-Screening-for-MRSA-by-Dr-T-V-Rao-MD.pptx

1. Screening for
MRSA
Dr.T.V.Rao MD
13-11-2023 Dr.T.V.Rao MD @ ClinicalMicrobiology 1

2. 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.

3. 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.

4. Colonization Sites
Dr.T.V.Rao MD @ MRSA
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5. 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

6. 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).
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7. 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,
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8. Community associated Staphylococcus
•Strains causing
community-associated
infections are often
resistant only to ß-
lactam agents and
erythromycin, may be
resistant to
fluoroquinolones
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9. 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
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10. 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.
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11. 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
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12. 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.
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13. Collecting Specimens for Detecting MRSA
•Patients were
swabbed with
rayon-tipped
swabs on
admission at 4
body sites: nostrils,
perineum, axilla,
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14. 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.
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15. Chromogenic Agars help in Identification
•In addition, there
are now several
FDA-approved
selective
chromogenic agars
that can be used for
MRSA detection
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16. 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.
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17. 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
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18. 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.
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19. 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.
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20. 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.
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21. 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
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22. 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.
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23. 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

24. 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).

25. 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.
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26. 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
13-11-2023 Dr.T.V.Rao MD @ MRSA

27. 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.
13-11-2023 Dr.T.V.Rao MD @ MRSA

28. In spite of Many Developments in Control of MRSA
HAND WASHING STILL BEST EASIER OPTION
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29. 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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30. • Program Created by Dr.T.V.Rao MD for Medical
professionals for improving awareness on
Hospital Associated Infection with spread of
MRSA
•Email
•doctortvrao@gmail
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