Staphylococcus Flashcards
Catalase test –> positive or negative indicates what?
Positive catalase test = Micrococcaceae family -> Staphylococcus or Micrococcus genus
Negative catalase test = Streptococcaceae family -> Streptococcus genus
How do you further differentiate Catalase Positive bacteria?
With a Nitrofurantoin or Lysostaphin Susceptibility test or with a Dextrose fermentation test
Catalase positive= Staphylococcus or Micrococcus
Nitrofurantoin or Lysostaphin susceptible = Staphylococcus
Positive Dextrose fermentation = Staphylococcus
Not susceptible = Micrococcus
Negative Dextrose fermentation = Micrococcus
How do you differentiate Staphylococcus species?
With a coagulase test
Coagulase positive: Staphylococcus aureus
S. aureus produces both exocoagulase and endocoagulase
exocoagulase: binds to serum immunoglobulins and this exocoagulase-Ig complex cleaves fibrinogen to fibrin. detected with coagulase tube test.
endocoagulase: aka clumping factor is bound permanently on the bacterial surface, and cleaves fibrinogen to fibrin diretly. detected by slide agglutination (cultured bacteria sample mixed w/ blood drop on a slide) or latex-agglutination
Coagulase negative: S. epidermidis, S. haemolyticus, S. saprophiticus, S. hominis
Morphology and Culture of Staphylococcus aureus.
Gram positive staphylococci, grape clusters
1uM cocci
Catalase+, Coagulase+
Faculattive anaerobic
Agar: 2-3mm wide golden colonies (au=gold), due to a non-diffusible fat soluble pigment they create which does not diffuse into the medium.
Blood agar: yellow golden colonies that are beta-hemolysing.
Can be enriched in 7.5% NaCl agar medium (note that L. monocytogenes is also salt resistant up to 10%)
Staph aureus virulence factors (10)
Polysaccharide capsule
Secreted polysaccharide slime layer
Protein A (of Staph A): A cell wall protein that binds Fc regions of IgG, inhibiting complement binding and activation. Inhibits opsonization of the bacterium.
Teichoic acid and lipoteichoic acid: Bind to mucosal cells, mediate mucosal adherence
Coagulases: exocoagulase, and endocoagulase aka clumping factor Generates Fibrin and clotting
Hyaluronidase: Spreading factor, allows ECM penetration
Staphylokinase aka Fibrinolysin: another spreading factor
Ctyolysins: alpha, beta, gamma, and delta toxins. Lysis of RBCs, as well as lysis of other cell types.
Leukocidin: causes lysis of leukocytes
Superantigens (3): 1. Exfoliative toxin 2. Toxic shock syndrome toxin TSST 3. Enterotoxins A-F
What is the mechanism of action of superantigens
Superantigens bind to MHC-2 molecules on APCs, (remember the class 2 is on APCs, and tho it is variable it is much less variable than the class 1s).
then bind to to the variable regions of the alpha or beta chains (or both) of the TCR on a T-helper cell, CD4+. They display broad specificity, activating as many as 20-40% of the T helper population.
Causes massive release of cytokines IFN-gamma, IL-2, TGF-beta,
Septic shock
What are the virulence factors of Staphylococcus aureus
What is the definition of a virulence factor?
Virulence factors are molecules produced by pathogens that aid in:
colonization of a niche in the host (this includes attachment to cells)
immunoevasion, evasion of the host’s immune response
immunosuppression, inhibition of the host’s immune response
cell entry and exit (if the pathogen is an intracellular one)
obtain nutrition from the host
and factors that cause damage to the host
What is the habitat of Staphylococcus aureus?
What is the means of transmission?
What are the 3 broad categories of clinical diseases it causes?
S. aureus is carried as a member of the normal flora of nasopharynx, mucous membranes, and skin.
S.a causes pyogenic infections, invasive infections, and exotoxin mediated syndromes
What are the types of skin (dermis and epidermis) infections caused by Staphylococcus aureus
Folliculitis - infection of an individual hair follicle or a patch of multiple separate hair follicles
Paronychia - infection of the fingernail or toenail beds.
Impetigo - patchy red sores in the epidermis which quicly burst and form a hard yellow crust. typically on the face. bullous impetigo - involves larger deepr boils filled with pus non bullous - the crusty dry kind.
Furuncle aka a Boil- a deeper, larger infection around a hair follicle, which penetrates into the subcutaneous/subdermal tissue
Carbuncle -Multiple Furuncles overlapping with one another forming an overlapping cluster which may go very deep and wide, down to the bone even.
What are the sub-epidermal infections caused by Staphylococcus aureus?
cellulitis - infection of the sub-dermal fat (cellulite)
phlegmone - a deep, sub-dural purulent infection causing swelling from pus buildup in the deep tissue layers.
dactylitis - infection of toe or finger around the nail
What are the deep pyogenic infections caused by S. aureus
septic arthritis (pus filled ankle/other joint)
osteomyelitis
mediastinitis
peritonitis
bacterial meningitis
plueritis
abscess formation in any organ parenchyma, brain, lung, renal abcess(except heart, it causes endocarditis, but the patient would die before it could progress to a myocardial abcess)
What types of pyogenic infections can be caused by S. aureus
Epidermal
Sub-epidermal
Deep pyogenic infections: bones, any of the serous membranes, parenchymal infections of all of the organs.
Eye infections
Ear infections
Respiratory tract infections
Urogenital infections
Cardiovascular infections: Vasculitis, endocarditis thrombophlebitis (vein inflammation related to thrombus)
Generalized infection: Bacteremia, Sepsis.
What are the exotoxin mediated syndromes caused by S. aureus
Food poisoning - vopmiting, diahhrea due to secreted enterotoxins exotoxins, which increase GI secretions
Exfoliative dermatitis - massive skin peeling/flaking due to exfoliative toxin
Toxic epidermal necrolysis (TEN) - severe/lethal problem causes separation of the epidermis from the dermis and then total death of the epidermal layer, leaving the patient severely exposed to infection and sepsis
Toxic shock syndrome: toxic shock syndrome toxins, the superantigens
What are the invasive infections that S aureus can cause?
Bacteremia/Septicemia
Sepsis
Infection of any of the pleural membranes, pleuritis peritonitis
Osteomyelitis
Endocarditis
Meningitis
How is the diagnosis Staphylococcus aureus infection performed?
All of the clinical signs caused by S.a are non-specific and may be caused by other bacteria as well.
Diagnosis: smear or culture of clinical patient specimens
Gram positive staphylococcus.
Catalase +
Coagulase +
DNAse + (digests DNA in a DNA impregnated Agar)
Mannitol + (grows on mannitol salt agar of 7.5% and can ferment mannitol generating pH drop and color change of the media from red -> yellow)
Sensitive to nitrofurantoin, lysostaphin, or dextrose fermentation tests.
Antibody tests against clumping factor aka endocoagulase or Protein-A
Bacteriophage typing - culturing and then spotting known bacteriophages that specifically target S. aureus, and more specifically target certain strains of S aureus. The bacteriolysis pattern determines the strain.
Serological tests are not useful
How is S. aureus treated?
Prevented?
First, an antibiogram must be performed. ~90% produce beta-lactamase ~10% are resistant to methicillin/oxacillin
If antibiogram indicates, b-lactam and a beta-lactamase inhibitor, like amoxicillin + clavulanic acid
For MRSA or severe infections cephalosporins or vancomycin.
For VRSA use Quinupristin-Dalfopristin (Streptogramins inhibit 50S peptidyltransferase), Daptomycin (Ca++ binder, mycelle formation, bact membrane lysis), Linezolid (50s n-formyl-Met inhibitor)
Pevention: no specific prevention methods,
but if a health worker is determined to carry S aureus nasally, it is elminated with Rifampin and mupirocin.
What are the coagulase negative staphylococci?
S. epidermidis
S. saprophyticus
S. hemolyticus
S. hominis
They are all facultative pathogens, which are part of the normaflora of the skin and mucosa
Every Sailor Hires Hookers.
What is the name,
habitat,
characteristics,
culture,
and infections
caused by the coagulase negative
Staphylococcus e…
Staphylococcus Epidermidis
Normaflora of human skin
Gram positive staphylococci, ~1um
Small white cultures, No hemolysis
Catalase +, Coagulase neg, mannitol neg
Facultative pathogen, causes no infection on in-tact skin or mucosa.
Common nosocomial infection forming biofilm on plastic instruments, catheters, cannulas.
Leads to subsequent bloodstream infection aka bacteremia, can then cause sepsis
What components is the biofilm formed on clinical implants/cannulas comprised of?
Becteria, usually S.e,
Exopolysaccharides
Matrix proteins
Fibrin, Fibrinogen
What is the treatment for an S. e
Remove the infected plastic device.
treat based on the antibiogram.
Most S. epidermidis is resistant to beta-lactams and is termed MRSE. (methicillin res. S.e)
often resistant to vancomycin or linzolids as well.
What are the names of the two S. h… coagulase negative staphylococci?
Morphology?
Culture?
Habitat?
S. heamolyticus
S. hominis
They form white colonies.
S. hemolyticus is very weakly hemolytic
S. hominis has no hemolysis.
Catalse + , Coagulase neg, Mannitol agar neg,
Normal flora of the skin
Also cause nosocomial facultative infections, forming biofilms on medical plastic devices,
They are the second most common bacteria to cause these types of infections, S. epidermidis is the first.
What is the name of the coagulase negative S. s…
Morphology
Culture
Habitat
Infections
S. saprophyticus
Gram positive staphylococci ~1uM
No hemolysis
coagulase neg, novobiocin resistant, urease positive
Part of the normal flora of the female genital tract and perineum.
Causes honeymoon cystitis, displaced bacteria from the vagina into the urethra causing Urinary tract infections and bladder infections (cystitis).
S. saprophyticus urease activity generates NH3 which irritates the mucosa, causing the inflammation and cystitis.
