October 6, 2008

Germs That Survive Onslaught ‘Become More Resistant’

Bacteria which survive attack with disinfectants and antiseptics become more resistant to the chemicals, scientists have found. The discovery is bad news for hospitals trying to tackle the spread of superbugs by ensuring wards and equipment are kept clean. It also points to a new way for bacteria to become immune to antibiotic drugs, say researchers.Biocides, the bacteria-killing chemicals in disinfectants and antiseptics, are universally used in hospitals to clean surfaces, sterilise medical instruments and equipment and decontaminate skin before surgery.At the right levels, the chemicals destroy most micro-organisms. However, new research has shown that if weak doses are used the bugs can survive and grow stronger.Bacteria have inbuilt protein pumps that expel many toxic substances from their cells. These pumps remove antibiotics and make bugs drug resistant. One such organism is MRSA, a superbug version of bacterium Staphylococcus aureus.A study by US scientists has shown that the same process can make bacteria immune to biocides. Experts exposed S. aureus taken from the blood of patients to low concentrations of several biocides and bacteria-killing dyes. The effect of allowing some of the bugs to survive was that mutants were created which could not be harmed by the chemicals.Study leader Dr Glenn Kaatz, from the Department of Veterans Affairs Medical Centre in Detroit, said: "We found that exposure to low concentrations of a variety of biocides and dyes resulted in the appearance of resistant mutants. The number of efflux pumps in the bacteria increased." The study suggests bacteria repeatedly exposed to low levels of biocides may build up immunity both to disinfectants and antibiotics.

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