Consider the following statements : 1. Biofilms can form on medical implants within human tissues. 2. Biofilms can form on food and food processing surfaces. 3. Biofilms can exhibit antibiotic resistance. Which of the statements given above are correct ?

The correct answer is D, 1, 2 and 3. Biofilms form on almost any moist surface, including implants and food equipment, and they are notoriously hard to kill with antibiotics.

A biofilm is a community of microbes, mostly bacteria, that sticks to a surface and wraps itself in a slimy matrix of sugars, proteins and DNA that it makes itself. Dental plaque is the most familiar example. Inside the body, biofilms grow on catheters, artificial joints, heart valves and other implants, causing infections that often return until the device is removed. In the food industry they form on cutting boards, pipes and processing lines, where germs such as Listeria and Salmonella can survive cleaning. The matrix blocks drugs and the slow-growing cells inside resist them, so biofilm bacteria can be up to a thousand times more tolerant of antibiotics.

A, B and C are wrong because each leaves out one correct statement.

Exam tip: biofilm = microbes in a self-made slime matrix; dental plaque is one; grows on implants and food surfaces; resists antibiotics.