What is the Difference Between MRSA and MSSA

The main difference between MRSA and MSSA is that MRSA is resistant to methicillin, whereas MSSA is susceptible to methicillin. 

MRSA and MSSA are two Staphylococcus aureus strains that have different resistance to methicillin, a narrow-spectrum β-lactam antibiotic. 

Key Areas Covered

1. What is MRSA
     – Facts, Features, Behaviour
2. What is MSSA
     – Facts, Features, Behaviour
3. Similarities Between MRSA and MSSA
     – Outline of Common Features
4. Difference Between MRSA and MSSA
     – Comparison of Key Differences

Key Terms 

MRSA, MSSA

What is MRSA

MRSA is the methicillin-resistant Staphylococcus aureus. It is resistant to the β-lactam antibiotic, methicillin. The symptoms of MRSA infections include:

• Severe skin infections
• Pneumonia in the lungs
• Bacterial infections of the heart
• Infections in surgical sites
• Infections in bones and joints

Figure 1: MRSA

Moreover, MRSA infections can be either hospital-related or community-related. Therefore, the risk factors of MRSA include:

• Hospital stays
• Use of invasive medical devices
• Skin-to-skin contact
• Overcrowded and unsanitary environments
• HIV infection
• Injected drug abuse
• High prevalence of sexual activity

Treating MRSA is challenging because many antibiotics are no longer effective against MRSA. But alternative antibiotics can be potentially effective. Vancomycin can be prescribed for complex skin infections, catheter infections, bone infections, bacteremia, and pneumonia. Moreover, clindamycin and linezolid are effective against superficial skin infections and pneumonia. However, maintaining good personal hygiene, avoiding sharing personal items, covering skin lacerations, and regular sterilization are helpful for the prevention of MRSA.

What is MSSA

MSSA is the methicillin-susceptible Staphylococcus aureus. Most importantly, it is resistant to methicillin. Therefore, it is easy to treat MSSA infections since it is sensitive to antibiotics. Mostly, MSSA is a community-acquired infection. The risk factors of MSSA include skin-to-skin contact, contact with surface items contaminated with bacteria, and sharing personal items. Cephalexin is used in the treatment of skin infections in MSSA. Meanwhile, nafcillin is essential for treating pneumonia. Additionally, good personal hygiene, avoiding sharing personal items, covering skin lacerations, and getting early treatments prevent MSSA infections.

Figure 2: S. aureus

Moreover, skin infections of MSSA can cause redness, swelling, warmth, pain, and pus. When the infections go further into the body, it causes blood poisoning and toxic shock syndrome. MSSA can also cause bacteremia, the presence of bacteria in the bloodstream. It is often called septicemia and blood poisoning. Bloodstream infections are severe and can be life-threatening. 

Similarities Between MRSA and MSSA

• MRSA and MSSA are two Staphylococcus aureus strains with different levels of resistance to methicillin.
• They occur due to the application of the β-lactam antibiotic, methicillin. 

Difference Between MRSA and MSSA

Definition

MRSA refers to a group of Staphylococcus aureus that are resistant to methicillin. In contrast, MSSA refers to the Staphylococcus aureus that is susceptible to methicillin.

Resistant to Methicilin

MRSA is resistant to methicillin, while MSSA is susceptible to methicillin.  

Type of Infection

While MRSA tends to be a hospital-acquired infection, MSSA is a community-acquired infection. 

Treatments

MRSA is difficult to treat, while MSSA is easy to treat.

Type of Treatment

Vancomycin, clindamycin, and linezolid are used to treat MRSA, while cephalexin and nafcillin are used to treat MSSA. 

Conclusion

In brief, MRSA and MSSA are two Staphylococcus aureus strains with different resistances to methicillin, a β-lactam antibiotic. MRSA is resistant to methicillin. Therefore, vancomycin, clindamycin, and linezolid are used to treat MRSA. However, MRSA is difficult to treat. It is mainly a hospital-acquired infection. In comparison, MSSA is susceptible to methicillin. It is easy to treat, and cephalexin and nafcillin are important in treating MSSA. Mostly, it is a community-acquired infection. Therefore, the main difference between MRSA and MSSA is the methicillin resistance.

References:

1. MRSA infection. Mayo Clinic. Mayo Foundation for Medical Education and Research.
2. MSSA bacteremia: What is it, what causes it, and how is it treated?. WebMD. 

Image Courtesy:

1. “Methicillin-Resistant Staphylococcus aureus (MRSA) (8423119167)” By NIAID – Own work (CC-BY 2.0) via Commons Wikimedia
2. “Staphylococcus aureus appearance on agar plates” By HansN.- Own Work (CC-BY 3.0) via Commons Wikimedia