Question 51
Read the following extract about an unexpected breakthrough in understanding how Streptococcus, a type of bacteria that causes throat infection, can resist medicines. Then answer the question that follows.
Bacteria form colourful colonies, often yellow or red. George Liu, a scientist working at the University of California, San Diego, was studying two varieties of Streptococcus — a normal strain and a mutant strain that could not produce a toxin that causes illness. The mutant strain also did not form colourful colonies, unlike the normal strain.
Liu’s experiments were not going well, and his bacteria sometimes just died off for no apparent reason. He then realised that the laboratory beakers and flasks had been cleaned with bleach which had not been properly rinsed off.
When Liu reviewed his results, he noticed that the normal strain of bacteria survived the bleach more often than the other strain. Perhaps the toxin somehow protected the bacteria against the bleach?
Then Liu remembered how his mother would make him eat brightly coloured vegetables as a child. The pigments in these vegetables contain substances called antioxidants. Antioxidants protect cells from damage caused by other molecules in the body known as free radicals. Liu wondered if it was the pigment, and not the toxin, that was protecting the bacteria.
He could not understand why producing a pigment that is resistant to bleach would be an advantage for Streptococcus bacteria. Then he recalled that the chemical name for bleach’s active ingredient is hypochlorite — one of the chemicals released by immune cells when they fight bacterial infections. Further experiments confirmed that he was right. Quite by chance, George Liu’s research helped to show how bacteria can develop resistance to medicine.
Why did Liu initially think the toxin might be protecting the bacteria from bleach?
Bacteria form colourful colonies, often yellow or red. George Liu, a scientist working at the University of California, San Diego, was studying two varieties of Streptococcus — a normal strain and a mutant strain that could not produce a toxin that causes illness. The mutant strain also did not form colourful colonies, unlike the normal strain.
Liu’s experiments were not going well, and his bacteria sometimes just died off for no apparent reason. He then realised that the laboratory beakers and flasks had been cleaned with bleach which had not been properly rinsed off.
When Liu reviewed his results, he noticed that the normal strain of bacteria survived the bleach more often than the other strain. Perhaps the toxin somehow protected the bacteria against the bleach?
Then Liu remembered how his mother would make him eat brightly coloured vegetables as a child. The pigments in these vegetables contain substances called antioxidants. Antioxidants protect cells from damage caused by other molecules in the body known as free radicals. Liu wondered if it was the pigment, and not the toxin, that was protecting the bacteria.
He could not understand why producing a pigment that is resistant to bleach would be an advantage for Streptococcus bacteria. Then he recalled that the chemical name for bleach’s active ingredient is hypochlorite — one of the chemicals released by immune cells when they fight bacterial infections. Further experiments confirmed that he was right. Quite by chance, George Liu’s research helped to show how bacteria can develop resistance to medicine.
Why did Liu initially think the toxin might be protecting the bacteria from bleach?
