Methicillin-resistant Staphylococcus aureus (MRSA) kills about 18,000 people each year in the U.S. The “super bug” — so-called for its evolved resistance to some traditional antibiotics — has also been found in domestic animals and antibiotic-fed livestock, such as pigs and sheep. But up until now, MRSA has not been definitively isolated in any wildlife populations.
In a recent pilot study examining wild animals at a University of Iowa wildlife rehabilitation clinic, researchers looked at 37 species and a total of 114 animals to determine the prevalence of MRSA and the related methicillin-sensitive S. aureus (MSSA).
Of the 114 animals examined, seven (6.1%) were MSSA-positive and three (2.6%) were MRSA-positive. The MRSA-positive results were obtained from two Eastern Cottontall rabbits (Sylvilagus floridanus) and one migratory shorebird, a Lesser Yellowlegs (Sylvilagus floridanus).
Additionally, antibiotic resistance testing of the bacterial isolates (from the rabbits) revealed resistance to tetracycline and erythromycin, while the third isolate (from the shorebird) showed resistance to erythromycin, clindamycin, and levofloxacin.
All three S. aureus isolates tested positive for the Panton-Valentine leukocidin (PVL) gene.
The PVL gene codes for a pore-forming cytotoxin (protein) which derives from genetic material from a bacteriophage (a virus that infects bacteria) that, once incorporated into the genomes of S aureus, makes them more virulent. The toxin creates pores in the membranes of infected cells causing them to leak nutrients that the bacteria feeds on. PLV-infected S. aureus can cause necrotizing pneumonia, which can kill its victims within 72 hours.
As this was a pilot study using a limited sampling of animals from a single pool of animals, it is not clear how pervasive the problem may be. However, given that MRSA was isolated from a migratory bird, this could represent a potent vector for the superbug — allowing it to spread through wildlife populations in the future.
But, according to the researchers (Wardyn et al):
“Our results suggest that S. aureus, including MRSA, is being carried by wild animals, although at a low prevalence with the limited number of animals tested. Additional studies are needed to determine how this may impact human health.” [source]
Normal S. Aureus causes skin infections but if it enters the bloodstream, it can result in a life-threatening illness. This is normally treated with antibiotics. However, due to the rapid mutation and reproductive rates of bacteria, combined with the over-use of some antibiotics (especially in hospitals), many species of bacteria quickly evolve resistance to these drugs, making them into “super bugs” like MRSA. Many infections occur outside of hospitals and can be contracted by contact with infected people or animals. These are known as “community-associated” or “community-acquired” strains.
The results of the study, Methicillin-resistant Staphylococcus aureus in Central Iowa Wildlife (Wardyn, Kauffman, Smith*) were published last week in Journal of Wildlife Diseases.
*University of Iowa College of Public Health
Top Photo: (Lesser Yellowlegs) Wwcsig; CC – By – SA 3.0