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Microbiology, 2021

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14.3 • Mechanisms of Antibacterial Drugs 579<br />

Antimetabolite Drugs<br />

Metabolic<br />

Pathway<br />

Target<br />

Mechanism of Action Drug Class Specific Drugs Spectrum of Activity<br />

Mycolic<br />

acid<br />

synthesis<br />

Interferes with the<br />

synthesis of mycolic acid<br />

Not<br />

applicable<br />

Isoniazid<br />

Narrow spectrum against<br />

Mycobacterium spp.,<br />

including M. tuberculosis<br />

Table 14.6<br />

CHECK YOUR UNDERSTANDING<br />

• How do sulfonamides and trimethoprim selectively target bacteria?<br />

Inhibitor of ATP Synthase<br />

Bedaquiline, representing the synthetic antibacterial class of compounds called the diarylquinolines, uses a<br />

novel mode of action that specifically inhibits mycobacterial growth. Although the specific mechanism has yet<br />

to be elucidated, this compound appears to interfere with the function of ATP synthases, perhaps by<br />

interfering with the use of the hydrogen ion gradient for ATP synthesis by oxidative phosphorylation, leading<br />

to reduced ATP production. Due to its side effects, including hepatotoxicity and potentially lethal heart<br />

arrhythmia, its use is reserved for serious, otherwise untreatable cases of tuberculosis.<br />

LINK TO LEARNING<br />

To learn more about the general principles of antimicrobial therapy and bacterial modes of action, read this<br />

article (https://openstax.org/I/22AntiMicrob) for a general overview of antimicrobial therapy strategies and<br />

read this article (https://openstax.org/I/22AntiMicRes) on the mechanism of action of antimicrobial classes.<br />

Clinical Focus<br />

Part 2<br />

Reading thorough Marisa’s health history, the doctor noticed that during her hospitalization in Vietnam,<br />

she was catheterized and received the antimicrobial drugs ceftazidime and metronidazole. Upon learning<br />

this, the doctor ordered a CT scan of Marisa’s abdomen to rule out appendicitis; the doctor also requested<br />

blood work to see if she had an elevated white blood cell count, and ordered a urine analysis test and urine<br />

culture to look for the presence of white blood cells, red blood cells, and bacteria.<br />

Marisa’s urine sample came back positive for the presence of bacteria, indicating a urinary tract infection<br />

(UTI). The doctor prescribed ciprofloxacin. In the meantime, her urine was cultured to grow the bacterium<br />

for further testing.<br />

• What types of antimicrobials are typically prescribed for UTIs?<br />

• Based upon the antimicrobial drugs she was given in Vietnam, which of the antimicrobials for<br />

treatment of a UTI would you predict to be ineffective?<br />

Jump to the next Clinical Focus box. Go back to the previous Clinical Focus box.

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