A 65-year-old man comes to the emergency department due to fevers, chills, and confusion. He has a history of poorly controlled diabetes mellitus with a nonhealing ulcer of the left foot. His temperature is 38.3 C (101 F), blood pressure is 90/60 mm Hg, pulse is 112/min, and respirations are 22/min. On examination, there is slight erythema surrounding his left foot ulcer with foul-smelling discharge. No heart murmur is auscultated, the lungs are clear, and the abdomen is soft and nontender. Blood cultures are obtained, and he is started on broad-spectrum antibiotics. Twenty-four hours later, blood cultures grow β-lactamase-producing Bacteroides species. Which of the following is most likely to provide appropriate antimicrobial coverage for this patient?

Question

A 65-year-old man comes to the emergency department due to fevers, chills, and confusion.  He has a history of poorly controlled diabetes mellitus with a nonhealing ulcer of the left foot.  His temperature is 38.3 C (101 F), blood pressure is 90/60 mm Hg, pulse is 112/min, and respirations are 22/min.  On examination, there is slight erythema surrounding his left foot ulcer with foul-smelling discharge.  No heart murmur is auscultated, the lungs are clear, and the abdomen is soft and nontender.  Blood cultures are obtained, and he is started on broad-spectrum antibiotics.  Twenty-four hours later, blood cultures grow β-lactamase-producing Bacteroides species.  Which of the following is most likely to provide appropriate antimicrobial coverage for this patient?

Quizplus · Accepted Answer

Areas of necrosis and diminished blood supply (such as chronic, nonhealing ulcers) facilitate the growth of anaerobes. Bacteroides are gram-negative anaerobic rods that can produce β-lactamase, an enzyme that breaks down penicillins. β-lactamase inhibitors such as tazobactam, clavulanic acid, and sulbactam prevent these enzymes from functioning. The combination of piperacillin (extended-spectrum penicillin) and tazobactam is effective against a large number of gram-positive, gram-negative, and anaerobic bacteria and would be the most appropriate option among the medications listed. Other antimicrobials with anaerobic activity include metronidazole, carbapenems, and clindamycin (in most cases). In patients with diabetes who have a necrotic (foul-smelling) infected ulcer, broad-spectrum antimicrobial coverage should be used as polymicrobial infection with organisms other than Bacteroides may be present. (Choice A) Azithromycin is a macrolide antibiotic that binds to the 50S subunit of bacteria ribosomes, thereby inhibiting protein synthesis. It is used for infections with Chlamydia, Mycoplasma, Haemophilus influenzae, and Moraxella catarrhalis. Anaerobic activity against many Fusobacterium and some Bacteroides species may be limited. (Choice B) Ceftriaxone is a third-generation parenteral cephalosporin with poor anaerobic activity. It is active against H influenzae, Klebsiella pneumoniae, and Neisseria and Serratia species. (Choice C) Ciprofloxacin is a second-generation quinolone that acts by interfering with bacterial DNA gyrase (topoisomerase II). Ciprofloxacin is active against most gram-negative rods and bacilli, including Legionella and Pseudomonas aeruginosa. It is not effective against anaerobic infections. (Choice E) Vancomycin is a tricyclic glycopeptide that inhibits the synthesis of peptidoglycan, a main component of the cell wall of gram-positive bacteria. It is used against methicillin-resistant Staphylococcus aureus as well as Clostridium difficile. Educational objective: Piperacillin-tazobactam is a combination of extended-spectrum penicillin with β-lactamase inhibitor. It is effective against most gram-negative enteric rods (including Pseudomonas aeruginosa) and against Bacteroides fragilis.

A 65-Year-Old Man Comes to the Emergency Department Due to Fevers