Strains of methicillin-resistant staphylococcus aureus (MRSA) that are acquired in the community may be more virulent than hospital-associated strains because they secrete small peptides that disable immune cells, as reported in Nature Medicine.
The majority of infections seen in the emergency room in the US are due to community-associated (CA) MRSA. Some strains of CA-MRSA can be especially virulent, causing sepsis and skin infections. Michael Otto and colleagues found that CA-MRSA strains produce much higher levels of a cluster of small peptides -- called phenol soluble modulins -- than strains of bacteria acquired from hospitals. The authors showed that mutant bacteria that couldn't make these peptides were much less virulent in mice.
The peptides seem to have several functions that allow the bacteria to cause severe disease: they contribute to activation of inflammation, and also kill neutrophils and red blood cells. As neutrophils are key immune cells involved in clearing bacterial infections, secretion of phenol soluble modulins seems to be one way that CA-MRSA evades elimination by the immune system
Michael Otto (NIAID, Hamilton, MT, USA)
Abstract available online.
(C) Nature Medicine press release.
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