Streptococci and Other Streptococci-like Organisms.

Streptococci and Other

Streptococci-like Organisms

W.B. Saunders Company items and derived items copyright © 2001 by W.B. Saunders Company.

Case Study

9-year-old boy complains of fever and sore throat On examination, his pharynx is red and his tonsils are

swollen His cervical lymph nodes are also swollen A throat culture is taken


Points to Consider

Clinical symptoms presented by the patient The serious complications that may result from this type

of infection How to recover and identify the infecting organism What other species are involved in clinical infections Other points to consider


Streptococcus and Enterococcus: General Characteristics

Gram-positive, facultatively anaerobic cocci

Most are typically spherical; some may appear elongated



Appear in chains when smears are prepared from broth cultures

Catalase-and oxidase-negative


Streptococcus and Enterococcus: Habitat and Clinical Infections

Habitat Indigenous respiratory

tract microbial flora of animals and humans

Certain species are also found in the gastrointestinal and urogenital tracts of humans

Clinical infections Upper and lower

respiratory tract infections

Urinary tract infections Wound infections Endocarditis


Streptococcus and Enterococcus: Cell Wall Structure

Thick peptidoglycan layer Teichoic acid C=carbohydrate layer

present except in viridans group

Capsule in S. pneumoniae and in young cultures of most species



Hemolytic Patterns Beta (ß) a clear,

colorless zone around the colony caused by complete hemolysis of the red blood cells in the agar


Streptococcus and Enterococcus: Hemolytic Patterns

Alpha (a):hemolysis showing a greenish discoloration around the area surrounding the colony due to incomplete hemolysis of the red blood cells in the agar


Streptococcus and Enterococcus: Hemolytic Patterns

No hemolysis (gamma): colonies show no hemolysis or discoloration


Classification of Streptococcus and Enterococcus

Species Hemolysis Group Antigen

CommonTerms

Disease Association(s)

S.pyogenes ß A Group Astreptococci

Pharyngitis; scarlet feverpyoderma; rheumaticfever; AGN

S.agalactiae ß B Group Bstreptococci

Neonatal sepsis;puerperal fever;pyogenic infections;pneumonia; meningitis

S. equisimilis ß C Group Cstreptococci

Pharyngitis; impetigo;pyogenic infections

E. faecalisE. faeciumE. durans

S. bovisS. equinus

Alpha or nohemolysis ( rarely ß )

Alpha ()ornone (rarely ß)

D

D

Enterococci

Nonenterococci

Urinary tract infectionsWound infectionsBacteremia;EndocarditisUrinary tract; pyogenicinfections;Endocarditis infections

S. pneumoniae Alpha ()hemolysis

Pneumococcus Bacteremia;pneumonia;meningitis;

Viridans andNonhemolyticS. sanguisS. salivariusS. mitis ornonhemolytic S. milleri S. mutans

Other species

Alpha ()hemolysis or

nohemolysis

- Viridans strep Endocarditis

Dental caries


Biochemical Identification

Susceptibility tests Bacitracin (0.04 units) or

“A” disk Identifies Group A

streptococci

Group A streptococcus is susceptible to “A” disk (left)



Susceptibility test Trimethoprim sulfamethoxazole

(SXT) Inhibits beta-hemolytic

streptococcal groups other than A and B

Group A streptococcus growing in the presence of SXT



Susceptibility test Optochin “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 other viridans streptococci do not lyse



PYR hydrolysis Substrate L-pyrrolidonyl-

napthlyamide (PYR) is hydrolyzed by Group A Streptococci and Enterococcus sp.

As specific as 6.5% NaCl broth for Enterococcus sp.

More specific than Bacitracin for Group A streptococci

PYR test for Group A streptococci and enterococci. Both are positive for this test (right); left is a negative result



Hydrolysis Hippurate hydrolysis

Differentiates Group B streptococci from other beta hemolytic streptococci

Group B streptococci hydrolyzes sodium hippurate



Christie-Atkins, Munch-Petersen (CAMP) test Detects the production of

enhanced hemolysis that occurs when -lysin and the hemolysins of Group B streptococci come in contact

Group B streptococci showing the classical “arrow-shaped hemolysis near the staphylococcus streak



Bile Esculin hydrolysis Ability to grow in 40% bile and

hydrolyze Esculin are features of streptococci that possess Group D antigen

Growth in 6.5% NaCl broth Differentiates Group D

streptococci from enterococci

Both Group D streptococci and enterococci produce a positive (left) bile Esculin hydrolysis test.


Clinically Significant Streptococci: Streptococcus pyogenes or Group A Beta-Hemolytic Streptococci

Bacterial structure

Fimbrae: attachment and adherence

M protein: major virulence factor

Hyaluronic acid capsule: prevents phagocytosis


Streptococcus pyogenes or Group A Streptococci: Additional Virulence Factors

Hemolysins Streptolysin O Streptolysin S

Erythrogenic toxin Enzymes

Streptokinase DNases Hyaluronidase


Streptococcus pyogenes (Group A) Streptococcal Infections

Acute bacterial pharyngitis Sore throat Malaise Fever/headache

Scarlet fever Pyodermal infections

Impetigo Erysipelas

Erysipelas due to Streptococcus pyogenes


Post–Group-A Streptococcal Infections

Rheumatic fever from pharyngeal infections only Fever Inflammation of the heart, joints, blood vessels, and

subcutaneous tissues Chronic, progressive damage to the heart valves


Post–Group-A Streptococcal Infections

Acute glomerulonephritis from either cutaneous or pharyngeal infections More common in children than adults Antigen-antibody complexes deposit in the glomerulus Inflammatory response causes damage to the glomerulus

and impairs the kidneys


Invasive Group A Streptococcal Infections

Streptococcal toxic shock syndrome Multi-organ system failure similar to staphylococcal toxic shock Initial infection may have been pharyngitis, cellulitis, peritonitis,

or other wound infections


Invasive Group A Streptococcal Infections: “Flesh-Eating Bacteria”

Cellulitis Severe form of infection that is life-threatening Bacteremia and sepsis may occur In patients necrotizing fasciitis, edema, erythema, and pain in

the affected area may develop Streptococcal myositis resembles clostridial gangrene


Laboratory Diagnosis: Group A Streptococcus

Grams stained wound smear showing gram-positive cocci in chains with numerous “polys”



Colony morphology Transparent, smooth, and

well-defined zone of complete or- hemolysis



Identification Catalase-negative Bacitracin-susceptible PYR-positive Bile-esculin–negative 6.5% NaCl-negative

Group A streptococci is susceptible to Bacitracin disk (left); The right shows resistance


Group B -Hemolytic Streptococcus (Staphylococcus agalactiae)

Has been known to cause mastitis in cattle Colonize the urogenital tract of pregnant women Cause invasive diseases in newborns

Early-onset infection Late-onset disease


Staphylococcus agalactiae: Invasive Infections

Early-onset infection Occurs in neonates who are less than 7 days old neonates Vertical transmission of the organism from the mother Manifests in the form of pneumonia or meningitis with

bacteremia Associated with a high mortality rate


Staphylococcus agalactiae: Invasive Infections

Late-onset infection Occurs between 1 week and 3 months after birth Usually occurs in the meningitis form Mortality rate is not as high as early-onset

In adults Occurs in immunosuppressed patients or those with

underlying diseases Often found in a previously healthy adult who just

experienced childbirth


Laboratory Diagnosis: Group B -Hemolytic Streptococcus

Colony morphology Grayish-white, mucoid,

creamy, narrow zone of -hemolysis

Presumptive Identification tests Catalase-negative Bacitracin-resistant


Laboratory Diagnosis: Group B -Hemolytic Streptococcus

Presumptive identification tests Bile-esculin-hydrolysis–

negative Does not grow in 6.5%

NaCl CAMP-test–positive

S. agalactiae shows the arrow-shaped hemolysis near the staphylococcus streak, showing a positive test for CAMP factor


Identification Schema

Schema to differentiate Group A and B from other b-hemolytic streptococci


Streptococcus Group D and Enterococcus Species

Members of the gut flora Associated infections

Bacteremia Urinary tract infections Wound infections Endocarditis


Laboratory Diagnosis: Streptococcus Group D and Enterococcus Species

Microscopic morphology Cells tend to elongate

Colony morphology Most are non-hemolytic,

although some may show or, rarelyhemolysis

Possess Group D antigen


Laboratory Diagnosis: Streptococcus Group D and Enterococcus Species

Identification tests Catalase: may produce a weak catalase reaction Hydrolyze bile esculin Differentiate Group D from Enterococcus sp. with 6.5% NaCl or

PYR test



Schema to differentiate Enterococcus and Group D streptococci from other nonhemolytic streptococci


Other Streptococcal Species

Viridans group Members of the normal oral and nasopharyngeal flora Includes those that lack the Lancefield group antigen Most are hemolytic but also includes nonhemolytic

species The most common cause of subacute bacterial endocarditis

(SBE)


Streptococcus pneumoniae

General characteristics Inhabits the nasopharyngeal areas of healthy individuals Typical opportunist Possess C substance

Virulence factors Polysaccharide capsule

Clinical infections pneumonia meningitis bacteremia sinusitis/otitis media


Laboratory Diagnosis:Streptococcus pneumoniae

Microscopic morphology Gram-positive cocci in

pairs; lancet-shaped


Laboratory Diagnosis:Streptococcus pneumoniae

Colony morphology Smooth, glistening,

wet-looking, mucoid

-Hemolytic CO2enhances

growth


Laboratory Diagnosis: Streptococcus pneumoniae

Identification Catalase negative Optochin-

susceptibility-test–susceptible

Bile-solubility-test–positive



Schema to differentiate S. pneumoniae from other -hemolytic streptococci


Streptococcus-Like Organisms

Aerococcus Gram-positive cocci that tend to form tetrads -hemolytic; and may resemble viridans group May be confused with Enterococcus biochemically


Streptococcus-Like Organisms

Leuconostoc Resemble streptococci microscopically; colonies resemble

viridans group or Enterococcus Found in plants, vegetables, and dairy products

Pediococcus Found in nature; used in bioprocessing and biopreservation

of foods such as cheese, meats, and vegetables Rarely seen in human infections; has been associated with

septicemia


Points to Remember

General characteristics and hemolytic patterns of

streptococcal and enterococcal species Infections produced by pathogenic species Microscopic and colony morphology Tests used to identify these species Emergence of resistant strains

Streptococci and Other Streptococci-like Organisms.

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