MRSA
Definition
Methicillin-resistant Staphylococcus
aureus (MRSA) is a bacterium
responsible for difficult-to-treat infections
in humans. MRSA is by definition a strain
of Staphylococcus aureus that is resistant
to a large group of antibiotics called the
beta-lactams, which include the penicillins
and the cephalosporins.
HA–MRSA Characteristics

Hospital–associated strains of S.
aureus still cause about 85% of
all MRSA cases.
 Hospital patients with S. aureus
infections are five times more
likely to die in the hospital than
are patients without the infection.
 Multi-drug resistant (MDR)
 Vancomycin is one of the few
remaining treatments for HAMRSA, but it is no longer
effective in every case due to
rising MICs.
Courtesy of the CDC
This electron micrograph depicts
large numbers of Staphylococcus
aureus bacteria, which were
found on the inside surface of a
catheter. The sticky-looking
substance woven between the
round cocci bacteria is known as
a “biofilm”. Biofilms help to
protect the bacteria.
Evolution
From HA and CA-MRSA
1961 – MRSA first described
 Until recently, most MRSA infections started in
hospitals, especially among surgery and
immunocompromised patients. (HA-MRSA)
 In the 1990s, new strains of MRSA began to
strike healthy people in community settings.
(CA-MRSA)
 These two types of MRSA are now known as
hospital-associated MRSA (HA–MRSA) and
community-associated MRSA (CA–MRSA).

CA–MRSA
Characteristics



Staphyloccal bacteria that have become
resistant to beta-lactam antibiotics but
NOT multi-drug resistant (MDR).
Several antibiotics remain effective
against CA–MRSA, but it is an
aggressive and rapidly evolving form of
S. aureus.
Usually appears as a skin infection, but
it can spread quickly to a bloodstream
infection or a very serious form of
pneumonia.
Courtesy of the CDC
Cutaneous abscess
caused by methicillin–
resistant
Staphylococcus aureus
bacteria.
MRSA
Prevalence in Shiraz
 Prevalence
is increasing!!
MRSA in Nemazi hospital patients
• 2000 = 33%
• 2010 = 49.5%
Pattern of sensitivity Staphylococcus
aureus, Nemazi hospital -2000










Vancomycin
Rifampin
Chloramphnicole
Clindamycin
Ciprofloxacin
Co-trimoxazole
Gentamycin
Cephalothin
Amikacin
Erythromycin
100%
100%
94
89
87
85
70
70
66
70
IR
R
Total
33
(35.5)
84
(90.
3)
93 (100) 93
93
(100 (100)
)
93
(100)
50
(53.8)
56
(60.2)
71
(76.3)
Cefexime
Rifampicin
Ciprofloxacin
Oxacillin
65
44
58
(69.9) (47.3) (62.4)
Clindamycin
93
(100)
Cotrimoxazol
Vancomycin
Linozolid
9
93
60 (64.5)
(9.7) (100)
Erythromycin
S
Penicillin G
Gentamicin
Staphylococcus aureus antibiotic pattern
in nemazi hospital -2010
1 (1.1) 1 (1.1)
1
(1.1)
3
(3.2)
2
(2.2)
27
(29)
46
33
(49.5) (35.5)
43
(46.2)
37
(39.8)
21
(22.6)
92
(98.9)
93
(100)
93
(100)
93
(100)
93
(100)
93
(100)
93
(100)
93
(100)
MRSA in IRAN
224 S.aureus Isolated from:






blood
Pelural
CSF
ascitis
Joint
Total
210
5
5
3
1
224
Staphylococcus aureus
Identification
 Isolates


identification:
Gram Stain
Coagulase
 Antibiotic


Susceptibility Test
Disk diffusion Method (CLSI protocol)
 MRSA

●Catalase
●Dnase
& VRSA :
Oxacillin & Vancomycin screen plate
MIC determination (E test) for Oxacillin &
Vancomycin
MRSA & VISA in Iran

Growing on Oxacillin Agar Screen plate (ASP)



224 Isolates
84(37.5%) positive
MICOX> 8 μg/ml
MRSA
Vancomycin MIC(Etest)

All Isolates
MIC< 4 μg/ml
No suspected
VISA/VRSA
Reporting:
(according CLSI 2006 )
 MRSA
and methicillin-resistant,
coagulase-negative staphylococci
should be reported as resistant to all
other penicillins, carbapenems,
cephems, and β-lactam/β-lactamase
inhibitor combinations, regardless of in
vitro test results with those agents.
Staphylococcus aureus in Iran
(N0=224)
FU
GM
0
(0)
QD
53 80
4 215 92 20 78 72 5
71 70 102
(24) (36) (2) (96) (41) (9) (35) (32) (2) (32) (31) (45)
VA
T
AK
KF
C
CIP
OX
RP
TS
PG
LZD
ER
CD
R
0
72
8
(0) (32) (4)
S 170 130 220 9 131 203 146 148 218 151 150 122 224 224 152 216
(76) (58) (98) (4) (58) (90) (65) (66) (97) (67) (68) (55) (100) (100) (68) (96)
IR
1
14
(0.5) (6)
0
(0)
0
1
1
(0) (.5) (.5)
0
(0)
4
1
2
(2) (.5) (1)
3
(1)
0
(0)
0
(0)
0
(0)
0
(0)
0
(0)
CD=Clindamycin, ER=erythromycin, LZD=linezolid, PG=PenicillinG, TS=Co-trimoxazol,
RP=Rifampin, OX=Oxacillin, CIP=Ciprofloxacin, C=Chloramphenicol, KF=Cephalothin,
AK=Amikacin, T=Tetracycline, VA=Vancomycin, QD=Quinupristin-dalfopristin, GM=Gentamycin,
FU=Fusidic acid