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Staphylococcus Aureus
Characteristics:
Staphylococcus aureus is gram-positive cocci usually seen under the microscope as irregular grape-like clusters. Staphylococci are recognized by their production of catalase; only S. aureus is coagulase positive. It can also hydrolyze mannitol that other strains cannot do (Levinson, 2006).
Morphological Phenotype:
The colonies can be recognized by their characteristic golden colour due to the presence of a carotenoid pigment called Staphyloxanthin (Levinson, 2006).
Isolation and Cultivation:
The organism produces yellow golden colonies and a clear area around them in blood agar due to beta hemolysis. All of the Staphylococci are catalase positive (positive catalase test). From the strains of staphylococci, S. aureus can be identified by a positive coagulase test, golden colonies and growth on mannitol salt agar. (Levinson, 2006).Model organisms
Biology Experiments and Reference Organism:
New strains of S. aureus have developed resistance to common antibiotics and experiments are performed to obtain information about their sensitivity to antibiotics and to study the development and mechanism of resistance in these organisms.
Infections:
Staphylococcus aureus is associated with multiple skins and pyogenic infections i.e. Folliculitis, Cellulitis, impetigo, furuncles, conjunctivitis, endocarditis, osteomyelitis, septic arthritis, food poisoning, Toxic shock syndrome and scalded skin syndrome, etc.
One of the most common diseases also includes Hospital-acquired pneumonia, septicemia and surgical or wound site infections (Levinson, 2006).
Role in Disease:
Multiple components of the cell wall such as Protein A, teichoic acids, Polysaccharides and peptidoglycan have antigenic, virulent and protective properties.
Protein A is especially anti-phagocytic. The production of certain exotoxins including enterotoxin, PV leucocidin and others that play an important role in the pathogenesis of the disease.
Multiple enzymes, such as coagulase, hyaluronidase, proteases and nucleases, enhance the penetration of the organism (Levinson, 2006).
3. Klebsiella pneumoniae
Characteristics:
Klebsiella pneumonia is a gram-negative rod associated mainly with a hospital-acquired infection, but primary infections are also common. It has a very large polysaccharide capsule. It is non-motile and lactose fermenter. It is a part of the normal flora of skin, mouth and gastrointestinal system (Levinson, 2006).
Morphological Phenotype:
The colonies of K. pneumoniae can be recognized by a striking mucoid appearance on cultures due to the large capsule. The organism appears under the microscope as a gram-negative bacillus with a thick capsule (Levinson, 2006).
Isolation and Cultivation:
Klebsiella can be identified from the cultures taken from blood, urine or pleural fluid and may be identified by simple gram staining due to the thick and regular capsule. The colonies appear pink on McConkey’s agar.
These are non-motile, Citrate positive, Urease positive and indole negative. TSI results may appear yellow because of slow fermentation with gas production such that the medium is lifted (Jawetz et al., 2016; Levinson, 2006; Microbewiki.kenyon.edu, n.d.).
Infections:
The organism is an important respiratory pathogen and causes pneumonia with a characteristically thick and red sputum, clinically described as Red Currant……
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