Chapter 19 - Pathogenic Gram-Positive Bacteria Flashcards
Gram-Positive Bacterial Pathogens
What are the two major groups based on DNA?
What are the characteristics within the two groups
(with examples)?
Two Major Groups:
- Low G + C Bacteria
- High G + C Bacteria
Characteristics:
Low G+C Bacteria:
a. Cocci (Staphylocoocus, Steptococcus, and Enterococcus)
b. Bacilli (Bacillus, Clostridium, and Listeria; Mycoplasms)
High G+C Bacteria
a. Rod-shaped (Corynebacterium, Mycobacterium, and Proprionibacterium)
b. Filamentous (Nocardia and Actinomyces)
Staphylococcus
(Outline)
Structure and Physiology
Pathogenicity
Epidemiology
Staphyloccal Diseases
Diagnosis, Treatment, Prevention
General Knowledge:
- Normal members of every human’s microbiota.
- Can be opportunistic pathogens
Staphylococcus: Structure and Physiology
Describe the characteristics.
Structure and Physiology
- Gram-positive cocci, nonmotile, facultatively anaerobic prokaryotes
- Cells occur in grapelike clusters
- Salt-tolerant (on human skin)
- Tolerant of dessication (survival on environmental surfaces)
- synthesizes catalase
Staphylococcus: Structure and Physiology
What are the two species commonly associated with Staphylococcus diseases?
-
Staphylococcus aureus
* More virulent and produces a variety of disease conditions depending on site of infection - Staphylococcus epidermidis
- Normal microbiota of human skin
- Opportunistic pathogen in immunocompromised patients or when introduced into the body via intravenous catheters or prosthetic devices sucha s articial heart valves.
Staphylococcus: Pathogenicity
What is Pathogenicity?
Three features in which results in the pathogenicity of Staphylococcus?
Pathogenicity
(The ability of a microorganism to cause disease)
Three Features:
- Structural Defenses against Phagocytosis
- Enzymes
- Toxins
Staphylococcus: Pathogenicity
What is involved in the structural defenses against phagocytosis?
Staphylococcus: Pathogenicity
- Protein A interferes with humoral immune responses by inhibiting opsonization. It also inhibits the completment cascade.
- Bound coagulase enzyme that converts fibrinogen (soluble blood protein) into fibrin (insoluble) molecules. Fibrin clots hide the bacteria from phagocytic cells. (Why?)
- Synthesize polysaccharide slime layers (capsules) These inhibit leukocyte chemotaxis and phagocytosis. Facilitate attachment of Staphylococcus
Staphylococcus: Pathogenicity
The Production of Enzymes: What are the enzymes that contribute to pathogenicity?
Describe them.
Staphylococcus: Pathogenicity
- Cell-free coagulase: triggers blood clotting
- Hyaluronidase: breaks down hyaluronic aid; enables bacteria to spread between cells
- Staphylokinase: dissolves fibrin threads in blood clots; allows S. aureus to free itself from blood clots
- Lipases: digest lipids; allows staphylococcus to grow on skin and in oil glands.
- B-lactamase (penicillinase): Breaks down penicillin. Does not inhibiting the natural defenses of the body. Allows bacteria to survive treatment with B-lactam antimicrobial drugs.
Staphylococcus: Pathogenicity
What do toxins contribute to pathogenicity?
Describe the contributions.
Staphylococcus: Pathogenicity
- S. aureus produces toxins more frequently than S. epidermis
1. Cytolytic toxins: Alpha, beta, gamma, delta and leukocidin
2. Exfoliative toxins: Causes skin cells to separate and slough off.
3. Toxic-shock syndrome toxin(TSS): Causes toxic shock syndrome.
4. Enterotoxins: Five proteins (A, B, C, D, E). Simulate symptoms associated with food poisoning. Are heat stable, active at 100oC for up to 30min.
Staphylococcal Diseases
What are three categories of Staphylococcual diseases?
Staphyloccal Diseases
- Noninvasive
- Cutaeous
- Systemic
Staphylococcus Diseases
Describe Noninvasive Diseases
Staphylococcus Diseases
- Food poisoning: due to ingestion of enterotoxin-contaminated food.
- Consumed bacteria do not continue to produce disease, lasts less than 24 hours.
- Symtoms include: nausea, severe vomiting, diarrhea, headache, sweating, and abdominal pain.
- Staphylcoccus aureus.
Staphylococcus Disease
Describe Cutaneous Diseases
e.g. Staphylococcal scalded skin syndrome, Impetigo, Folliculitis, Sty, Furuncle and carbuncle
Staphylococcus Disease
- Staphylococcal scalded skin syndrome (a reddening of the skin that begins near the mouth, spreads over entire body, followed by large blisters with clear fluid lacking bacteria or wbcs)
- Impetigo: small red patches on face and limbs (children whose immune systems are not fully developed) patches develop pus filled with bacteria and wbcs.
- Folliculitis: infection of a hair follicle. When the base of the follicle becomes red, swollen and pus filled. called sty at base of eyelid.
- Furuncle: boil is large, painful raised nodular extension of folliculitis into surrounding tissue.
- Carbuncle: several furuncles coalese. Extend deeper into the tissues, thrigger fever adn chills.
Staphylococcus Diseases
Describe Systemic Diseases
Staphylococcus Diseases
- cause a wide variety of potentially fatal systemic infections when they are introducted into deep tissues. (e.g. blood, heart, lungs, and bones
- Staphyloccoal Toxic shock syndrom: Occurs when TSS toxin is absorbed through the blood
- Characterized by fever, vomiting red rash, low BP loss of sheets of skin
Other Diseases:
- Bacteremia: presence of bacteria in blood
- Endocarditis: present in the lining of the heart
3. Pneumonia: an inflammation of lungs where alveoli and bronchioles become filled with fluid
- Osteomyelitits: bacteria invades the bones causing inflammation of bone marrow and surrounding bone.
Diagnosis, Treatment,
Streptococcus Diseases
What are the diseases associated with Group A Streptococcus?
Group A streptococcus
- Pharyngitis
- Scarlet Fever
- Pyoderma & Erysipelas
- Impetigo
- TSLS
- Necrotizing fasciitis
- Rheumatic fever
- Glomerulonephritis
Group A Streptococcus
What is Pharyngitis?
Group A streptococcus:
Pharyngitis (“strep throat”): inflammation of the pharynx
- accompanied by fever, malaise, and headache.
- Back appears red, with swollen lymph nodes and purulent abscesses covers the tonsils.
- Purulent (pus-containing) abscesseses covering the tonsils
