A practicing general physician (GP) notices that several of her patients have co

Question

A practicing general physician (GP) notices that several of her patients have come to see her because their bacterial infections will not clear. She asks a pathologist in her practice to characterize the bacteria strains that her patients have. The pathologist’s report summarized in Table 1. With that information, the GP creates a short list of antibiotics that she could prescribe. Table 2 lists those antibiotics, their spectrum characteristics, and their mechanism of action. Using both of these tables, which antibiotic(s) might the GP prescribe for each patient, and why? (6 points)

There is more than one correct answer for each patient, but you only need to report one.

Table 1. Pathologist’s report.

Patient

Bacteria Characteristics

Antibiotic prescribed

Rationale for antibiotic choice

#1

Gram (-), cell wall present, Polymixin B resistant

#2

Gram (+), cell wall present, Streptomyocin and Gentamicin resistant

#3

Gram (+), cell wall present, Oxacillin resistant, patient allergic to tetracycline

Table 2. Common antibiotics and their properties.

Remember: Broad-spectrum antibiotics work against both Gram-positive and Gram-negative bacteria. Narrow-spectrum antibiotics are only effective against specific families of bacteria.

Antibiotic

Spectrum

Mechanism of Action

Penicillin

Broad

Inhibits functioning of transpeptidase

Oxacillin

Narrow (Gram +)

Inhibits functioning of transpeptidase

Amoxicillin – clavulanic acid

Broad

Amoxicillin inhibits peptidoglycan formation; clavulanic acid inhibits beta-lactamases that destroy amoxicillin

Cefazolin

Broad

Inhibits peptidoglycan formation

Vancomycin

Narrow (Gram +)

Inhibits synthesis of peptidoglycan

Gentamicin

Narrow (Gram -)

Inhibits protein synthesis

Tetracyclins

Broad

Inhibits protein synthesis

Trimethoprim-sulfa-methoxazole

Broad

Inhibits synthesis of folic acid which is needed for bacteria to survive

Polymyxin B

Narrow (Gram -)

Disrupts cell membrane structure and therefore permeability

Streptomyocin

Broad

Inhibits protein synthesis

Patient

Bacteria Characteristics

Antibiotic prescribed

Rationale for antibiotic choice

#1

Gram (-), cell wall present, Polymixin B resistant

#2

Gram (+), cell wall present, Streptomyocin and Gentamicin resistant

#3

Gram (+), cell wall present, Oxacillin resistant, patient allergic to tetracycline

Explanation / Answer

They are aminoglycosidase, broad spectrum, but exihibit more bactericidal efficacy against Gram Negative bacteria. Protein synthesis inhibitors.

The bacteria is resistance towards naroow spectrum, Gram negative soecific polymixin B.

It will act on bacterial cell wall.Beta-lactum group.

Resistance to Streptomycin, Gentamycin or aminoglycosidase group.

The patient is resistant towards oxacillin, which is semisynthetic form of penicillin, and belongs to bata lactum group. Hence antibiotics of same group cannot be prescribed.

Also the patient has allergy towards tetracycline, so similar group cannot be used.

Cefazolin, Vancomycin are usually administered through injection.

Patient Bacteria Characteristics Antibiotic prescribed Rationale for antibiotic choice #1 Gram (-), cell wall present, Polymixin B resistant Gentamycin

They are aminoglycosidase, broad spectrum, but exihibit more bactericidal efficacy against Gram Negative bacteria. Protein synthesis inhibitors.

The bacteria is resistance towards naroow spectrum, Gram negative soecific polymixin B.

#2 Gram (+), cell wall present, Streptomyocin and Gentamicin resistant Penicillin

It will act on bacterial cell wall.Beta-lactum group.

Resistance to Streptomycin, Gentamycin or aminoglycosidase group.

#3 Gram (+), cell wall present, Oxacillin resistant, patient allergic to tetracycline Trimethoprim-sulfa-methoxazole

The patient is resistant towards oxacillin, which is semisynthetic form of penicillin, and belongs to bata lactum group. Hence antibiotics of same group cannot be prescribed.

Also the patient has allergy towards tetracycline, so similar group cannot be used.

Cefazolin, Vancomycin are usually administered through injection.

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