Staphylococcus and Streptococcus Flashcards
Staphylococcus
- one of the most opportunistic infections in hospitals
- gram stain purple
- grapes
- facultative anaerobes
- grow in high salt
- catalase positive
- skin, soft tissues, bones, urinary track
Pathology depends on
- production of surface proteins that mediate adherence to host tissues
- secretion of extracellular toxins
Alpha toxin
genome and plasmid
B toxin
shingomyelinase C
Gamma toxin
detergent like action
Y toxin
cell lysis
-S and F pore formation
Exfoliative toxins
Staphylococcal scalded skin syndrome SSSS
- mostly in young children
- produced by 5-10% of S aureus
Enterotoxins
- contaminated food
- stable to healing, gastric enzymes
Toxic Shock Syndrome Toxin-1 (TSS-1)
- can penetrate mucosal barriers (systemic infection)
- death by hypovolemic shock (leads to multi-organ failure)
Staphylococcal enzymes
- coagulase (fibrinogen) cells clump
- Hyaluronidase (hydrolyzes connective tissue)
- Fibrinolysin (dissolve fibrin clots)
- Lipases (hydrolyze lipids) ensure survival of fatty tissue
Spread
- tissue-degrading enzymes (lipase) cutaneous, subcutaneous tissues
- hyaluronidase (connective tissue)
Staphylococcal Scalded Skin Syndrome SSSS
- young children
- localized erythema (redness/inflammation) starts around mouth, covers entire body in 2 days
- large blisters
- skin peels
- mortality rate is low
- Bullous impetigo is a localized form
Staphylococcal food poisoning
- not an infection
- food contaminated by humans
- recovery occur within hours
- symptoms: vomiting, nausea, diarrhea, abdominal pain
Toxic schock syndrome
- fever, hypotension, rash
- desquamation, vomiting, diarrhea
- organs involved: CNS, GI, hematologic, hepatic, muscles and renal
- mortality 5%
- high rate of occurrence
Cutaneous infections (pyogenic)
- impetigo (pus filled vesicles, dry crusted lesions)
- folliculitis
- furuncles (bolis)
- carbuncles (require surgical drainage and antibiotics)
Pneumonia
- aspiration of oral secretions
- very young, elderly, chronically ill
- patchy infiltrates, abscesses
Osteomyelitis and septic arthritis
- dissemination to bone, secondary infection, or migration from adjacent site
- localized pain, high fever
Septic arthritis
-painful, red joints, pus present on aspiration
Staphylococcus epidermis
- major component of skin flora
- opportunistic infection
- noncomial infection
- endocarditis - native heart valves
Staphylococcus saprophyticus
- urinary track infections (UTIs)
- coagulase-negative
Identification of S. aureus
B hemolytic: sheep blood agar (rings)
- yellow pigmented (aureus)
- coagulase positive
- Mannitol fermentation
Identification of S. epidermis
Non-hemolytic: sheep blood agar
- non-pigmented
- does not ferment mannitol
- coagulase negative
Antibiotic therapy
- Resistant to penicillin (penicillinase)
- B-lactam antibiotics (often ineffective, modified penicillin binding proteins)
- Vancomycin (current drug of choice, resistance has been observed)
Vancomycin resistance
- Low level: thicker, more disorganized cell wall, drug may be trapped in cell wall; unable to reach membrane
- High level uncommon: vanA gene operon from enterococci, modified peptidoglycan layer cant bind vancomycin
Streptococcus
- gram positive
- facultative anaerobes
- chains or pairs
- catalase negative
Hemolysis on sheep blood agar alpha
partially hemolysis, green color
Hemolysis on sheep blood agar beta
complete clearing around the colony
Hemolysis on sheep blood agar gamma
No color change, no hemolysis
Hemolysis and streptococcus
- Groups A and B (beta)
- Group D (alpha or gamma)
- S. pneumoniae and viridans (alpha)
S. pyogenes
- avoids phagocytosis (hyaluronic acid capsule), inactivate complement cascade C3b, C5a
- adheres to surface of host cell by 10 dff antigens
- invades epithelial cells (M and F proteins)
S. pyogenes toxins and enzymes
- heat-labile toxins SpeA, SpeB, SpeC, SpeF
- act as super antigens: TH cells enhanced release proinflamatory cytokines
- Streptolysin S : B-hemolyses
- Streptolysin O: oxigen labile, inhibited by cholesterol in skin infections
Steptokinase (A and B)
- rapid spread in tissues
- cleave plasminogen to plasmid, which cleaves fibrin and fibrinogen resulting in lysis of blood clots and fibrin deposits
- alpha-spreptokinase antibodies useful markers for infection
DNases A-D
- breakdown of free DNA in pus
- reduces viscosity, facilitates spread
- alpha-DNase B antibodies an important maker for skin infection
Pharyngitis (strep throat)
- 2-4 day after exposure
- sore throat, fever, malaise, headache
- red posterioir pharynx with exudate pus
- Scarlet fever due to pyrogenic exotoxin
Pyoderma (impetigo)
- skin infection
- direct contact with an infected person
- enters to break in skin
- blisters form, fill with pus, break, crust over
- regional lymph nodes enlarge
Erysipels
- accute skin infection
- pain infamation, lymph nodes enlarged, systemic signs (fever, chills, leukocytosis)
Cellulitis
- skin and deeper subcutaneus tissues
- hard to tell infected from uninfected skin
- local inflamation systemic signs
Acute stage of eryspelas
- erythma redness
- bullae blisters
Necrotizing fasciitis
- deep on subcutaneus tissue
- extensive destruction of muscle, fat
- introduced through break in skin
- toxicity multiorgan failure, death
Rheumatic fever
- can occur after pharyngeal strep only
- inflammatory changes in heart, joints, blood vessels, subcutaneous tissue
- specific class IM protein types
Acute glomerulonephritis
- occur after pharyngeal or pyodermal strep
- acute inflammation of renal glomeruli: edema hypertension, hematuria, protein in both blood and urine
Laboratory diagnosis S. pyogenes
- microscopy: Gram + cocci, pairs or chains, associated with leukocytes
- Antigen detection: group specific carbohydrate in throat swab
culture on blood agar + antibiotics PHARYNGITIS
swab tonsils
culture on blood agar + antibiotics IMPETIGO
pus from a closed lesion
culture on blood agar + antibiotics NECROTIZING FASCIITIS
blood tissues
culture on blood agar + antibiotics ERYSIPELAS and CELLULITIS
not useful
PYR test
+: red color
-: white no color change
Treatment, prevention control S. pyogenes
- penicillin (oral cephalosporin if allergic to pen)
- oxacillin or vancomycin id S. aureus is also present
- can prevent rheumatic fever
- resistant to tetracyclines, sulfonamides, erythromycin, macrolides
S. pneumoniae
- alpha hemolytic
- pneumolysin (degrades red blood cells under aerobic conditions)
- grows well on sheep blood agar
- no group antogen
Diagnosis S. pneumoniae
- spinal fluid
- direct gram stain
- detection of capsular antigen
- optochin sensitive
Treatment prevention contral S. pneumoniae
- levofloxacin or vancomycin-ceftriaxone
- resistance to penicillin, erythromycin, tetracycline, cephalosporins
- anticapsular vaccin prevention
- 23 different capsule polysaccharies
