Chapter 19: Objectives Flashcards
Contrast the virulence of Staphylococcus aureus with that of Staphylococcus epidermidis in humans.
- S. aureus protein A positive, S. epidermidis protein A negative
- S. Aureus coagulase positive, S. epidermidis negative
- S. aureus slime layer positive, S. epidermidis positive
- S. Aureus catalase positive, S. epidermidis positive
- S. aureus hyaluronidase positive, S. epidermidis hyaluronidase negative
- S. aureus staphylokinase positive, S. epidermidis staphylokinase negative
- S. aureus lipase positive, S. epidermidis lipase positive
- S, aureus β-lactamase positive, S. epidermidis negative
- S. aureus toxins positive, S. epidermidis negative
Discuss the structural features, enzymes, and toxins of Staphylococcus that enable it to be pathogenic.
- Protein A
- Coagulase
- Slime layer
- Hyaluronidase
- Staphylokinase
- Lipases
- β - lactamase
- Cytolytic toxins
- Exfoliative toxins
- Enterotoxins
Protein A (staphylococcus structural defense against phagocytosis; antiphagocytic)
Coats the cell surface; interferes with humoral immune responses
Bound coagulase (staphylococcus structural defense against phagocytosis; antiphagocytic)
- Converts fibrinogen into fibrin molecules
- Fibrin clots hide the bacteria from phagocytic cells
Slime layers (staphylococcus structural defense against phagocytosis; antiphagocytic)
Capsules:
- Inhibit leukocyte chemotaxis and phagocytosis
- Facilitate attachment of Staphylococcus to surfaces
Enzymes (staphylococcus)
- Secreted by the pathogen
- Dissolve structural chemicals in the body
Cell free coagulase (Staphylococcus enzymes)
Triggers blood clotting
Hyaluronidase (staphylococcus enzymes)
- Breaks down hyaluronic acid
- Enables the bacteria to spread between cells
Staphylokinase (staphylococcus enzymes)
- Dissolves fibrin threads in blood clots
- Allows Staphylococcus Aureus to free itself from clots
Lipases (Staphylococcus enzymes)
- Digest lipids
- Allow Staphylococcus to grow in skin and in oil glands
β-lactamase (Staphylococcus enzymes)
- Breaks down penicillin
- Allows bacteria to survive treatment with β- lactam antimicrobial drugs
Toxins (Staphylococcus)
Chemicals that harm tissues or trigger host immune responses that cause damage
- Cytolytic toxins
- Exfoliative toxins
- Toxic- shock syndrome toxin
- Enterotoxins
Toxemia (staphylococcus toxins)
Refers to toxins in the bloodstream that are carried beyond the site of infection
Cytolytic toxins (staphylococcus toxins)
- Alpha, beta, gama, delta, and leukocidin
- Disrupts the cytoplasmic membrane of a variety of cells
- Leukocidin can lyse leukocytes specifically
Exfoliative toxins (staphylococcus toxins)
- Cause skin cells to separate and slough off
- Exfoliative toxin causes reddened patches of the epidermis to slough off
Toxic-shock syndrome toxin (staphylococcus toxins)
Causes toxic shock syndrome
Enterotoxins (staphylococcus toxins)
- A, B, C, D, and E
- Stimulate symptoms associated with food poisoning
- Are heat stable, active at 100℃ for up to 30 minutes
What are the three categories of Staphylococcus diseases?
- Noninvasive (food poisoning)
- Cutaneous (various skin conditions)
- Systemic (Variety of infections when bacteria invade deeper tissues)
Describe the symptoms of staphylococcus food poisoning
Consumed bacteria do not continue to produce disease/ toxins, so the course of the disease is rapid usually lasting 24 hours or less.
- Nausea
- Severe vomiting
- Diarrhea
- Headache
- Sweating
- Abdominal pain
List the six pyogenic lesions caused by Staphylococcus aureus.
Cutaneous: various skin conditions
- Scaled skin syndrome
- Impetigo
- Folliculitis
- Sty
- Furuncle
- Carbuncle
Describe scaled skin syndrome
- Caused by S. aureus
- Exfoliative toxin causes reddened patches of the epidermis to slough off
- Blisters contain clear fluid lacking bacteria or WBC
Describe impetigo
- 80% caused by S. aureus
- Reddened patches of skin become pus filled vesicles that eventually crust over
- Generally affects children
Describe folliculitis
- Infection of a hair follicle in which the base of the follicle becomes red, swollen, and pus filled
- Staphylococcus aureus (cutaneous lesion)
Describe sty
- When the infection of a hair follicle occurs at the base of the eyelid
- Staphylococcus aureus (cutaneous lesion)
Describe furuncle
- A large, painful raised nodular extension of folliculitis into surrounding tissue
- Staphylococcus aureus (cutaneous lesion)
Describe carbuncle
When several furuncles coalesce, it extends deeper into the tissues, triggering fever and chills.
What are five systemic and potentially fatal diseases caused by Staphylococcus
- Staphylococcal toxic shock syndrome
- Bacteremia
- Endocarditis
- Pneumonia
- Osteomyelitis
Describe staphylococcal toxic shock syndrome
- Occurs when TSS toxin is absorbed through the blood
- Life-threatening, occurs when the body is not getting enough blood flow. Lack of blood flow means the cells and organs do not get enough oxygen and nutrients to function properly
- Characterized by fever, vomiting, red rash, low blood pressure, loss of sheets of skin
Describe bacteremia
- Presence of bacteria in blood
- Systemic disease caused by staphylococcus
Describe endocarditis
- Present in the lining of the heart
- Systemic disease caused by staphylococcus
Describe pneumonia
- An inflammation of lungs where alveoli and bronchioles become filled with fluid
- Systemic disease caused by staphylococcus
Describe osteomyelitis
- Bacteria invades the bones causing inflammation of bone marrow and surrounding bone
- Systemic disease caused by staphylococcus
If gram positive bacteria in grapelike arrangements, and are able to clot blood:
They are coagulase positive Staphylococcus aureus
Discuss the history of Staphylococcal resistance to antimicrobial drugs
- Only 5% of strains are susceptible to penicillin
- Methicillin, a semisynthetic form of penicillin, which is not inactivated by β-lactamase, is the drug of choice for staphylococcus infections
- Methicillin-resistant S. aureus (MRSA) is resistant to common antimicrobial drugs, including penicillin, macrolides, aminoglycosides, and cephalosporin; vancomycin is used to to treat MRSA infections
- Vancomycin-resistant S. aureus arose (VRSA)
Describe classification of streptococcal strains
- Gram-positive cocci, facultative anaerobes
- Arranged in pairs or chains
- Catalase negative (H2O2 catalase test negative)
- Classified on:
- Antigens
- Type of hemolysis (alpha, beta, gamma)
- Cell arrangement
- Physiological properties
- Often categorized based on Lancefield classification: divided into serotypes based on bacteria’s antigens including serotypes A through H and K through V
Hemolysis zone of Streptococcus pyogenes
Beta
Hemolysis zone of Streptococcus pneumoniae
Alpha
Hemolysis zone of Enterococcus faecalis
Gamma
Describe two structures in Streptococcus pyogenes that enable this organism to survive the body’s defenses.
- Protein M: interfers with opsonization and lysis by destabilizing complement
- Hyaluronic acid capsule: remain hidden from phagocytic cells
Protein M
- Structural feature of Streptococcus pyogenes that enables the organism to survive the body’s defenses
- Interferes with opsonization and lysis by destabilizing complement
Hyaluronic acid capsule
- Structural feature of Streptococcus pyogenes that enables the organism to survive the body’s defenses
- Because hyaluronic acid is normally found in the body, white blood cells may ignore bacteria “camouflaged” by this type of capsule
Identify four kinds of enzymes that facilitate the spread of Streptococcus pyogenes in the body
- Streptokinases
- Deoxyribonucleases
- C5a peptidase
- Hyaluronidase
Identify the action of pyrogenic toxins in causing disease symptoms by Streptococcus pyogenes
- Also known as Erythrogenic toxins
- Stimulate the release of cytokines that cause fever
- Toxin genes carried on bacteriophages
What are treatments for Group A: streptococcus pyogenes
Treatment:
- Penicillin is effective
- Sensitive to erythromycin, cephalosporin, bacitracin
What are seven diseases caused by Streptococcus pyogenes (group A) and the treatments available.
- Pharyngitis (strep throat)
- Rheumatic fever
- Scarlet fever
- Pyoderma
- Erysipelas
- Necrotizing fasciitis
- Glomerulonephritis
Treatment: - Penicillin is effective
- Sensitive to erythromycin, cephalosporin, bacitracin
Pharyngitis
- Also known as strep throat
- Inflammation of the pharynx
- Purulent (pus containing) abscesses covering the tonsils
- Group A Streptococcus: Streptococcus pyogenes
Rheumatic fever
- Complication of untreated streptococcal pharyngitis
- Inflammation damages the heart valves and muscle
- Autoimmune response against heart antigens
- Damaged heart valves and achy joints
- Group A Streptococcus: Streptococcus pyogenes
Scarlet fever
- Involve lysogenized strain of S. pyogenes (due to pyrogenic toxins)
- Strawberry red tongue
- Chest rash develops that spreads across the body
- Group A Streptococcus: Streptococcus pyogenes
Pyoderma
Pus-producing lesions involving lymph nodes, pain and inflammation
- Group A Streptococcus: Streptococcus pyogenes
Prefix Pyro-
- Causes fever
- Example: Pyrogenic
Prefix Pyo-
- Produces pus
- Pyoderma
Erysipelas
- Involves surrounding superficial lymphatic tissue and triggers pain and inflammation
- Group A Streptococcus: Streptococcus pyogenes
Necrotizing fasciitis
- Characterized by redness, intense pain, and swelling at the site of infection
- Bacteria digest the muscle fascia (connective tissue) and fat tissue
- Patients develop fever, nausea, mental confusion, drop in blood pressure
- Affected tissue must be removed completely
- Group A Streptococcus: Streptococcus pyogenes
Glomerulonephritis
- Antibodies bound to antigens of Group A Streptococcus are not removed from circulation and instead accumulate in the glomeruli (small blood vessels) of the kidneys’ nephrons (filtering units)
- Puffy face due to retention of fluid by damaged kidney, tea colored urine due to hematuria
- Autoimmune disorder
- Group A Streptococcus: Streptococcus pyogenes
Identify the conditions under which group A Streptococcus causes disease.
- Often causes diseases when normal competing microbiota are depleted
- When adaptive immunity is impaired
- Streptococcus is not a normal member of the microbiota of the skin Gram-positive bacteria in short chains or pairs in cutaneous specimens, can provide preliminary diagnosis of: pyoderma, erysipelas, and necrotizing fasciitis
- Streptococci are normally in pharynx so a rapid strep test is used to identify the presence of group A streptococcal antigens
What is a rapid strep test used to identify
The presence of Group A: Streptococcus pyogenes
Discuss the epidemiology, diagnosis, treatment, and prevention of infections with Streptococcus agalactiae
- often infects newborns and immunocompromised patients
- ELISA test used to diagnosis
- Penicillin G or ampicillin
- Vaccination for women to protect future children
Epidemiology of Streptococcus agalactiae
- Often infects newborns without specific antibodies
- Older immunocompromised patients also at risk
Diagnosis of Streptococcus agalactiae
- ELISA test used to identify group B streptococcus, utilizing antibodies directed against the bacteria’s distinctive cell wall polysaccharides
Treatment of Streptococcus agalactiae
- Penicillin G is the drug of choice, or ampicillin
Prevention of Streptococcus agalactiae
- Immunization of women can protect future children
Identify the normal sites of viridans streptococci in the human body
- Mouth
- Pharynx
- GI tract
- Genital tract
- Urinary tract
But are opportunistic
List three serious diseases Viridan Streptococci cause.
- Dental caries
- Meningitis
- Endocarditis
Describe how the structure of Streptococcus pneumoniae affects its pathogenicity
- Gram-positive cocci the mostly form pairs
- Unpigmented, alpha-hemolytic colonies on blood agar
- Polysaccharide capsule (required for virulence)
- Phosphorylcholine in cell wall
- Secretory IgA protease
- Pneumolysin
Streptococcus pneumoniae: Phosphorylcholine
- Stimulates cells to phagocytize the bacteria
Streptococcus pneumoniae: Secretory IgA protease
- Destroys IgA
Streptococcus pneumoniae: Pneumolysin
- Binds to cholesterol in the cytoplasmic membranes of epithelial cells, producing pores that result in lysis of cells
Streptococcus pneumococcal disease: Pneumococcal pneumonia
- Bacteria multiply in the alveoli, damaging the alveolar lining , allowing fluid, RBCs and leukocytes to enter the lungs
Streptococcus pneumococcal disease: Sinusitis and Otitis Media
- Bacteria can invade sinuses and middle ear causing pus and inflammation
Streptococcus pneumococcal disease: Bacteremia and Endocarditis
- Colonize in blood and heart
- Both in Staph and Strep
Streptococcus pneumococcal disease: Pneumococcal meningitis
- Can spread to the meninges
Diagnosis of Streptococcus pneumococcus
- Gram of sputum smears, positive
- Confirmed with Quellung reaction - Anti-capsular antibodies cause the capsule to swell
Quellung reaction
- Used to identify pneumococci, in which anti capsular antibodies cause the capsule to swell
Treatment of Streptococcus pneumoniae
- Penicillin
Prevention of Streptococcus pneumoniae
- Vaccine made from purified capsular material
