Gram positive Streptococci

Streptococcus

• _{Gram positive} • _{Non motile}

• _{Ovoid to spherical in shape}

facultative anaerobic, Catalase negative (staphylococci are catalase positive).

Ferment sugar even in the presence of oxygen

• _{Require nutrient rich environments}

• _{Identified by their growth patterns on blood agar}

Summary of differences between

staphylococci and streptococci

• _{Gram stain and morphology} – _{Both Gram +}

– _{Staphylococci: bunched cocci}

– _{Streptococci: chained cocci (S. pneumoniae form diplococcus)} • _{Enzyme tests}

– _{Staphylococci: catalase +} – _{Streptococci: catalase} -• _Growth

Streptococcus

and

Enterococcus

: Cell Wall

Structure

• _{Thick peptidoglycan layer} • _{Teichoic acid}

• _{C=carbohydrate layer present except}

in viridans group

– _{C carbohydrates used in}

Lancefield grouping of

Streptococcus spp. (EXCEPT S. pneumoniae and S. viridans)

– _{Groups A, B, C, D, etc.}

• _{Capsule in S. pneumoniae and in}

Clinically Significant Streptococci: Streptococcus

pyogenes or Group A Beta-Hemolytic Streptococci

• _{Bacterial structure}

– _{Fimbrae: attachment and}

adherence

– _{M protein: major virulence}

factor: resistance to phagocytosis

– _{Hyaluronic acid capsule:}

• _{Streptococci are subdivided into groups by}

antibodies that recognize surface antigens

• _{The most important groupable streptococci are}

A, B and D.

• _{Among the groupable streptococci, infectious}

disease (particularly pharyngitis) is caused by

group A (Pyogenic)

• _{Streptococcus pneumoniae (a major cause of}

human pneumonia)

• Streptococcus mutans and other so-called

viridans streptococci (among the causes of

dental caries) do not possess group antigens.

• _{The hemolysis reaction is important in grouping}

streptococci.

• _{The hemolysis reaction along with one}

physiologic characteristic is sufficient for a

• _{Group A and group B streptococci are}

beta hemolytic

• _{Group D are usually gamma or non}

• Streptococcus pneumoniae and viridans

streptococci are alpha hemolytic ("green")

Streptococcus pyogenes or Group A Streptococci: Virulence Factors

• _Hemolysins

– _{Streptolysin O, can be detected by ASO test} – _{Streptolysin S (O2 stable)}

• _{Erythrogenic toxin} • _Enzymes

– _{Streptokinase} – _DNases

S. pyogenes

Streptococcus pyogenes (Group A) Streptococcal Infections

• _{Acute bacterial} pharyngitis

– _{Sore throat} – _Malaise

– _{Fever/headache}

• _{Scarlet fever}

• _{Pyodermal infections} – _Impetigo

– _Erysipelas

• _Cellulitis Erysipelas due to

Scarlet Fever

• _{Rash is an inflammatory reaction to the}

erythrogenic toxin

• _{The toxin produced by a gene}

“

Flesh-Eating Bacteria

”

Cellulitis

– _{Severe form of infection that is life-threatening}

Invasive Group A Streptococcal Infections

• _{Streptococcal toxic shock syndrome}

– _{Multi-organ system failure similar to}

staphylococcal toxic shock

– _{Initial infection may have been pharyngitis,}

Group A streptococcal infections affect all ages with

peak incidence at 5-15 years of age.

Ther serious complications including: 1- Rheumatic fever

2- Invasive bacteremia)

Affect primarily those with some underlying

defect in their immune system including:

infants, elderly people

and those immunocompromised).

Rheumatic fever

 _{An inflammatory disease affecting primarily the}

heart and joints.

 _{The mechanism of chronic immunopathology}

 _{Early termination of throat infections with}

penicillin therapy decreases the incidence of the

Acute glomerulonephritis

Bacteremia and toxic-shock

.

 _{The newly described invasive (and sometimes}

fatal) forms of the disease with a toxic shock-like

disease (including rash, fever and shifting of Fluid from the bloodstream to peripheral

tissues and/or with resulting edema) necrotizing myositis and fasciitis.

 _{Production of pyrogenic toxins (A, B and C) are}

Laboratory diagnosis

1. Direct detection - the antigen is extracted from a throat swab.

a. The antigen extract will then bind with antibody

specific to the group A streptococcal carbohydrate. b. This has classically involved agglutination of

antibody coated beads.

2. Lancefield grouping of isolated beta hemolytic colonies.

Colonies are beta hemolytic and their growth is

inhibited by bacitracin (presumptive diagnosis).

Patient serum shows antibodies to streptolysin

O (ASO titer test), or other streptococcal antigens The strains of the bacteria possesses O and S

Bacitracin

• _{A filter paper disc impregnated with the}

antibiotic Bacitracin is placed on a blood agar plate containing bacteria

• _{If there is a zone of inhibition around the}

disk it is indicative of a Group A streptococci

Biochemical Identification

• _{Susceptibility tests}

– _{Bacitracin (0.04 units) or}

“A” disk or “Taxo A” disk

• _{Identifies Group A}

streptococci

Biochemical Identification

• _{Susceptibility test}

– _{Trimethoprim sulfamethoxazole}

(SXT)

• _{STX Inhibits other}

beta-hemolytic streptococcal groups

but not A and B

Group A streptococcus growing in the presence of SXT

• _{Group A}

Resistance to STX

Biochemical Identification

• _{PYR hydrolysis}

– _{Substrate L-pyrrolidonyl-}

b-napthlyamide (PYR) is hydrolyzed by Group A Streptococci and

Enterococcus sp.

PYR test for Group A

Group B streptococcus

(

S. agalactiae

)

These organisms cause neonatal meningitis and

septicemia after transmission from the

Group B Streptococcus

• _{Colony morphology}

– _{Grayish-white, mucoid,}

creamy, narrow zone of b -hemolysis

• _{Presumptive Identification} tests

Biochemical Identification

Munch-Petersen (CAMP) test

– _{Detects the production of}

enhanced hemolysis that occurs when b-lysin and the hemolysins of Group B

streptococci come in contact

Group B streptococci showing the classical “arrow-shaped

Group B streptococcus

The organism can be identified on the basis of:

1. Beta hemolysis

2. hydrolysis of hippurate

3. CAMP reaction

• _{CAMP is an abbreviation for the names of the 4}

individuals who originally described the test.

Group B streptococci produce a factor that increases

Identification Schema

Group D streptococcus

Group D streptococci are divided into:

• _{those that will grow in 6.5% saline (enterococci)}

• _{and those that will not (non-enterococci)}

Streptococcus Group D

Group D = S. bovis

• _{Members of the gut flora (Natural habitat is large} intestine)

• _{Associated infections}

– _Bacteremia

– _{Urinary tract infections} – _{Wound infections}

Biochemical Identification

– _{Ability to grow in 40% bile and}

hydrolyze Esculin are features of streptococci that possess Group D antigen (we use BE slants in lab instead of plates) • _{Growth in 6.5% NaCl broth}

– _{Differentiates Group D}

streptococci from enterococci

• _{Enterococci are often resistant to penicillin.}

• _{Enterococci are distantly related to other}

streptococci and have been moved into the genus

Enterococcus the most commonly isolated is ;

E. (S.) faecalis.

• _{Enterococci are found in the gut flora.}

• _{A significant cause of urinary tract infections}

 _{(much less common than E. coli)}

• _{A source of opportunistic infections including:}

 _{intra-abdominal}

 _septicemia

 _endocarditis

Bacterial Pneumonia

Streptococcus pneumoniae

• _{Often secondary}

infection following influenza virus

Microscopic morphology

Laboratory Diagnosis:

Streptococcus pneumoniae

• _{Colony morphology} – _{Smooth, glistening,}

wet-looking, mucoid

– _a-Hemolytic – _CO2enhances

growth

– _{As colony ages,}

Laboratory Diagnosis:

Streptococcus pneumoniae

– _{Catalase negative} –

Optochin-susceptibility-test– (susceptible)

– _{Bile-solubility-test–}

Biochemical Identification

for streptococcus pneumoniae

• _{Susceptibility test}

– _{Optochin “P” disk or “Taxo P” disk}

• _{Differentiates S. pneumoniae from other}

alpha-hemolytic streptococci (Viridans group) • _{Bile solubility test}

– _{S pneumoniae lyses in a suspension of sodium deoxycholate while}

Streptococcus pneumoniae

• _{Streptococcus pneumoniae is responsible for}

pneumonia, bacteremia, otitis media, meningitis, sinusitis, peritonitis and arthritis

Resistance of Streptococcus pneumoniae to penicillin and other beta-lactams is increasing worldwide.

Viridans streptococci

• _{A diverse group of species commonly found orally}

(including S. mutans).

• _{Cause endocarditis after release into the}

bloodstream from tooth extraction.

• _{They are also involved in dental caries.}

• _{Are ailpha hemolytic and negative for other tests}

described above.

Treatment

Group A: treatment start with penicillin,

Erythromycin or another macrolide can be used in patients who are allergic to penicillin

Group B treatment: Penicillin or ampicillin + one of aminoglycosides

Clindamycin, and Vamcomycin are treatments of choice

Streptococcus pneumonia treatment with penicillin.

penicillin-resistant strains may also be resistant to erythromycin, macrolides, and clindamycin and the quinolones.

Vaccination

– _{Vaccine possible} – _{Target against M}

• _{Is there a vaccine that can prevent infections?}

• _{Yes. There are two different vaccines – one primarily for adults and one for children.} The vaccine for adults has been available for many years and is called the

pneumococcal polysaccharide vaccine (Pneumovax or Pneu-Imune). It is effective in preventing the most serious complications of pneumococcal infection. The pediatric vaccine is called the pneumococal conjugate vaccine (Prevnar) and is only for use in children under 5 years of age.

• _{Possible problems}