Transcript Methicillin Resistant Staphylococcus Aureus

Methicillin Resistant Staphylococcus Aureus
Barbara Jennings-Spring
Seminar in Molecular Biology 360
Smith College
What Is MRSA?
MRSA Is “Methicillin Resistant Staph Aureus”
*It is a bacteria that is resistant to a synthetic penicillin
methicillin. Staph aureus colonizes skin, nasal passages,
and many other mucous membranes.
*Also causes a variety of disseminated, lethal infections in
humans.
* It has the ability to transfer resistant genes easily to other
species directly and indirectly
*Overuse of antibiotics is the one of the major reasons for
the evolution of MRSA
Overview
To gain a better understanding of the molecular
mechanisms involved with (MRSA) and how
biotechnology continues to combat this super-bug in
hospitals and communities throughout the world.
Research
History Of MRSA
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The Basic Biology Of Staphylococcus Aureus
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Molecular Basis For Virulence
•
Clinical Presentation Of Disease
•
Detection Of Pathogen
•
Biotechnology Treatments
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Public Health Control Strategies
•
Political And Social Impediments
History Of Antibiotic Resistance
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1941 Penicillin
1943 Streptomycin
1945 Cephalosporins
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1950 Tetracycline
1952 Erythromycin
1956 Vancomycin
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1960 Methicillin
1962 Lincomycin
1962 Quinolones
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1970 Penems
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1980 Monobactams
2010 Is this the end of an antibiotic era???
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The Basic Phenotypic Characteristics Of
Methicillin Resistant Staphylococcus Aureus
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Gram positive
Non-motile
Spherical
Grows in chains
Resembles clumps of grapes
Golden color
Hemolytic pattern on blood agar
Produces coagulase and catalase enzymes
The molecular genetics of antimicrobial resistance includes
three main pathways:
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Microevolutionary changes-a single point
mutation
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Macroevolutionary change- rearrangements
occur
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Acquisition of foreign DNA
What are some examples of how single point mutations
occur over time?
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Beta lactamases will confer resistance to B- lactams
(penicillins, cephalosporins)
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If you get a single point mutation (substitution of base
pair) that involves the target action of PCN or the
cephalosporin drug, you will extend the spectum of
action of that B-lactamase enzyme
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so that a broad range of the cephalosporin or penicillin
family will show resistance instead of one single
cephalosporin or penicillin family
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Mutations on the rpoB gene (RNA polymerase) alters
antibiotic binding site, preventing drug action.
What Are Some Examples Of Macro
Evolutionary Changes With Resistance?
Rearrangement of DNA
segments-by transposons
 Transposon—”Jumping Gene”
that contributes to antibiotic
resistance
 Transposons- Contain genes that
are for the coding of antibiotic
resistance
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How is the Acquisition of Foreign DNA from
other species accomplished?
-Conjugative
plasmids: Found inside cytoplasm.
Possess the ability to transfer resistance genes
to the same and different species
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Horizontal gene transfer is common in bacteria
and is accomplished by the process known as
Transformation in Staph. aureus.
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Examples of horizontal Gene Transfers
(HGT)
http://
/
www.bioteach.ubc.ca/Biodiversity/AttackOfTheSuperbugs
How Staph Aureus acquires
resistance to methicillin
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http://www.jci.org/cgi/content/full/114/12/1693/F1
http://www.jci.org/cgi/content/full/114/12/1693/F1
Mechanism of Antibiotic
Resistance in MRSA
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http://www.bioteach.ubc.ca/Biodiversity/AttackOfTheSuperbugs/
Important Virulence Factors for MRSA: Cell Wall Structures
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Cytoplasmic membrane- osmotic barrier
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Consists of thick polysaccharide capsule (slime layer;
adhesin). Capsules are just tricks to avoid host defenses
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Petidoglycan-Used for osmotic stability so bacterial cell
wall does not burst due to hypertonic states.
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Protein A- immunological disguise. Inhibits oponization ,
Binds IG’s, leukocyte, chemoattractant,
anticomplementary.
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Techoic Acid-Acts as a receptor for bacteriophages.
Attachment site for mucosal cell receptors.
Invasive enzymes As Other
Virulence Factors
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Coagulase Complex-Produces enzymes that coagulate blood
and seal off infection
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Protease, lipase, & DNase provide nourishment for MRSA
bacterium
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FAME-Important in abscess formation. Also it could change
anti-bacterial lipids and prolong survival of MRSA in wound.
Staphylokinase-Plasminogen activator enzyme that lyses
fibrin clots
Hyaluronidase-It is the spreading factor; hydrolyzes
haluronic acid in synovial joints
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Virulence Factors Cont: Extracellular
Products and Toxins (hemolysins) Of MRSA
Invasion
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Leukocidins-The name implies their job!
Leukocidins kill wbc’s. Membrane damaging toxin
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Alpha, beta, delta toxin-binds to cell surface, forms
pores leaks.
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Superantigens: (type 1 toxin) Toxic shock
syndrome toxin (TSST-1)
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Staphylococcal Enterotoxin-food poisoning
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Exfoliation toxin-scalded skin syndrome
Virulence Factors Cont: Mechanism Of
Superantigens And The Stimulation Of Cytokine
Release
http://textbookofbacteriology.net/staph.html
Summary of Virulence
Determinants Of Staph. Aureus
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http://textbookofbacteriology.net/stap
h.html
http://textbookofbacteriology.net/staph.html
Source of MRSA Infections
Some infections are caused by own
epithelial flora-self contamination
 Nasal carriage most common
 Hospitals
 *Dirty hands, towels, and daycare
 Airborne?????
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Predisposing Factors Of Host
Resistance
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Integument injury via surgery
Burns and trauma
Foreign objects like indwelling catheters,
metals, sutures, implants
A history of chronic bacterial infections with
multiple rounds of antibiotics
Hormonal changes and stress
Immunocompromised (AIDS, Diabetes,
Chemo)
Clinical Manifestations Of MRSA
The lesion usually starts out as an
small cut or break in the skin. The
lesions can range from small
abrasions to large, gaping abscesses
 Even the most benign localized
abrasion (from tampon insertion) can
become the fuel for a devastating,
disseminated MRSA systemic infection
that do not respond to multi-antibiotic
combinations
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MRSA Infections Go Everywhere
Integumental and soft tissue
 Suppurative arthritis-first causative
agent
 Osteomyelitis-First causative agent
 Bacteremia-First causative agent
 Pneumonia
 Acute and chronic Endocarditis-#1
 Bacterial Meningitis-first causative
agent
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Menstrual Toxic Shock By MRSA
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Most major organs fail with
disseminated MRSA (TSS-1)
www.web.net/terrafemme/ cashnightmare.htm
More MRSA Infections
Toxic shock Syndrome-Super
absorbent tampons- #1 causative
reason
 Urinary tract Infections
 Scalded skin syndrome and impetigo
from picking pimples
 Food poisoning-Enterotoxin A in
spoiled or contaminated food.
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Carbuncle(Boil)
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tahilla.typepad.com/.../ super_bug_091404.jpg
44 y/o IV drug abuser with back pain and
Staph Osteomyelitis of lumbar spine
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Staph
osteomyelitis and
discitis involving
L5, with
extension across
the L4-5 disc to
erode L4 and
extension into
S1. The L5
vertebral body is
destroyed.
(33.210, 33.250,
diskitis)
Case 72
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Classic Toxic Shock: Scalded
Skin Syndrome
www.aafp.org/afp/ 20000815/804.html
Staph. Aureus Impetiigo
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Don’t pick your face!!!!!
www.med.sc.edu:85/ fox/staphimpetigo.jpg
Getting A Lab Diagnosis For
MRSA
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http://jcm.asm.org/cgi/content/full/38/6/2378
How Accurate Can Your
Diagnosis Of MRSA Be?
TABLE 1. Comparison of the levels of accuracy of reactions of S. aureus isolates on
CHROMagar Staph aureus, DNase, and MSA and of coagulase testing of CoNS after
18 to 24 h of incubation
% of isolates showing positive
reactions
Identification method
CHROMagar Staph
aureus
DNase
MSA
Coagulaseb
Accuracy of medium in
discriminating S. aureus and
CoNS
S. aureus
(n = 114)
CoNS
(n = 22)
100
0a
100
100
98.0
98.0
100
4.6
36.5
0
98.0
98.0
100
95.4
63.5
100
Sensitivity (%) Specificity (%)
a
S. chromogenes produced a natural carotenoid (orange or red) pigment and gave a
slightly pink color. The isolate was identified by API20 Staph.
b
All coagulase testing was confirmed by the standard tube method.
http://jcm.asm.org/cgi/content/full/38/6/2378
Current Drug Treatments For MRSA
 [Methicillin-resistant] –MRSA Drugs
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of Choice:
Linezolid(protein synthesis inhibitor),
Daptomycin,
Vancomycin
Alternatives: Synercid, Rifampin
Third-Line agents: TMP-SMX
Drugs In Development
Oritavancin-can be given once daily
 Tigecyclin-orally broad antimicrobial
activity
 Dalbavancin- Currently undergoing
clinical trials. Has long half-life so it
can be given once per week
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(FDA, 2005)
How Close Is Staph Vaccine?
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Pretty close. The results of the phase
3 testing of the vaccine (Staph VAX)
will be presented soon according to
the NIH.
Public Health Response-What Is
Being Done To Combat MRSA?
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The CDC provides technical help and referrals to state and local
health departments, doctors, nurses, and other professionals
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The CDC provides national program of surveillance for serious
infections with MRSA.
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CDC launched evidence-based educational campaign to prevent
antimicrobial resistance
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CDC building national resource library to identify genetic patterns or
relationships
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CDC researching the role of staph toxins-to provide answers for
hospitals and researchers
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*For more info go to www.cdc.goc
What can you do to prevent MRSA
from attacking You?
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Keep draining infections of skin, covered with clean dry bandages
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Talk to your physician about wound management techniques
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Advise family to wash hands frequently with soap and water, count
to at least “20”,especially after dressing a gaping wound.
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Avoid sharing personal items such as towel, razors, bed linens with
people who have sores or have come home from the hospital
recently
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Wipe objects down with alcohol.
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If you are in the hospital please advise you nurse or physician to
wash their hands before touching you or your hospital equipment
What Are The Social And
Political Costs To Us?
The Real Cost Of Infectious Diseases
Like MRSA
Rising Rates Of Resistant Bacterial
Infections=Rising Budget
That’s All Folks!! Any
Questions????
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Staph cells attaching photo courtesy of Dr. Sharon peacock- University of Oxford
References
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1 Mitchell, David.MRSA.”what’s New”. Inoculum. Volume 8, number 2
(1999) 1-12.
2 textbookofbacteriology.net/resantimicrobial.html
3 healthsciences.columbia.edu/
dept/ps/2007/mid/2006/transcript_02_mid22.pdf
4 http://www.bioteach.ubc.ca/Biodiversity/AttackOfTheSuperbugs
5. Foster, Timothy. The staphylococcus aureus “superbug”.J. clin
Ivestigation
Volume number114 (2004) 1693-1696.
6. www.channing.harvard.edu/4a.htm
7. ww.ncbi.nlm.nih.gov.
8. www.aafp.org/afp/ 20000815/804.html
9. Journal of Clinical Microbiology, June 2000, p. 2378-2380, Vol. 38, No. 6
0095-1137/04.00+0
10. www.FDA.com (FDA archives)
11.www.postgradmed.com/issues/2001/10_01/hoel.htm
12. www.cdc.gov/ncidod/hip/aresist/mrsa_CDCactions.htm
13. www.medscape.com