Methicillin resistant Staphylococcus – the South African perspective
Dr Marijke Henton BVSs., M.Med.Vet (Bact), UP
The resistance of bacteria to antibiotics has been a concern for a number of years, but is now far more than just a concern, as the incidence of resistant pathogens and opportunists is increasing expotentially in South Africa.
Methicillin resistant strains of Staphylococcus have been isolated from animals for the past 20 years or more, but the increase has been frighteningly rapid over the last few years.
The incidence and disease distribution of resistant strains in South Africa is broadly similar to the incidence in other parts of the world, as quoted in this insightful article, except that Staphylococcus schleiferi is rarely found here at present. South African resistant strains are also usually resistant to many other antibiotics.
Tests for oxacillin and cloxacillin resistance were initially based on methicillin, as the result for methicillin resistance was far more accurate for predicting this type of resistance. The current most accurate method of determining resistance is by detecting PBP2a production or the presence of the mecA gene. These tests are too costly and time-consuming for ordinary diagnostics, but they are used by researchers to determine the accuracy of the various commercial laboratory tests for methicillin resistance. There are a number of such tests and their accuracy depends on both the test conditions and the species of Staphylococcus involved. Not all laboratories in South Africa use the currently recommended tests. The test preferred for determining resistance in Staphylococcus aureus differs from that which is mostr accurate for e.g. Staphylococcus pseudointermedius. The accuracy of the various commercial tests is still being compared by researchers, with far more work being done on the human S. aureus pathogen than the veterinary pathogen S. pseudointermedius.
The research in this article showing that isolates from pets and their owners are often the same, should be another concern for veterinarians. We are all in close contact with our patients, and may bring these extremely resistant strains home to our loved ones.
Antibiotic stewardship is the science of using antibiotics in a responsible manner, and it is imperative that veterinarians and other health care workers adhere to the precepts.