Staphylococcus Flashcards
Name the bacteria
- gram positive, non-fastidious, facultative coccus
- catalase positive
- opportunist
- major cause nosocomial (hospital borne) infections
- part of normal flora– especially healthcare workers
- colonization higher in diabetics, HIV+, burn patients
- predominant site is anterior nare
- also skin, vagina, axilla, perineum, and oropharynx
Staphylococcus aureus
Which antibiotics are Staphylococcus aureus frequently resistant to?
Penicillin
Methicillin (MRSA)
Vancomycin (VRSA)
What is the major difference betweent the MRSA strains that originated in the communiteis vs the hospitals? Whichs strain is more sensitive? What is the most common community strain?
MRSA-CA has produced PVL toxin, whereare MRSA-HA does not
MRSA-CA (community) is more sensitive
USA300
Which groups of people are at a higher rist for S. aureus infection?
- newborn (scalded skin syndrome)
- youngh children with poor hygeine (skin infections)
- menstruating women (toxic shock syndrome)
- patient with intravascular catheters (bactermia & IE)
- surgery and burn patients, patients with LRT disease
S.aureus virulence structural and quorum sensing? , enzymatic, and toxins
-
structural
- Capsule: inhibits chemotaxis & phagocytosis, adherence to foreign bodies
- Peptidoglycan: inhibits phagocytosis, endotoxin-like activity
- teichoic acid: regulates cationic concentration at cell membreane, binds Fn
- Protein A: binds IgI, inhibits opsonization, complement activation
-
quorum sension
- regulated by agr locus
What is the name for density dependent gene expression in bacterial cells?
quorum sensing
S. aureus virulence enzymes?
- coagulase: converts fibrinogen to fibrin (causes plasma to clot)
- catalase: removes hydrogen perodixe
- hyaluronidase: hydrolyzes hyaluronic acids, spreading factor
- lipases: hydrlyzes lipids
- Nucleases: digest DNA and RNA, spreading factor
S. aureus virulence toxins?
- 5 cytolytic or membrane-damaging toxins
- alpha, beta, delta, gamma, PVL
- toxic for WBC, RBC, macrophages, platelets, and fibroblasts
- 2 exfoliative toxins
- A and B
- serine proteases, digest achors holdign epiermis to dermis
- >20 enterotixins
- A-E and G-X
- toxic shock syndrome toxin-1
- superantigents act systmatically
How do superantigens work?
They bind the T-cell to the antigen without requiring a specific fit. This results in polyclonal activation of T-cells. Will see a cytokine storm. An antigen is not needed.
How does surface protein A aid in the virulence of S. aureus?
surface protein A binds Fc portion of immunoglobulins. Improper antibody coating prevents proper opsonization and phagocytosis
What is the name of the disease shown in the photo and as described below:
- common on face and limb
- starts as small macule–> pustule–> honey brown crust
What is the most common bacterial cause of this disease? Second most common?
How would you identify this bacteria?
Disease: impetigo (epidermis and dermis)
caused by S. aureus (80%) and P. pyogenes (20%)
bacteria present in blisters
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
Foliculitis: pyogenic infection of hair follicules
hordeolum/Stye (eyelid foliculitis)
caued most commonly by S. aureus
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
How would you identify this bacteria?
Folliculitis: pyogenic infection of hair follicles
Furuncle (boil): several hair follicles & adjacent tissue
S. aureus is most common cause
Abscess aspirate, gram stain – gram (+) coccus
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
Disease usually occurs on nape of neck, upper back, or buttocks
Initially tight, erythematic skin that later effaces and releases pus
- Carbuncle
- Furuncles coalesce, extend deep SC tissue, many sinus tracts
- Cause most commonly my S. aureus
Name the corresponding diseases caused by S. aureus:
- Afer surgery/trauma
- edema, erythema, pain, accumulation of purulent material
- Introduce dinto ductal system through cracke nipples
- tender, fever, fatigue, may require drainage
- Bacteria has entered blood stream
- mostly after surgery
- How would you identify?
- infection of heart wall
- Wound infections
- Mastitis
- Bacteremia
- culture the blood (staining = unrewarding)
- Endocarditis
- life threatening (50% mortality)
How is S. aureus pneumonia caused? What percent of community pneumona is cause by S. aureus? Noscomial?
- Due to aspiration or oral secretions or hematogenous
- serious, since those who develop are already ill
- PVL in <5% hospital MRSA but in all community MRSA
- 2% community and 20% nosocomial pneumonia
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
- osteomyelitis
- S. aureus most common caus eof acute OM with pain and fever
- in children, usually in metaphyseal area of long bones
- in adults, occurs in vertebra; rarely affects long bones
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
painful, pus in synovial fluid in te knee, wrist, ankles and hips
How would you identify this bacteria?
Septic arthritis
most common cause is N. gonorrhoea in sexually active group
also cause by S. aureus (#1 cause children and older adults)
Culture the blood to identify
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
- abrupt onset perioral erythema (coves entire body in 2 days)
- large bullae/blisters with fluid (no organism)
How would you identify this bacteria?
Scalded skin syndrome (Ritter’s Disease)
ETA/ETB break desmoglein-1 in desmosomes –> cell separation
Check naropharyngeal samples (bacteria rarely in blisters)
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease?
- erythema does not extend beyond the borders of the blisters
Bullous Impetigo (localized form of SSSS)
bacteria CAn be isolated from skin lesions
What is the name of the disease shown in the photo? What bacteia most commonly causes this disease? What are the 2 toxins that are responsible and what are the different situations in which they present?
- red tongue, whole body rash, desquamation in palms and soles (2-3 weeks after onset)
- Occurs most frequently in menstruating women, linked to tampon use
How would you identify this bacteria?
Toxic Shock Syndrome (TSS) caused by S. aureus
>90% menstruation and 50% other TSS due to TSST-1
other 50% non menstruation caused by enterotoxin B
can be in vaginal samples– blood samples are negative
What is the disease caused by heat resistant toxins produced by bacteria in food at room temp? Characterized by severe vomiting within 3-6 hours. What is the recommended treatment?
How would you identify the bacteria?
food poisoinin– commonly caused by S. aureus
toxins impact CNS
toxin detectable in vomitus by latex agglutination (no bacteria)
Replacement of fluid (no antibiotic therapy) is recommended
check the food (no bacteria in feces)
What disease is characterized by inflammation of intestinal mucus membrane, watery diarrhea, abdominal cramps and fever after the use of broad spectrum antibiotics?
What bacteria are often responsible for this disease?
Antibiotic associated enterocolitis
Resistant bugs overgrow: S. aureus and C. difficile (more common)
- What type of colony does Staphylococcus aureus produce on blood agar?
- What will the gram stain look like?
- Catalase test?
- Culture on mannitol salt agar?
- Tellurite-glycine agar?
- Coagulase test?
- beta-hemolytic colonies
- grape-like clusters
- Positive catalase test
- Can grow on salt agar (fermentation lowers pH = color change red to yellow)
- selective due to high salt
- differential due to mannitol fermentation
- Can grow- selective due to glycine
- differrential due to tellurite to tellurium reduction (turns black)
- Positive coagulase (only S. aureus)
What is the collective name for all Staphylococcus bacteria that are not S. aureus?
coagulase negative Staphylococci (CNS or CONS)
Where is Staphylococcus epidermidis found?
What is its most important virulant factor?
- Found
- Normal skin (100%) and nare flora
- URT, GIT, & UGT
- from self, patients, hospital personal, contaminated devices
- biofilm– it is the most common cause of intravascular device associated infections (months)
What tests results woudl you expect to identify S. epidermidis?
On blood agar?
Catalase?
Coagulase?
Mannitol?
Tellurite?
- Positive gram stain– looks like clusters of grapes
- white, non-hemolytic colonies on blood agar
- catalase (+)
- coagulase (-)
- Unable to ferment mannitol
- Unable to reduce tellurite
Where are are colonies of Staphylococcus saprophyticus located?
What disease does it commonly cause?
- Location
- normal to colonize skin and genitourinary mucosa
- endogenous spread to urinary tract in colonized women
- Disease
- UTI in women (~20%)
- often drug resistant
- UTI in women (~20%)
What test results woudl you expect to identify S. saprophyticus?
gram stain?
catalase?
coagulase?
mannitol?
Novobiocin?
- gram stame (purple clusters of grapes)
- catalase (+)
- coagulase (-)
- slow mannitol fermenter
- frequently antibiotic resistant
- Novobiocin-resistant
