Staph Handout 1

8/3/2019 Staph Handout 1

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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.)

Staph Handout 1

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