poisoning or skin infections to life threatening infections such as septicemia. It can easily invade breached skin or tissues causing infection. Staphylococcus aureus infections are responsible for causing a number pus forming and abscesses in humans .It has also known to cause food poisoning When it invades breached or injured skin it can cause boils , furunculosis , styes , folliculitis, formation of carbuncle, wound followed by colonization and a variety of pyogenic infections. Some of the serious infections caused by staphylococcus aureus are mastitis, pneumonia, impetigo, toxic shock syndrome, infective endocarditis, osteomyelitis and gastroenteritis. (Bruckner & Rosenstein, 1994, pg. 103) Anyone can easily develop a staphylococcal infection but people who are mostly prone to get affected by staphylococcus aureus infection are newly born infants, mothers who are breast feeding .People who have diabetes or any vascular disease or cancer are also likely to get infected by staphylococcal infection. Moreover drug users who inject drugs or people who possess a weak immune system are also prone to it. Moyer, Tiedje, Dobbs & Karl, (1996) found that Staphylococcus aureus bacterium has a protein at its surface known as protein A which binds constant region of antibodies to each other and in this way antibodies stay fixed at the surface in a way that does not allow them to direct macrophages. Another protein released by staphylococcus aureus is coagulase which activates the clotting mechanism and in this way a mesh of plasma proteins surround the bacteria, although staphylococcus can itself survive inside the mesh but it immune cells do not possess the ability to penetrate so coagulation occurs and in this way staphylococcus is also distinguished form other organisms belong to same group. As it can also secrete hyaluronidase and collagenase so it can degrade proteins of connective tissue and those present between epithelium which allows sudden spread of bacteria into sites that are previously inaccessible. It has also ability to cause disease by formation of enterotoxins such as ingestion of unhygienic and contaminated food. Usually staphylococcus aureus cause disease by elaboration of toxins without any invasive infection. It sometimes can also lead to bullous exfoliation of skin. (Moyer, Tiedje, Dobbs & Karl, 1996, pg63 -93) CLINICAL SAMPLES REQUIRED FOR TESTING: In order to clinically diagnose staphylococcal aureus bacterium we need to gather specimens such as blood, tracheal aspirate, spinal fluid swab and pus. Smears of staphylococcus aureus are visible when seen in smears of pus and sputum which are stained .Moreover specimens are planted on blood agar plates and it is seen that these specimens give rise to colonies usually in 18 to 20 hours at a provided temperature of 37 degrees. In order for hemolysis to occur, a gap of several days is taken at normal room temperature. Staphylococcus aureus ferment mannitol and others organisms related to same group cannot carry out fermentation of mannitol. Specimens are taken and are contaminated with mixed flora on a media which has about 6 to 8 % of sodium chloride, the salt will inhibit most other normal flora but staphylococcus aureus will remain unaffected. In order to identify a person who is carrying staphylococcus aureus in his nasal cavity, mannitol salt agar is used. (Klein & Smith, 2009, pg. 343-356) CURRENT MICROBIAL TESTING PROTOCOLS: Sometimes a test known as catalase test is carried out as a clinical sample which is used as a testing indicator for identification of staphylococcus aureus in which a drop from a solution of hydrogen peroxide is placed on a slide followed by placing a small amount of bacterial growth on it and bubbles are formed which shows that oxygen gas has been produced indicating presence of the organism. Another test known as coagulase test is often carried out for clinical testing in which human plasma which is dilute in nature is taken and is mixed with growth from colonies that have grown on agar at a temperature of 37 degrees. If a clots form in less than six hours it indicates presence of staphylococcus aureus. With advance researches resistance to antibiotics such as penicillin G can also help in predicting a positive test for beta lactamase. Antibiotic pattern are also a helpful tool for indication of infection caused by staphylococcus aureus. Also serological and typing tests are done nowadays in which antibodies to teichoic acid have been detected in prolonged deep infections but these tests are performed rarely. (Funk. 1997, pg. 164) CRITICAL DISCUSIION OF MOLECULAR VERSUS PHENOTYPIC IDENTIFICATION: N315 and Mu5o are some of the early genomes of staphylococcus aureus that were detected in year 2001. After that numerous researches were carried out and many other sequenced genomes of staphylococcus aureus bacterium were submitted to public databases which helped researchers to work more on staphylococcus aureus. As an outcome of numerous researches related tp staphylococcus aureus it was seen that it has produced a variety of strains and variety of sequenced genomes. Each its strain has different surface protein and thus produces a different toxin. With invention of advance technologies such as sequencing and microarrays ,phenotypic study of staphylococcus has shown that acquisition of mobile genetic elements encoding resistance and virulence genes may lead to identification of more strains and so their prevention can be worked upon in a more better way. (Scherrer, Corti, Muehlherr, Zweifel & Stephan 2004, pg64). The well-known prevalence of strains of organism's resistance to antibiotics such as penicillin G and vancomycin has been assigned to horizontal gene transfer of genes encoding metal resistance and having virulence. The genome of staphylococcus aureus bacterium is the most common among the rest of the group. It possesses the most sequenced structure when it is compared to genomes of other organisms. Its actual genome is based upon NCTC 8325 introduced by a microbiologist named as Peter A. It is a complete circular genome and has an average length of 842 nucleotides. (Chiang, Chang, Lin, Yang & Tsen 2006 pg. 133-178). In reference to an article which was published in “US National Library of Medicine on 15 June 2012”, to compare the molecular and phenotypic characteristics of community associated methicillin-resistant staphylococcus aureus at a rural hospital,a research was carried out in which hospital history did not co related well with MRSA that was emerged in hospitals and interestingly the history even did not co relate with those genotypes that emerged in those patient who were not given an access to health care. “The results gathered indicated no relevance between patient risk factor epidemiology in relation to the MRSA isolates’ genotypic and antimicrobial resistance characteristics. The ever-increasing shift of healthcare from acute hospitals to non-acute and home settings may in part explain the findings. As CA-MRSA strains enter healthcare settings, and HA-MRSA strains disseminate to the community, isolate genotype and antimicrobial susceptibility phenotype provide different pieces of information to track movement of strains and inform community clinical practice and hospital infection control efforts.” (Peterson, Davis & Julian, 2012, pg. 3-4)   According to an article published in World Applied Sciences Journal 15 (12) on the topic entitled as Phenotypic and Molecular Identification of Staphylococcus aureus Isolated from Egyptian Salted Fish , sixty samples of sardine fish , 30 samples of Molouha fish and 30 samples of Fesikh fish were taken and were studied for identification of staphylococcus aureus and the results concluded that antimicrobial sensitivity property of staphylococcus aureus strains made its isolates sensitive to antibacterial agents such as ciprofloxacin gentamycin etc. Isolates also revealed different patterns to antimicrobial resistance .In order to confirm presence of staphylococcus aureus it was confirmed by PCR using two oligonucleotides primers of genes Sau234-1501 and COAG2_COAG3.Results indicated that all isolates of staphylococcus aureus were coagulase positive. 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