4A: Cocci Of Medical Importance

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Medical importance of Gram + and Gram - cocci

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They are the most significant infectious agents

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Cocci are often members of

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Human normal flora

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Cocci tend to stimulate formation of...

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Pus

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And are therefore known as

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Pyogenic cocci - stimulate pus formation in infection

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The most common infectious species in the pyogenic cocci are (4- Gram + or - ?)

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1) Staphylococcus +

2) Streptococcus +

3) Enterococcus +

4) Neisseria -

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The Staphylococci inhabit the...

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Skin and mucous membranes

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Characteristics of Staphylococci (3)

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1) Gram +

2) Cocci

3) Clusters

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Other traits of Staph (2)

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1) Catalase positive

2) Most are beta hemolytic

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Staphylococci are responsible for...

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80,000 deaths in the US

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Important human Staph pathogens are (5)

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1) S. aureus

2) S. epidermitis

3) S. capitis

4) S. hominis

5) S. saprophyticus

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Staphylococcus aureus (O2 requ.)

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Facultative anaerobe

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Important fact/characteristic of Staph aureus

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Considered among most resistant of all non-spore forming pathogens

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Staph aureus is resistant to (3)

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1) High NaCl

2) Ph extremes

3) High temperatures

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Important Staph aureus virulence factor

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Coagulase + (97%) = enzyme that clots plasma

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Staph aureus is normal flora of the human... (4)

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1) Nares

2) Skin

3) Nasopharynx

4) Intestine

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Infections with Staph aureus range from...

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Local to systemic

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4 Local infections with Staph aureus

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1) Folliculitis

2) Boil or furuncle

3) Carbuncle

4) Impetigo

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Folliculitis

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Infection of hair follicles that produces superficial inflammation

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Boil or Furuncle

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Results when inflammation of 1 hair follicle/sebaceous gland progresses into a large, red abscess or pustule

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Carbuncle

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Deeper lesion created by cluster of furuncles into 1 large mass which is very painful and can be fatal

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Impetigo

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Inflammation/swelling of the skin which breaks open and peels away

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2 Systemic infections with Staph aureus

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1) Osteomyelitis

2) Pneumonia

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Osteomyelitis

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1)Most systemic staph infections spread from localized cutaneous infection to the bloodstream where it attaches to bone

2) Organism establishes itself in the bone and destroys it

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Pneumonia (what happens, fatality rate, pts. who develop this pneumonia)

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1) Pt. develops lung abscesses

2) 50% fatal

3) People dealing with cystic fibrosis, influenza, and the measles are more susceptible

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Staphylococcal bacteremia is dangerous because

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It has a high mortality rate especially of hospitalized patients with chronic dz.

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Toxigenic Staph aureus diseases are...

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Diseases associated with the toxins produced by Staph aureus

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Examples of toxigenic staph aureus dz.'s (3)

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1) Food intoxication

2) Scalded skin syndrome

3) Toxic shock syndrome

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Food intoxication (2)

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-Caused by enterotoxins

-Common in potato salads and sauces because organism is resistant to increased salt and high temps.

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Scalded skin syndrome (2)

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-Toxin causes bright red flush then blisters and peeling

-Seen in babies when organism enters through umbilical cord

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Toxic shock syndrome

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Seen in women who use super absorbant tampons which bind magnesium

This increases the production and release of toxins responsible for toxic shock syndrome

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Other important Staphylococci

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Coagulase negative Staph

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Coagulase negative Staph include

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Anything that isn't Staph aureus (only coagulase + Staph)

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Coagulase negative Staph are a common

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Nosocomial infectant in immunocompromised patients

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Coagulase negative Staph organisms include (4)

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1) S. epidermitis

2) S. hominis

3) S. capitis

4) S. saprophyticus

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The organisms :

1) S. epidermitis

2) S. hominis

3) S. capitis

live on...(5)

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1) Skin

2) Surgical wounds

3) Shunts

4) IV's

5) Prosthetic devices

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They create....

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Biofilms

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S. saprophyticus are found in (2)

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1) Lower respiratory tract

2) Vagina

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S. saprophyticus causes

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UTI's - second most common cause of UTI's (especially in sexually active women)

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Clinical concerns for S. aureus:

They produce this virulence factor

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95% of S. aureus have penicillinase (cleaves beta-lactam ring of penicillins)

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Clinical concerns regarding MRSA (6)

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Staph aureus strain that is resistant to:

1) Methicillin

2) Gentamicin

3) Cephalosporin's

4) Tetracycline

5) Erythromycin

6) Quinolones

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How many new cases of S. aureus/ year and how many deaths?

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-New cases / year = 94,000

-Deaths / year = 19,000

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How infections are handled with Staph aureus (2)

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-Infections must be "cut out" in order to clear the pus and foreign bodies for the abscesses to heal

-Systemic infections require long term antibiotic therapy because they respond slowly

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Prevention of Staph infections (preventing spread) (5)

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1) Hand washing

2) Use care with any dressings and discharges

3) Follow protocol and pay attention to IV's

4) Screen all patients for pathogenic organisms in outbreak situations

5) Treat asymptomatic carriers to prevent spread

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Characteristics of Streptococci (3)

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1) Gram positive

2) Cocci

3) Chains and pairs

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Streptococci O2 requirements

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Facultative anaerobic

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Streptococci are catalase....

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Negative

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Streptococci colonies are (2)

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1) Small

2) Non-pigmented

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Streptococci are sensitive to (4)

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1) Drying

2) Heat

3) Disinfectants

4) Drugs

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Streptococci of medical importance (5)

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1) S. pyogenes

2) S. agalactiae

3) E. faecalis

4) S. mutans and other viridians Strep

5) S. pneumoniae

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Group A strep is known as

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Streptococcus pyogenes

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Streptococcus pyogenes are what classified under what type of hemolysis?

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Beta-hemolytic Strep

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Streptococcus pyogenes are the...

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Most serious Strep pathogen

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Strep pyogenes generates many virulence factors including (3) and describe

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1) Surface antigen - hyaluronic acid capsule (mimics acid in our body)

2) Toxins - Erythrogenic toxin induces fever and is responsible for scarlet fever

3) Enzymes - Streptokinase (digests fibrin clots) and hyaluronidase (destroys our tissue)

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How many humans are carries of Strep pyogenes?

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5-15%

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Strep pyogenes skin infections include (4) and describe

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1) Impetigo - itching, burning papules

2) Strep throat

3) Erysipelas - Enters through small wound/incision on face/extremities and spreads to dermis and subcutaneous layers

4) Necrotizing fasciitis - Infects fascia (connective tissue around muscles and other organs)

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Systemic infections from Strep pyogenes

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1) Scarlet fever

2) Septicemia

3) Strep toxic shock syndrome

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Scarlet fever (Cause and effects)

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-Strain of S. pyogenes that codes for erythrogenic toxin (induces fever and causes skin to turn bright red)

-Causes diffuse rash that spreads over body and will slough off within a number of days

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Septicemia results from

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Results from local infections

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Strep toxic shock syndrome (and % of fatality)

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Deep tissue infection with bacteremia that rapidly progresses to multiple organ failure

-30% fatal

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Strep is known for

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Binding with antibodies in blood and precipitating onto tissue

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Long term complications resulting from Strep pyogenes infection (2 and define)

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1) Rheumatic fever - A delayed inflammatory condition of the joints, heart, and subcutaneous tiss. (precipitates on heart tissue,, joints, and subQ tiss.)

2) Acute glomerulonephritis (AGN) - a disease of the kidney glomerulus and tubular epithelia (precipitates onto kidney tiss)

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Rheumatic fever follows what kind of infection

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Follows cases of Strep pharyngitis in children

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Rheumatic fever involves what tissues in body?

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Inflammation of joints, muscles and connective tissue

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Signs and symptoms of rheumatic fever (5)

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1) Carditis (infl. of heart tiss.)

2) Abnormal ECG

3) Painful arthritis

4) Nodules under skin

5) Fever

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Length of rheumatic fever and effects on pt.

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Lasts 3-6 months

Most people end up ok but some get cardiac complications like damage to valves if carditis is severe (come in later as stroke pts.)

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Acute glomerulonephritis (2 steps)

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-Antibodies form against Strep cell wall cross and react with the host membranes

-This triggers inflammation and injures tissues when immune complex (Ag-Ab complex) deposits or precipitates onto basement membranes of kidneys

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Group B strep is known as

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Streptococci agalactiae

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S. agalactiae resides in (3)

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1) Vagina

2) Pharynx

3) Large intestine

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S. agalactiae / Group B strep is most prevalent cause of

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Neonatal

1) Pneumonia

2) Sepsis

3) Meningitis

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Complications of neonatal Group B strep

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Long term neurological complications or death

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Group B strep infection of babies can be prevented by

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Screening mom in 3rd trimester

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Group D Strep is also known as

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Enterococcus faecalis

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Enterococcus organisms reside

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as normal flora of large intestine

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Enterococcus faecalis is commonly seen in (4)

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1) Elderly undergoing surgery

2) UTI's

3) Wounds

4) Endocarditis

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VRE

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Vancomycin resistant Enterococcus - has rising resistance

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Big concern for VRE and MRSA

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If Vancomycin resistant plasmid is transferred to MRSA - it will be a completely resistant organism

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Alpha Hemolytic strep is sometimes known as

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Viridans strep

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Viridans Strep reside

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As normal residents of oral cavity

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Alpha hemolytic strep infect body by

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Gaining entrance through dental or surgical procedures (not highly invasive on their own)

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Alpha hemolytic strep is responsible for

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Dental caries due to slime layer formation

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A major complication of viridans strep infections is

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Subacute endocarditis

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Subacute endocarditis (2 steps)

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-Bacteria settle on areas of the heart lining or valves that have been previously injured

-Biofilms called Vegetation form and release clots/masses of bacteria into body

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Streptococcus pneumoniae is formerly known as

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Diplococcus / pneumococcus

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Streptococcus pneumoniae is shaped as

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Lancet shape

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What percentage of bacterial pneumonias are from Strep pneumoniae

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60-70% - primary infecting agent of immunocompromised pts.

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Streptococcus pneumoniae also causes (2)

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Meningitis and otitis media

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Virulence factor of pathogenic strains of Strep. pneumoniae

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All pathogenic strains form capsules

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Percentage of people who carry Strep pneumoniae and where

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5-50% in nose and nasopharynx

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Protection against strep pneumoniae

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Can get vaccine