The article is a summary on treating MRSA and other Staph aureus skin infections and colonization. If you have had Staph aureus infections, this article is a great way to prevent further problems with this bacteria. As an infection doctor, this is one of the most common reasons that I see people. This article is packed with information. If you are looking for a solution to your problem, skip to the Treat and Prevent Section or listen to the video.

MRSA: An Intro to the Microbiome

What is the Microbiome?

Being human is anything but static. Humans are home to many bacteria, viruses, and fungi. In this section, I will summarize the concept of microbiome and why it is important to remember that you have more bacterial cells that make up your body than human cells (10 to 14th compared to 10 to 13th). Bacteria colonize any surface in contact with the environment, such as the skin, mouth, upper respiratory tract, gastrointestinal system, urinary tract, vagina. Scientists call the environment and bacteria which grow in it the microbiome. Different microbes prefer a particular surface based on multiple factors, including pH, temperature, protein sources, oxygen content, and moisture/salinity.

Staphylococcus aureus lives on the skin of the groin, perineum (between genitals and anus), axillae (armpits). But the nasopharynx (nose and throat) is its primary habitat. As many as 25% or more of the population harbors S. aureus in the nose. Much less are colonized with MRSA (2-4%). A discussion of the complex relationship between S. aureus and humans in colonization and infection follows.

Compared to oral and intestinal surfaces, bacterial colonization on the surface of the skin is sparse. The 1.2 kg of total body weight accounts for bacteria, with skin bacteria weighing approximately 0.2 kilograms and intestinal bacteria weighing 1 kg. Bacteria reside on the skin’s surface generally as commensals or “neutralists,” a relationship with the human host that is neither beneficial nor detrimental.

Bacteria utilize various elements on the surface, such as carbon, oxygen, nitrogen, potassium, magnesium, iron, and calcium, to grow optimally. However, given the right circumstances, such as trauma, skin abrasion, or excessive dryness (xerosis), there is a transition from more significant colonization to infection. 

MRSA: A Bacteria of the skin and upper respiratory tract

The most common bacteria associated with skin infections are Streptococcus and Staphylococcus. Streptococcus causes impetigo, a superficial infection. It causes wound infections from injury or after surgery, and cellulitis, an ascending infection associated with fever, rash and pain, and site swelling. Staphylococcus aureus infections can get more severe if left unaddressed. 

With Staph and Strep, deeper infections can occur. These infectious such as necrotizing fasciitis or a muscle abscess (pyomyositis), may require surgical intervention. An untreated Staphylococcus aureus infection can put a person at risk for deep tissue and heart valve infections. Staphylococcus aureus can sometimes follow viral respiratory infections leading to severe, life-threatening pneumonia.

Staphylococcus aureus is easy to see on Gram staining. They stain Gram-positive (purple) and appear as grape-like clusters in the microscope. They grow readily on culture media, including blood cultures. Newer testing methods, including a nasal swab for PCR, help detect colonization of Staph aureus in the nares and tell between MRSA and MSSA. Colonization has clinical utility for treatment and pre-operative planning.

MRSA: Common Questions

What is MRSA?

Methicillin-resistant Staphylococcus aureus is a ubiquitous bacterium that resides on the skin and nasal-oropharynx of humans and other animals. The ecological niche of Staphylococcus aureus in the nares (nose). Other areas of the skin populated by this bacterium include the axillae (armpits), groin, perineal area (area between genitals and anus). Contamination of fomites (inanimate objects such as keys, computers, phones, etc.) can represent a transmission source to other people. Although colonization generally comes before infection, outbreaks may occur where colonization was not evident.

Methicillin-resistant Staphylococcus aureus (MRSA). This bacteria carries resistance to methicillin, oxacillin, and cefazolin, newer iterations of penicillin. These antibiotics treated penicillin-resistant Staph. Resistant bacteria produce an enzyme beta-lactamase, which breaks down the penicillin structure (beta-lactam ring) and reduces activity. Unfortunately, not long after their release, bacteria became resistant to the newer antibiotics. 

In the ’80s and ’90s, a growing percentage of community-associated infections from MRSA appeared. Various proteins expressed by MRSA, such as the Panton Valentin Leukocidin (PVL) and others, are associated with outbreaks and, to some extent, a greater virulence (more severity) of infection. Co-association with the colonization of MRSA and MSSA can be attributable to a risk of diseases after surgery. 

I had a Spider bite that got infected with MRSA. Is this possible?

Typically, when someone is in the process of developing an infection with Staphylococcus aureus, the area may feel a sharp pain. Although the sensation is similar to an insect or spider bite, it is seldom the case. Indeed, in various geographic locations, the bite of a brown recluse or hobo spider, to name a few, can result in an erythematous lesion with central necrosis (dark center). 

Often, “spider bites” are abscesses that culture Staphylococcus aureus in the wound. In one study by Moran et al., a report of a spider bite had an adjusted odds ratio of 3 (that means that those with this history were 3x more likely than those without an MRSA infection.

 What are the risk factors for MRSA infection?

 This question is one with a complicated answer. 

 Miller and Binh an Diep CID 2008 had an excellent way of representing risk factors in three areas:

 Risk factors of behaviors and exposures: skin-to-fomite contact (shaving, tattoos, rug burns, etc.), skin-to-skin contact, antibiotic exposure

 Host defenses: Skin integrity, Antimicrobial peptides, an area that is in its infancy but essentially looking at proteins that the skin produces which neutralize bacteria, etc., medications that affect the immunity such as biologicals, e.g., TNF-a antagonists (etanercept, etc.), chemotherapy, steroids, etc. Immunodeficiency states. 

 Pathogen factors: These relate to virulence factors, toxins produced—strain type, etc.

 Here is a list of other risk factors:

1. Locations: Prisons, athlete groups/gyms, hospitalization, military, reservations
2. Behaviors: Men who have sex with men, Elicit drug use (meth/heroin), shavers
3. Conditions: HIV, Hepatitis C, Diabetes mellitus and cirrhosis, Job’s syndrome, Paraplegia
4. Medications:  Recent antibiotic exposure, Steroid use (prednisone) or other immunosuppressants, possible association with nonsteroidal agents (NSAIDS)
5. Devices: Hemodialysis catheters, Peripherally inserted central catheters (PICC), foleys, PEG tubes, etc.

Treat and Prevent MRSA Infection

A common question that comes up is, “I went to the ED and was diagnosed with MRSA. How can I prevent myself from getting MRSA again?”

 Here are some 9 suggestions for avoiding colonization and preventing infection:

Summary: Treating MRSA

Patients will commonly come into the clinic to search for answers on reducing the risk of future infections. As summarized in the previous sections, underlying conditions, behaviors, and medications predispose to recurrent Staph infections. Optimal control of future disease needs to include strategies to improve these conditions and risk factors. Someone with untreated diabetes and elevated glucose will continue to develop Staphylococcus aureus infections despite approaches to eradicate colonization.

There are three ways that I approach patients with persistent MRSA infections and colonization:

Address the risk factor 

For a state of colonization to transform to a state of infection; there is often a risk factor that one can identify. Some are more obvious than others. Occasionally, upon examining a patient, I can tell the risk factor. For instance, some men (swimmers, other athletes) are shavers; some women shave closer to the groin or mons pubis. Using a dull razor, not using a cream or moisturizer to shave, or not treating the razor with alcohol before use can break the skin and allow the bacteria to cause an infection. 

Sometimes, a new sexual partner of a patient was colonized with Staph and increased the risk of transmission enough to lead to folliculitis and abscesses. On the examination, I will often observe a patient scratching themselves with dry skin or folliculitis and even attempt to express a lesson in front of me. 

People who are chronic sitters, e.g., truck drivers, writers, bloggers (one of many reasons I have a standing desk), are also prone to folliculitis on the buttock, which can then cause an abscess. 

Below I have listed several ways to reduce the risk of Staph aureus infection.

Address the infection

The infection state may be an abscess or other skin lesions. To address the infection, physicians perform an incision and drainage of a boil, if present, or sometimes allow it to mature and resolve spontaneously. Some data support that antibiotics have a limited role after an incision and drainage of a small <2cm abscess. Though with larger abscesses, there is a lower failure rate with a proper incision and drainage. Antibiotic considerations include trimethoprim-sulfamethoxazole (Bactrim), doxycycline, and possibly clindamycin (some resistant isolates).

Address the colonization state

The usual colonization site is in the nose. To reduce this, I prescribe a surgical cleanser, such as Hibiclens, which can be applied 2 to 3 times weekly – lather on the skin and rinse off. You can use an antibiotic ointment such as Bactroban – apply a cotton swab with the ointment in each naris twice daily for one week. I usually begin this protocol two weeks after the acute infection.

Thanks for reading This! Dr. Cirino

Further reading (below are a few references and links):

Boeker S et. al. Methicillin-resistant Staphylococcus aureus: risk factors associated with community-onset infections in Denmark – Clinical Microbiology and Infection. 2008. Clin Micro and Infection. Danish Community-MRSA group.

Moran er al. N Engl J Med 2006; 355:666-674   (Epidemiology)
https://www.ncbi.nlm.nih.gov/pubmed/27668900

https://www.ncbi.nlm.nih.gov/pubmed/18510460

Please feel free to post any questions or comments.