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Scientists react to a study into strains of MRSA that spread in the community rather than in hospitals, recommending controlled use of antibiotics.
Professor Chris Thomas, Professor of Molecular Genetics, University of Birmingham, said:
“The key message is that strains of MRSA that are spreading in the community are better able to infect the young and healthy, precisely because they are not actually trying so hard to be resistant as the bugs that have been encountered in hospitals for many years. Staphylococcus aureus becomes MRSA by getting a new enzyme for making its cell wall, and this changes the cell wall – the more enzyme, the more resistant it is and the more different it is but this affects its ability to switch on virulence functions. So if you don’t make so much you can still be resistant and virulent at the same time. Thus we now need to worry about community super bugs that are fine tuned to spreading outside of hospitals and we all need to be extra vigilant about hygiene and unnecessary use of antibiotics.”
Professor Richard James, Director of the Centre for Healthcare Associated Infections, University of Nottingham, said:
“It is an elegant study that demonstrates the contradictory role of the SCCmec type II element found in HA-MRSA strains in both conferring resistance to methicillin whilst reducing virulence, via an as yet uncharacterised effect on the agr regulatory system. In contrast, the SCCmec type IV element found in CA-MRSA strains was associated with a lower level of methicillin resistance and higher virulence.
“The study needs to be extended to include other SCCmec elements found in HA-MRSA strains and in CA-MRSA strains in order to confirm the significance of the findings.
“The study offers an intriguing clue how the virulence of CA-MRSA strains may be targeted by novel drugs.”
Dr Kim Hardie, Associate Professor, Faculty of Medicine & Health Sciences, University of Nottingham , said:
“The study described provides novel insight into how bacteria balance the need to survive in adverse conditions (the presence of antibiotics in hospitals) with a requirement to overcome the natural defences of the host they invade (by producing toxins etc, which do not need to be as potent or plentiful if infections are primarily occurring within people weakened by prior trauma or infection in hospitals). The way that this study has addressed the interplay between these in the selection of strains characterised will prompt other researchers to bear this possible mechanism in mind when they investigate new disease causing bacteria. A more comprehensive study involving more strains is needed to confirm and indicate how universal the reported observations are.
“This study will trigger innovative thought to underpin the development of new therapies, which will be urgently required if, as predicted, the combination of methicillin resistance and enhanced toxin production within the same strain enters the general British public, as it is starting to do in the US.
“Controlling the use of antibiotics in the community should reduce the need for strains in this environment to acquire resistance mechanisms, and practicing effective hygiene will prevent transfer of strains between the hospitals and the community and thus reduce the likelihood that they will swap genes and create offspring that combine antibiotic resistance with the ability to infect healthy individuals.”
‘Methicillin resistance reduces the virulence of healthcare-associated Methicillin-resistant Staphylococcus aureus by interfering with the agr quorum sensing system’ by Justine Rudkin et al., published in Journal of Infectious Diseases on Thursday 2nd February.