Streptococci & Corynebacteria Lecture 3

Streptococci Streptococci: Streptococcus pneumoniae (pneumococcus). Overview Classification of streptococci Hemolytic properties on blood agar Serologic (lancefield groupings). Streptococcus pneumoniae (pneumococcus). Corynebacteria. Sterptococci and staphylococci are the main groups of medically important gram+ cocci

Streptococci Gram positive Non-motile Catalse negative Arranged in pairs or chains. Because of their complex nutritional requirements, blood enriched medium is generally used for their isolation.

Classification of Streptococci. They are classified by several schemes. Hemolytic properties on blood agar. αhemolytic  S.viridance & S.pneumoniae βhemolytic  Group A & Group B γhemolytic  Enterococci Serologic (lancefields) groupings. used for the classification of Beta- hemolytic streptococci X-hemoletyic they will cause chemical changes on the HB resulting in green pigments

Beta-hemolytic Streptococci The most important group in this genus are Group A, and B Streptococci: Group A Streptococci (S.pyogenes) Usually cause throat infections (Acute pharyngitis). Nasopharyngeal carriage is common especially in colder months and particularly among children. It does not survive well in the environment , its habitat is infected patients and also normal human carriers. It can spread person to person via skin contact and via respiratory tract. One of the member of this species can cause necrotizing fasciitis (flesh eating bacteria) S.Pyogenes is a major cause of cellulitis (inflammation of subcutaneous connective tissue.)

Group A Streptococci (S.pyogenes) Acute pharyngitis (strep throat) is associated with purulent inflammation. Sunburn like rash may develops on the neck, trunk, and extremities in response to the release of pyrogenic exotoxin (scarlet fever). 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

Scarlet fever Streptococcal pharyngitis Flesh-eating Bacteria

Beta-hemolytic Streptococci Group B streptococci (S.agalactiae). It is found in the vagino cervical 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.

Group B Streptococci Group A Streptococci

Non-hemolytic Streptococci Also called 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.

Enterococci

Alpha Hemolytic Streptococci There is mainly 2 clinically important species : 1. Streptococcus veridance part of the oral flora, mostly avirulent Streptococcus mutans is member of the viridancs group that cause dental caries. They may also infect abnormal or damaged heart valves during bacteraemia. At risk patients should receive prophylactic penicillin before undergoing dental procedures. 2. Streptococcus pneumoniae

Streptococcus virdiance

Streptococcus pneumoniae glistening appearance. Colonies appear alpha hemolytic on blood agar plate. Colonies shoes glistening appearance because of the presence of capsule.

S. pneumoniae Acute bacterial pneumonia bacteremia meningitis Leading cause of death especially in older adults Viral infection predisposes to strep pneumonia by: Increased volume and viscosity of secretions and inhibition of the action of bronchial cilia bacteremia meningitis middle ear infections (otitis media) - children

S.pneumoniae and Eye Infections It causes hypopyon corneal ulcer . It is a disk-shaped central corneal ulcer with hypopyon. Hypopyon  sterile pus in the anterior chamber. Perforation secondary to ulcer is common Hypopyon is inflammatory cells in the anterior chamber of the eye. (yellowish exudate )

S.penumoniae may also cause: acute mucopurulent conjunctivitis. Purulent conjunctivitis of the new born.

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.

Pathogenic C.diphtheriae Commensal Diphtheriods Gram Positive Rods Corynebacteria Pathogenic C.diphtheriae Commensal Diphtheriods The only pathogenic member of this genus Normal Flora , RT, Urethra , Skin, Conjunctiva

Corynbacteria diphtheriae. Aerobic. non-spore-forming. Non-motile. Uncapsulated. Catalase +ve (like staphylococcus). Small gram positive rods. Chinese letter pattern, angular arrangement. Not considered part of the normal flora.

Corynebacterium diphtheriae They cause diphtheria  acute respiratory or cutaneous disease that maybe life threatening. It is found in the throat and nasopharynx of carriers and in patient with diphtheria. It has a very strong single exotoxin that inhibits protein synthesis. It is heat-labile. Antitoxin is available & used in treatment.

Clinical Significance of C.diphtheria Disease can represent in two 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 subcuaneous tissue via wound or cut in the skin. It leads to a chronic , nonhealing ulcer with a gray membrane .

C.diphtheria & Eye Infections

Immunity to C.diphtheria The toxin produces a toxoid that retains the antigenicity abut not the toxicity of the molecule  it is used in the vaccine. DPT= Diphtheria, tetanus, and pertussis Children should get 5 doses of DTaP vaccine, one dose at each of the following ages: 2 months, 4 months, 6 months, 15 to 18 months, 4 to 6 years.

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.

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.