Gram + Bacteria (Cocci): Staphylococcus & Streptococcus

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Gram + Cocci:
Staphylococcus & Streptococcus
Nestor T. Hilvano, M.D., M.P.H.
Learning Objectives
1. Contrast Staphylococcus aureus with Staphylococcus epidermis in
terms of virulence in humans.
2. Discuss the structural and enzymatic features and toxins of
Staphylococcus that allow it to evade the body's defenses.
3. Describe cutaneous lesions and systemic diseases caused by
Staphylococcus aureus.
4. Discuss briefly staphylococcal resistance to antimicrobial drugs
5. Describe two structures in Streptococcus pyogenes that allow this
organisms to survive against the human defense mechanisms.
6. Identify the conditions under which Group A streptococci cause disease.
7. Discuss the epidemiology, diagnosis, treatment, and prevention of
Group B (Streptococcus agalactiae ) infections.
8. Identify the normal location of viridans streptococci in the human body
and describe three serious diseases they cause.
9. Describe how the structure of Streptococcus pneumoniae affects its
pathogenicity.
10.Discuss the diagnosis, treatment, and prevention of pneumococcal
diseases.
11.Describe Enterococcus as to pathogenicity and the diagnosis, treatment,
and prevention of their diseases.
Staphylococcus
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Gram + in _____, facultative anaerobic
yellow in culture
Catalase positive
SEM- grapelike
S. aureus – virulent; coagulase +;1/3 pop. are
colonized (no illness) & common source of germs
to others
• S. epidermidis – normal flora of human skin;
opportunistic pathogens
Pathogenicity of Staphylococcus
• Protein A – binds with IgG
• Bound coagulase – forms
clot that hide bacteria from phagocytes
• Polysaccharide slime layers – facilitate
attachment to surfaces (catheters, shunts,
artificial heart valves)
• Enzymes – leukocidin, hyaluronidase,
staphylokinase, lipase, and beta-lactamase
• Toxins – exfoliative toxins, TSS toxins, and
enterotoxins
Epidemiology of Staph Infection
• Found in human skin
• Transmitted through
- direct contact and via fomites
• 20% - 40% adults are carriers
• Prevention
- proper hand washing, aseptic
techniques, proper cleaning of wound,
use of antiseptics
Staph. Cutaneous Diseases
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Folliculitis – infection of hair follicles; pus-filled vesicles
Furuncle – commonly called _____; localized superficial
Carbuncle – extends deeper
Rx: antibiotics; drainage (I & D)
What is the most common causative agent of boil?
Staph. Cutaneous Diseases
• Scalded skin syndrome – red skin; blisters;
slough off within 2 days; caused by
exfoliative toxin
• Impetigo – mostly in young children; red
patches; pus-filled vesicles that crust; 80%
caused by S. aureus
• Wound infections – surgical infection by
contaminated personnel, equipment
Staphylococcus Food Poisoning
• Caused by enterotoxin-contaminated food
(salad, processed meat, ice cream, pastries)
• Food remain at room temp. or warmer for
several hours
* Does reheating of (inoculated) food inactivate
enterotoxins? Why?
a) toxins are heat labile
b) toxins are heat stable
• Symptoms appear within four hours after
ingestion; self limiting; usually resolved about 24
hours (consumed staph do not continue to produce toxins)
Staph. Systemic Diseases
• Toxic Shock Syndrome
- first described in 1978
- 1980 = 299 cases, 25 deaths, caused by
tampons (fever, rash, hypotension,
diarrhea, vomiting)
- TSS toxin in wound or abraded vagina
absorbed into blood; results to low BP/
inadequate O2 supply to vital organs
- Penicillin resistant
Staph. Systemic Diseases
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Bacteremia
Endocarditis
Meningitis
Pneumonia and Empyema (fluid with pus)
Osteomyelitis
Diagnosis and Treatment of Staph. Infection
• Dx: - identify S. aureus in gram stain, ______;
and coagulase _____.
• Only 5% susceptible to penicillin today;
methicillin drug of choice (semi-synthetic)
• MRSA – resistant to beta-lactam antibiotics
(penicillin, methicillin, and cephalosporins)
- nosocomial infections
- called “superbug”, discovered in UK (1961),
now found worldwide
- vancomycin used to Rx
Streptococcus
• Gram + cocci in ____ (a. chain b. clumps)
• Auxotrophs –requires complex media (Vit. B,
aa., purines + pyrimidines)
• Catalase negative
• Facultative anaerobe
Group A β-hemolytic Streptococcus
• Streptococcus pyogenes
• Pathogenicity
– protein M and Hyaluronic capsule (evades
phagocytosis)
- enzymes (streptokinase dissolves blood clot;
hyaluronidase facilitates spread of organisms)
- toxins (pyrogenic; pyogenic)
• White colonies sorrounded by zone of betahemolysis (clear zone)
• Infect the pharynx or skin
Group A Streptococcal Diseases
• Strep throat (pharyngitis) – spread via ___
(a. ingestion b. respiratory droplets).
• Scarlet fever – reaction to erythrogenic
toxin; fever of 101˚F (38.3˚C), strawberry
tongue, red rash (by capillary distensions)
within 24 hrs. and fades in a week followed
by peeling.
Group A Streptococcal Diseases
• Necrotizing fasciitis – flesh-eating strep (1994 England;
1998 Texas); enter thru breaks in skin; toxins destroy
muscle and fat tissues, toxemia, organ failure, > 50% die;
spread along fascia of muscle
• Post-streptococcal Glomerulonephritis –
autoimmune, anti-strep antibodies cross-react w/
antigens in glomerular b.m.; obstruct blood flow, HPN,
and low urine output; transplant
Rheumatic Fever
• Autoimmune; cardiac valve diseases
• Major criteria include: carditis; polyarthritis;
chorea; subcutaneous nodules (small, painless
bumps); rash (a red, irregular rash on the trunk)
• Minor criteria include: fever; arthralgia; previous
rheumatic carditis; changes in the ECG pattern;
abnormal sedimentation rate or C-reactive
protein (laboratory tests performed on blood)
• Diagnosis - made when two of the major criteria,
or one major criterion plus two minor criteria, are
present along with evidence of a strep infection.
Diagnosis and Rx of Streptococcal
Infection
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Identify organisms in skin
Identify Group A strep Antigens
Penicillin; susceptible to topical bacitracin
Erythromycin or cephalosporin –
penicillin-sensitive patients
Group B Strep: Strep. agalactiae
• Gram + cocci, in chains, beta-hemolytic
• 25% in normal vaginal flora of women; can
cause UTI and endometritis in women
• Cause neonatal disease (bacteremia,
meningitis, pneumonia) through birth canal
or health care workers
• Dx – ELISA and agglutination tests
• Pen G drug of choice
Alpha-Hemolytic Strep. viridans
• Produce a green pigment (incomplete)
• Inhabit the mouth, pharynx, GIT, urinary, and
genital tracts
• Opportunists; one cause of dental caries;
subacute endocarditis with vegetative
growths on valves
• Susceptible to penicillin
Streptococcus pneumoniae
• Gram + cocci in short chain, commonly in pairs
(lancet-shaped diplococci)
• Polysaccharide capsules and phosphorylcholine in
cell walls confer virulence.
• Pharyngeal microbiota
• Can colonize lungs, sinuses, and middle ear
• 85% of cases of pneumonia
• Dx: Gram stain of sputum, quellung reaction
(anticapsular antibodies caused swelling of
capsules), optochin test (differentiate S. pneumonia
from other alpha-hemolytic strep, inhibition around
the disc) agglutination test
Enterococcus
• under Group D Strep
• unencapsulated; prod. gas on sugar
fermentation; nonhemolytic
• Harbor normally in intestinal tracts of human and
animals
• E. faecalis and E. faecium – can be pathogenic
in human; secrete bacteriocins (proteinaceous
toxins produced by bacteria to inhibit growth of
other bacteria)
• Serious disease to urinary tract and bloodstream
• Dx. – not sensitive to bile, lack capsule= which
distinquishes from S.pneumoniae
• Prev. – good hygiene and aseptic technique
Homework
1.
2.
3.
4.
5.
Define terms – pyrogenic, pyogenic, furuncle, carbuncle, folliculitis,
bacteriocins, nosocomial infection, optochin test, and Quellung
reaction.
Differentiate staphylococcus and streptococcus as to morphology in
gram stain (+/-, clusters/chain) and reaction to catalase test (+/-).
Identify microbes: a) gram + cocci, coagulase +; b) gram + cocci,
group A beta hemolytic; c) gram + cocci, alpha hemolytic; d) gram +
cocci lancet-shaped
Discuss staphylococcal toxic shock syndrome.
Identify the most common causative bacteria of :
__scalded skin syndrome
__sore throat (pharyngitis)
__lung infection
__commonly isolated in GIT
__ dental caries opportunist
a. streptococcus viridans
b. enterococcus faecalis
c. staphylococcus aureus
d. streptococcus pneumonia
e. streptococcus pyogenes

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