Download Gram positive cocci Family Micrococcaeceae

Family Micrococcaeceae
The gram positive cocci is the most frequent
isolated from the clinical specimens.
The family micrococcaeceae include the
following genera:
 Staphylococcus.
 Micrococcus.
 Planococcus.
 Stomatococcus.
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The genus staphylococcus is composed of
several spp. Many of them are a part of the
normal flora.
Staph are catalase positive gram positive
cocci arranged in single pairs tetrads and
short chain predominantly in cluster. Non
motile, non spore forming with limited
capsule formation aerobic or facultative
anaerobe .
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Staph is initially differentiated by coagulase
into
1. Coagulase positive (Staphlycoccousaureus)
2. Coagulase negative (CoNS): more than 35
spp of CoNS is identified those of clinical
sigenificant are:
S. epidermidis, S. saprophyticus.,
S.haemolyticus.
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It is the most important isolates it is
responsible for infection from mild to a life
threatening infections.
It is recovered from any clinical sample and
an important cause of hospital acquired
infections.
Increase drug resistance in the last decade is
an important concern.
It can be found in the external environment
and the anterior naris in 20-50 % of adults.
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Peptidoglycan and tiechoic acid: it play an
important role in adherence, activation of
complements and chemotaxises of PMN.
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Protein A: has the ability to bind to the FC
portion of all IgG .
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Capsular polysaccharides: prevent the
ingestion of the MO by the PMN
(polymophnuclear leucocyte).
Enzymes :
1.Catalase inactivate toxic H2O2 and free radicals
formation in PMN.
2. Clumping factor: it is responsible of binding of
staph to both fibrin and fibrinogens.
3. Coagulase (staphylocoagulase) it is found free
form in the medium or cell bound it thrombin like
molecule called coagulase-reacting factor (CRF) to
form coagulase- CRF complex the complex
resemble thrombin and directly convert fibrinogen
to fibrin leading to clot formation.
4. Staphylokinase it causes fibrinolysis.
 Hyaluronidase.
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Hemolysin and leukocidin:
Toxins:
1. Enterotoxin: Heat stable exotoxin (100C
for 30min) it cause food poisoning.
2. TSST1(toxic shock syndrome toxin) it is
called superantigen
3. Exfoliative toxin or epidermolysin Strains
produce this toxin cause staphylococcus
scaled skin syndrome.
1. Skin and wound infection: S. aureus infection are
suppurative. typically it cause abscess. It causes
folliculitis, furuncle, carbuncle and bullous
impetigo & post surgical wound infection.
2. Scalded skin syndrome (Ritter's disease)
extensive exfoliative dermatitis occur in new born
baby. It occur in adult only in patients with renal
failure.
3. Staphylococcal food poisoning caused by staph
produce heat stable enterotoxin, it cause vomiting
abdominal pain with or without diarrhea NO fever.
4. Toxic shock syndrome : it is fatal multi systemic
disease and could be associated with
menstruation or not associated with
menstruation. Toxic shock syndrome is
manifested by an abrupt onset of high fever,
vomiting, diarrhea, myalgia, rash, and
hypotension with cardiac and renal failure in the
most severe cases. It often occurs within 5 days
after the onset of menses in young women who
use tampons, but it also occurs in children or in
men with staphylococcal wound infections.
5. S. aureus also cause bactermia,endocarditis,
meningitis, osteomylitis and pneumonia.
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The role of this mo as an etiologic agent of
diseases has become increasingly evident. These
mo is always isolated from the normal flora of skin.
Infection is predominantly hospital acquired. Most
common hospital acquired infection caused by S.
epidermidis are UTIs, prosthetic valve endocarditis
and intravascular catheter and CSF shunt
infection. Septicemia reported in
immuncompromised patient.
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It is associated with UTI in young sexually active
female (true urinary pathogen) . It is rarely found
on other mucous membrane or skin surfaces. In
urine culture it may be found in low
concentration but still considered pathogenic.
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Sample is taken from the site after proper
cleansing of the area and transport immediately
without delay to avoid dryness of the sample.
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Microscopical examination: Direct gram stain
smear to see gram positive or variable cocci
arranged in single.
Pairs tetrad or clusters inside and outside the
PMN.
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Isolation
staph grows readily on routine culture medium
particularly SBA (sheep blood agar) within 24 hr.
On SBA after 18-24 hr of incubation at 35-37 C
Staph aureus produce round smooth colony with
hemolytic zone with golden yellow pigment.
S epidermidis produce non hemolytic white colony .
S. saprophyticus produce larger colonies only 50%
produce yellow colonies.
MSA (mannitol salt agar) is good selective culture
media for isolation of S. auerus. It diagnosed by
mannitol fermentation .
On Identification :
 Catalase differentiated staph from Streptococci.
 Staph differentiated from micrococci on basis of
a. oxidative fermentation reaction. Staph ferment
glucose while micrococci fail to form acid under
anaerobic condition.
b. modified oxidase test staph –ve, micrococci
+ve.
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Identification of staph auerus :
Slide coagulase :Clumping factor formerly
referred to as cell bound coagulase it causes
agglutination in human and rabbit serum
detected by slide method.
Tube coagulase: strain of Staph aureus does
not produce clumping factor should be
investigated for coagulase production by tube
method (staphylocogulase).
Isolates do not produce clumping factor or
staphylocoagulase are reported as CoNS.
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Antimicrobial susceptibility :
Broth microdilution or disk diffusion susceptibility
testing should be done routinely on Staph aureus
isolates from clinically significant infections.
Resistance to penicillin G can be predicted by a
positive test for β-lactamase; approximately 90%
of S aureus produce β- lactamase. Increasing
resistance to alternative antibiotics is of major
concern.
Testing of CoNS is dependent on source and
determination if the isolate is a likely pathogen.
Resistance to nafcillin (and oxacillin and
methicillin) occurs in about 35% of S aureus and
approximately 75% of S epidermidis isolates.
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Isolates resistant to penicillinase resistant penicillin called
methicillin resistance staph. (MRSA =S.aureus,
MRSE=epidermidis).
In the past MRSA was associated with hospital acquired
infection since the late 1990s, however, MRSA has been
found to be associated with community acquired infections.
Oxacillin and other penicillinase- resistant penicillin such as
methicillin , naficillin cloxacillin , constitutes the drug class
of choice for treating staphylococcal infection .
Staphylococcal resistance to the penicillinase- resistant
penicillin is due to the presence of a unique penicillin
binding protein (PBP2a or PBP2'). The penicillin binding
protein , which has a low affinity for binding all β-lactam
drugs, is encoded by mec a gene.
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Disk diffusion method using Oxacillin disk
If disk susceptibility is not clear using oxacillin salt
agar screening test , use Mueller hinton agar with
4% NaCl and 6µg/ml oxacillin.
PCR for mec A gene
Detection of PBP2a using latex, fluorescence
technology.
All oxacillin resistant staph should be considered
resistant to all β lactam drug regardless the in vitro
test results.
Vancomycin remain the DOC for MRSA, but
increase resistance to glycopeptides call for
restrictive use of these drugs.
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Vancomycin is the drug of choice and
sometimes the only drug available for serious
staphylococcus infection. And thus the
development of vancomycin resistance has
been a serious concern.
The most accurate susceptibility is done by
nonautomated method. Detection of these strain
should be reported to the CDC.
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Minor skin infections are usually treated with an
antibiotic ointment such as a nonprescription tripleantibiotic mixture. In some cases, oral antibiotics may
be given for skin infections. Additionally, if abscesses
are present, they are surgically drained. More serious
and life-threatening infections are treated with
intravenous antibiotics.
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Several different types of antibiotics have been used
to treat staph infections. The choice of antibiotic
depends on the type and severity of the infection as
well as drug-resistance patterns of the particular
bacterial type. Some of the antibiotics that have been
used to treat staph infections are cephalosporines,
nafcillin ,oxacillin, rifampin and clinamycin.
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Combinations of antibiotics and other antibiotics
can also be used.
MRSA treated with vancomycin.
Treatment of vancomycin resistant staph is by the
use of daptomycin