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PowerPoint Lecture Slides for
MICROBIOLOGY
Pathogenic Gram-PositiveCocci (Staphylococci)
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Stainpurple when gram-stained
Can be categorized into 2 major groups
Genera of cocci-shaped organisms- Staphylococcus,Streptococcus, andEnterococcus
Genera of bacilli-shaped organisms- Bacillus,Clostridium,Listeria, Corynebacterium,Mycobacterium,Propionibacterium,Nocardia, andActinomyces
Gram-Positive Pathogens
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Normal members of every humans microbiota
Can be opportunistic pathogens
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Gram-positive cocci, nonmotile, facultative
anaerobesCells occur in grapelike clusters because cells
division occurs along different planes and the daughtercells remain attached to one another
Salt-tolerant: allows them to tolerate the saltpresent on human skin
Tolerant of desiccation: allows survival on
environmental surfaces (fomites)
Structure and Physiology
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Two species are commonly associated with
staphylococcal diseases in humansStaphylococcus aureus-The more virulent strain thatcan produce a variety of conditions depending on thesite of infection
Staphylococcus epidermidis-Normal microbiota ofhuman skin that can cause opportunistic infections inimmunocompromised patients or when introduced intothe body
Structure and Physiology
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Staph infections result when staphylococci
breach the bodys physical barriersEntry of only a few hundred bacteria can result in
disease
Pathogenicity results from 3 featuresStructures that enable it to evade phagocytosis
Production of enzymes
Production of toxins
Pathogenicity
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1. Protein A coats the cell surface
Interferes with humoral immune responses bybinding to class G antibodies
Inhibits the complement cascade
2. Clumping Factor (Bound coagulase)Converts the soluble blood protein fibrinogen ininsoluble fibrin molecules that form blood clots
Fibrin clots hide the bacteria from phagocytic cells
Structural Defenses Against Phagocytosis
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3. Synthesize loosely organized polysaccharide slime
layers (often called capsules)Inhibit chemotaxis of and phagocytosis by leukocytes
Facilitates attachment of Staphylococcus to artificialsurfaces
Structural Defenses Against Phagocytosis
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1. Coagulase
Triggers blood clotting
2. Hyaluronidase
Breaks down hyaluronic acid, enabling the bacteria to
spread between cells
3. Staphylokinase
Dissolves fibrin threads in blood clots, allowing
Staphylococcus aureus to free itself from clots
Enzymes
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4. Lipases
Digest lipids, allowing staphylococcus to grow on theskins surface and in cutaneous oil glands
5. F-lactamase
Breaks down penicillin
Allows the bacteria to survive treatment with F-lactam antimicrobial drugs
Enzymes (cont.)
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Staphylococcus aureusproduces toxins more
frequently than S.epidermidis1.Cytolytic toxins
Disrupts the cytoplasmic membrane of a variety ofcells
Leukocidin can lyse leukocytes specifically
2. Exfoliative toxins
C
auses the patients skin cells to separate from eachother and slough off the body
Toxins
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3. Toxic-shock-syndrome toxin
Causes toxic shock syndrome
4. Enterotoxins
Stimulate the intestinal muscle contractions, nausea,
and intense vomiting associated with staphylococcalfood poisoning
Toxins (cont.)
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III.
Virulence factors of Staphylococcus aureus
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3 categories
Noninvasive Disease
Food poisoning from the ingestion of enterotoxin-contaminated food
Cutaneous Disease Various skin conditions including scalded skin
syndrome, impetigo, folliculitis, and furuncles
Staphylococcal Diseases
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Systemic Disease
Toxic shock syndrome-TSS toxin is absorbedinto the blood and causes shock
Bacteremia-presence of bacteria in the blood
Endocarditis-occurs when bacteria attack thelining of the heart
Pneumonia-inflammation of the lungs in whichthe alveoli and bronchioles become filled with
fluid Osteomyelitis-inflammation of the bone
marrow and the surrounding bone
Staphylococcal Diseases
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Diagnosis
Detection ofGram-positive bacteria in grapelikearrangements isolated from pus, blood, or other fluids
Treatment
Methicillin is the drug of choice to treat staphylococcalinfections
Is a semisynthetic form of penicillin and is notinactivated by F-lactamase
Diagnosis, Treatment, and Prevention
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Diagnosis
Specimen
Smear
Culture
Film
Biochemical Reactions
Antibiogram
Typing
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Prevention
Hand antisepsis is the most important measure inpreventing nosocomial infections
Also important is the proper cleansing of wounds andsurgical openings, aseptic use of catheters or indwelling
needles, an appropriate use of antiseptics
Diagnosis, Treatment, and Prevention (cont.)