A 10 year old girl presents with sore throat and fever. She denies any cough or rhinorrhea. A throat culture grows bacitracin-sensitive bacterial colonies. The infecting organism would be protected from the lytic action of detergents by its?
Correct Answer: Peptidoglycan layer
Description: This girl has streptococcal pharyngitis. The infecting organism is group A beta-hemolytic streptococcus (S. pyogenes); its growth is inhibited by the placement of a bacitracin disk on the throat culture plate. (Beta-hemolysis occurs as the result of the bacterial hemolysin streptolysin S). This is a gram-positive bacterium and therefore possesses a very thick peptidoglycan layer that would protect it from lysis by detergents. (Note that gram-positives also contain teichoic acid.) In contrast, gram-negatives have a thin peptidoglycan layer. Keratin-like proteins in the spore coat and calcium ion chelators (dipicolinic acid) are found in spores formed by species of Bacillus and Clostridium. These protect the spores from the elements: dehydration, heat, chemicals, radiation, etc. Lipopolysaccharide in the outer membrane and a periplasmic space are found in gram-negative organisms. The lipopolysaccharide is an endotoxin and the periplasmic space contains beta-lactamase in some species. Ref: Ray C.G., Ryan K.J. (2010). Chapter 25. Streptococci and Enterococci. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.
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