1. Streptococci & Corynebacteria

2. Streptococci Cocci: spherical Morphology:
Gram positive, cocci in chains
Sterptococci and staphylococci are the main groups of medically important gram+ cocci

3. 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 throat
3. 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
Morphology>> chain (short or long), pairs (diplococci)

4. 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

5. 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

6. Alpha-Hemolytic Streptococci
There are mainly 2 clinically important species: 1. Streptococcus viridans 2. Streptococcus pneumoniae

7. 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.
RHD is caused by rheumatic fever. Rheumatic fever is caused by streptococcal (strep) infection.
Treating strep throat with antibiotics can prevent rheumatic fever.
regular antibiotics (usually monthly injections) can prevent patients with rheumatic fever from contracting further strep infections and causing progression of valve damage.
Streptococcal infection in throat or as a bacteremia.

8. Streptococcus viridans

9. 2. Streptococcus pneumoniae
Colonies appear alpha hemolytic on blood agar plate.
Colonies shoes glistening appearance because of the
presence
of capsule.
Gram positive diplococci

10. S. pneumoniae Infection
Bacterial pneumonia
Leading cause of death especially in older adults
Bacteremia
Meningitis
Otitis media (middle ear infections)
Sinusitis
Meningitis: inflammation of the meninges (protective membranes covering the brain and spinal cord)

11. 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.

12. Risk Factors
Compromised 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.

13. 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.

14. Complications include:
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.
Glomerulonephritis :acute inflammation of the kidney

15. Scarlet fever
Streptococcal pharyngitis

16. 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.

17. 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.

18. Enterococci

19. Corynebacteria

20. 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.

21. 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.

22. 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 .

24. 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.

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

26. 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

27. 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.