7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 1/20

Stain purple when gram stained

Can be divided into 2 major groups :

Genera of cocci-shaped organisms- Staphylococcus,Streptococcus, and Enterococcus

Genera of bacilli-shaped organisms- Bacillus,Clostridium, Listeria, Corynebacterium,

 Mycobacterium, Propionibacterium, Nocardia, and Actinomyces

Gram-Positive Pathogens

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 2/20

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 3/20

Normal members of human bacterial flora

Can be opportunistic pathogens, causing a widerange of local or sistemic diseases

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 4/20

Gram-positive cocci, nonmotile, facultativeanaerobes

Cells occur in grapelike clusters because cells divisionoccurs along different planes and the cells remainattached to one another;

Salt-tolerant: allows them to tolerate the salt presenton human skin;

Tolerant of desication: allows survival on

environmental surfaces (fomites);

Structure and Physiology

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 5/20

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 6/20

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 7/20

Two species are commonly associated withstaphylococcal diseases in humans

Staphylococcus aureus:the more virulent strain that canproduce a variety of conditions depending on the site of infection

Staphylococcus epidermidis (white) normal flora of human skin that can cause opportunistic infections inimmunocompromised patients or when introduced intothe body

Stapylococcus saprophiticus (yellow) rarely pathogen

Structure and Physiology

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 8/20

“Staph’ infections result when staphylococci breach the body’s physical barriers 

Entry of only a few hundred bacteria can result indisease

Pathogenicity results from 3 features

Structures that enable it to evade phagocytosis

Production of enzymes

Production of toxins

Pathogenicity

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 9/20

1. Protein A coats the cell surface

Interferes with humoral immune responses bybinding to class G antibodies

Inhibits the complement activation 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

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 10/20

3. Synthesize loosely organized polysaccharide slimelayers (often called capsules)

Inhibit chemotaxis of and phagocytosis by leukocytes

Facilitates attachment of staphylococcus to artificialsurfaces

Structural Defenses Against Phagocytosis

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 11/20

1. Coagulase

Triggers blood clotting2. Hyaluronidase

Breaks down hyaluronic acid, enabling the bacteria to

spread between tissues cells3. Staphylokinase

Dissolves fibrin threads in blood clots, allowingStaphylococcus aureus

to free itself from clots

Enzymes

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 12/20

4. Lipases

Digest lipids, allowing staphylococcus to grow on theskin’s surface and in cutaneous oil glands 

5.  -lactamase

Breaks down penicillinsAllows the bacteria to survive treatment with -lactam antimicrobial drugs

Enzymes

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 13/20

Staphylococcus aureus produces many toxins, morefrequently than S.epidermidis 

1. Cytolytic toxins

Disrupts the cytoplasmic membrane of a variety of cells

Leukocidin can lyse leukocytes specifically

2. Exfoliative toxins: cause the patient’s skin cells toseparate from each other and slough off the body

Toxins

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 14/20

3. Toxic-shock-syndrome toxin (TSST-1)

Causes toxic shock syndrome4. Enterotoxins

Stimulate the intestinal muscle contractions, nausea,

and intense vomiting associated with staphylococcalfood poisoning

Toxins

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 15/20

III.

Virulence factors of Staphylococcus aureus

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 16/20

3 categories of diseases:

Noninvasive diseases:• Food poisoning from the ingestion of enterotoxin-

contaminated food

Cutaneous disease:

• Various skin conditions including scalded skinsyndrome, impetigo, folliculitis and furuncles

Staphylococcal Diseases

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 17/20

Systemic Disease

• Toxic shock syndrome-TSST-1 toxin isabsorbed into 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

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 18/20

Diagnosis:

Detection of Gram-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 -lactamase

Diagnosis, Treatment, and Prevention

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 19/20

Diagnosis

Specimen

Smear Culture

Film

Biochemical Reactions

Antibiogram

Typing

7/30/2019 Sta Philo Coccus

http://slidepdf.com/reader/full/sta-philo-coccus 20/20

Prevention:

Hand antisepsia is the most important measure inpreventing nosocomial infections;

Also important is the proper cleansing of wounds andsurgical procedures, aseptic use of catheters orindwelling needles, an appropriate use of antiseptics;

No effective vaccines are available.

Diagnosis, Treatment, and Prevention