Which characteristic is a hallmark of antibiotic-resistant bacteria?

• A. Greater genetic diversity in small populations
• B. Sensitivity to all known antibiotics
• C. Survival of strains after antibiotic treatment
• D. Limited growth in nutrient-rich environments

Answer: (C)

The hallmark of antibiotic-resistant bacteria is their ability to survive after antibiotic treatment. This characteristic is primarily due to genetic mutations or the acquisition of resistance genes which enable these bacteria to withstand the effects of antibiotics that would normally inhibit their growth or kill them. Resistance can arise through various mechanisms, such as altering the antibiotic target site, producing enzymes that inactivate the drug, or actively expelling the antibiotic from the bacterial cell.

In contrast, greater genetic diversity in small populations does not specifically pertain to antibiotic resistance, as resistance can be present in both diverse and less diverse populations. Sensitivity to all known antibiotics is, by definition, the opposite of antibiotic resistance. Lastly, limited growth in nutrient-rich environments does not relate to the classification of resistant bacteria; instead, many bacteria, regardless of resistance, can thrive in such conditions. Therefore, the ability to survive antibiotic treatment is the defining characteristic of antibiotic-resistant bacteria.