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Chapter 4. Infection and Antibiotics

You are preparing your patient for a colostomy reversal. The procedure is scheduled for 9 A.M. The junior resident asks you about the timing of giving prophylactic antibiotics to the patient. Your response is:

A. 6 hours prior to incision

B. 1 hour prior to incision

C. 1 hour after making the incision

D. At the time of incision

Answer: B. It has been shown that antibiotic administration 30 minutes to an hour to skin incision is adequate. At the time of incision, adequate tissue concentration of the antibiotic should be achieved. This will not occur if given at the time of incision and definitely not after an hour after making the incision.

A 65-year-old female is readmitted 3 weeks after being admitted for pneumonia and treated with antibiotics for a week. Her major complaint is worsening diarrhea. Clostridium difficile is sent and comes back positive. Which antibiotic would you choose?

A. IV vancomycin

B. Metronidazole

C. Clindamycin

D. Cefepime

Answer: B. The treatment for Clostridium difficile infection is IV metronidazole or oral vancomycin. Clindamycin and cephalosporins are actual offenders.

What is one of the usual mechanisms of penicillin resistance?

A. Dissociation of the peptidyl-tRNA

B. Efflux pumps

C. Plasmids that code for β-lactamase

D. Cross-linking of peptidoglycan

Answer: C. The usual mechanism of penicillin resistance is through plasmids that code for β-lactamase. Most β-lactam antibiotics work by inhibiting cell wall synthesis. Some bacteria produce β-lactamase, which hydrolyzes the β-lactam ring within the antibiotic, making it ineffective. One known mechanism of fluoroquinolone resistance is via efflux pumps that decrease intracellular quinolone concentration. The mechanism of action of lincosamides is through the premature dissociation of the peptidyl-tRNA from the ribosome by binding to the 23S portion of the 50S subunit of bacterial ribosomes. The interference of cross-linking of peptidoglycan is the mechanism of action of β-lactams where there is cross-linking of peptidoglycan by covalently binding to and inactivating a bacterium’s transpeptidase enzymes.

During the repair of an incisional hernia, you inadvertently create 2 enterotomies. Some intestinal content has spilled into the incision. The circulating nurse asks you for the wound classification.


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