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MEDICAL MICROBIOLOGY CASE STUDY 
 
 
Case study 1 
 
The patient is a 6 years old male who had been in good health with no significant medical problems. In late September he presented to his paediatrician’s office with a complaint of sore throat, fever, headache, and swollen glands in his neck for the past 36 h. On physical examination (PE), he had fever of 38ºC, a red posterior pharynx, and yellowish exudates on his tonsils, and multiple, enlarged, tender cervical lymph nodes. 
 
Discussion 
 
The patient is thought to have acute pharyngitis, the major causes of these are bacteria (most common caused one is streptococcus pyrogenes, Group A strep-GAS), virus (adenovirus, epstain-barr, other respiratory viruses like rhinovirus, coronavirus, influenza A, B and cytomegalovirus, rotavirus). Streptococci are microorganisms that are generally found in young school-age children with running nose and cold symptoms; the infection is probably due to virus. 
 
However, laboratory tests are required to determine the cause of the disease/line and treatment. If a bacterial infection is present antibiotics can be administered and if a viral infection is present antibiotics should not be given. The tests usually prescribed are rapid strep test and throat culture. 
 
Rapid strep test is based on Antigen-antibody reaction and throat culture confirm presence of GAS which takes place in the blood agar. In the blood agar medium, the throat swab grows to shows bacteria cause haemolysis and that bacteria are group A Streptococcus since it’s known to be the major causes of beta haemolysis, GABHS. More than 95% of GAS is sensitive to the antibiotic bacitracin. 
 
INFECTIOUS AGENT<img src="/i/anchor.gif" class="WikiAnchor" alt="Anchor" id="wikitext@@anchor@@_GoBack" title="Anchor: _GoBack"/> 
 
Acute pharyngitis is one of the most common childhood illnesses to be diagnosed in an outpatient setting (Bisno, 2001). The frequent causes of the disease are considered to be Viruses and Streptococcus pyogenes but particular attention is usually given only to streptococcal cases, which may be followed by severe early and late complications and are the only ones for which antibiotic treatment is definitely indicated (Bisno et al., 2002; Bisno, 2001). 
Group A Streptococcus (S.pyogenes) is the causative agent in Gas infections, including strep throat (streptococcal pharyngitis). GAS is spherical gram-positive bacteria that grow in long chains and also the cause of Group A streptococcal infections. S. pyogenes exhibits streptococcal group A antigen on its cell wall and leads to the complete disruption of erythrocytes and the release of haemoglobin (beta-hemolysis) when cultured on blood agar plates and are therefore called Group A (beta-hemolytic) Streptococcus, GABHS (Cooper RJ et al 2001). 
Figure: Streptococcus pyogenes 
<img src="http://img.medscape.com/pi/emed/ckb/infectious_diseases/211212-1641790-225243-1608843.jpg" alt="external image 211212-1641790-225243-1608843.jpg" title="external image 211212-1641790-225243-1608843.jpg" style="height: 218px;" /> 
source: emedicine.medscape.com 
GROUP A STREPTOCOCCAL INFECTIONS. pyogenes causes many serious human diseases ranging from mild superficial skin infections to life-threatening systemic diseases. An infection typically begins in throat or skin. Mild S. pyogenes infections include pharyngitis (&quot;strep throat&quot;) and skin infections like impetigo etc. Infections due to certain strains of S. pyogenes can however be associated with the release of bacterial toxins. 
VIRULENCE FACTORS 
S. pyogenes has several virulence factors that enable it to attach to host tissues, evade the immune response, and penetrate the host tissue layers. Polysaccharide capsule composed of hyaluronic acid surrounds the bacteria, which protects them from phagocytosis by neutrophils. The Streptococcus pyogenes stand-alone Mga regulator has been shown to positively control surface-expressed virulence factors like the antiphagocytic M protein during exponential growth condition and was implicated to contribute to the acute infection process (Tomas F., 2010). 
S. pyogenes releases some of proteins, including several virulence factors, into its host: 
Streptolysin O and S: These are toxins which are the basis of the organism's beta-hemolytic property. Streptolysin O is cardiotoxic and also affects neutrophils, platelets, and sub-cellular organelles.Hyaluronidase: mainly degrades hyaluronan (hyaluronic acid), a linear, non-sulfated polysaccharide composed of repeating disaccharide units [D-glucuronic acid (1-β-3) N-acetyl-D-glucosamine (1-β-4)] n (Nermeen S. El-Safory, 2010), an important component of connective tissue. 
Streptococcal pyogenic exotoxins (Spe) A and C: these are secreted by strains of S.pyogenes and also are responsible for the rash of scarlet fever etc. 
Streptokinase: this activates plasminogen enzymatically, a proteolytic enzyme, into plasmin which in turn digests fibrin and other proteins. 
Streptodornase has been shown to exhibit no activity against RNA and digests native DNA more rapidly than single-stranded DNA (Ian C. L., and Brian G. C., 2004). Stretodornase protect the bacteria from being trapped in neutrophil extracellular traps (NETs). 
Streptococcal chemokine protease is responsible for preventing the migration of neutrophils to the spreading infection by degradation of the chemokine IL-8. 
CONCLUSION 
 
Throat infections that are associated with secretion of certain toxins can lead to scarlet fever. And, other toxigenic S. pyogenes infections which may lead to streptococcal toxic shock syndrome, that can be life-threatening. S. pyogenes can however, cause disease in the form of post-infectious &quot;non-pyogenic&quot; (not associated with local bacterial multiplication and pus formation) syndromes. S. pyogenes is found frequently, but it is not possible to distinguish simple carriers from patients with a true infection (Susanna Esposito et al., 2004). GAS infections are generally diagnosed with a Rapid Strep Test or by culture. 
 
 
REFERENCES 
Bisno, A. L., Acute pharyngitis. New England journal of medicine, 2001, 344: 205–11. 
Bisno, A. L., Gerber, M. A., Gwaltney, J. M., Jr, Kaplan, E. L. &amp; Schwartz, R. H. (2002). Diagnosis and management of group A streptococcal pharyngitis: a practice guideline. Clin Infect Dis 25, 574–583. 
Cooper RJ et al. Principles of appropriate antibiotic use for acute pharyngitis in adults: Background. Annals of internal medicine, 2001, 134:509–17. 
Droghetti, Nadia Faelli, Annalisa Lastrico and Nicola Principi, Aetiology of acute pharyngitis: the role of atypical Bacteria, Journal of Medical Microbiology, 2004, 53, 645–651 
Ian C. Locke and, Brian G. Carpenter. Functional characteristics of the streptococcal deoxyribonuclease ‘streptodornase’, a protein with DNase activity present in the medicament Varidase. Enzyme and Microbial Technology, Volume 35, Issue 1, 6 July 2004, Pages 67-73. 
J. Boukadida, N. Hannechi, N. Boukadida, H. Ben Said, H. Elmherbech and S. Errai, b-haemolytic streptococci in acute pharyngitis, Volume 9, Nos 1/2 ,January 2003. 
Nermeen S. El-Saforya, Ahmed E. Fazaryb, c and Cheng-Kang Lee. Hyaluronidases, a group of glycosidases: Current and future perspectives. Carbohydrate Polymers Volume 81, Issue 2, 11 June 2010, Pages 165-181. 
Tomas Fiedlera, Bernd Kreikemeyer, Venelina Sugarevaa, Sylvio Redanza, Regina Arlta, Kerstin Standara and Andreas Podbielskia. Impact of the Streptococcus pyogenes Mga regulator on human matrix protein binding and interaction with eukaryotic cells. International Journal of Medical Microbiology, Volume 300, Issue 4, April 2010, Pages 248-258. 
 
Susanna Esposito, Francesco Blasi, Samantha Bosis, Roberta Droghetti, Nadia Faelli, Annalisa Lastrico and Nicola Principi, Aetiology of acute pharyngitis: the role of atypical bacteria. J Med Microbiol 53 (2004), 645-651; DOI: 10.1099/jmm.0.05487-0