Micro J210 Staphylococci
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What is stap. epidermidis?
How do Staph aureus and Staph epi look upon Gram-staining?
-Grape like clusters of gram-positive cocci
What is the color on staph aureus on a BHI and blood agar plate?
-Golden yellow opaque colonies
What color is staph epi on a BHI and blood agar plate?
What are the biochemical tests to determine if its staph aureus or staph epi?
- -Catalase: converts hydrogen peroxide to water and oxygen. Enzyme
- -Coagulase: coagulase plasma and blood
- -Mannitol fermentation: Mannitol is form of sugar. Organisms that utilize mannitol as a food source will produce acit. Phenol red is the indicator used. It is read at a neutral ph but turns yellow if conditions become acidic.
What are the results for the catalase test for staph aureus and epi?
-Both will positive because an air bubble will be produced due to 02 production
What are the results of the coagulase test for staph aureus and epi?
- -aureus: positive, due to clump
- -epi: negative
What are the results for the mannitol fermentation test?
- -Aureus: positive, gas uses it, it will be yellow for acid production
- -Epi: negative, purple
How common are staphy aureus and epi?
Both are normal flora of human skin and mucous surfaces
What are the carriage rates?
- -Aureus- 20-40%, mostly around nares/mouth. Mosit areas
- -Epi- 100% on the skin
How pathogenic are staph aureus and staph epi?
- Staph aureus is a serious pathogen specially in immunocompromised. Top killer in the hospital
- Staph Epi is normally non-pathogenic but an opportunistic pathogen
What kind of lesions does staph aureus cause?
- -Pyogenic: pus producing, attracts a lot of PMNS to the site of infection
- -the pus must be out to heal
What is pus?
-Whitish-yellow substance produced during inflammatory responses of teh body that can be found in regions of pyogenic bacterial infections
How does staph aureus affect host recovery from disease?
Staph induces pus production and cells of the immune system do not work well within the pus microenvironment
What is the composition of pus?
Dead and live PMN, dead and live bacteria, dead tissue debris and fluid, low O2 and low ph
How is staph aureus spread?
Strictly human to human from nasal mucosa, skin (direct contact)
What are the virulence determinants of staph aureus?
- -Lipoteichoic acid: surface molecules that help attachment. Thick PG layer
- -Catalase: 2 H2O2 + catalase = H20 + 02
- -Protein A: Surface molecule that binds to Fc portion of IgG, so that IgG cannot bind to anything else
What are anti-host virulence determinants of Staph aureus?
- Exotoxins: Live bacteria
- -Hemolysin: lyses RBC
- -Leukocidin: kills WBC
- -Coagulase: wall off the area of infection, results in low 02 and ph, leading to necrosis. Clots the plasma around lesion
- -Exfoliatin: causes skin peeling SSSS
- -Enterotoxin: Causes food poisoning/vomiting
- -Other exotoxins: occurs in some strains of S. aureus
What is SSSS?
Staph scalded skin syndrome
What happens when a pimple is squeezed?
-Release of bacteria into the blood
What is bacteremia?
-Bacteria in the blood
What is septicemia?
Presence of actively growing bacteria or their toxins in the blood (blood poisoning or septic shock)
What is somethingemia?
- -Something in the blood
- Examples: meningococcemia, toxemia, hyperlipidemia
What are three common types of skin infections caused by staph aureus?
-Impetigo, boil, and furuncle/carbuncle
What is impetigo?
- -A contagious skin infection taht usually produces blisters or sores on the face (mostly), sometimes hands
- -Most common skin infections among kids of low hygiene
- -3rd world countries
- -Superficial staph
What is a boil?
- -folliculitis, skin abscess
- -Infection of hair follicle
- -Pus filled lumps that are tender, warm and/or painful
What is a furuncle/carbuncle?
- -Abscess larger than a boil, usually back of the neck
- -Require surgical draining
- Furuncle: acute, round firm, tender, circumscribed, perifollicular staph infection that usually presents as central pus area
- -Carbuncle: two or more confluent furuncles with separate heads
Why are furuncles, caruncles, impetigo and folliculitis considered primary pyodermas?
- -Usually caused by staph aureus
- -They rarely require hospitalization
- -They may respond to local treatment
- -Recurrence may be prevented by decreasing staph aureus carriage
What population is particularly susceptible to SSSS?
- -New borns
- -Umbilican stump infection (omphalitis) may be one of the sites of infection which leads to SSSS
- -Not serious, self-limiting, happens in low hygiene deliveries
What causes SSSS?
-Exfoliatin toxin: released by S. Aureus strains taht are infected with a virus that has the genetic information for production of toxin
How do we identify the source of SSSS strains?
-Screen the virus within the Exfoliation-secreting strains of S. aureus (phage typing)
What is an enterotoxin? an exoenterotoxin?
- -An exotoxin that affects lining of GI tract
- -Some strains of S. aureus release this toxin inot the food
What kind of vomiting is observed with staph food poisoning?
- -Projectile vomiting: Toxin has direct neural effect in the brain cetners
- -Toxin is a superantigen: stimulate T cells nonspecifically
- -most common type of food poisoning in US
- -Staph in food releasing toxins in the food then we eat that food
what is a superantigen?
-Cytokines released nonspecifically presenting cells
What are some common foods associated with Staph food poisioning?
-Processed meats, chicken, creams (desserts), mayonnaise-containing dishes
How do foods become toxigenic?
Person with lesions on hand prepare the food, contaminated food sits at room temp for hours, bacteria grow and release toxin within the food. Person consumes the toxin contaminated food
What is a pure toxemia?
Bacteria die in acid stomach, toxin is acid stable and enters the blood
What is the incubation time for staph food poisoning?
- 4 hours
What antibiotic theraphy should you use for staph food poisoning?
- -None since bacteria are not causing the problem
- -Self-limiting conditions. just treat the symptoms (fluid replacement)
What is osteomyelitis?
- -Bone marrow inflammation.
- -many different types of bacterica can cause this, however sstaph aureus most common
- -May require amputation
What are the signs and symptoms of osteomyelitis?
- -Limb may be very painful, especially when it is moved
- -Fever and the skin over the painful limb may be swollen, hotter and redder than surrounding areas
- -General ill feeling
- -If the osteomyelitis has been present for some time, and there is a break in the skin, there may be some pus discharge from the area
What is a lung infection by S aureus?
- - Pneumonia
- -Abscess formation in lungs of immunocompromised
- -Rare but highly fatal
- -Gram stain of teh sputum smear shows staph aureus
- -Gram positive, usually affect the debilitated, elderly or immunocompromised, and responsible for nosocomial infections acquired during lengthy hospital stay
What staph disease is usally associated with young, healthy, menstruating women?
- -Toxic shock syndrome
- -1978-80, deaths traced to use of rely tampoms.
- -Staph grew on the tip of the tampons and released toxin (Toxin-1 or TSST-1)
- -Toxin in blood caused the condition
- -results in septic shock with multiple organ failures and possible death
What are the signs and symptoms of toxic shock syndrome and why do they not seek medical attention?
- -Flu-like symptoms such as fever, chills, muscle ches, nausea, vomiting and diarrhea
- -Dehydration and decreased urine output
- -Hypotension with weak and rapid pulse
- -confusion, disorientation or other mental changes (alarming, and reason they do not seek medical attention)
- -Swelling in hands, feet, and ankles
- -Red rash, taht covers the whole body, followed by peeling skin (may be difficult to see in dark-skinned individuals) (sunburn like)
- -Strawberry tongue
Can males get Toxic Shock syndrome?
- -non-menstrual toxic shock syndrome occur in males and females of all age groups that are usually associated with localized or systemic infections
- -In femals use of contraceptive sponges, diaphragms or intrauterine devices
What is the purpose of antibiotic therapy in Toxic shock syndrome?
- -No bacteria in blood but treat with antibiotic to destroy source of bacteria in the wound
- -remove foreign object and change tampons frequently
How fragile is staph aureus?
- Very stable to drying and heat
- Enterotoxin is heat stable (dont save the food)
Is there immunity from staph infections once you get it?
- -No because staph hides itself from cells of immune system
- -Wall off the area of infection with coagulase
- -Releases toxins that paralyze immune system (Toxic shock) kills leukocytes
- -Some people are more susceptible than others (30% recurrence)
How has the treatment of staph aureus changed in the last 25 years?
- -An increasing number of patients are being seen with skin infections by staph aureus taht are resistant to many antibiotics
- -MRSA (Super bug, 1970)
- -PRSA- 1942
- -VISA- 1997
Are there problems associated with the current staph aureus therapy?
- -Emergence of VRSA
- -No vaccine
- -New innovative phage therapy (certain phages destorying virus staph)
What is a superbug?
- Symptoms: Minor skin problems, deep abscesses, can reach bone marrow, joints, bloodstream, major organs, can lead to death
- Problem: bacteria has evolved to survive common antibiotics
- Risk environments: hospitals, long-term care facilites, sporting facilites/equipment, and crowded, unsanitary living conditions
What are likely sources for nosocomial infections?
- -Infections are considered nosocimal if they first appear 48 hours or more after hospital admission or within 30 days after discharge.
- -Contact, hospital personnel or devies
- -Common vechicle: contaminated equipments (Catheters)
What is a iatrogenic infection?
- -Brought forth by a healer
- Example: osteomyelitis following a bone surgery
What are risk factors for nosocomial infections?
Advanced age, underlying disease, severity of illness, transplantation, GI surgery, exposure to medical devices, heavy exposure to antimicrobial therapy, prolonged hospital stay, interinstituational transfer of a patient
What is a biofilm?
- -Complex aggregation of microorganisms marked by the excretion of a protective and adhesive matrix
- -Microbial biofilms develop when microorganisms irreversibly adhere to a submerged surface and produce extracelluar polymers that faciliate adhesion adn provide a structural matrix
- Example: dental plaque
What is staph epi?
- -Normal flora
- -Have emerged as a major nosocomial pathogen associated with infections mediated by implanted medical devices
What can a health caregiver do to reduce nosocomial infections?
- -Hand washing after touching the patient and items contaminated by bodily fluids, secretions, excretions or objects
- -Wearing gowns
- -Appropriate disposal of items taht came in contact with the infected patient and appropriate handing of laundry
- -Infected patients should be placed in isolation in a side-room to limit the spread of infection
What is the chain of infection?
-Portal of entry, susceptible host, infectious agent, reservoirs, portal of exit, means of transmission, repeat
How can you differentiate staph aureus from streptococci biochemically?
- -Flow chart
- Catalase test, coagulase test, pattern of hemolysis on blood agar, optochin test, bacitracin sensitivity test, CAMP test
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