Methicillin-resistant Staphylococcus aureus (MRSA) is a type of staph bacteria that has developed resistance to several common antibiotics, including methicillin, amoxicillin, and penicillin. Staphylococcus aureus lives harmlessly on the skin and in the nose of about one-third of the population. MRSA is concerning because its antibiotic resistance makes infections more difficult to manage compared to standard staph infections. Understanding where this bacterium can reside is important, especially regarding its presence in the mouth.
MRSA Presence in the Mouth
MRSA can be found in the mouth, which is recognized as an independent site of colonization, though the anterior nares (nostrils) are the primary location for S. aureus carriage. Colonization means the bacteria are present without causing an active infection or noticeable symptoms. Reports indicate that MRSA carriage rates in the oral cavity can be high, sometimes comparable to nasal rates. This oral presence acts as a reservoir, potentially leading to infection in other body sites or cross-infection to other people.
Factors Increasing Oral Risk
The presence of MRSA in the mouth is often linked to conditions that disrupt the natural balance of oral microbes. A significant factor is the recent or frequent use of broad-spectrum antibiotics, which eliminate competing bacteria and allow resistant strains like MRSA to establish themselves. Patients with compromised immune systems or chronic illnesses, such as those in long-term care facilities, also have a higher incidence of oral MRSA colonization. Removable oral appliances, particularly dentures, create surfaces where MRSA can preferentially colonize and form biofilms. Poor general oral hygiene is a risk factor, as are recent dental procedures or oral surgery that create open wounds, providing a pathway for the bacteria to cause an active infection.
Signs of an Oral MRSA Infection
An active MRSA infection in the oral cavity presents with signs that are typically more severe or persistent than standard bacterial infections. Symptoms often mirror those of a skin or soft tissue infection, but they occur inside the mouth or on the surrounding facial tissue. This includes the formation of abscesses—painful, pus-filled masses—in the gums, cheeks, or around the teeth.
Infection may also manifest as persistent, non-healing sores or ulcers that appear red, swollen, and warm to the touch. Severe pharyngitis (sore throat) that fails to improve with common antibiotics can signal MRSA involvement, especially if accompanied by systemic symptoms like fever and chills. If the infection spreads to deeper tissues, it can cause cellulitis, a rapidly spreading, painful swelling around the mouth or face.
Diagnosis and Treatment
Confirming an oral MRSA infection requires specific laboratory testing, as symptoms alone are not unique to MRSA. A healthcare provider will take a culture, often a swab of the infected area or fluid draining from an abscess, and send it for analysis. The lab identifies the organism and performs susceptibility testing to determine which antibiotics are effective against that particular strain.
Treatment for a localized oral MRSA infection often begins with source control, which involves incision and drainage (I&D) of any abscesses to remove the pus. If antibiotics are necessary, they must be chosen from a limited selection of medications known to overcome the bacteria’s resistance. These specific antibiotics include oral options like trimethoprim/sulfamethoxazole or doxycycline, or intravenous medications like vancomycin or linezolid for more severe cases. Following the full course of treatment is important to ensure the infection is eradicated and prevent further antibiotic resistance.