Affects: Cats
Methicillin-resistant Staphylococcus aureus (MRSA) is a group of Staphylococcus aureus strains that are resistant to β-lactam antibiotics. The β-lactam group is a broad-spectrum group of antibiotics that includes several widely used drugs, including methicillin, oxacillin, and cephalosporins. Therefore, MRSA is responsible for several difficult-to-treat infections in humans. It caused more than 100,000 deaths worldwide attributable to antimicrobial resistance in 2019. Strains unable to resist these antibiotics are classified as methicillin-susceptible S. aureus, or MSSA.
MRSA infection is common in hospitals, prisons, and nursing homes, where people with open wounds, invasive devices such as catheters, and weakened immune systems are at greater risk of healthcare-associated infection. MRSA began as a hospital-acquired infection but has become community-acquired, as well as livestock-acquired. The terms HA-MRSA (healthcare-associated or hospital-acquired MRSA), CA-MRSA (community-associated MRSA), and LA-MRSA (livestock-associated MRSA) reflect this.
Signs And Symptoms: In humans, Staphylococcus aureus is part of the normal microbiota present in the upper respiratory tract, and on skin and in the gut mucosa. However, along with similar bacterial species that can colonize and act symbiotically, they can cause disease if they begin to take over the tissues they have colonized or invade other tissues; the resultant infection has been called a "pathobiont".
After 72 hours, MRSA can take hold in human tissues and eventually become resistant to treatment. The initial presentation of MRSA is small red bumps that resemble pimples, spider bites, or boils; they may be accompanied by fever and, occasionally, rashes. Within a few days, the bumps become larger and more painful; they eventually open into deep, pus-filled boils. About 75 percent of CA-MRSA infections are localized to skin and soft tissue and can be treated effectively.
Risk Factors: A select few of the populations at risk include:
People with indwelling implants, prostheses, drains, and catheters
People who are frequently in crowded places, especially with shared equipment and skin-to-skin contact
People with weak immune systems (HIV/AIDS, lupus, or cancer patients; transplant recipients; severe asthmatics; primary immune deficiencies, etc.)
Diagnosis: Diagnostic microbiology laboratories and reference laboratories are key to identifying MRSA outbreaks. Normally, a bacterium must be cultured from blood, urine, sputum, or other body-fluid samples, and in sufficient quantities to perform confirmatory tests early on. Still, because no quick and easy method exists to diagnose MRSA, initial treatment of the infection is often based on "strong suspicion" and techniques by the treating physician; these include quantitative PCR procedures, which are employed in clinical laboratories to detect and identify MRSA strains quickly.
Another common laboratory test is a rapid latex agglutination test that detects the PBP2a protein. PBP2a is a variant penicillin-binding protein that imparts the ability of S. aureus to be resistant to oxacillin.