Download Pathogenic Gram-Positive Bacteria Coccus: Staphylococcus

Pathogenic Gram-Positive Bacteria
Coccus:
 Staphylococcus
 Streptococcus
Bacillus:
 Bacillus
 Clostridium
 Corynebacterium
 Listeria
 Mycobacterium
Staphylococcus
1) Characteristics
a) Facultative anaerobes; Nonmotile; irregular clusters
b) Grows best aerobically
c) Found in soil, water, and skin of humans
d) Catalase-positive (Streptococcus are catalase-negative)
e) Three clinically important species:
i) S. aureus – most virulent (coagulase positive)
ii) S. epidermidis – agent of opportunistic infections associated with indwelling
equipment (catheters, prosthetics)
iii) S. saprophyticus – agent of UTI
2) Epidemiology
a) Transmission
i) Coagulase positive: autoinfection (carrier), direct contact (person with lesion),
contaminated food or fomite (survive long periods of drying)
ii) Coagulase negative: autoinfection (infections associated with implanted catheters
and prosthetic devices), UTI
3) Pathogenesis and Virulence Factors
a) Adhesions
i) Teichoic acid
ii) MSCRAMMs
b) Protein A
c) Pyrogenic exotoxins
i) Enterotoxins (multiple types)
(1) Heat stable, superantigens resistant to gut enzymes
ii) Toxic Shock Syndrome Toxin (TSST-1)
(1) Superantigen  toxic shock syndrome, directly cytotoxic
d) Membrane damaging toxins
i) Beta-, Delta-, Gamma-Hemolysins
(1) Beta-hemolysin – degrades sphingomyelin lysing numerous cells
(2) Delta-hemolysin – dissociates into subunits to disrupt cell membranes
(3) Gamma-hemolysin – combine with PV proteins that lyse WBC
ii) Leukocidins
(1) Two-component toxins which lyse WBC by forming pores
e) Exfoliation
i) A = heat stable; B = heat labile
ii) Dissolve epidermal mucopolysaccharide matrix (desquamation)
iii) Superantigen function
f) Enzymes
i) Coagulase
(1) Initiates fibrin polymerization on surface bacteria (protect from phagocytosis)
(2) Clumping factor permits binding to fibrinogen and fibrin
ii) Hyaluronidase/Staphylokinase
(1) Permits invasion of tissues and dissolves fibrin clots formed by coagulase
4) Diagnosis
a) Culture
i) Pus/surface swab, blood, sputum specimen inoculation onto Mannitol Salt agar
(MSA)  successful growth, Gram stain, catalase test, coagulase test
(1) MSA contains 7.5% NaCl which inhibits growth of other normal flora
(2) Catalase differentiates from Streptococcus
(3) Coagulase differentiates more virulent S. aureus from other species
(4) Microdilution/disk diffusion susceptibility tests should be done
Staphylococcus aureus
Clinical Findings
i) Furuncle (boils) & Carbuncle
(1) Infected patient is often a carrier (anterior nares)
(2) Lesions of a hair follicle, sebaceous gland or sweat gland
(3) Resolves upon spontaneous drainage of pus
(4) Multiple boils form a carbuncle which can spread to the blood
ii) Impetigo
(1) Production of exfoliative toxins produce large blisters in superficial skin
(2) Often affects young children (face and limbs)
(3) Macule that develops into pustules (rupture and crust)
(4) Can occur as wound infection following surgery
iii) Scalded Skin Syndrome (SSS)
(1) AKA Ritters Disease
(2) Production of exfoliative toxins that cause erythema (redness of skin) and
epidermal desquamation at remote sites from staphylococcal infection
(3) Face, axilla groin affected first then all parts of the body possible
(4) Most common in neonates and children <5y
Clinical Findings – Primary Infections
i) Toxic Shock Syndrome
(1) High fever, vomiting, diarrhea, sore throat, and myalgia
(2) ~48h can progress to shock with evidence of renal and hepatic damage
(3) Rash may develop followed by desquamation at a deeper level than SSS
(4) Originally associated with tampon use  growth of bacteria on tampon and
release of TSST-1 into blood
(5) TSS-Staphylococcus found in vagina, on tampons, in wounds, localized infections,
or throat (never the blood)
ii) Staphylococcal Food Poisoning
(1) Incubation 1-6h
(2) Ingestion of enterotoxin-contaminated food
(3) Nausea, vomiting, and diarrhea (no fever)
(4) Toxins are heat-stable so reheating food does not inactivate toxins (cannot taste
in food)
(5) Antibiotics are not useful
Methicillin-Resistant Staphylococcus aureus
i) MRSA
(1) <10% of S. aureus strains susceptible to Penicillin but many still susceptible to
penicillin-derivatives
(2) Nosocomial and community-acquired
(3) MRSA expressed a new resistance gene on a plasmid, mecA
(4) CA-MRSA genetic distinction resided in the production of new types of PV
leukocidins (more virulent)
(5) Treated with Vancomycin  vancomysin-resistant MRSA
(6) Development of such resistant strains appears to derive from resistance
generated in Enterococcus that is transmitted to Staphylococcus through
conjugation
Characteristic
S. aereus
S. epidermidis
S. saprophyticus
Color of
Colonies
Often yellow
White
White to pale grey
Hemolysis
Most isolates
A few isolates
Non-hemolytic
Coagulase
production
Yes
No
No
Mannitol
fermentation
Yes
No
Yes
Novobiocin
Sensitive
Sensitive
Resistant
Streptococcus
1) Characteristics
a) Facultative Anaerobes; Nonmotile
b) Blood agar is preferred because satisfies growth requirements and can differentiate
groups based upon hemolysis patterns
c) Catalase-negative (Staphylococcus catalase-positive)
d) Classification by Group-Specific Surface Carbohydrate:
i) Group A (S. pyogenes)
ii) Group B (S. agalactiae)
iii) Group C (S. dysgalactiae)
iv) Group D (S. bovis, Enterococcus)
v) Non-Groupable (S. pneumonia, Viridans)
e) Classification by Hemolysis Pattern:
i) Alpha (Group D and Non-groubable)
ii) Beta (Groups A, B, C, F, G)
iii) Non-hemolytic (Some Group D and Non-Groupable)
2) Epidemiology
a) Transmission
i) Direct contact, Fomites or Contaminated respiratory droplets (GAS), In utero or
during birth (GBS), direct contact with nasal secretions or contaminated respiratory
droplets (S. pneumonia or Pneumococcus)
3) Pathogenosis
a) M Protein/Lipoteichoic Acids/Protein F
i) Adherence to nasopharynx and skin epithelia
ii) M protein and C5a peptidase block phagocytosis and PMN recruitment, respectively
b) Streptodornase/Streptokinase
i) DNase and Fibrinolysin to break up Neutrophil Extracellular Traps (NET) which are
networks of granule protein (fibrin) and chromatin to capture pathogens so PMN
antimicrobials can kill microbes
c) Pyrogenic Exotoxin (Erythrogenic Toxin) A,B,C
i) Superantigens  toxic shock syndrome
ii) Pyrogenic Exotoxin A is produced by Streprtococcus carrying lysogenic phage
iii) Streptococcal TSS and Scarlet Fever
d) Diphosphopyridine Nucleotidase
i) Lyse WBC
e) Streptolysin O/Streptolysin S
i) O – anaerobic hemolysin that is rapidly inactivated in the presence of oxygen
ii) S – aerobic hemolysin, induced upon bacteria to exposure to serum
iii) Both damage tissue cells and lyse phagocytes
Streptococcus pyogenes (GAS)
Clinical Findings
i) Streptococcal Pharyngitis (strep throat)
(1) Sore throat, fever, headache (tonsil, soft palate, uvula -> red, swollen, covered
with yellow exudate)… 1 wk duration
ii) Impetigo
(1) Small vesicle surrounded by erythema on face or lower extremities. Enlarges
over a few days, develops into pustule, breaks to form crusted lesion
iii) Erysipelas
(1) Spreading area of erythema/edema (face), pain, fever, lymphadenopathy
(2) Previous history of strep throat
iv) Streptococcal TSS
(1) Involves any site of GAS infection
(2) Myalgia, chills, severe pain at infected site
(3) Necrotizing fasciitis and myonecrosis, nausea/vomiting, diarrhea, hypotension,
shock, organ failure
v) Scarlet Fever
(1) Buccal mucosa, temples, cheeks are deep red
(2) Tongue covered with yellow-white exudate and red papilla  strawberry tongue
(3) “Sandpaper” rash on d2 (chest  extremities)
vi) Acute Rheumatic Fever (ARF)/Acute Glomerulonephritis (AGN)
(1) (ARF) fever, carditis, chorea (involuntary movement disorder), arthritis 3 weeks
following strep throat
(a) recurrent attacks of S. pyogenes can result in damage to heart
(2) (AGN) 3-6 weeks after strep throat or skin infection – lesions of glomeruli
Diagnosis
i) Ag detection  rapid detection kit for Group A Carbohydrate
ii) Culture  blood agar (beta hemolysis)
(1) Also test susceptibility to Bacitracin (GAS susceptible while others are not)
Streptococcus agalactiae (GBS)
Characteristics
i) Leading cause of sepsis and meningitis in the first few days of life
ii) Normal resident of the GI tract, can spread to vagina
iii) GBS can gain access to amniotic fluid/colonize as newborn passes through birth
canal
iv) GBS capsule binds serum Factor H (binds to host cell glycosaminoglycans or GAG and
degrades C3b) to prevent alternative pathway of complement activation
v) Onset is first few days of life  presents as respiratory distress, fever, lethargy,
irritability, hypotension, pneumonia (common) and meningitis
vi) Diagnosis by detection of group B Ag in blood and culture on Blood agar
Streptococcus pneumonia
Virulence Factors and Pathogenesis
i) Choline Binding Protein
(1) Binds phosphocholines of bacterial cell wall with carbohydrates of nasopharynx
epithelia
ii) Capsule
(1) Prevents C3b deposition on bacterial cell surface
(2) Blocks phagocytosis
iii) Pneumolysin
(1) Produced but not secreted
(2) Production of peroxides during growth induces autolysins
(3) Pneumolysin is released:
(a) Directly cytotoxic to endothelial cells (dissemination into bloodstream)
(b) Impairs ciliary action (paralyzed)
(c) Directly suppresses phagocytic activity
(d) Suppresses local inflammatory immune response (incr. anti-inflamm
cytokines)
(e) Triggers platelet activation (DIC can occur from concurrent vascular leakage
due to endothelial damage in lungs)
Pathogenesis
i) Impaired host defense  lungs  replication (toxin release) in alveolus  toxin
causes disease symptoms (DIC can result)
Clinical Findings
ii) Infections most common in young and old
iii) Pneumococcal pneumonia
(1) Leading cause of pneumonia in world
(2) Shaking chills, high fever, cough (tinged with blood), chest pain
iv) Pneumococcal Meningitis
(1) One of the 3 leading causes of bacterial meningitis (N. meningitides, H. influenza)
(2) Headache, still neck, fever, photo irritability
v) Other infections
(1) Otitis Media – most frequent cause, millions of cases each year
(2) Sinusitis
(3) Bacteremia
Diagnosis
i) Gram positive diplococcic
ii) Inoculation onto blood agar  susceptibility to Optochin (others are not)
Prevention and Treatment
i) Pneumococcal Conjugate Vaccine (PCV13)
(1) 4 doses (2,3,6,12-15 mo)
ii) Pneumococcal Polysaccharide Vaccine (PPSV23)
Characteristic
Group A
Streptococcus
Group B
Viridans
Streptococcus
Enterococci
Streptococcus
Hemolysis in
agar
b
b
a
a, o, r, g
Growth in 6.5%
NaCl
-
-
-
+
Bacitracin
sensitivity
+
-
-
-
Bile solubility
-
-
-
-
Optochin
sensitivity
-
-
-
-
Bacillus anthracis
Characteristics
1) Aerobic or facultative anaerobes; nonmotile; spore-forming
2) All other species are low-virulence saprophytes found in air, soil, water
3) Protein capsule
Epidemiology
1) Anthrax = ideal biowarfare agent since B. anthracis have long-life, stability, and require few
spores to produce infections
2) Transmission – direct contact with spores (through skin), ingestion of spores (rare) or
inhalation of spores
3) B. cereus and B. subtilis – infections of eye, soft tissues and lung associated with
immunosuppression, trauma, indwelling catheters or contaminated medical equipment
4) B. cereus can also produce an enterotoxin (incr cAMP) and cause diarrhea
Virulence Factors and Pathogenesis
1) Protein Capsule
a) Adherence to tissues
b) Effective blockade of phagocytic uptake
2) Anthrax toxin
a) Protective Antigen (PA)
i) Binds to ATR on host cell surface
ii) Host furin cleaves PA into monomer
b) Edema factor (EF)
i) EF functions as an adenylate cyclase to increase cAMP
c) Lethal factor (LF)
i) Protease that cleaves MAPKK proteins and induces TNF secretion  induces cell
death of macrophages and endothelial cells
Clinical Findings
1. Cutaneous Anthrax
a. 2-5d after spore exposure
b. Erythematous papule  vesicular lesion  ulcerative lesion  scab (black
eschar)
c. Accompanied by mild systemic symptoms
2. Pulmonary anthrax
a. 1-2d after spore exposure
b. Mild fever, nonproductive cough quickly progresses to respiratory distress and
cyanosis (alveoli are destroyed)
Diagnosis
1) Culture: blood agar  non-hemolytic growth, gram stain (gram-positive bacillus)
Prevention
2) Anthrax Vaccine Absorbed (AVA)
Corynebacterium diphtheria
Characteristics/Epidemiology/Pathogenesis
1. Facultative anaerobe; pleomorphic (club-shaped bacillus)
2. Colonize skin, respiratory tract, GI tract, and urogenital tract (can be asymptomatic
carriers)
3. Transmission: Contaminated respiratory droplets (remain viable for hours)
4. Diptheria Toxin (DTX)
a. Encoded by a lysogenic phage
b. B subunit serves as ligand for host receptor
c. A subunit inactivates elongation factor-2 (EF-2)
d. One DTX molecule can inactivate all EF-2 within the cell
e. Cells die following uptake of DTX
5. Bacteria  pharynx/larynx/tonsils  replication (toxin production) 
pseudomembrane where produces DTX
Clinical Findings
3) Diphtheria
a) Begins as an “exudative pharyngitis”
i) Sore throat, low-grade fever, malaise
b) Exudate on tonsils, pharynx, and larynx, evolves into a grayish “pseudomembrane”
(necrotic epithelia embedded in fibrin, RBC, and WBC  active bacteria)
c) Removal results in capillary damage and bleeding
d) Complications: breathing obstruction, cardiac arrhythmia, coma
Diagnosis
1) Culture: blood agar and Cystin-Tellurite agar
a) No hemolysis on blood agar and growth on tellurite agar
b) Tellurite inhibits growth of most URT microbes: tellurite is reduced by C. diphtheria
producing black colony coloration
c) PCR performed to confirm presence
Prevention and Treatment
1) DTaP vaccine
2) Antimicrobials and Diphtheria Antitoxin
Listeria monocytogenes
Characteristics/Epidemiology/Pathogenesis
1) Facultative anaerobe; motile; pyschrophile (growth at 4 degrees C)
2) Found in intestinal tracts of many animals
3) Transmission: contaminated food (unpasteurized milk, cheeses, contaminated ice cream,
raw vegetables, raw meat, cold cuts) or congenital to newborn (during labor/delivery)
4) Internalin
a) Adherence to enterocytes, M cells, phagocytes, hepatocytes, fibroblasts
b) Induces uptake by cells (endosome or phagosome)
c) Actin reorganization to move into other cells acquiring a double membrane vacuole
5) Listeriolysin O
a) Degrades endosome/phagosome/vacuole membranes to escape into cytosol and avoid
lysosomal fusion
6) Bacterial infection proceeds in enterocytes with potential spread to CNS
Clinical Findings
1) Listeriosis
a) Nausea, abdominal pain, watery diarrhea, fever (self-limiting)
b) Bacteria may disseminate to other sites – sepsis
c) Tropism for CNS – meningitis
d) Fecal contamination at birth can transmit Listeria to newborn
Diagnosis
1) Culture: Mueller-Hinton agar with added sheep RBC  gram stain, catalase test (positive),
evident small zone of hemolysis
2) Can also inoculate PALCAM agar with food source