Staphylococcus: Additional Flashcards
What is Staphylococcus aureus (SAU)?
An opportunistic pathogen responsible for numerous infections, ranging from mild to life-threatening. It is an important community-acquired pathogen with increasing drug resistance.
What are some virulence factors (VF) of Staphylococcus aureus?
Examples include enterotoxins, cytolytic toxins, protein A, and exfoliative toxins.
What is enterotoxin?
Heat-stable exotoxins that cause diarrhea and vomiting. They are categorized into groups A to E and G to J.
How stable are enterotoxins?
Stable at 100°C for 30 minutes. Reheating contaminated food does not prevent disease.
What are the main causes of food poisoning related to enterotoxins?
Mainly Enterotoxin A, B, and D.
What enterotoxins are associated with Toxic Shock Syndrome?
Enterotoxin B and C, G and I.
What is Staphylococcal Pseudomembranous Enterocolitis?
Caused by Enterotoxin B, which acts as a superantigen.
What is Toxic Shock Syndrome Toxin-1 (TSST-1)?
Previously known as Enterotoxin F, it is a chromosomal-mediated toxin causing the majority of menstruating-associated TSS and approximately 50% of non-menstruating cases.
What is the role of TSST-1 as a superantigen?
It stimulates T-cell proliferation and the production of a large number of cytokines.
How does TSST-1 affect endothelial cells?
At low concentrations, it causes leakage; at higher concentrations, it is cytotoxic to these cells.
How is TSST-1 absorbed in the body?
Absorbed through the vaginal mucosa, leading to systemic effects, particularly with tampon usage.
What is exfoliative toxin?
Also known as Epidermolytic Toxin, it has two types: Exfo Tox A and Exfo Tox B.
What condition is caused by exfoliative toxins?
Staphylococcal Scalded Skin Syndrome (SSS), also known as Ritter’s Disease, most common in newborns and children under 5 years of age.
What are cytolytic toxins?
Toxins that affect RBCs and leukocytes, including hemolysins and leukocidins.
What types of hemolysins does SAU produce?
Four types: alpha, beta, gamma, and delta.
What is the effect of A-hemolysin?
It damages platelets and macrophages, causing severe tissue damage.
What is B-hemolysin also known as?
Sphingomyelinase C or Hot-Cold Lysin, which acts on sphingomyelin in erythrocyte membranes.
What is the significance of gamma-hemolysin?
Found only in Panton-Valentine Leukocidin (PVL), it is lethal to polymorphonuclear leukocytes and suppresses phagocytosis.
What enzymes are produced by Staphylococcus aureus?
Examples include coagulase, protease, hyaluronidase, and lipase.
What is the role of hyaluronidase?
It hydrolyzes hyaluronic acid in connective tissues, allowing bacteria to spread during infection.
What is the function of protein A?
Identified in the cell wall of SAU, it binds the Fc portion of Immunoglobulin G (IgG), blocking phagocytosis and negating IgG’s protective effects.
What is the primary reservoir for Staphylococci in humans?
Human Nares
Where can Staphylococci colonize in the human body?
Vagina, pharynx, axilae, and other skin surfaces
Where is nasal carriage of Staphylococci common?
In hospitals, particularly in patients
What factors increase colonization of Staphylococci in patients?
Frequent contact with hospital workers and certain medical conditions
In which settings do patients commonly develop Staphylococci infections?
Nurseries, burn units, and after surgery or other invasive procedures
What are key infection control practices for Staphylococci?
Hand hygiene, environmental cleaning and disinfection, use of personal protective equipment
What was the increase in Methicillin-Resistant Staphylococcus aureus (MRSA) infections from 2011 to 2016?
Increased from 4.1% to 9.2%
How is Staphylococci transmitted?
Direct contact with unwashed, contaminated hands and contact with inanimate objects (fomites)
What is decolonization in the context of Staphylococci?
A process to reduce colonization for specific populations
What are Staphylococci?
Catalase (+), gram (+) cocci; spherical cells (0.5 to 1.5 um) that appear singly, in pairs, and in clusters.
Greek: staphle - bunches of grapes.
What is the family classification of Staphylococci?
Member of the family ‘Staphylococcaceae’.
What are the characteristics of Staphylococci?
Nonmotile, non-spore forming, and aerobic or facultatively anaerobic; few strains are obligate anaerobes.
What is the colony appearance of Staphylococci?
Medium size (4-8mm) colonies after 18-24hr incubation; cream-colored, white, or rarely light gold, and ‘buttery looking’.
What are Small Colony Variants (SCV)?
Rare strains that are fastidious, requiring CO2, Hemin, or menadione for growth; colonies are 1/10 size of wild-type strain even after 48hrs of incubation.
What is the clinical significance of Staphylococci?
Common isolates in the clinical laboratory, responsible for numerous suppurative infections; normal inhabitants of the skin and mucus membranes of humans and other animals.
How are Staphylococci initially differentiated?
By the ‘coagulase test’.
What does a positive coagulase test indicate?
A clot formed in a tube containing plasma caused by ‘staphylocoagulase’.
Example of Coag (+): S. Aureus, S. Intermedius, S. pseudintermedius, S. Hyicus, S. Delphini, S. Lutrae, S. Agnetis, and some strains of S. Schleiferi.
What is the clumping factor?
Causes bacterial cells to agglutinate in plasma; basis for ‘slide coag (+)’; considered an obsolete test.
What is the purpose of the Tube Coag Test?
Only used for definitive testing.
What assays provide presumptive identification of S. Aureus?
Rapid latex and Hemagglutination assays.
What is the most clinically significant species of Staphylococci?
S. Aureus (SAU).
What infections are caused by S. Aureus?
Causes various cutaneous infections and purulent abscesses, including impetigo and cellulitis.
Impetigo and Cellulitis: superficial skin and soft tissue infection.
What are carbuncles?
Cutaneous infections that can progress to deeper abscesses, producing bacteremia and septicemia.
What toxin-induced diseases are caused by S. Aureus?
Common cause of infective endocarditis and diseases such as food poisoning, ‘Scalded Skin Syndrome’ (SSS) and ‘Toxic Shock Syndrome’ (TSS).
What are Coagulase-negative Staphylococci (CoNS)?
Includes S. Epidermidis, S. Saprophyticus, S. Lugdunensis, and S. Haemolyticus.
What infections does S. Epidermidis cause?
Causes healthcare-acquired or nosocomial infections.
What is the association of S. Saprophyticus?
Mainly associated with UTIs in young women sex workers.
What infections are linked to S. Haemolyticus?
Recovered from wounds, septicemia, UTI, and native valve infection.
What is the significance of S. Lugdunensis?
Like S. Aureus, it is slide coag (+) and needs tube coag test for differentiation; can be an aggressive pathogen associated with catheter-related bacteremia and endocarditis.
What are the types of Micrococci?
Catalase (+), coagulase (-), gram (+) cocci found in the environment and as members of indigenous skin microbiota.
How are Micrococci differentiated from CoNS?
Easily differentiated; they produce a yellow pigment.
What are other cat (+), gram (+) cocci recovered from humans?
Includes ‘Rothia mucilaginosa’ and ‘Alloiococcus otitis’.
What factors determine SAU infections?
- Virulence factor
- Size of the infectious dose
- Status of the host’s immune system
How are SAU infections initiated?
When a breach of the skin or mucosal barrier allows staphylococci access to adjoining tissues or the bloodstream.
What is the normal defense mechanism against SAU infections?
Individuals with a healthy immune system can combat the infection more easily than those with impaired immune systems.
What happens once initial barriers are crossed in SAU infections?
It activates the host’s acute inflammatory response, leading to the proliferation and activation of polymorphonuclear cells.
What is a focal lesion in the context of SAU infections?
Production of toxins and enzymes.
What type of infections are caused by SAU?
Suppurative infections (discharge or pus).
What is an abscess in SAU infections?
An abscess is filled with pus and surrounded by necrotic tissues and damaged leukocytes.
What are benign skin infections caused by SAU?
Folliculitis, furuncles, and bullous impetigo.
What are opportunistic infections in SAU infections?
Infections that occur from previous skin infections such as cuts, burns, and surgical incisions.
What is folliculitis?
Relatively mild inflammation of a hair follicle or oil gland; infected area is raised and red.
What are furuncles?
Large, raised, superficial abscesses that are an extension of folliculitis.
What are carbuncles?
Large, more invasive lesions that develop from multiple furuncles, can progress into deeper tissues; present with fever and chills.
How does bullous impetigo differ from nonbullous impetigo?
Staphylococcal pustules are larger and surrounded by a small zone of erythema.
What is impetigo?
A highly contagious infection easily spread by direct contact, fomites, or auto inoculation.
What can increase colonization of SAU?
Blocked hair follicles, sebaceous glands, and sweat glands.
How can SAU infections be misidentified?
They can be misidentified as insect or spider bites.
Who is particularly predisposed to developing staphylococcal infections?
Immunocompromised individuals, particularly those undergoing chemotherapy.
What is Scalded Skin Syndrome (SSS)?
A bullous exfoliative dermatitis primarily in newborns and previously healthy young children.
What causes Scalded Skin Syndrome?
Staphylococcal exfoliative or epidermolytic toxin; present at a lesion distant from the site of exfoliation.
What is the mortality rate of Scalded Skin Syndrome in children and adults?
Low (0%-7%) in children; can be 50% in adults.
What is another name for Scalded Skin Syndrome?
Ritter’s Disease.
What characterizes Scalded Skin Syndrome?
Cutaneous erythema followed by profuse peeling of the epidermal layer of the skin.
What is the healing time for Scalded Skin Syndrome?
Complete healing occurs after around 10 days.
What must Scalded Skin Syndrome be differentiated from?
Toxic Epidermal Necrolysis (TEN).
What is Toxic Shock Syndrome?
A rare but potentially fatal multisystem disease; localized infection.
What are the symptoms of Toxic Shock Syndrome?
Sudden onset of fever, chills, vomiting, diarrhea, muscle aches, and rash.
When was Toxic Shock Syndrome first described?
In 1978, associated with women using highly absorbent tampons.
What are the two categories of Toxic Shock Syndrome?
Menstruating-Associated and Nonmenstruating-Associated.
What is the source of contamination in Staphylococcal Food Poisoning?
Infected food handler.
What are the symptoms of Staphylococcal Food Poisoning?
Gastrointestinal disturbances appearing rapidly at 2-8 hours and resolving within 24-48 hours.
What is Staphylococcal Bacteremia?
Observed among intravenous drug users; contaminated needles or from a focal lesion.
What can local SAU infections progress to?
Bacteremia leading to secondary pneumonia, endocarditis, or bone infection.
What is Staphylococcal Pneumonia?
Occurs secondary to influenza virus infection; characterized by multiple abscesses and focal lesions.
What are the symptoms of Staphylococcal Osteomyelitis?
Fever, chills, swelling, and pain.
What is Septic Arthritis?
SAU infection in children; history of rheumatoid arthritis, diabetes mellitus, or recent joint surgery.
