Epidemiology and Control of
Methicillin-Resistant
Staphylococcus aureus
in hospitals
Maria Kapi,MD
Registrar of Medical Microbiology
Laiko General Hospital of Athens, Greece
Readings: MRSA
What are MRSA?
If we want to understand what are
MRSA, we should first know:
1.
2.
What are Staphylococci?
What is Staphylococcus aureus?
What are MRSA?
3. What are penicillin and methicillin?
4. What are PBPs?
5. What are beta-lactams and beta-
lactames?
Staphylococci: Gram positive cocci
( from Greek staphyle, means bunch
of grapes ) that occur singly and in
pairs, short chains and irregular
grape-like clusters.
Staphylococcus aureus: is the
staphylococcus which has the ability to
clot plasma or in other words, which is
coagulase positive. More than 80% of
Staphylococcous aureus strains produce
beta-lactamases.
Penicillin: is the antibiotic agent that
Alexander Fleming a Scottish physician
discovered in 1929. In 195 only 15% of
S.aureus was susceptible to penicillin.
Approximately 5% of S.
aureus today are sensitive
to penicillin.
Methicillin: was with oxacillin the new line
of penicillins in 1959, which became a
new hope to the treatment of St. aureus. In
1961 the St. aureus became resistant to
methicillin. Strains that are
oxacillin and methicillin
resistant, historically termed
Methicillin-Resistant S.aureus
(MRSA)
PBPs: are penicillin-binding proteins.
They are responsible for the final
stages of peptidoglycan synthesis of
the bacterial cell wall structure.
Inhibition of one or more of these
essential enzymes leads to bacterial
lysis.
Beta lactams: are the antibiotics that contain
the beta lactam ring. These are : penicillins,
cephamycins, cephalosporins, carbapenems
monobactams. The ring structure is
common to all beta-lactams and must be
intact for antibacterial action. They are cell
wall synthesis inhibitors.
Beta lactamases: are enzymes that
catalyse the hydrolysis of the betalactam ring and inactivate these group
of antibiotics. Genes encoding these
enzymes are widespread in the
bacteria.
What MRSA are doing?
Methicillin Resistant Staphylococcus
aureus, when its cell is exposed to βlactam antibiotics, a supernumerary βlactam-resistant PBP (PBP2a), takes
over the the biosynthetic functions of
the normal PBPs. This protein is
responsible for the methicillin
resistance.
Heteroresistance of MRSA
All the cell in the population may have
the genetic information for resistance ,
which is encoded by the mecA gene.
Only a small number of cells can
actually express the resistant
phenotype under in vitro testing
conditions. This phenomenon is termed
heteroresistance.
Why are MRSA important?
1.
2.
Hospital –acquired infections. MRSA
are common nosocomial pathogens
around the world.
The treatment is very difficult.
Vancomycin often is the only drug of
choice for severe infections.
Why are MRSA important?
3.
MRSA with reduced susceptibility to
glycopeptides. Since 1996 has been
identified in Europe, Asia and United
States. That increases the possibility
some strains became fully resistant to
glycopeptides.
4.
MRSA are easily transmissible
between patients.
MRSA in Europe.
In England and Wales, from
January to December 1999
methicillin resistance was
37% of the S.aureus reports.
Except Scandinavia and
Netherlands most countries
have high rates of MRSA.
MRSA in the United States
From January till December 1999, 52,3%
MRSA are associated with nosocomial
infections in intensive care unit patients.
The increase
in resistance
is 37% from
1994-98.
Epidemiology of MRSA
Mode of Transmission. Is transmitted
by contact with a person who has
MRSA infection or is colonized with
the organism.Hands of the health
care workers is the most common
mode of transmission from patient
to patient.
Epidemiology of MRSA
Reservoirs .Colonized and infected
patients are the major reservoir of
MRSA. Although has been isolated
from environmental surfaces, these
are not the most likely source of
spread.
Epidemiology of MRSA.
Risk factors. The factors that have been
identified as increasing the risk of
MRSA infection are:

Increased length of hospital stay
 Multiple hospitalizations
 Wounds
Epidemiology of MRSA.
Risk factors
Invasive procedures
 Greater than 65 years old
 Severe underlying disease.
Administration of broad-spectrum
antibiotics.


Costs of MRSA
Directly attributable costs:
 “ hotel costs” of extended lengths of
stay
 the cost of diagnostic procedures,
 morbidity and mortality that can
follow infection
 glycopeptides are more expensive
than other antibiotics e.t.c
Costs of MRSA
Costs of control:
 costs of involvement of the infection
control team.
 temporary closure of wards or
theatres.
 re-deployment of staff.
Control of MRSA in Hospitals
General Principles:
 Prevention of acquisition and spread
of infection by patients and staff
 Priorities are high risk units, such as
intensive care units and patients who
are susceptible to infection.
Control of MRSA in Hospitals
 Handwashing.
Health care workers
should wash their hands before and
after contact with all patients, even
when gloves are worn. A written
protocol detailing proper hand wash
technique should be available for
reference.
Control of MRSA in Hospitals
 Gloves
should be worn when in contact
with any body substance. Gloves
should be changed and hands washed
immediately after contact with each
resident.
 Appropriate use of antimicrobials.
Monitoring and auditing of drug use.
Control of MRSA in Hospitals
 Isolation
is necessary for infected
patients and possible carriers in a
single room or preferably in an
isolation unit with designated staff.
Isolation reduce staphylococcal crossinfection.
Control of MRSA in Hospitals
 Ward
Closure should be considered
when new patients become infected
with MRSA. The presence of strains of
MRSA causing invasive infection is
another indication.
 Screening of patients for MRSA at the
nose, throat and perineum.
Control of MRSA in Hospitals

Carriage of MRSA by health care
workers. During outbreaks staff should
be reminded of the handwashing and
transient carriage of MRSA. Staff with
infected or colonized lesions should
not be at work especially in critical
areas, as intensive care units,
cardiothoracic words e.t.c.
Control of MRSA in Hospitals
 Treatment
of carriers. Nasal carriage is
treated topical with mupirocin.
 Systemic treatment of infections The
glycopeptide antibiotics are currently
the agents of choice for treatment.
 Microbiological characterization of
MRSA.
Antimicrobial resistance: is a
major threat to public health.
Bacterial resistance to multiple
antibiotics characterises the present
decade. Finding organisms resistant to
over 10 different antibiotics is not
unusual. Globally we need to look at
how antibiotics are used and
reduce their inappropriate use.