INFECTIOUS DISEASE EXAM MASTER 2024 QUESTIONS WITH COMPLETE ANSWERS GRADED A+

Case A 2-year-old girl presents with a fever and an inflamed throat. Her mother states the child does not want to eat. You decide to treat her with 7 days of penicillin. After 4 days, the mother calls your office to report that the child has not significantly improved. You suspect the child's infection may be caused by penicillin-resistant bacteria. Question What is the likely mechanism of resistance in this case? - CORRECT ANSWER Correct answer: Acquisition of the enzyme β-lactamase Explanation Bacteria carrying a plasmid with the gene for β-lactamase would confer resistance to antibiotics containing the β-lactam ring, such as penicillin and amoxicillin. β-Lactamase is an enzyme that cleaves and inactivates antibiotics like penicillin. The antibiotic penicillin consists of a thiazolidine ring fused to a β-lactam ring (see image). A variable "R" group is attached to the β-lactam ring by a peptide bond. Penicillin inhibits bacterial cell growth by inhibiting the enzyme catalyzing the last step in cell wall synthesis. This step involves the cross-linking of the peptidoglycan strands. Under normal conditions, a peptide bond forms between the terminal glycine on one proteoglycan strand, with the terminal D-Ala-D-Ala unit on the other strand forming the Gly-D-Ala cross-link. The enzyme catalyzing this reaction is glycopeptide transpeptidase. Penicillin inhibits this reaction by mimicking the D-Ala-D-Ala unit, forming a covalent bond between the R- INFECTIOUS DISEASE EXAM MASTER 2024 QUESTIONS WITH COMPLETE ANSWERS GRADED A+ group of penicillin and the active site serine of glycopeptide transpeptidase. The penicilloyl-enzyme complex is enzymatically inactive; therefore, penicillin acts as a transition state analog. Bacterial plasmids often carry genes that confer resistance to a specific antibiotic. Other examples of enzymes carried on plasmids that convey antibiotic resistances are chloramphenicol acetyltransferase, which inactivates chloramphenicol, and phosphotransferases, which modify aminoglycosides such as neomycin and gentamicin. These plasmids can be passed from a resistant to a sensitive bacterial cell, conveying resistance to a particular antibiotic; therefore, many strains of resistant bacteria have arisen, which cause problems in treating the patient. Resistance to penicillin is not due to mutations in the Case A healthy couple presents for an evaluation prior to travel to the Dominican Republic; they leave in 1 month and will stay there 4 weeks. The CDC lists the Dominican Republic as a malaria-endemic area, but it is not considered to have a resistant strain of Plasmodium falciparum. Question What is the best advice for this couple? - CORRECT ANSWER Correct answer: "You should both take chloroquine weekly starting 1 week before travel." Explanation