A pinboard by
Kate Worthing

I am a veterinarian and PhD candidate from the Sydney School of Veterinary Science, Australia


Bacteria from cats may kill MRSA 'superbug' from humans

Bacteria are generally thought of as germs that are dangerous to our health. However, all humans actually have several species of bacteria that live on our skin and inside our bodies without causing any disease. One bacterial species that commonly lives on human skin is called Staphylococcus aureus (also known as 'Golden Staph'). Up to 30% of healthy humans have Staphylococcus aureus living on their skin, generally with no ill effects. However, when skin becomes compromised by conditions such as wounds or allergies, Staphylococcus aureus can invade deeper into the skin and create infections. These infections used to be easy to treat with antibiotics, but the rise of antibiotic resistance has made some Staphylococcus infections difficult or even impossible to treat.

One of the most important types of resistant bacteria is called methicillin-resistant Staphylococcus aureus, or MRSA. MRSA can be carried by healthy members of the community but is also a major cause of death in hospitals, particularly as a cause of bloodstream infections in critically ill patients. Just as humans have certain bacterial species that live on their skin, so too do dogs and cats. Such species include Staphylococcus pseudintermedius in dogs and Staphylococcus felis in cats. While staphylococci generally like to stick to their host species, they can occasionally be carried by other mammalian species. This means that Staphylococcus pseudintermedius can occasionally cause disease in humans, and MRSA can occasionally cause disease in animals.

In a microscopic world where literally millions of bacteria are competing for the valuable real estate of mammalian skin, bacteria must compete with their neighbours to ensure they survive. Our research team has been examining whether staphylococci from dogs and cats could potentially outcompete dangerous human pathogens such as MRSA. We found that Staphylococcus pseudintermedius isolated from a cat can inhibit the growth of MRSA from humans. We plan to investigate the structure of the inhibitory compound produced by Staphylococcus pseudintermedius. If its structure can be determined, we may be able to use this inhibitory compound to formulate a new treatment for MRSA in humans.


Methicillin-resistant Staphylococcus aureus emerged long before the introduction of methicillin into clinical practice.

Abstract: The spread of drug-resistant bacterial pathogens poses a major threat to global health. It is widely recognised that the widespread use of antibiotics has generated selective pressures that have driven the emergence of resistant strains. Methicillin-resistant Staphylococcus aureus (MRSA) was first observed in 1960, less than one year after the introduction of this second generation beta-lactam antibiotic into clinical practice. Epidemiological evidence has always suggested that resistance arose around this period, when the mecA gene encoding methicillin resistance carried on an SCCmec element, was horizontally transferred to an intrinsically sensitive strain of S. aureus.Whole genome sequencing a collection of the first MRSA isolates allows us to reconstruct the evolutionary history of the archetypal MRSA. We apply Bayesian phylogenetic reconstruction to infer the time point at which this early MRSA lineage arose and when SCCmec was acquired. MRSA emerged in the mid-1940s, following the acquisition of an ancestral type I SCCmec element, some 14 years before the first therapeutic use of methicillin.Methicillin use was not the original driving factor in the evolution of MRSA as previously thought. Rather it was the widespread use of first generation beta-lactams such as penicillin in the years prior to the introduction of methicillin, which selected for S. aureus strains carrying the mecA determinant. Crucially this highlights how new drugs, introduced to circumvent known resistance mechanisms, can be rendered ineffective by unrecognised adaptations in the bacterial population due to the historic selective landscape created by the widespread use of other antibiotics.

Pub.: 21 Jul '17, Pinned: 25 Aug '17

Molecular Characterization of Methicillin-Resistant Staphylococcus aureus Isolated from Australian Animals and Veterinarians.

Abstract: This study aimed to determine the frequency and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) from Australian animals and whether animal-derived MRSA was similar to that from Australian veterinarians. A total of 1,080 clinical coagulase positive Staphylococcus isolates from Australian animals were collected during 2013. Sixteen (4%) of 360 S. aureus isolates were MRSA. Most MRSA came from companion animals, while none came from livestock. MRSA isolates were characterized using whole genome sequencing. ST22-IV (EMRSA-15) was the most common clone in dogs and cats. Clonal complex (CC) 8 was most common in horses. Most ST22-IV isolates were resistant to ciprofloxacin. Animal-derived MRSA genomes were interrogated for the presence of host-specific genetic markers (staphylokinase gene [scn], chemotaxis-inhibiting proteins gene [chp], staphylococcal complement inhibitor gene [sak], enterotoxin A gene [sea], and Von Willebrand Factor binding protein gene [vwb]). A subset of MRSA genomes previously collected from Australian veterinarians was also interrogated. There was no clear pattern in the distribution of host-specific markers among animal and veterinarian isolates. Animal- and veterinarian-derived MRSA were intermingled in the phylogenetic tree. The absence of MRSA in Australian livestock is in stark contrast with its presence in livestock from other countries. Possible explanations include Australia's geographic isolation, the absence of live animal importation into Australia, and most notably, the restrictions placed on the use of antimicrobials of critical importance in Australian livestock.

Pub.: 10 Jun '17, Pinned: 25 Aug '17