Lecture | Staphylococcus Flashcards
Greek term that means “bunches of grapes”
Staphle
gram positive cocci, so round, that may appear in singles, in pairs, in clusters, or even in tetrads.
Staphylococcus spp.
non-motile and non spore forming
Staphylococcus spp.
When it comes to growing of Staphylococcus spp. in culture, they can be considered as
aerobic or facultatively anaerobic
means you have to grow them in an environment without oxygen.
obligate anaerobes
In culture, colonies are produced after how many hours
18-24 hours of incubation.
appearance of Staphylococcus spp.
medium size, cream colored, white, or rarely light gold and buttery looking especially Staphylococcus aureus.
Common isolates in the clinical laboratory and are responsible for several suppurative infections.
Staphylococci
term of infection by pus-producing organism
suppurative infection
most virulent species of staphylococci
S. aureus
S. aureus is present among the indigenous flora of the
skin, eye, upper respiratory tract, gastrointestinal tract, urethra, and frequently in our vagina.
infections are frequently acquired when colonizing strains gain access to a normally sterile site as a result of
trauma or abrasion to the skin or mucosal surface
S. aureus is the most common cause of
Spinal epidural abscess, suppurative intracranial, septic arthritis, and osteomyelitis.
infection especially in pre-pubertal children.
septic arthritis
may be recovered from brain abscesses, typically following trauma.
suppurative intracranial phlebitis
It causes various cutaneous infections and purulent abscesses.
S. aureus
skin and soft tissue infections can be superficial, such as
impetigo or cellulitis.
Cutaneous infections can progress to deeper abscesses, such as
carbuncles
Cutaneous infections can progress to deeper abscesses and involve other organ systems and produce
bacteremia and septicemia.
cause of infective endocarditis
S.aureus
S.aureus is a common cause of toxin-induced diseases, such as
food poisoning
What is SSS
scalded skin syndrome
What is TSS
toxic shock syndrome
“protein A” has sites that is able to bind the
FC portion of IgG.
Protein A protects the organism from
opsonization and phagocytosis of neutrophils
Coagulase is an enzyme that can even lead to
fibrin formation around the bacteria
an enzyme around the bacteria that protect the bacteria from phagocytosis
Coagulase
Coagulase helps this to disrupt the beta lactam portion of the molecule rendering the antibiotic useless against this organism
penicillinase or beta-lactamase
4 Types of Hemolysin
- Alpha toxins
- Beta toxins
- Delta toxins
- Gamma toxins
able to destroy or hemolysed your red blood cells, neutrophils, macrophages, and platelet.
Hemolysin
disrupts smooth muscle in blood vessels
Alpha toxins
toxic to erythrocytes, leukocytes, hepatocytes, and platelets
Alpha toxins
acts on sphingomyelin in the plasma membrane of erythrocytes
Beta toxins
Beta toxins is also called
sphingomyelinase C or “hot-cold” lysin
“hot-cold” feature associated with Beta toxin is seen as enhanced hemolytic activity on
incubation at 37° C and subsequent exposure to cold (4° C)
Beta toxins is exhibited in this test
Christie, Atkins, and Munch-Petersen (CAMP) test
performed in the laboratory to identify group B streptococci.
Christie, Atkins, and Munch-Petersen (CAMP) test
bacterias capable of producing delta toxin
S.aureus, S. epidermidis, and S. haemolyticus
toxin that is cytolytic to erythrocytes and demonstrates nonspecific membrane toxicity to other mammalian cells.
Delta toxins
produced by all strains of S. aureus
Gamma toxins
Gamma toxins function in association with PVL. pvl stands for?
PantonValentine leukocidin
an exotoxin lethal to polymorphonuclear leukocytes.
PVL
PVL has been implicated as contributing to the invasiveness of the organism by
- suppressing phagocytosis
associated with severe cutaneous infections and necrotizing pneumonia.
PVL
Spreading factor; Permits bacteria to spread through connective tissues
Hyaluronidase
breaks down the proteoglycans in our connective tissue
Hyaluronidase
lyses the formed-fibrin clots
Staphylokinase
similar to streptokinase produced by Streptococcus
Staphylokinase
Able to degrade fats and oils that are often accumulated the surface of our body
Lipase
degradation of fats and oil facilitates the ability of S. aureus to colonize especially in our
sebaceous glands
Destroys protein
Protease
Exotoxin TSST-1 is also known as
pyrogenic exotoxin C
Responsible for the Toxic shock syndrome
Exotoxin TSST-1
illness most common in women 15-25 years of age who use tampons during menstruation
Toxic shock syndrome
cause of the majority of staphylococcal food poisoning cases
Enterotoxins A-E
cause the epidermal layer of the skin to slough off
Exfoliative Toxins
known to cause staphylococcal SSS (Skin Scald Syndrome)
Exfoliative Toxins
Most significant Exfoliative Toxins
epidermolytic toxin A & B
Associated with our community acquired methicilin-resistant Staphylococcus aureus
Panton-Valentine leukocidin toxin
cause fever, desquamation, hypotension, and could even lead to bacterial shock and death
exotoxin-TSST 1 or the pyrogenic exotoxin C
common source of hospital-acquired infections
S. epidermis
contaminant in improperly collected blood culture specimens
S. epidermis
less virulent than S.aureus and are opportunistic pathogens.
S.epidermis
cause of UTIs; Prosthetic valve endocarditis
S.epidermis
commonly isolated CoNS. It has been reported in wounds, bacteremia, endocarditis, and UTIs
S.haemolyticus
Usually involve implantation of medical devices; infection can even resemble S.aureus infection
S. lugdunensis
Identification of this bacteria is important because this particular genus is resistant to oxacillin
S. lugdunensis
associated with UTIs in young sexually active females; it is the second most common cause, after E. coli
S. saprophyticus
they are both community-associated and hospital acquired infections.
S. lugdunensis and S. aureus
organism is more virulent than other is known to contain the gene mecA
S. lugdunensis
gene which encodes oxacillin resistance.
gene mecA
also display resistance to your vancomycin.
S.haemolyticus
Opportunistic Pathogens
- S. Warneri
- S. Capitis
- S.simulans
- S. Hominis
- S. Schleiferi
3 Modes of Transmission
- Endogenous strain
- Direct contact
- Indirect contact
MOT: sterile site by traumatic introduction
Endogenous strain
MOT: person-to- person, fomites
Direct contact
MOT: aerosolized
Indirect contact
Laboratory dx: Specimen
No special considerations
Laboratory dx: Microscopy
Gram positive cocci
used to eliminate contamination by gram-negative organisms in heavily contaminated specimens such as feces.
Phenylethyl alcohol (PEA) or Columbia colistin-nalidixic acid (CNA)
Staphylococcus aureus growing on Sheep Blood Agar would produce
beta-hemolytic, creamy, buttery-looking colonies.
name “aureus” has something to do with the production of the
Staphyloxanthin or golden yellow pigment
a coagulase positive organism.
Staphylococcus aureus
coagulase negative staphylococci
S.epidermis & S.saprophyticus
(non-staphylococcus aureus organisms)
mannitol sugar agar contains a high concentration of salt with a percentage of
7.5%-10%
phenol red as the pH indicator
Mannitol Salt Agar
makes the medium selective for Staphylococcus
high NaCl concentration (7.5%) in MSA
incorporation of this distinguishes S. aureus from most CoNS (Coagulase negative staphy)
mannitol and phenol red
S. aureus ferments mannitol and produces a
yellow halo
S. aureus ferments mannitol and produces a yellow halo as a result of
acid production altering the pH
CHROMagar is for the identification of
methicillinresistant Staphylococcus aureus (MRSA)
CHROMagar for the identification of methicillinresistant Staphylococcus aureus (MRSA) isolates through
selective and differential formation of mauve-colored colonies
grow on media containing blood, orming colonies about one tenth the size even after 48 hours or more of incubation
small colony variants (SCVs)
appear as small, pinpoint, nonhemolytic, and nonpigmented colonies on blood agar.
small colony variants of S. aureus
Catalase Test is used to differentiate
Catalase positive Micrococcus & Staphyloccocus from Catalase negative Streptococcus
Catalase is an enzyme that converts the hydrogen peroxide into?
oxygen and water
positive result of Catalase test
presence of bubbles (effervescence)
this bacteria is coagulase positive both in slide and tube test
S.aureus
Bound coagulase, or “clumping factor” is performed on
Slide Test
Free coagulase or staphylocoagulase is performed on
Tube Test
formerly referred to as cell-bound coagulase and causes agglutination
Clumping factor
directly converts fibrinogen to fibrin
Clumping factor
resembles thrombin and indirectly converts fibrinogen to fibrin
coagulase-CRF complex
positive result of slide coagulase test
clumping/agglutination within 30 seconds
positive result of tube coagulase test
clot formation
a negative result of slide test should always be followed up by
a tube coagulase test.
an extracellular molecule that causes a clot to form when bacterial cells are incubated with plasma.
Staphylocoagulase
Staphylocoagulase reacts with a thermostable, thrombin-like molecule called
coagulase- reacting factor (CRF)
In Tube coagulase test, look for clot formation after
4 hours of incubation at 37° C
If no clot appears fter 4 hours of incubation at 37° C during Tube coagulase test, what should be done
tube should be left at room temperature and checked the next day.
Fibrinolysin activity is enhanced at
37° C.
organisms that may present false positive result in slide test
S.Lugdugensis and S.schleiferi
organisms that may present false positive result in Tube Test
S.Intermedius and S.hyicus
Testing for pyrrolidonyl arylamidase activity can be used to differentiate S. aureus (negative) from
S. lugdunensis, S. intermedius, and S. schleiferi (positive).
It is hydrolyzed to L-pyrrolidone and β-
naphthylamine, which combines with p- dimethylaminocinnamaldehyde to form a red compound.
substrate pyroglutamylβ-naphthylamide (L-pyrrolidonyl- β-naphthylamide)
Bright red precipitate
PYR Test
Voges- Proskauer positive result
- formation of acetoin from glucose or pyruvate
- Red color = S. aeurus
a test to determine whether an organism that is inoculated in the plate is susceptible to 5-ug novobiocin disk.
Novobiocin Susceptibility Test
this organism is resistant to novobiocin and lack of a Zone of inhibition.
S. saprophyticus
In Microdase test, Staphylococcus epidermidis screening plate may show resistance to
Bacithracin (Taxo A) and furazolidone (Fx)
a modified oxidase test, detects your Cytochrome C; and used for differentiating Micrococcus spp. from Staphylococcus spp.
Microdase Test
In Microdase Test, Micrococcus spp. turn color ? within how how many mins
blue within 2 minutes.
bacteria is positive for both the 2-hour PYR and ornithine decarboxylase tests.
S. lugdunensis
kits use plasma-coated carrier particles
latex.
detect both clumping factor (with fibrinogen) and protein A
latex kit
kits that detect both clumping factor (with fibrinogen) and protein A and contain antibodies that bind capsular antigens 5 and 8, or other surface molecules.
Third-generation agglutination kits
These kits often have a higher specificity and sensitivity than the traditional plasma slide test and are quicker than the tube coagulase test.
latex kit
more sensitive, they are generally less specific.
Third-generation agglutination kits
Using Third-generation agglutination kits, False-positive results can occur with
S. saprophyticus, S. hominis, and S. haemolyticus.
mediated by the mecA gene, which encodes an altered penicillin-binding protein, PBP-2a
B-Lactamase
The mainstay of antistaphylococcal therapy is the use
methicillin, naficillin, and oxacillin
due to the gene mecA which is carried on a mobile cassette known as SCCmec
MRSA
using cefoxitin disk, MRSA zone of inhibition is
> 22 mm is reported as susceptible
using cefoxitin disk with zone sizes that is less or equal (</= 21 mm) is reported as ? and it is most probably a?
oxacillin resistant , MRSA
To screen isolates of S.aureus for oxacillin resistance, we use
Mueller Hinton agar supplemented with 4% sodium chloride and containing your 6 ug/ml of oxacillin inoculated unto a cotton swab and incubated 24 hours at 35C
gold standard for MRSA detection
Molecular nucelic acid probes or pCR amplification
Macrolide Resistance
- Clindamycin
- Efflux pump, MRSA
- Methylase enzyme that alters the ribosomal binding site.
- D-zone test
useful when discrepant macrolide test results are obtained (e.g., erythromycin resistant and clindamycin susceptible).
modified double disk diffusion test (D-zone test)
to determine the organism’s susceptibility to Clindamycin, what is used?
modified Kirby-Bauer test or D zone test
most commonly used cell wall–active agent that retains activity and is an alternative drug of choice for the treatment of infections with resistant strains
Vancomycin
Any clinical isolates that are identified as oxacillin-resistant S. aureus or coagulase-negative staphylococci and been found to be resistant to
vancomycin
resistant to vancomycin should be considered resistant to all other
beta-lactam antibiotics.
Alternatives for vancomycin
Linezolid & Daptomycin
