A 77-year-old woman is brought to the emergency department due to fever and confusion. The patient has a history of Alzheimer dementia and lives in a nursing home. Temperature is 38.4 C (101.1 F), blood pressure is 104/74 mm Hg, pulse is 110/min, and respirations are 18/min. Suprapubic tenderness is present on physical examination. Urinalysis shows numerous bacteria and leukocytes, and urine culture grows Pseudomonas aeruginosa. Further analysis reveals that the isolated organism produces an enzyme that is located on the cytoplasmic surface of the cell membrane and that catalyzes the transfer of acetyl groups to exogenous substances. The bacteria are most likely resistant to which of the following antibiotics?

Question

A 77-year-old woman is brought to the emergency department due to fever and confusion.  The patient has a history of Alzheimer dementia and lives in a nursing home.  Temperature is 38.4 C (101.1 F), blood pressure is 104/74 mm Hg, pulse is 110/min, and respirations are 18/min.  Suprapubic tenderness is present on physical examination.  Urinalysis shows numerous bacteria and leukocytes, and urine culture grows Pseudomonas aeruginosa.  Further analysis reveals that the isolated organism produces an enzyme that is located on the cytoplasmic surface of the cell membrane and that catalyzes the transfer of acetyl groups to exogenous substances.  The bacteria are most likely resistant to which of the following antibiotics?

Quizplus · Accepted Answer

11ec160b_3bef_910e_9249_0dacad7ba1bd_MD0001_00 Pseudomonas aeruginosa is a gram-negative, opportunistic pathogen with multiple mechanisms of antibiotic resistance, including beta-lactamases, efflux pumps, and antibiotic-modifying enzymes. Antibiotic-modifying enzymes add chemical groups (eg, acetyl, adenyl, phosphate) to a target drug and are the most common mechanisms of aminoglycoside (eg, gentamicin) resistance. Altered aminoglycosides have a reduced ability to bind to the 16S ribosomal RNA within the 30S ribosomal subunit, leading to increased minimum inhibitory concentrations and reduced bactericidal effects. Most antibiotic-modifying enzymes arise via transfer of plasmids or transposons rather than chromosomal mutations. (Choices A, D, and E) Cephalosporins (eg, ceftazidime), carbapenems (eg, imipenem), and penicillins (eg, piperacillin) are beta-lactam drugs that exert their effect by interfering with the cell wall. Resistance to cephalosporins and penicillins occurs largely because of the bacterial secretion of beta-lactamase, an enzyme that hydrolyzes the beta-lactam ring and inactivates the antibiotic. Carbapenems are not very susceptible to most beta-lactamases due to additional chemical components surrounding their beta-lactam ring; however, resistance to carbapenems can occur due to carbapenemase, which is primarily seen in Enterobacter species. (Choice B) Fluoroquinolones (eg, ciprofloxacin) block enzymes (DNA gyrase, topoisomerase) responsible for bacterial DNA synthesis. Resistance usually occurs due to genetic mutations that prevent drug binding to these enzymes or to the increased expression of antibiotic efflux pumps. Educational objective: Aminoglycoside (eg, gentamicin) resistance is most commonly due to antibiotic-modifying enzymes. These enzymes add chemical groups to the antibiotic, which diminishes its ability to bind to the 16S ribosomal RNA within the 30s ribosomal subunit. __________ References: Mechanisms of antibiotic resistance. (http://www.ncbi.nlm.nih.gov/pubmed/27227291)

A 77-Year-Old Woman Is Brought to the Emergency Department Due