Screening for MRSA

03/05/2023 Dr.T.V.Rao MD @ ClinicalMicrobiology 1

Screening for MRSA

Dr.T.V.Rao MD

What is MRSA? MRSA is Staphylococcus aureus with resistance to a specific class of antibiotics, penicillinase-

resistant penicillin's.

MRSA stands for methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus is the scientific name for the bacteria that cause ‘staph’ infections, including:

most frequently, skin and soft tissue infections, such as boils deeper infections, including invasion of the bloodstream and spreading around the body to

cause serious, life threatening infections such as septicemia, abscesses, meningitis and pneumonia

MRSA were first reported in 1961 in England. It took only a few months from introduction of the first penicillinase-resistant antibiotic to

recognition of infections from MRSA.

What is MRSA? (cont.)Clinically, MRSA isn’t particularly different than staph without methicillin

resistance. Methicillin resistance by itself is not an added risk for the individual having a staph

infection. Other antibiotics are still available to treat MRSA infections.

However, MRSA is a concern to medical and public health communities in general.

It represents a marked increase in antibiotic resistance in staphylococci. Different antibiotics need to be used to treat and prevent it.

• More expensive antibiotics, such as vancomycin, often have more side effects, and increasing their use may result in additional antibiotic resistance in staphylococci, potentially rendering them in the future very difficult to treat.

• Reducing the number of staph infections caused by MRSA is important in fighting against antibiotic resistance.

03/05/2023

Colonization Sites

Dr.T.V.Rao MD @ MRSA

Infections

What are the different kinds of strains of MRSA?MRSA developed from methicillin-susceptible staph because methicillin and

its relatives, such as oxacillin, were widely used and selected for resistant strains.

This selection process has happened at least several times in the last 10-30 years.

In the 1960s, strains of MRSA emerged in hospitals.• Hospital strains tend to be resistant to additional antibiotics, and often cause

bloodstream infections.

In the 1990s, new strains of MRSA emerged in the community.• Community strains tend to produce toxins that lead to skin infections and

abscesses but are less often resistant to other antibiotics.

Over time, hospital strains have moved to the community while community strains have also been brought into the hospital.


HOW WE DEFINE MRSA IN OUR LABORATORY

• Strains that are oxacillin and methicillin resistant, historically termed methicillin-resistant S. aureus (MRSA), and are resistant to all ß-lactam agents, including cephalosporins and carbapenems, although they may be susceptible to the newest class of MRSA-active cephalosporins (e.g, ceftaroline).


MRSA and Drug Resistance• Strains of MRSA causing

healthcare-associated infections often are multiply resistant to other commonly used antimicrobial agents, including erythromycin, clindamycin, fluoroquinolones and tetracycline,


Community associated Staphylococcus

•Strains causing community-associated infections are often resistant only to ß-lactam agents and erythromycin, may be resistant to fluoroquinolones


Rationale for MRSA screening

• Colonized patients constitute the main reservoir for nosocomial transmission• Colonized patients are only detected by active surveillance

sampling of muco-cutaneous swabs• Hospitalized patients carrying MRSA are at high risk to

develop a MRSA infection• High mortality (RR 1.9 vs MSSA, RR > 10 vs no infection) and

prolonged hospital stay (2-13 days) is associated with MRSA infections


Classification of Risk Factors for MRSA Infections

• There are certain factors that increase the risk of a person contracting MRSA. These factors include: have previously had MRSA are coming from a high risk environment (e.g. hospital or nursing home) 1 patients with a chronic wound, e.g. Leg ulcers 2indwelling medical devices e.g. catheter 3 being admitted as an inpatient in another hospital within the last 6 months drug therapy that reduces the auto-immune response.


Potential benefits for rapid MRSA identification •Patient care – Early appropriate treatment with

improve clinical outcome – Reduced empirical use of glycopeptides• Infection control – Early MRSA isolation/cohorting –

Decrease in nosocomial transmission rate – Decrease in MRSA morbidity and mortality – Cost saving • Shorter patient stay Fewer preventive isolation days • Lower medical liability costs


Who should be screened for MRSA? NHS

Guidelines • MRSA screening is usually carried out in people who need to be

admitted to hospital for planned or emergency care. • In particular, it's recommended for certain groups at the highest risk of

becoming infected with MRSA while they're in hospital. These include:• People who have been infected or colonised (carry the bacteria on their

skin) with MRSA previously • People being admitted to certain "high-risk" hospital units – including

surgery, cancer, kidney and trauma units • People who aren't staying in hospital overnight don't usually need to be

routinely screened.


Collecting Specimens for Detecting MRSA

•Patients were swabbed with rayon-tipped swabs on admission at 4 body sites: nostrils, perineum, axilla,


How should clinical laboratories test for MRSA

• In addition to broth microdultion testing, the Clinical and Laboratory Standards Institute (CLSI), recommends the cefoxitin disk screen test, the latex agglutination test for PBP2a, or a plate containing 6 μg/ml of oxacillin in Mueller-Hinton agar supplemented with 4% NaCl as alternative methods of testing for MRSA.. In addition, there are now several FDA-approved selective chromogenic agars that can be used for MRSA detection.


Chromogenic Agars help in Identification

•In addition, there are now several FDA-approved selective chromogenic agars that can be used for MRSA detection


Why are oxacillin and cefoxitin tested instead of methicillin?

• First, methicillin is no longer commercially available in the United States. Second, oxacillin maintains its activity during storage better than methicillin and is more likely to detect heteroresistant strains. However, cefoxitin is an even better inducer of the mecA gene, and tests using cefoxitin give more reproducible and accurate results than tests with oxacillin.


If oxacillin and cefoxitin are tested, why are the isolates called “MRSA” instead of “ORSA”?

• When resistance was first described in 1961, methicillin was used to test and treat infections caused by S. aureus. However, oxacillin, which is in the same class of drugs as methicillin, was chosen as the agent of choice for testing staphylococci in the early 1990s, and this was modified to include cefoxitin later. The acronym MRSA is still used by many to describe these isolates because of its historic role.

Ref 1 CLSI. 2013. Performance standards for antimicrobial susceptibility testing. CLSI approved standard M100-S23. Clinical and Laboratory Standards Institute, Wayne, PA.• 2Bannerman, TL. 2003. Staphylococcus, Micrococcus and other catalase-

positive cocci that grow aerobically. In P.R


How is the mecA gene involved in the mechanism of resistance?

• Staphylococcal resistance to oxacillin/methicillin occurs when an isolate produces an altered penicillin-binding protein, PBP2a, which is encoded by the mecA gene. The variant penicillin-binding protein binds beta-lactams with lower avidity, which results in resistance to this class of antimicrobial agents.


Are there additional tests to detect oxacillin/methicillin

resistance?• Nucleic acid amplification tests,

such as the polymerase chain reaction (PCR), can be used to detect the mecA gene, is the most common gene that mediates oxacillin resistance in staphylococci. However, mecA PCR tests will not detect novel resistance mechanisms such as mecC or uncommon phenotypes such as borderline-resistant oxacillin resistance.


Can Healthy People Get MRSA? • MRSA skin infections are showing up

more frequently in healthy people, with none of the usual risks factors. This type of MRSA - called community-associated MRSA (CA MRSA) - has been reported among athletes, prisoners, and military recruits. Outbreaks have been seen at schools, gyms, day care centres and other places where people share close quarters.


Who is at risk for MRSA? those most at risk:

• Spend a lot of time in crowded places such as hospitals, schools or rooms Share sports equipment Share personal hygiene items Play contact sports Overuse or misuse antibiotics


What do you understand by Vancomycin Resistance

• Since 1996, MRSA strains with decreased susceptibility to vancomycin (minimum inhibitory concentration [MIC], 4 – 8 μg/ml) and strains fully resistant to vancomycin (MIC ≥ 32 μg/ml) have been reported.

How can people protect themselves from MRSA? Collective public vigilance and demands for better application of infection

control standards to reduce healthcare-associated MRSA

In the hospital Hand washing before and after seeing each patient Care of IV lines

At the personal level Wash hands or other body surfaces, especially after skin-to-skin contact with other

people and with healthcare settings Avoid sharing potentially contaminated items, such as towels, unwashed clothing Clean and cover abrasions/cuts as soon after they occur as possible Seek healthcare consultation at the first signs of possible infection

Decolonization Decolonization entails treatment of persons colonized with a specific MDRO, usually MRSA, to eradicate carriage of that organism However, decolonization of persons carrying MRSA in their nares has proved possible with several regimens that include topical mupirocin alone or in combination with orally administered antibiotics (e.g., rifampin in combination with trimethoprim- sulfamethoxazole or ciprofloxacin) plus the use of an antimicrobial soap for bathing(303).


Can Chemical baths help in reducing MRSA incidence

• In one report, a 3-day regimen of baths with povidone-iodine and nasal therapy with mupirocin resulted in eradication of nasal MRSA colonization(304). These and other methods of MRSA decolonization have been thoroughly reviewed.

03/05/2023 Dr.T.V.Rao MD @ MRSA

WHAT REALLY WE NEED TODAY • Always washing your hands after using the toilet or

commode (many hospitals now routinely offer hand wipes) • Always washing your hands or cleaning them with a hand

wipe immediately before and after eating a meal • Following any advice you're given about wound care and

devices that could lead to infection (such as urinary catheters) • Reporting any unclean toilet or bathroom facilities to staff –

don't be afraid to talk to staff if you're concerned about hygiene

03/05/2023 Dr.T.V.Rao MD @ MRSA

General Hygiene too Matters • The hospital

environment, including floors, toilets and beds, should be kept as clean and dry as possible. • Patients with a known or

suspected MRSA infection should be isolated. • Patients should only be

transferred between wards when it is strictly necessary.


In spite of Many Developments in Control of MRSAHAND WASHING STILL BEST EASIER OPTION


References • What are the susceptibility patterns of clinical S. aureus isolates? CDC

resources Laboratory Testing for MRSA• 2MDRO Prevention and Control Healthcare Infection Control Practices

Advisory Committee (HICPAC) CDC

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• Program Created by Dr.T.V.Rao MD for Medical professionals for

improving awareness on Hospital Associated Infection with spread of

MRSA•Email

•[email protected] MD @ ClinicalMicrobiology