Microbio Lec 5 - Streptococcus

MICROBIOLOGY LECTURE 5 – Genus Streptococcus Notes from Lecture USTMED ’07 Sec C – AsM Generalities 1. 2. 3. 4.

Gram positive cocci that grow in pairs or chains Widely distributed in nature 27 recognized species Some are members of the normal human flora

5.

Others are associated with important human disease attributable to infection by streptococci and to sensitization to them

6.

The most important of the human pathogens: a. Streptococcus pyogenes (Group A)

b. c. d. e.

7. 8.

b.

Alpha hemolysis showing partially hemolyzed RBC immediately surrounding the colonoy

Enterococcus faecalis(Streptococcus faecalis) (Group D) Streptococcus pneumoniae some of the oral streptococci

Streptococcus pyogenes (Group A) streptococcileading bacterial cause of pharyngitis and cellulitis; inciting factor of two important immunologic diseases: acute rheumatic fever and acute glomerunephritis Streptococcus agalactiae (Group B streptococci)leading cause of neonatal sepsis and meningitis

c.

Enterococcus faecalis – important cause of hospital acquired urinary tract infections and endocarditis

d.

Viridans group streptococci – most common cause of endocarditis Streptococcus bovis – may also cause endocarditis

e.

9.

an indistinct zone of partial lysis of red blood cells causing a green to greenish brown discoloration of the medium immediately surrounding the colony

Streptococcus agalactiae (Group B)

Elaborates a variety of extracellular substances and enzymes Streptococci cause a wide variety of infections:

a.

There is a clear colorless zone around a streptococcal colony in which the RBC have undergone complete destruction Alpha hemolysis on 5% sheep blood agar

Gamma hemolysis on 5% sheep blood agar Gamma denotes lack of hemolysis; the RBC surrounding the colonies are intact

Macroscopically there is no apparent hemolytic activity or discoloration produced by the colony

Most species are facultative anaerobes; maybe strictly anaerobic to capnophilic

10. Have

complex nutritional requirements necessitating blood or serum enriched medium for isolation

11. Carbohydrates are fermented with the production of lactic acid but not gas

12. Catalase negative 13. Can be classified as to:

a. b.

c.

clinical presentation(pyogenic,oral,enteric)

CLASSIFICATION OF STREPTOCOCCI

1.

a.

serological properties (Lancefield grouping A-H, K-V) based on the antigenic composition of cell wall carbohydrates • serogroups A,B,C,D and G – most commonly found associated with human disease

b.

c. d.

Hemolytic patterns in blood agar plates

• •

Beta hemolysis – clear zone of hemolysis around the colony as a result of complete lysis of the red blood cells

e.

2.

Alpha hemolysis – zone of partial hemolysis with a greenish discoloration of the medium

c.

Gamma hemolysis – no color change or lysis of red blood cells ; nonhemolytic Biochemical (physiological) properties • Sugar fermentation reactions • Tests for the presence of enzymes

• e.

Tests for susceptibility or resistance to certain chemical agents

d. e. f. 3.

c.

d. Beta hemolysis on 5% sheep blood agar 4. There is complete lysis of RBC surrounding the colony that can be seen macroscopically

main human pathogen associated with local or systemic invasion and poststreptococcal immunologic disorders PYR positive(hydrolysis of L-pyrrolidonyl-2napthylamide) usually susceptible to bacitracin

members of the normal flora of the female genital tract an important cause of neonatal sepsis and meningitis beta hemolytic hydrolyzes sodium hippurate gives a positive response to CAMP test

Groups C and G streptococci a. occur sometimes in the nasopharynx

b.

antigenic specificity of the capsular polysaccharide

contains the group A antigen beta hemolytic

Group B streptococcus – Streptococcus agalactiae a. contains the group B antigen

b.

•

d.

Group A streptococcus – Streptococcus pyogenes

may cause sinusitis, bacteremia or endocarditis beta hemolytic identified by reactions with specific antisera for groups C or G

Group D streptococci

a.

enterococcal – Enterococcus faecium Enterococcus durans • Part of the normal enteric flora

• • •

Usually nonhemolytic; occasionally alpha hemolytic PYR positive Grow in the presence of bile

• • • •

Hydrolyze esculin (bile esculin positive) Grow in 6.5% NaCl resistant to penicillin G Some strains are vancomycin resistant

c.

usually alpha nonhemolytic

d.

part of the normal flora occasionally cause bacteremia or endocarditis can be found in brain abscesses and other infections

e. f.

b.

• • • • •

5.

• • • •

a.

Sometimes cause bacteremia in patients with colon carcinoma Nonhemolytic and PYR negative Grow in the presence of bile Hydrolyze esculin (bile esculinpositive) Do not grow in 6.5% NaCl Sensitive to penicillin

Beta hemolytic streptococci that form minute colonies (