S. pyogenes is sensitive to bacitracin. The virulence factors that aid in S. pyogenes' spread and inflammation are the following: hyaluronidase aids in the break down of connective tissue, streptokinase converts plasminogen to plasmin promoting fibrinolysis, DNase digests cellular DNA, and the M protein prevents the host's immune system from phagocytosing the bacteria.
Meltzer et al. report on the morbidity caused by group A streptococci in particular the most extreme and life-threatening case, necrotizing fasciitis. Metlzer also explains the necessary information for a proper diagnosis and effective treatment. "The diagnosis of necrotizing fasciitis is based on the history, gram staining, culture, radiography, and, ultimately, surgical exploration. This infection is treated with antibiotics, hyperbaric oxygenation, and surgical debridement."
McArthur et al. review the importance of streptokinase's role in the activation of plasmin to plasminogen at the surface of the bacteria and how this activity allows the bacteria to be invasive. By understanding the mechanism of streptokinase, it allows for strategies to be developed to disrupt its activity and treat the severe infections caused by S. pyogenes.
Figure A shows an example of impetigo; yellow crusts have formed along the border of the rash.
Answer 1: Sporothrix schenckii is a fungus that is normally found in soil or plants such as roses (Rose Gardener's Disease). When cultured at different temperature it either presents as branched hyphae at 25 degrees Celsius or as single cells at 37 degrees Celsius
Answer 2: Staphylococcus aureus is a catalase +, coagulase +, Gram + cocci.
Answer 3: Streptococcus mutans is an alpha-hemolytic, bile-esculin negative, optochin-resistant Gram + cocci.
Answer 4: Staphylococcus epidermidis is a catalase +, coagulase -, novobiocin-sensitive Gram + cocci.
1. Meltzer DL, Kabongo M. Necrotizing fasciitis: a diagnostic challenge. Am Fam Physician. 1997 Jul;56(1):145-9. Review. PMID:9225671 (Link to Abstract)
2. McArthur JD, Cook SM, Venturini C, Walker MJ. The role of streptokinase as a virulence determinant of Streptococcus pyogenes--potential for therapeutic targeting. Curr Drug Targets. 2012 Mar;13(3):297-307. Review. PMID:22206253 (Link to Abstract)
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