Streptococci & Corynebacteria - PowerPoint Presentation

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Streptococci & Corynebacteria

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Streptococci

Cocci

: spherical

Morphology:

Gram positive,

cocci in chains

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Characteristics of Streptococci

Morphology>>

Gram positive,

cocci

Arranged in chains, and some spp. arranged in pairs

2. Habitat>>

Usually found as a normal flora in throat3. Culture>>

They are Facultative anaerobic

Because of their complex nutritional requirements, blood enriched medium is generally used for their isolation.

4. Biochemical Reactions>>

Catalase negative (don’t produce catalase enzyme)

5. Non- motile

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Note

Blood Agar (BA):

It is basal media has been enriched by adding blood, so we call it Enriched media

.

It allow the growth of fastidious and pathogenic bacteria.

BA is also Differential media used to differentiate between hemolytic and non-hemolytic bacteria

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Classification of Streptococci

Streptococci are classified by several schemes:

A) Hemolytic properties on blood agar>>

α

-hemolytic:

S.viridance &

S.pneumoniae

β

-hemolytic:

S.

pyogenes

S.

agalactia

γ

-hemolytic: Enterococci spp.B) Serologic (Lancefields) groupings>>Used for the classification of Beta- hemolytic streptococci to: group A (S. pyogenes), group B (S. agalactia), group D,……….. group V

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Alpha-Hemolytic Streptococci

There are mainly 2 clinically important species:

1. Streptococcus viridans

2. Streptococcus

pneumoniae

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1. Streptococcus

viridans

Part of the oral and throat flora, mostly a-virulent

Streptococcus

mutans

is member of the

viridancs group that cause dental caries.

S.

viridans

can cause infection (

strep throat)>> rheumatic fever>> Rheumatic Heart

Disease (RHD)

In RHD they infect heart valves>> heat failure and death.

At risk patients should receive prophylactic penicillin before undergoing dental procedures.

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Streptococcus viridans

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2. Streptococcus

pneumoniae

Gram positive

diplococci

Colonies appear alpha hemolytic on blood agar plate.

Colonies shoes glistening appearance because of the

presence

of capsule.

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S. pneumoniae Infection

Bacterial pneumonia

Leading cause of death especially in older adults

Bacteremia

Meningitis

Otitis media (middle ear infections)

Sinusitis

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S.pneumoniae and Eye Infections

1. It causes

Hypopyon

corneal ulcer.

It is a disk-shaped central corneal

ulcer with hypopyon.

Hypopyon>> is inflammatory

cells in the anterior chamber of the

eye with sterile pus (yellowish exudate)

Perforation secondary to ulcer is

common

2. Acute

muco

-purulent conjunctivitis.

3. Purulent conjunctivitis of the new born.

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Risk FactorsCompromised corneal epithelial integrity caused by contact lens wear, corneal trauma, or corneal surgery.

Inappropriate use of topical antibiotics could eliminate the natural protection by the normal flora, this can predispose cornea to develop opportunistic infections, particularly when combined with corneal disease or trauma.

Trauma, including chemical & thermal injuries.

Contact lenses users have 1.5% chance of developing infectious keratitis.

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Beta-Hemolytic Streptococci

The most important

spp. in this genus are Group A, and B

Streptococci

1. S.

pyogenes

(Group A

Streptococci)

Part of throat flora,

does not survive well in the

environment.

It can spread person to person via skin contact and via respiratory tract

.

S.

pyogenes Infections:Usually cause throat infections (strep throat) or (acute pharyngitis) which is associated with purulent inflammation.

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Nasopharyngeal carriage is common especially in colder months and particularly among children.

One of the member of this species can cause necrotizing fasciitis (flesh eating bacteria)

Scarlet fever: sunburn-like

rash may develops on the neck, trunk, and extremities in response to the release of pyrogenic

exotoxin.

Complications

include: Acute rheumatic

fever>> 2-3

weeks after the initiation of pharyngitis. Characterized by fever, rash,

carditis

and arthritis.

Acute glomerulonephritis, rare, occur as soon as 1 week after pharyngitis.

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Streptococcal pharyngitis

Scarlet fever

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2.

S.

agalactiae (Group

B

Streptococci)

It is found in the

vaginocervical tract of female carriers, urethral

of male carriers as well as GI tract.

Can

be transmitted sexually and from infected mother to her infant at birth.

It

is a leading cause of meningitis and septicemia in neonates, with a high mortality rate.

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Non-Hemolytic Streptococci

Group

D streptococci or Enterococci

They are not very virulent but are important cause of nosocomial infections, especially that they have developed multiple antibiotic resistance.

They are part of the fecal normal flora.

They can also colonies skin and mucous membranes especially in hospital setting.

Not like other Streptococci they are highly resistant to environmental and chemical agents and can persist on non living objects.Vancomycin

resistant Enterococci is a major concern in hospitals.

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Enterococci

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Corynebacteria

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Corynbacteria diphtheriae

Characteristics:

1. Morphology>>

Small gram positive

rods

Chinese letter pattern, angular arrangement.

2. Culture>>

aerobic

3. Biochemical reactions

>>

Catalase

+

ve

(

like

staphylococcus).4. non-spore-forming.5. Non-motile.

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6. Un-capsulated.

7. Not considered part of the normal flora.

8. They cause diphtheria>>

Acute

respiratory or cutaneous disease that maybe life threatening.

9. It is found in the throat and

nasopharynx of carriers and in patient with diphtheria.10. It

has a very strong single exotoxin that inhibits protein synthesis.

11. It

is heat-labile.

Antitoxin

is available & used in treatment.

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C. diphtheria Infection

Disease can represent in tow forms:

Upper respiratory tract

infection>>

Localized

infection (usually the

throat).

There is a distinctive thick, grayish, adherent

pseudomembrane

that coats the throat.

Disease progress and generalized symptoms occur due to toxin.

Mainly affect heart and peripheral nerves.

Cutaneous diphtheria>>

C.diphtheria

can gain entry to

subcutaneous tissue via wound or cut in the skin.It leads to a chronic , non healing ulcer with a gray membrane .

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C.diphtheria & Eye Infections

It can cause

acute membranous conjunctivitis It is an acute inflammation of the conjunctiva,

characterized by formation of a true membrane on

the conjunctiva

.

Now-a-days it is of very rare occurrence

, because of markedly

decreased incidence

of diphtheria.

It

is because of the fact

that immunization

against

diptheria

is very effective.

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Immunity to C.diphtheria

Children should get 5 doses of DTP vaccine, one dose at each of the following ages: 2 months, 4 months, 6 months, 18 months, 4 to 6 years.

DPT

= combination vaccines against three infectious diseases in humans: diphtheria,

pertussis,

and tetanusThe

vaccine components include the bacterial toxoid

>> a chemically modified toxin from a pathogenic microorganism, which is no longer toxic but is still antigenic and can be used as a vaccine

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Treatment of C.diphtheria

Anti-toxin.

Passive immunization with preformed diphtheria toxin antibodies.It is sensitive to many antibiotics including penicillin.

Patient must be isolated because the disease is highly contagious

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C. diphtheroids

They are morphologically similar to

C.diphtheriae but the are not pathogenic.

They

live in nose, throat,

nasopharynx , skin, urogenital tract and conjunctiva.

They do not produce exotoxin.

May

rarely cause disease in the

immunocompromized

.