Conditions · Infectious and tropical diseases

MRSA and other multidrug-resistant organism infections !

Some bacteria resist many antibiotics. MRSA, VRE and resistant gram-negative bacteria cause hard-to-treat infections, mostly in hospitals, and spread by hands.

Updated 2026-11-01

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What it is

Infections caused by bacteria that resist several antibiotic classes, mainly methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and gram-negative bacilli producing extended-spectrum beta-lactamases (ESBL) or carbapenemases (such as KPC). They are harder to treat and spread between patients by contact.

Who gets it

Antimicrobial resistance is a global public-health threat. In Colombia and Latin America, ESBL-producing Enterobacterales and carbapenem-resistant Klebsiella pneumoniae (notably KPC) and Pseudomonas or Acinetobacter are frequent in intensive care units. Colombia's Instituto Nacional de Salud monitors resistance and antibiotic use in hospitals; community-acquired MRSA causes skin infections in otherwise healthy people.

Causes

MRSA: Staphylococcus aureus resistant to beta-lactams through an altered penicillin-binding protein (PBP2a, mecA gene)
VRE: enterococci resistant to vancomycin
ESBL-producing Enterobacterales (E. coli, Klebsiella)
Carbapenem-resistant Enterobacterales (e.g. KPC-producing Klebsiella pneumoniae)
Multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii

Risk factors

Recent hospitalisation, intensive care stay or long-term care residence
Recent or repeated broad-spectrum antibiotic use
Invasive devices: central lines, urinary catheters, ventilators, drains
Surgery, dialysis, wounds and immunosuppression
Close contact, shared equipment and skin trauma (contact sports, barracks, prisons) for community MRSA
Injection drug use

Pathophysiology

Resistance arises through mutation or, more often, acquisition of mobile genes (plasmids, transposons) encoding enzymes that destroy antibiotics, altered targets, efflux pumps or reduced permeability. Antibiotic pressure selects resistant strains, which colonise skin, nose or gut and spread on hands and surfaces; colonisation becomes infection when barriers are breached by wounds or devices.

Classification

Colonisation versus infection
Hospital-acquired versus community-acquired (e.g. CA-MRSA)
By organism: MRSA, VRE, ESBL, carbapenem-resistant Enterobacterales, resistant Pseudomonas or Acinetobacter
By site: skin and soft tissue, bloodstream, pneumonia, urinary tract, surgical site, bone and joint

Symptoms and signs

Depend on the site: boils, abscesses or cellulitis in skin MRSA
Fever and chills in bloodstream infection
Cough, sputum and hypoxaemia in pneumonia
Dysuria, fever or flank pain in urinary infection
Redness, discharge or wound breakdown at surgical or line sites
Failure to improve on usual antibiotics

Diagnosis

Clinical: Suspected from the setting (hospital, prior antibiotics, devices, known colonisation) and the infection site. Colonisation alone, without signs of infection, is not treated with antibiotics but triggers isolation precautions.
Tests: Cultures from the infected site and blood before antibiotics when possible, with antimicrobial susceptibility testing; rapid molecular tests detect mecA, vanA/B or carbapenemase genes. Screening swabs (nasal for MRSA, rectal for VRE and carbapenemase producers) identify carriers.
Imaging: According to site: chest radiography for pneumonia, ultrasound for abscesses, echocardiography in S. aureus bacteraemia, MRI for bone infection.

Differential diagnosis

Infection by a susceptible organism
Colonisation without infection
Non-infectious inflammation (drug fever, gout, venous thrombosis)
Undrained collection or retained device as the cause of treatment failure

Goal of treatment

Treat true infections with antibiotics active against the resistant organism, control the source, and stop spread to other patients through infection-prevention measures and antibiotic stewardship.

Treatment

Procedure: Source control: drainage of abscesses, removal of infected catheters and devices, debridement.
Medical: Antibiotic selection guided by susceptibility testing and local resistance data: e.g. vancomycin, linezolid or daptomycin for MRSA; linezolid or daptomycin for VRE; carbapenems for ESBL producers; newer beta-lactam and beta-lactamase inhibitor combinations, polymyxins or other agents for carbapenem-resistant organisms, under infectious-disease advice.
Follow-up: Nursing priorities: contact precautions (gown and gloves), single room or cohorting, dedicated equipment, the five moments of hand hygiene, environmental cleaning, flagging of carriers and drug-level and kidney monitoring for agents such as vancomycin.
Conservative: Antibiotic stewardship: avoid unnecessary or overly broad antibiotics, shorten courses and de-escalate once cultures return.

Drugs for this condition

Complications

Sepsis and septic shock
Infective endocarditis and metastatic abscesses
Osteomyelitis and septic arthritis
Longer hospital stays and higher mortality than susceptible infections
Clostridioides difficile infection from broad antibiotic use
Outbreaks within hospital units

Prognosis

Outcome depends on the site, the organism, prompt active therapy and source control. Uncomplicated skin MRSA usually does well after drainage; bloodstream infections and carbapenem-resistant gram-negative infections in critically ill patients carry high mortality.

Prevention

Hand hygiene by all staff and visitors
Contact precautions for colonised or infected patients
Care bundles for central lines, urinary catheters and ventilators
Antibiotic stewardship programmes and surveillance
Not sharing towels, razors or sports equipment (community MRSA)

Test yourself

Think of the answer, then tap the question to see it.

What is the genetic basis of methicillin resistance in Staphylococcus aureus?

The mecA gene, which encodes an altered penicillin-binding protein (PBP2a) with low affinity for beta-lactams.

Which isolation precautions are used for a patient with MRSA or VRE?

Contact precautions: gown and gloves, single room or cohorting, dedicated equipment and strict hand hygiene.

Which carbapenemase-producing organism is especially common in Colombian intensive care units?

KPC-producing Klebsiella pneumoniae.

Should asymptomatic colonisation with an MDRO be treated with antibiotics?

No; colonisation without infection calls for isolation precautions, not antibiotic treatment.

Which test is recommended in Staphylococcus aureus bacteraemia to look for endocarditis?

Echocardiography.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Methicillin-resistant Staphylococcus aureus (MRSA) Basics | MRSA | CDC (Centers for Disease Control and Prevention (CDC), 2024); Antimicrobial resistance (World Health Organization (WHO), 2025).

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