3.10 Flashcards
Typical Bacteria
• Gram stain differentiation
§ Reflects a fundamental differentiation based on
permeability, presence or absence of outer membrane
and cell wall thickness
• Cellular morphology
§ 4 typical cell types
v Gram (+) rods v Gram (+) cocci v Gram (-) rods v Gram (-) cocci
• Gram positive rods have more in common with
(1) than with gram negative rods
gram positive cocci
Ø Gram positive cocci (2)
- Staphylococci
* Streptococci
• Staphylococci (3)
types (3)
found in?
§ S. aureus; S. saprophyticus; S. epidermidis
§ Found in many body sites; primarily skin infections &
wounds; carbuncles; abscesses; leading to life
threatening deep tissue infections: osteomyelitis,
endocarditis
§ Severe intoxications; Food poisoning
Streptococci (4)
§ Alpha or beta hemolysis v Alpha: S. pneumoniae v Beta: Groups A-T; Group A most prevalent in human disease § Oxygen-tolerant anaerobes
Gram negative cocci (2)
- Neisseria meningitidis
* Neisseria gonorrhea
Gram positive rods (2)
- Non-Spore-forming aerobic rods
* Spore-forming rods
Non-Spore-forming aerobic rods
§ Corynebacterium diphtheriae and related diphtheroids
Spore-forming rods (3)
§ Aerobic: Bacillus anthracis (anthrax)
§ Anaerobic: Clostridium species
v C. botulinum; C. tetani; C. perfringens; C. difficile
Ø Gram negative rods
• Enteric bacteria (3)
§ Enterobacteriaceae (facultative anaerobes)
v Escherichia coli; Salmonella spp.; Shigella spp.;
Yersinia spp. (pestis; pseudotuberculosis)
§ Vibrio cholerae; Campylobacter jejuni; Helicobacter pylori
Significant non-enteric Gm- rods: (5)
§ Pseudomonas aeruginosa § Haemophilus influenzae § Bordetella pertussis § Brucella abortus § Legionella pneumophila
Gram negative rods (contin.)
• Strictly anaerobic Gm- rods
§ Bacteroides fragilis (4)
ü Most common organism in the human intestine.
ü Can cause serious disease when deposited into deep tissues.
(abscesses)
ü Can be also be found in gingival pockets
ü Very stinky
Acid-fast bacteria
• Mycobacterium tuberculosis; M. leprae
Spirochetes (4)
- Treponema pallidum (syphilis)
- Leptospira spp. (hemorrhagic fever)
- Borrelia recurrentis (relapsing fever)
- Borrelia burgdorferi (Lyme disease)
Strictly intracellular bacteria (5)
- Chlamydia trachomatis (most common STD)
- Chlamydia pneumoniae
- Rickettsiae (Rocky mountain spotted fever)
- Ehrlichia (arthropod borne)
- Coxiella burnetti (Q fever)
staphyle =
cluster of grapes
coccus =
sphere
aureus =
golden colonies
Staphylococcus
Characteristics: (3)
Gram+ cocci, catalase+
o2?
staphylococcus aureus
O2 can be used (faculative anaerobe)
Ø catalase
Reduces the potential of phagocytes to kill
Ø coagulase (2)
The tissue-invasive potential of staphylococcal infections is directly
proportional to coagulase production (S.aureus; not in other Staph. species).
• coagulase binds prothrombin: fibrinogen is cleaved anti-phagocytic fibrin coating
clumping factor
fibrinogen-binding protein: cell surface proteins that bind to foreign
materials (like sutures) and to extracellular matrix.
Ø protein A
Anti-phagocytic, competes with neutrophils for Fc portion of opsonizing IgGs
(on cell surface of S.aureus but not on other staphylococcal strains)
Ø leukocidin
secretion: inhibits phagocytosis by granulocytes by forming pores in
phagosomal membranes, and kills phagocytes. Major factor in pus formation.
digestive enzymes
digestive enzymes proteases, DNase, nuclease, lipases
hyaluronidase (spreading factor: digests extracellular matrix)
staphylokinase
converts plasminogen to plasmin, increasing invasion by digesting
fibrin clots and cleaves C3b and IgG to inhibit phagocytosis
β-lactamase
Enzymatic digestion of penicillins (90% strains have plasmid-based antibiotic resistance)
α-, β-, γ-, and δ-toxins are all
hemolysins: lyse erythrocytes (lab phenomenon)
§ α-hemolysins (pores) are (4)
hemolytic, leukocytic, destroy skin, cause smooth muscle paralysis
§ β-hemolysins are cytolytic sphingomyelinases that destroy —
nerves
§ γ-hemolysins lyse like related — on neutrophil lysosomal membranes
leukocidin
Empyema:
Empyema: Collection of pus in a naturallyexisting anatomical cavity (e.g. lungs)
pyogenic infections:
pus-forming (massive amounts of neutrophils and other leukocytes are
lysed by bacterial factors (e.g. leukocidin) and release their lysosomal
contents in attempting phagocytic killing of the staphylococci).
Invasive pus-forming infections (4)
FOLLICULITIES
FURNUNCLES
CARBUNCLES
(SYSTEMIC) BACTEMIA FEVER
superangtigens- overrides the
specificity of the t cell response
Ø enterotoxins Heat-stable (cooking doesnt help!) toxins A, B, C1, C3, D, E are super-Aglike: cause of
gastrointestinal upset typical of food poisoning
(Vomiting may be induced by inflammatory reaction of subepithelial macrophages to
toxins with a resulting change in vascular permeability)
Toxic Shock Syndrome Toxin TSST:
mass activation of T cells leads to large
production of inflammatory cytokines (heat and protease-resistant TSST-1; chromosomal gene)
exfoliative toxin
{heat-stable, chromosomal), B (heat-labile, plasmid) : SSSS
staphylococcal scalded-skin syndrome
TSS: Toxic Shock Syndrome
Increased oxygenation of vagina by tampons, and
foreign surface adhesion, caused massive growth
SSSS: Staphylococcal Scalded Skin Syndrome
Ø exfoliative toxins A, B cause loss of layers of the skin in SSSS
Nester 04 Fig. Murray05 Fig.22-5
Neutralizing A
Nosocomial Staphylococci a
surgery, implant & instrument risk
Nosocomial (hospital instruments and
implants) infections
(often coagulase-negative S.epidermidis)
Endocarditis:
• acute: —% S.aureus
• if artificial heart valves: —% S.epidermidi
60
80
S.epidermidis:
dental extraction risk
most frequent causes of bacterial arthritis by age oeganism: staphylococcus aureus neonates 2 mo-2 ye 30-10 yr adult
10-125%
25-50%
25-50%
25-75%
Gram+ cocci, aerobic / facultatively anaerobic
coagulase+ catalase+
Epidemiology (4)
skin + mucosa +aerosols surface survival (hospital instruments, implants) nosocomial (hospitalacquired) high temperature (40ºC) and salt resistant
β-lactamase (plasmid): >—% penicillin resistant
90
penicillin-binding protein 2a (chromosomal): causes — Resistance
Methicillin
–% of hospital strains are MRSA; –% of community strains are MRSA
What can you do in case of (Enterococcus-derived) VRSA ? nothing
50
20
Coagulase─ : Other Staphylococci like S.epidermidis or S.saprophyticus (2)
- Thick cell wall, slime capsule, (S.saprophyticus: urease secretion → acute cystitis
- Opportunistic hospital pathogens (instruments, catheters, heart valves)
