New Study Shows the Source of MRSA in Humans

According to a study, a human strain of MRSA is of bovine origin most likely from cows. The Bacteria mutated to a form that could affect humans decades ago.  It became resistant to methicillin after it jumped to humans, according to a study published in mBio a Journal of the American Society for Microbiology (ASM).

The strain has spread in humans in several places at once, especially in Europe, North and South America, Africa and Asia. In their study, British and Danish researchers have sequenced the genomes of 43 human isolates of CC97, cattle and other animals and have traced the genetic relationships. The strains found in humans most resembled those found in cattle, the authors note.

CC97 with two different lines of descendants affect humans and seem to write the authors, have jumped to humans at two different times. They determined by analyzing the mutation rate that the first jumped to humans between 1894 and 1977 and the second between 1938 and 1966.

Human CC97 strains have developed resistance to methicillin, unlike other strains species.The researchers attribute this to the exposure of bacteria to antibiotics used to treat infections of Staphylococcus humans.

The authors say their findings "provide evidence that animals represent a reservoir for the emergence of new clones of Staphylococcus pathogenic to humans with the ability to spread pandemic" and "they have major implications for public health emphasizing the importance of surveillance for early detection of emerging bacteria and improved control measures transmission from livestock to humans

MRSA is any strain of Staphylococcus aureus that has developed, through the process of natural selection, resistance to beta-lactam antibiotics, which include the penicillins (methicillin, dicloxacillin, nafcillin, oxacillin, etc.) and the cephalosporins. Strains unable to resist these antibiotics are classified as methicillin-sensitive Staphylococcus aureus,. The evolution of such resistance does not cause the organism to be more intrinsically virulent than strains of Staphylococcus aureus that have no antibiotic resistance, but resistance does make MRSA infection more difficult to treat with standard types of antibiotics and thus more dangerous. MRSA kills about 37,000 people in the United States Each Year