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Are we being threatened by community
acquired organism
• 4 years-old Pakistani boy
– fever for 4 weeks duration,
– given amoxicillin syrup for 10 days
– One week prior to admission, he developed
abdominal distention.
• On physical examination
– febrile 40C
– abdominal mass felt in the left hypochondrial
area.
• 100cc of pus was aspirated
• Staphylococcus aureus
– Naficillin ----------------R
– Erythromycin -----------S
– Vancomycin ------------S
– Clindamycin ------------S
– Co trimexazole---------S
– Cefazolin ----------------R
– Ciprofloxacin------------S
• An 18-month-old girl
– fever
– lambing
• On physical examination
– febrile 38.5C
– swelling, redness, and marked tenderness
over the upper one third of the left leg below
the knee joint.
• deep vein thrombosis of the left popliteal
and posterior tibial veins
• A 3 months old girl
– fever at the age of 6 weeks
– diagnosed to have pharngitis
– given amoxacillin syrup for 5 days.
– fevers subside for one week,
– she develops fever again with proptosis of the
right eye.
Bilateral orbital abscess with extension probably through
the eroded bone into the right temporal fossa (extradural
collection)
• incision and drainage of the abscess
through the medial side of Rt eye was
done by the oculoplastic surgeon pus was
sent for culture.
• CSF : WBC 2400
• Staphylococcus aureus
– Naficillin ----------------R
– Erythromycin -----------R
– Vancomycin ------------S
– Clindamycin ------------S
– Co trimexazole---------S
– Cefazolin ----------------R
– Ciprofloxacin------------S
CA MRSA
Introduction
• Staphylococcus aureus has been
responsible for a great deal of human
morbidity and mortality throughout history
• The introduction of penicillin in the1940s
greatly improved the prognosis for patients
with severe staphylococcal infections
• Methicillin introduced in 1959, was
specifically designed to be resistant to βlactamase degradation
Introduction
• (MRSA) was first reported in the United
Kingdom in 1961
• Over the past several decades, infections
with (MRSA) among hospitalized patients
have become common.
• Recently, reports of MRSA infections
acquired outside of the hospital setting
have increased nationally, including
fatalities.
• CA-MRSA is new strain of MRSA
presenting from community in person
without tradition risk factor for MRSA
• differing from HA-MRSA in terms of :
– Epidemiology
– Abx sensitivity patterns
– Virulence
– Presentation
– Treatment
Definition of CommunityAcquired MRSA:
•
•
culture positive for MRSA should be in the
outpatient setting or within 48 hours after
admission to the hospital
The patient has no medical history in the past
year of:
–
–
–
–
–
Hospitalization
Admission to a nursing home
Dialysis
Surgery
Permanent indwelling catheters or percutaneous
medical devices
epidemiology
• Studies in both adults &pediatrics have
shown 15 to 45% increase in S.aureus
that are methicillin resistant ,and large
increase (up to 20 fold) in frequency of
CA-MRSA infection in children
» Current opinion in pediatrics 2005,17:67-70
epidemiology
• In Atlanta ; 72 % of community-onset Staph skin
and soft tissue infections are now due to MRSA
» www.eurekalert.org/pub_releases/2006- 03/euhssid030606.php
• In a Rural American Indian Community
– Of S .aureus isolates,
• (45%) MSSA
• (55%) MRSA
– (74%) of the MRSA, infections were classified as community
acquired.
» http://jama.ama-assn.org/cgi/content/abstract/286/10/1201
• risk for CA-MRSA infections
– Limited time for hygiene
– Sharing of personal items
– Skin cuts & abrasions
– Skin to skin contact
– Crowding
Genetics of methicillin resistance
• mechanisms of methicillin resistant
– hyperproduction of b-lactamases
– modification of normal PBP
– presence of an acquired PBP( PBP2a)encoded by the
mecA gene
» Ubukata K,etal,Antimicrob Agents Chemother 1999;33:1624–6
• The methicillin-resistance gene (mecA) is not
present in methicillin-susceptible strains and is
believed to have been acquired from a distantly
related species
» Enright MC,etal; Proc Natl Acad Sci USA 2002;99:7687–92
Genetics of methicillin resistance
• The mecA is carried on a mobile genetic
element, (SCCmec)
• CA-MRSA harboring SCCmec type IV has
been demonstrated to replicate more
rapidly than HA-MRSA isolates with other
SCCmec types
• This may account for its remarkable
success in displacing other MRSA strains
in some hospitals after its introduction
from the community
» Okuma K,etal; J Clin Microbiol 2002;40:4289–94
CAMRSA
• Characteristic:
• Pulse field gel electrophoresis (PFGE)
pattern
• Toxin genes:
• Enterotoxins (not present)
• Toxins shock – associated toxins (not present)
• Panton – Valentine leukocidin (present)
• Mec A cassette and subtype (mec IV )
• Resistance pattern
TOXIN ANALYSIS
• Panton – Valentine Leukocidin (PVL)
– first reported in 1932
– Combination of 2 proteins (Luk S and F)
– Potent mediator of inflammation and activator
of leukocytes
– PVL destroys leukocytes by creating lytic
pores
– Associated with necrotic infections
TOXIN ANALYSIS
• PVL genes are associated with communityonset staphylococcal skin infections and
necrotizing pneumonia
• PVL-producing S. aureus are rarely
responsible for other infections such as
septicemia, and endocarditis
» Vandenesch F,etal. Emerg Infect Dis 2003;9:978–84
Susceptibility testing
• detecting oxacillin (methicillin) resistance in
staphylococci that possess the mec gene may
be difficult because these strains exhibit
heteroresistance
• The observation of multiple resistance is a clue
for the microbiologist to the possibility of
methicillin resistance
• CA-MRSA resistant to b-lactam antibiotics only,
making it difficult to suspect methicillin
resistance
Susceptibility testing
• to enhance the expression of oxacillin
resistance
– incubation of tests at temperatures no greater
than 35 C
– obtaining final readings after a full 24 hours of
incubation
– supplementation of Mueller-Hinton broth or
agar with 2% NaCl for dilution tests
» National Committee for Clinical Laboratory
Standards; 2003
Susceptibility testing
• NCCLS recommends performing standard
disk diffusion test with cefoxitin (30 micg)
disks for detection of oxacillin (methicillin)
resistance
» National Committee for Clinical Laboratory
Standards; 2004
Susceptibility testing
• Several studies have showed that most CAMRSA strains are susceptible to
clindamycin
» Martinez-Aguilar G,etal. Pediatr Infect Dis J
2003;22:593–8
• Indusable resistant to clindamycin
– efflux pump encoded by msr genes
– ribosomal methylase, encoded by erm genes
(MLSB phenotype)
Rapid methods for detection of
methicillin resistance
• The detection of the mecA gene by PCR
considered the ‘‘gold standard’’ for the
detection of MRSA strains
• Velogene Rapid MRSA Identification
Assay
• colorimetric enzyme immunoassay that uses a
fluorescein- labeled mecA gene probe
• sensitivity of of 97%
• specificity of 100%
Rapid methods for detection of
methicillin resistance
• The MRSA-Screen
– is a slide latex agglutination test using latex
particles sensitized with a monoclonal
antibody against PBP2a
» Swenson JM,etal. J Clin Microbiol 2001;39:3785–8.
Prevention
• Prompt attention to breaches of the skin
• clean and dry
• Keeping fingernails clean and cut short
• changing towels, washcloths, underwear,
and sleepwear daily
Prevention
• Cochrane review did not find topical
antibiotics to be useful for eradicating
nasal MRSA
• applying mupirocin to the anterior nares
may be useful to diminish nasal
colonization by CA-MRSA and decrease
the likelihood of recurrences
» Chen SF: Staphylococcus aureus decolonization.
Pediatr Infect Dis J 24: 70-80, 2005
Prevention
• taking a bath twice a week for 15 minutes
in water mixed with regular strength Clorox
(one teaspoon per gallon of water)
appears to be helpful in preventing
recurrent infections
» Chen SF: Staphylococcus aureus decolonization.
Pediatr Infect Dis J 24: 70-80, 2005
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