Which of the following best defines the minimal inhibitory concentration (MIC)?

The highest concentration of an antibiotic that can be given to a patient without causing toxicity and that has been shown in clinical trials to reduce bacterial counts in vivo over time while sometimes permitting regrowth once the drug is withdrawn.

The concentration of antibiotic measured at the peak serum level after a standard dose that correlates with clinical success in patients with severe infections.

The lowest concentration of antibiotic that reduces viable colony counts by 99.9% on subculture onto antibiotic-free agar, demonstrating bactericidal activity.

The lowest antibiotic concentration that prevents visible growth of a bacterium in a standard in vitro assay.