MICROBIOLOGY-CATALASE NEGATIVE, GRAM-POSITIVE COCCI (STREPTOCOCCUS, ENTEROCOCCUS, AND SIMILAR ORGANISMS) Flashcards
What are the most commonly encountered bacteria in human infections?
S. pyogenes, S. agalactiae, S. pneumoniae, E. fecalis, and E. faecium.
iDENTIFY
- Catalase-negative
- Gram-positive cocci in pairs or chains
- Facultative anaerobe
STREPTOCOCCUS, ENTEROCOCCUS, AND SIMILAR ORGANISMS
CHARACTERISTIC NI Streptococcus
pyogenes (Group A)
- Gram-positive cocci in
chains - Lancefield group A
- Group A streptococcus
- β-hemolytic group A
streptococcus - Bacitracin sensitive
- PYR test positive
What are common habitats of Streptococcus
pyogenes in the human body?
- Not considered normal microbiota
- Inhabits skin and upper respiratory tract
of humans; carried on nasal, pharyngeal,
and sometimes anal mucosa
What are the modes of transmission for Streptococcus pyogenes
- Direct contact: person to person
- Indirect contact: aerosolized
droplets from coughs and sneezes
Virulence factors ni Streptococcus
pyogenes
Streptolysin O
Streptolysin S
Streptococcal pyrogenic exotoxins (SPEs)
M protein
Hyaluronidase
C5a peptidase
Erythrogenic toxin
Streptokinase
Protein F
DNASeB
Exotoxin B
IDENTIFY
- Responsible for the β-hemolytic pattern on blood agar plates
- Oxygen-labile, immunogenic, capable of lysing erythrocytes, leukocytes, platelets, and cultured cells in the absence of room air
- Inhibited by cholesterol in skin lipids (no immunity associated with skin
infections)
Streptolysin O
- Responsible for the β-hemolytic pattern on blood agar plates
- Oxygen-stable, nonimmunogenic hemolysin, capable of lysing erythrocytes,
leukocytes, and platelets in the presence of room air
Streptolysin S
- Erythrogenic toxins produced by the lysogenic strains
- Heat labile
- Superantigens, activating macrophages, T-helper cells, and immune mediators
Streptococcal pyrogenic exotoxins (SPEs)
- Causes the streptococcal ell to resist phagocytosis
- Enables the bacterial cell to adhere to mucosal cells
M protein
- Spreading factor
- Favors the spread of the organism through tissues
Hyaluronidase
- Serine protease capable of inactivating C5a
C5a peptidase
- Causes red spreading rash in scarlet fever
Erythrogenic toxin
- Causes lysis of fibrin clots
Streptokinase
- Fibronectin-binding protein that facilitates adhesion to epithelial cells
Protein F
- Protease that rapidly destroys tissue
Exotoxin B
Antigenic and antibodies can be detected following infection
DNASeB
What is the most common bacterial cause of strep throat?
Streptococcus pyogenes
What age group is most frequently affected by acute pharyngitis?
Children between ages 5 and 15 years old.
How is strep throat diagnosed?
By throat culture or a positive quick “strep” test.
What are the characteristic lesions of impetigo?
Perioral blistered lesions with honey-colored crusts.
What is a complication of impetigo?
Post-streptococcal glomerulonephritis (GN).
A superficial infection that extends into the dermal lymphatics.
erysipelas
What enzyme facilitates the spread of cellulitis?
Hyaluronidase (spreading factor).
A rapidly progressive infection of deep subcutaneous tissues facilitated by exotoxin B.
necrotizing fasciitis
Deeper infection involving subcutaneous or dermal tissues
Cellulitis
What toxins are associated with scarlet fever?
Streptococcal pyrogenic exotoxins (SPEs)
What are the characteristic symptoms of scarlet fever?
Rash of the upper face and trunk (sandpaper-like), and strawberry tongue.
Occurs in association with streptococcal pharyngitis
Scarlet fever
Multisystem involvement: renal and respiratory failure, rash, and diarrhea.
Streptococcal Toxic Shock Syndrome
What mediates streptococcal toxic shock syndrome?
Production of potent SPE.
Are blood cultures often positive in streptococcal toxic shock syndrome?
Yes.
What protein mediates rheumatic fever?
M protein.
Identify
Symptoms: Fever, endocarditis, subcutaneous nodules, and polyarthritis.
Rheumatic Fever
What type of infection typically leads rheumatic fever?
A respiratory tract infection believed to be caused by S. pyogenes.
What mediates acute glomerulonephritis?
M protein.
What are the symptoms of acute glomerulonephritis?
Edema, hypertension, hematuria, and proteinuria.
What causes immune complex deposition on the glomerular basement membrane in acute glomerulonephritis?
M protein.
What conditions can lead acute glomerulonephritis?
Post-impetigo or postpharyngitic.
What are the microscopic characteristics of Streptococcus pyogenes?
-Gram-positive cocci,
-short chains or pairs,
-round to oval-shaped, occasionally forming elongated cells resembling pleomorphic corynebacterial or lactobacilli.
What media are used for the cultivation of Streptococcus pyogenes?
-5% sheep blood agar
-chocolate agar.
-Throat swabs use 5% sheep blood agar with trimethoprim-sulfamethoxazole (SXT).
what are the colony characteristics of Streptococcus pyogenes on blood agar?
Small, transparent, and smooth colonies with β-hemolysis.
What is the purpose of the bacitracin test?
Presumptive identification and differentiation of β-hemolytic group A streptococci (S. pyogenes - susceptible) from other β-hemolytic streptococci.
What indicates a positive bacitracin test?
Any ZOI greater than 10 mm (SUSCEPTIBLE).
What indicates a negative bacitracin test?
No ZOI (RESISTANT).
What is the name of the disk used in the bacitracin susceptibility test?
TaxoA disk.
How many units of bacitracin are in the TaxoA disk used for susceptibility testing?
0.04 units.
What is the purpose of the PYR test?
Presumptive identification of Group A streptococci (S. pyogenes) and enterococci by the presence of the enzyme L-pyrrolidonyl arylamidase.
What indicates a positive PYR test?
Bright red color within 5 minutes.
What indicates a negative PYR test?
No color change or an orange color.
What enzyme hydrolyzes the substrate L-pyrrolidonyl-β-naphthylamide?
L-pyrrolidonyl arylamidase.
What is the product formed when L-pyrrolidonyl arylamidase hydrolyzes L-pyrrolidonyl-β-naphthylamide?
β-naphthylamine.
Which reagent is used to detect β-naphthylamine in the L-pyrrolidonyl arylamidase test?
N,N-dimethylaminocinnamaldehyde.
What type of reaction does L-pyrrolidonyl arylamidase catalyze?
The hydrolysis of L-pyrrolidonyl-β-naphthylamide.
Which serodiagnostic test is associated with pyoderma and skin infections?
Anti-Dnase B
What are some serodiagnostic tests for Streptococcus pyogenes infections?
Anti-streptolysin O (ASO), Anti-Dnase B, Antistreptokinase, and Antihyaluronidase.
What are the characteristics of Streptococcus agalactiae(Group B)
- Gram-positive cocci in chains
- Lancefield group B
- Group B streptococcus
- β-hemolytic group B streptococcus
- Bacitracin resistant
- CAMP test positive
- PYR negative
- Hippurate hydrolysis positive
- Resistant to SXT
What are common habitats of Streptococcus
agalactiae in the human body?
- Normal microbiota: Female genital tract and lower genital tract
- Occasional colonizer of upper respiratory tract
What are the modes of transmission for Streptococcus agalactiae
- Endogenous strain: gaining access to sterile sites probable
- Direct contact: person to person from mother in utero or during delivery; nosocomial transmission by unwashed
hands of mother or health care personnel
VIRULENCE FACTORS ni Streptococcus
agalactiae
-Capsule
-Others (DNAse, hyaluronidase)
Most important virulence factor
Capsule
Not been shown to be factors in infection
Others (DNAse, hyaluronidase)
How do neonates typically acquire pneumonia caused by Streptococcus pyogenes?
By inhaling organisms as they pass down the birth canal
At what age is pneumonia most commonly seen in neonates due to Streptococcus pyogenes?
0-2 months old
What are the common infections caused by Streptococcus pyogenes in neonates and infants?
Pneumonia, meningitis, and sepsis.
What postpartum infection can Streptococcus pyogenes cause in adults, and what can it lead to?
Endometritis, which can lead to pelvic abscesses and septic shock.
What are some of the infections caused by Streptococcus pyogenes in adults?
Bacteremia, pneumonia, endocarditis, arthritis, osteomyelitis, and skin and soft tissue infections.
Which group of adults is particularly at risk for Streptococcus pyogenes infections?
Immunocompromised adults.
What are the microscopic characteristics of Streptococcus pyogenes in clinical specimens and culture?
Gram-positive cocci that form short chains in clinical specimens and long chains in culture.
What are the colony characteristics of Streptococcus pyogenes on blood agar?
Grayish-white mucoid colonies surrounded by a small zone of β-hemolysis.
What medium is used for genital carriage of GBS during pregnancy?
Vaginal or rectal swab inoculated into Todd-Hewitt broth (gentamicin, nalidixic acid, or colistin and nalidixic acid) such as LIM.
What color do colonies of GBS appear on CHROMagar StrepB?
Mauve colored.
What is the purpose of the CAMP test?
To differentiate GBS (S. agalactiae - positive) from other streptococcal species.
What indicates a positive CAMP test?
Enhanced hemolysis is indicated by an arrowhead-shaped zone of beta-hemolysis at the juncture of the two organisms.
How does the CAMP factor function?
It acts synergistically with the beta-lysin of Staphylococcus aureus to enhance the lysis of red blood cells (RBCs).
How is the CAMP test set up on a sheep blood agar plate?
Staphylococcus aureus is streaked in a straight line on the agar, and the test organism (such as GBS) is streaked perpendicular to the S. aureus streak.
What enzyme is used for the presumptive identification of a variety of organisms in the hippurate hydrolysis test?
Hippuricase.
It is used for the presumptive identification of various organisms by detecting the production of the enzyme hippuricase.
Hippurate Hydrolysis test
CHARACTERISTICS NI Streptococcus
pneumoniae
- Gram-positive “lancet-shaped” cocci
- Alpha-hemolytic
- Bile solubility sensitive
- Optochin sensitive
- Positive Quellung reaction
What is the principle reaction involved in the Hippurate Hydrolysis test?
Hippuric acid is broken down into glycine and benzoic acid.
What is the visual indicator of a positive Hippurate Hydrolysis test?
purple-colored product indicates a positive test result.
Which compound is deaminated by ninhydrin in the Hippurate Hydrolysis test?
Glycine
What are common habitats of Streptococcus
pneumoniae in the human body?
Colonizer of the nasopharynx
- Key virulence factor
- Inhibits phagocytosis
- 80 antigenic types
Capsule
VIRULENCE FACTORS NI Streptococcus
pneumoniae
CAPSULE
PNEUMOLYSIN
PHOSPHORYCHOLINE
MODE OF TRANSMISSION NI Streptococcus
pneumoniae
Direct contact: person to person with contaminated respiratory secretions
- Activates the cell the classical complement pathway
- Mediates the suppression of the oxidative burst of the phagocytes
Pneumolysin
- Binds to receptors for platelet-activating factor in endothelial cells, leukocytes,
platelets, and tissue cells of the lungs and meninges providing for entry and
spread of the organism
Phosphorylcholine
What are some common infections caused by Streptococcus pneumoniae?
Sinusitis, otitis media, bacteremia, and meningitis.
What percentage of bacterial pneumonia cases are caused by Streptococcus pneumoniae?
95% of all bacterial pneumonia
What is the leading cause of bacterial meningitis in infants, young children, and adults in the US?
Streptococcus pneumoniae.
Which bacteria follow Streptococcus pneumoniae as common causes of bacterial meningitis in the US?
Neisseria meningitidis and Haemophilus influenzae.
How does optochin work in the susceptibility test?
Optochin interferes with the ATPase and production of ATP in microorganisms, inhibiting the growth of susceptible organisms and creating a zone of inhibition (ZOI) around the disk.
What is the purpose of the optochin (P disk) susceptibility test?
To determine the effect of optochin on an organism and differentiate Streptococcus pneumoniae (susceptible) from other alpha-streptococci (resistant).
What indicates a positive optochin test?
A ZOI of at least 14 mm with a 6 mm disk (SUSCEPTIBLE).
What indicates a negative optochin test?
No ZOI (RESISTANT).
What is the purpose of the bile solubility test?
To differentiate Streptococcus pneumoniae (positive; soluble) from alpha-hemolytic streptococci (negative; insoluble).
How does the bile solubility test work?
Bile or a solution of a bile salt (sodium deoxycholate) rapidly lyses pneumococcal colonies, depending on the presence of amidase.
What indicates a positive bile solubility test?
Colony disintegrates; an imprint of the lysed colony may remain in the zone.
What does the Quellung test detect?
Capsular subtypes of Streptococcus pneumoniae.
What indicates a negative bile solubility test?
Intact colonies.
How does the Quellung test work?
It is a microscopic “precipitin test” in which the capsules surrounding the pneumococci appear to swell.
what are the characteristics ni Enterococcus
- Previously classified as Group D
- PYR positive
- Posses group D antigen
- Grows in 6.5% NaCl
- LAP positive
HABITAT ni Enterococcus
- Normal microbiota: humans, animals, and birds
- E. faecalis and E. faecium are normal
flora of the human GIT and female GUT - Colonizers
Mode transmission ni Enterococcus
- Endogenous strain: gains access to sterile sites
- Direct contact: person to person
- Contaminated medical equipment
Which two Enterococcus species are most commonly encountered as pathogens?
E. faecalis and E. faecium.
From which body sites are Enterococcus species commonly isolated?
The respiratory tract and myocardium.
Which Enterococcus species is most commonly encountered?
E. faecalis.
Which Enterococcus species is more frequently resistant to vancomycin?
E.faecium
Give at least 3 Virulence Factors ni Enterococcus
- Aggregation substance
- Capsular polysaccharides
- Surface carbohydrates
- Ability to translocate across intact intestinal mucosa
- Hemolysis
- Lipoteichoic acid
- Gelatinase
- Superoxide production
- Peptide inhibitors
- Ability to adhere to extracellular
matrix proteins
What are some common infections caused by Enterococcus species?
Urinary tract infections, bacteremia, endocarditis, intraabdominal, pelvic, wound, and soft tissue infections.
What test can be used to differentiate enterococci from non enterococci based on salt tolerance?
The salt tolerance test.
What indicates a positive result in the salt tolerance test?
Visible turbidity in the broth, with or without a color change from purple to yellow.
What indicates a negative result in the salt tolerance test?
No turbidity or color change.
What concentration of NaCl is used in the broth for the High Salt Tolerance Test?
6.5% NaCl is used in the heart infusion broth.
What enzyme is detected in the Leucine Aminopeptidase (LAP) test?
Leucine aminopeptidase.
What are the components of the test medium used in the High Salt Tolerance Test?
The test medium contains 6.5% NaCl, heart infusion broth, glucose, and bromcresol purple as an indicator.
What indicates a positive LAP test?
Development of a red color within 1 minute after adding cinnamaldehyde reagent.
Which antibiotics are Enterococcus species intrinsically resistant to?
Cephalosporins and aminoglycosides.
What indicates a negative LAP test?
No color change or development of a slight yellow color.
What is VRE?
Vancomycin-resistant Enterococcus.
What substrate is used in the Leucine Aminopeptidase Test?
Leucine-beta-naphthylamide.
Are viridans streptococci groupable by Lancefield serology?
No, they are not groupable by Lancefield serology.
They are fastidious, some strains require increased carbon dioxide for growth, and they produce alpha-hemolysis or no hemolysis (greening) on sheep blood agar.
viridans streptococci
What smell is associated with viridans streptococci on chocolate agar?
Butterscotch smell.
What are the groups of viridans streptococci?
Mutans group, salivarius group, bovis group, anginosus group (previously S. milleri group), and mitis group.
Where is the S. anginosus group normally found?
In the oral cavity, oropharynx, gastrointestinal tract (GIT), and vagina.
How do viridans streptococci typically enter tissues?
During dental or surgical procedures.
What infections can viridans streptococci cause?
Tooth abscess, abdominal infections, and late onset prosthetic valve endocarditis.
What is the most common infection caused by viridans streptococci?
Subacute bacterial endocarditis, especially in previously damaged heart valves.
What condition can viridans streptococci cause following trauma or defects?
Meningitis.
Which viridans streptococci group plays a key role in the development of dental caries?
S. mutans.
What other conditions can viridans streptococci cause in immunocompromised patients?
Bacteremia and infection in other sterile sites.
