Delia, a five-year-old, woke up one morning complaining that she had a sore thro

Question

Delia, a five-year-old, woke up one morning complaining that she had a sore throat, headache and stomachache. Her tonsils appeared swollen, and a tonsular exudate, appearing as a cream-colored pus, was evident upon examining the child’s oropharynx. Her mother also took Delia’s temperature and noted the girl was running a low-grade fever. Suspecting strep throat (streptococcal pharyngitis), her mother made an appointment with the pediatrician.

The doctor first performed a rapid strep test, which works by detecting certain cell surface proteins on group A streptococci (GAS). This test is inexpensive and can detect GAS in a matter of minutes. However, rapid strep tests that come back negative are not especially reliable; about five out of every 100 patients with streptococcal pharyngitis will have a negative rapid strep test result. Therefore, despite Delia’s rapid strep test being negative, the doctor went ahead and ordered a bacterial culture. This was a wise decision because Delia had signs and symptoms that pointed to a case of streptococcal pharyngitis caused by the Gram-positive, nonmotile, encapsulated prokaryote Streptococcus pyogenes.

When cultures to detect S. pyogenes are performed, the patient’s sample (in this case a swab of the throat) is streaked out onto a specialized nutrient-rich agar called blood agar. Actively growing S. pyogenes can break down red blood cells (a process called beta hemolysis), and, therefore, is readily detectable on blood agar plates because a clear zone develops around its colonies. Based on the microbiology data that came back, Delia was treated for streptococcal pharyngitis. After 48 hours on an antibiotic, Delia felt much better and returned to school.

QUESTION: Assuming that Delia is not allergic to penicillin-based drugs, would a penicillin-family drug (amoxicillin, for example) typically be effective against S. pyogenes?

A. Penicillin-based drugs would effectively target the thick peptidoglycan layer within the pathogen’s cell wall. B. Penicillin-based drugs would be ineffective since the cell wall of S. pyogenes does not contain peptidoglycan. The porins within the pathogen’s outer membrane would exclude penicillin-based drugs, rendering these antimicrobials C. ineffective. D. Penicillin-based drugs would effectively target the mycolic acids present in the pathogen’s cell wall.

Explanation / Answer

Q1) Assuming Delia is not allergic to penicillin- based drugs, would a penicillin family drug (Amoxicillin for example) typically be effective against S.pyogenes.

Answer:-A - Penicillin based drugs would effectively target the thick peptidoglycan layer within the pathogen cell wall.

Explanation:-S.pyogenes is a Gram positive, beta - haemolytic, facultative anaerobic bacteria, it is sensitive to penicillin. It is found that amoxicillin is one of the best drug used against S.pyogenes. In Gm +ve bacteria there are penicillin binding proteins, which take part in the trans-glycosylation and trans- peptidation reactions, penicillin bind to these proteins and inhibits the peptidoglycan synthesis. Gm+ ve bacteria have thicker peptidoglycan layer, penicillin prevents the cross linking of peptidoglycan layer and interferes in the final stage of construction of the cell wall synthesis of the pathogen.

Option-B is wrong because S.pyogenes contains peptidoglycan layer.

Option-c is also incorrect as porins or the beta barrel proteins which cross a cellular membrane and act as a pore, by which molecules can diffuse. These porins are present in Gm-ve bacteria and Gm+ve mycobacteria not in S. pyogenes. So there is no chance of the role of porin making penicillin ineffective against S,pyogenes

Option- D is also incorrect because in S.pyogenes, mycolic acid is not found in the cell wall, rather teichoic acid is found and mycolic acid is present in the cell wall of mycobacteria that is in Tubeculosis mycobacterium the causative agent of the disease Tuberculosis.

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