Pathogenic Gram-Positive Bacteria Flashcards
Examples of Cocci and their morphology
Staphylococcus (in bunches), Streptococcus, (straight chain) and Enterococcus
Examples Bacilli
BLANCC
Bacillus,
Clostridium,
Listeria, Corynebacterium,
Nocardia,
Actinomyces
STAPHYLOCOCCI CLASSIFICATION
Family
Genus
Species (how many in total)
Family: Micrococcaceae
Genus: Micrococcus and Staphylococcus
Species:
S. aureus
S. saprophyticus
S. epidermidis
M. luteus
Over 33 species
General Characteristics STAPHYLOCOCCI
- Gram-positive cocci
- Non-motile
- Non–spore-forming
- Catalase-producing (catalase +ve)
- Facultative anaerobes
- Salt-tolerant
- Desiccation resistant
(survives in environt & on fomites) - ≈ 33 species
- 14-17 species associated with man
- Several veterinary pathogens
- Many non-pathogenic
Coagulase-Positive Staphylococci
Human Pathogen:
S. aureus
Animal-associated species:
S. intermedius
S. hyicus
S. delphini
S. schleiferi
Coagulase-Negative Staphylococci
S. epidermidis
S. saprophyticus
S. haemolyticus
What is the Habitat, Source, Staphytoccus aureus?
What type of infections does it produce?
What’s the mode of transmission?
What are the sources of the organism?
Skin, anterior nares (carriers): part of normal flora in humans and animals
Type of Infections: Produce Superficial- Deep, Local - Systemic infections
Mode of transmission: traumatic introduction
Source of organism:
self
infected human host
carrier
fomite or environment
Pathogenicity staphylococci
- Entry of only a few hundred bacteria can result in disease
- Pathogenicity results from 3 features:
Structures that enable it to evade phagocytosis
Production of enzymes
Production of toxins
What predisposing factors to S. aureus infections?
- Injuries: Breach in skin
- Immune response defects:
Chemotaxis defects
Opsonisation defects
Neutrophil functional defects - Diabetes mellitus
- Presence of foreign bodies
- Chronic infections
- Indwelling devices
Pathogenic Attributes of S. aureus: Structural Elements
What are the structural elements that contribute to the pathogenic attributes of S. aureus?
- Protein A coats the cell surface
Interferes with humoral immune responses by binding to class G antibodies
Inhibits the complement cascade - Clumping Factor (Bound coagulase)
Converts the soluble blood protein fibrinogen in insoluble fibrin molecules that form blood clots
Fibrin clots hide the bacteria from phagocytic cells
- Synthesize loosely organized polysaccharide slime layers (often called capsules)
Inhibit chemotaxis of and phagocytosis by leukocytes
Facilitates attachment of Staphylococcus to artificial surfaces
Pathogenic Attributes of S. aureus: Enzymes Synthesis
- Coagulase
Triggers blood clotting - Hyaluronidase
Breaks down hyaluronic acid, enabling the bacteria to spread between cells - Staphylokinase
Dissolves fibrin threads in blood clots, allowing Staphylococcus aureus to free itself from clots - Lipases
Digest lipids, allowing staphylococcus to grow on the skin’s surface and in cutaneous oil glands - Beta-lactamase
Breaks down penicillin
Allows the bacteria to survive treatment with Beta-lactam antimicrobial drugs
Pathogenic Attributes of S. aureus: Toxins
Staphylococcus aureus produces toxins more frequently than S.epidermidis
- Cytolytic toxins
Disrupts the cytoplasmic membrane of a variety of cells
Leukocidin (Panton-Valentine): kill PMNs
Heamolysin
Alpha: platelets/WBCs/tissue
Beta (hot/cold): sphingomyelin of RBCs
Gamma: host cell membranes
Delta: less lethal - Exfoliative toxins
Causes the patient’s skin cells to separate from each other and slough off the body (desquamation of skin)
Epidermolytic toxin
Phage group II staphylococci - Toxic-shock-syndrome toxin
Causes toxic shock syndrome
Multisystem disease
High fever
Hypotension
Shock - Enterotoxins
Stimulate the intestinal muscle contractions (abdominal pain), nausea, and intense vomiting associated with staphylococcal food poisoning (non-invasive). Pathogenicity is enterotoxins
Classification of Staphylococcal Diseases
- Localized or Systemic
- Invasive or Non-invasive
- Superficial or Deep
What are the most common Non invasive, Localized/Cutaneous and systemic Disease
Non invasive: Mediated mainly by toxin elaboration
Food poisoning from the ingestion of enterotoxin-contaminated food
Localized/Cutaneous:
Various skin conditions
scalded skin syndrome, extensive vesicular eruption of the skin
Impetigo (skin lesion with blisters that break and become covered with crusting exudate)
Styes infection of the follicle of eye lashes
Furuncles or folliculitis (infection of one hair follicle)
Carbancles (infection of several hair follicles)
Boils
Wound infections(progressive appearance of swelling and pain in a wound , (surgical wound infection seen after about 2 days from the surgery)
Systemic Disease”
Toxic shock syndrome-TSS toxin is absorbed into the blood and causes shock
Bacteremia-presence of bacteria in the blood
Endocarditis-occurs when bacteria attack the lining of the heart
Pneumonia-inflammation of the lungs in which the alveoli and bronchioles become filled with fluid
Osteomyelitis-inflammation of the bone marrow and the surrounding bone
Example of a difficult to treat systemic disease
Endocarditis-occurs when bacteria attack the lining of the heart causing inflammation
What are DEEP ABSCESSES?
Can be single or multiple
Breast abscess can occur in 1-3% of nursing mothers in puerperiem
Can produce mild to severe disease
Other sites - kidney, brain from septic foci in blood
What are the steps in dianosing a bacterial infection?
Specimen
Smear
Culture
Biochemical Reactions
Antibiogram
Typing
What would you expect to see in a Laboratory Diagnosis: Direct Smear Examination of S.aureus?
Microscopic Examination:
Gram-positive cocci
pairs and clusters
Numerous polymorphonuclear cells (PMNs)
On a micrograph:
Gram +ve cocci in bunches
What Cultural Characteristics would you expect to see in a Laboratory Diagnosis?
Colony morphology:
Smooth, butyrous, white to yellow, creamy
S. aureus may produce hemolysis on blood agar
Discuss the Catalase Identification Tests
What is the reagent?
- Reagent is H2O2
- Principle: tests for enzyme catalase
2 H2O2 ——> 2 H2O + O2
*Drop H2O2 onto smear
Bubbling = POS (Most bacteria, O2 generated)
No bubbling = NEG (Streptococci and other lactic acid bacteria, no O2 generated)
Discuss the Coagulase Identification Tests
What is the reagent
What are the 2 methods
reagent: citrated plasma
Detects enzyme coagulase
Cell-bound “clumping factor”
Extracellular enzyme “free coagulase”
Two methods
Slide test
Tube test: Tube test detects the extracellular enzyme “free coagulase”
What is the Novobiocin Susceptibility Test?
Test to differentiate coagulase-negative staphylococci from S.saprophyticus from urine samples
S. saprophyticus is resistant (top)
Other CNS are susceptible
Treatment
- Drain infected area
- Deep/metastatic infections
semi-synthetic penicllins
cephalosporins
erythromycin
clindamycin - Endocarditis
semi-synthetic penicillin + an aminoglycoside
Treatment & Antimicrobial Susceptibility
Treatment
Methicillin is the drug of choice to treat staphylococcal infections
For non–beta-lactamase producing S. aureus (methicillin-susceptible)
Penicillinase-resistant synthetic penicillins (methicillin, nafcillin, oxacillin, dicloxacillin)
For methicillin -resistant S. aureus (MRSA) and methicillin-resistant S. epidermidis (MRSE)
Vancomycin combined with rifampin or gentamicin
Emergence of vancomycin resistance
Prevention
Carrier status prevents complete control
Proper hygiene, segregation of carrier from highly susceptible individuals
Good aseptic techniques when handling surgical instruments
Control of nosocomial infections
Hand antisepsis is the most important measure in preventing nosocomial infections
Also important is the proper cleansing of wounds and surgical openings, aseptic use of catheters or indwelling needles, an appropriate use of antiseptics
