All of the drugs listed frequently cause C. difficile overgrowth and C. difficile associated diarrhea except vancomycin, which is often used as a treatment for persistent C. difficile infections.

Tetracycline antibiotics are contraindicated in pregnant women and small children due to their tendency to irreversibly stain developing teeth. They can also affect fetal bone growth and so are pregnancy category D (known incidence and risk of fetal harm).

Of the antibiotics listed, amoxicillin is the only one considered safe in pregnancy. Doxycycline and gentamicin are both pregnancy category D (known to cause fetal harm). Levofloxacin is category C (fetal harm can not be ruled out).

Penicillins belong to a larger class of antibiotics known as beta-lactams. These antibiotics inhibit cell-wall synthesis and are exclusively used to treat Gram positive bacteria. They are not effective against Gram negative bacteria or fungi. 

Fluoroquinolones are considered to be the treatment of choice for E. coli infections due to their effectiveness in relieving diarrhea and minimal serious adverse effects. Aminoglycosides and beta-lactam antibiotics may also be effective, as a second choice.

Gentamycin, an antibiotic and aminoglycoside, inhibits protein synthesis of gram-negative bacteria. It treats severe systemic infections. It may cause ototoxicity and nephrotoxicity, as well as anorexia, nausea, vomiting, and diarrhea. Diaphoresis is not a common side effect of gentamycin.

The correct answer is "inhibition of topoisomerase II," as this is the mechanism of action of fluoroquinolone antibiotics, such as levofloxacin.

The other choices are incorrect for the following reasons:

Blockage of tRNA-ribosome-mRNA complex binding is the mechanism of action of tetracycline antibiotics. 

Disruption of mycolic acid synthesis is the mechanism of action of various anti-fungal agents.

Disruption of peptidoglycan cross-linkage is the mechanism of action of vancomycin.

Inhibition of peptidoglycan synthesis is the mechanism of action of beta-lactam antibiotics.

Acyclovir is converted to acyclovir-triphosphate and incorporated into the synthetic pathway for viral DNA as a guanosine molecule. The initial phosphorylation of acyclovir is carried out by viral thymidine kinase. Acyclovir has a higher affinity for viral thymidine kinase than mammalian thymidine kinase. Therefore, acyclovir is specifically effective in virally infected cells.

Methisazone blocks synthesis of viral mRNA and proteins. This is especially evident in pox viruses. Methisazone has been used to treat small pox.

Amantadine affects the central nervous system, producing mild, reversible disturbances. High dosages have been reported to induce seizures