Streptococcus-AND- Enterococcus PDF

Preview

Summary

STREPTOCOCCUS AND ENTEROCOCCUSStreptococci Gram-positive Spherical, ovoid, or lancet shaped cocci o May be in pairs or in chains  If growth in broth culture Facultatively anaerobic o Catalase negative  Must be careful  Can obtain weak false positive catalase reaction o If obtained inoculum is fro...

Description

STREPTOCOCCUS AND ENTEROCOCCUS Streptococci -

-

-

Gram-positive Spherical, ovoid, or lancet shaped cocci o May be in pairs or in chains  If growth in broth culture Facultatively anaerobic o Catalase negative  Must be careful  Can obtain weak false positive catalase reaction o If obtained inoculum is from a media that has blood  Blood is RBC which has peroxidase activity  Similar to catalase (because of hemoglobin) o Aerotolerant Anaerobes  Grow in the presence oxygen but unable to use oxygen for respiration o Most but not all are beta hemolytic  Except  Enterococci  S. bovis o Can be used as differentiation between Streptococci and Staphylococci Classification HEMOLYSIS β

α or γ

α o

LANCEFIELD GROUP A B C D D D

NONE NONE

SPECIES Streptococcus pyrogenes Streptococcus agalactiae Streptococcus dysgalactiae Enterococci spp Enterococci spp Streptococcus bovis complex (reclassified into four new species) Viridans group Streptococcus pneumoniae

Lancefield group  Because of their polysaccharide, have a common C carbohydrate or polysaccharide that is found in cell wall  Except viridans  C group is basis for Lancefield group  Form of serotyping  Classification scheme discovered in the 1930s

By Rebecca Lancefield After recognising the antigen in the beta-hemolytic streptococci, they were then able to divide other streptococci in various serologic group designated by letters

 



Groups CLASSIFICATION A

ORGANISM S. pyogenes

B

S. agalactiae, S. halichoeri

C

S. equisimilis, S. equi, S. zooepidemicus, S. dysgalactaiae E. faecalis, E. faecium, E. durans, S. bovis (S. gallolyticus, S. infantarius) S. anginosus S. sanguis S. salivarius S. dysgalactiae S. mitis Lactococcus lactis S. suis S. pneumoniae,Viridans group

D

F, G, and L H K L M and O N R and S Nongroupable



Can cause disease in immunocompromised patients

Can cause disease in immunocompromised patients

Types of hemolysis HEMOLYSIS ALPHA

BETA GAMMA/NONHEMOLYTIC ALPHA-PRIME (αP) OR WIDE ZONE

-

NOTES Can cause disease in immunocompromised patients Can cause disease in immunocompromised patients

Abiotrophia or Granulicatella o Nutritionally variant streprococci  Pyridoxal or thiol dependent

DESCRIPTION Partial lysis of RBC Greenish discolouration of area around colony Complete lysis of RBC around colony Clear area around colony No lysis of RBC around colony No change in agar Small area of intact RBC around colony surrounded by a wider zone of complete hemolysis

-

 Satelliting o Will not grow on SBA or chocolate agar  Unless supplemented with Vitamin B6 or pyridoxine  Either by o Placing a pyridoxal disc o Streak the media with Staphylococcus  S. aureus is the one who will release the pyridoxine in RBC o Inoculate in a Vitamin B6 supplemented culture media Beta-hemolytic streptococcus species o S. pyogenes  Group A streptococcus (GAS)  Representative specie of this group  Flesh eating bacteria/Flesh eating Streptococcus  Virulence factor  M protein o Causes the bacterial cell wall to be antiphagocytic o Encoded in the gene EMM o Also place a role in the adherence to mucosal cells  Lipoteichoic acid o Affixed to the proteins on the bacterial surface o Permits bacterial adherence to the respiratory epithelium









 Together with M protein and fibronectin binding protein o Reason why S. pyogenes can cause pharyngitis/strep sore throat Streptolysin O o Antigenic, oxygen-labile enzyme o Produces subsurface hemolysis on blood agar plates o Anti streptolysin O (ASO) test  A test in serology to detect Streptolysin O  Especially on pneumatic fever Streptolysin S o Opposite of Streptolysin O o Non antigenic, oxygen-stable enzyme o Produces surface hemolysis  Observable hemolysis Streptokinase o Promotes fibrinolytic activity by converting plasminogen to plasmin o Similar to Staphylokinase Hyaluronidase o Enhance the spread of the organism through connective tissue

o 

Reason why S. pyogenes is called “flesh eating bacteria”

Pathogenecity  Strep sore throat/Pharyngitis o Commonly associated with S. pyogenes  Tonsillitis  Scarlet fever o Red, spreading rash o Strawberry tongue  Distinct symptom o Streptococcal pyrogenic exotoxin (SPE)  Causative enzyme  Formerly known as erythrogenic toxins  Four immunologically distinct exotoxin (super antigens)  SPE A  SPE B  SPE C  SPE F  Pyodermal infection o The worst effects of S. pyogenes infection o Skin infection o Three types associated with S. pyogenes  Impetigo  Localised skin disease  Usually starts as a small vesicle that would progress into crusty lesions after several days  Common in young children  Happens because of exposure o Abrasions o Insect bites  Erysipelas  Rare, usually seen in elderly patients  Acute spreading skin lesions that is intensely erythematous with plane demarcations but irregular edges  Cellulitis  Deeper invasion  Can be life threatening o Associated with  Bacteremia  Sepsis







o

Can lead to gangrene o If patient has co-morbidities  Vascular disease  Diabetes

Necrotising fasciitis o Invasive infection characterised by rapidly progressing inflammation and necrosis of the skin, subcutaneous fat, and even the underlying muscle o If worst comes to worse, amputation is imminent Sequelae (other diseases) of S. pyogenes o Disease brought about by other disease o Examples  Pneumatic fever  Usually affects heart valves o Serious damage  Follows S. pyogees Pharyngitis o Happens after one month of infection  Characterised by o Fever o Inflammation of the  Heart  Joints  Blood vessels  Subcutaneous tissue  Acute glomerulonephritis  Occur after cutaneous or pharyngeal infection o Not necessarily pharyngitis, but also skin infections  Common of children  Pathogenesis o Deposition of circulating immune complexes in the glomerulus  Triggers complement response (inflammation) that would destroy glomerulus then the kidneys

S. agalactiae  Group B streptococci  Associated diseases  Neonatal sepsis  Pneumonia

o

 Meningitis S. Pneumoniae  Alpha hemolytic, nongroupable  Antiphagocytic polysaccharide capsule  Virulence factor  Associated disease  Community acquired Pneumonia  Meningitis o Especially in infants and elderly Spontaneous bacteremia o In persons who do not have spleen  Otitis o Inflammation of the ear  Sinusitis  Spontaneous peritonitis Specimen appearance  Rusty sputum “Pneumococcal warrior”  Imagine a Knight o Has capsule (armour) o Lancet shaped (weapon) 

 

Commonly associated with the Gram morphology of the Streptococcus spp.  Gram positive, diplococci lobar pneumonia (shield with lung design)  cause of rusty sputum Otitis (pierces the ear with the lance) 

o o o

Viridans Streptococci  Associated diseases  Bacterial endocarditis o Common infection o Grow foliage (verde) in the heart valves  Eats heart valves slowly  Unlike S. aureus  Species  S. bovis o Most common o Bacteremia has been associated with the malignancies of the gastrointestinal tract  Colon cancer

-

Laboratory diagnosis o Proper sampling is very important  Sample must be obtained from the posterior pharynx and tonsillar area  Not in the tongue or cheeks and uvula o Normal bacterial microbiota living in their might interfere with the sample  Exudates must be touched with a swab  Respiratory tract specimen or skin swab  Have lesser value for Streptococcal sampling  has a lot of gram-positive microbiota as part of normal flora o Culture media  Streptococci will grow well on blood and chocolate agar  Vaginal/rectal swabs from pregnant women specifically for Group B Streptococci (S. agalactiae)inoculate first into  Lim/carrot broth/Todd-Hewitt Broth o Selective broth  Granada o Selective agar o Biochemical tests  Group A (S. pyogenes)  Susceptible to bacitracin o Bacitracin test  Principle  A disc (Taxo A) impregnated with a small amount of bacitracin (0.04) units is palced on an agar plate  Result  Positive o Susceptible  Any zone of inhibition greater than 10 mm  Negative o Resistant  No zone of inhibition  Beta-hemolytic  PYR positive o Produces pink colouration  Group B (S. agalactiae)  Beta hemolytic  Hippurate Hydrolysis positive







Positive CAMP text o Christie Atkins Munch Peterson (CAMP) test  Principle  Diffusible extracellular hemolytic protein o CAMP factor o Acts synergistically with the beta-lysin of S. aureus  Enhances RBC lysis o Produced by CAMP positive organisms  GROUP B Streptococci are streaked perpendicularly to a strake of S. aureus on SBA  Results o Positive  Enhanced hemolysis  Indicated by an arrowhead shaped zone of beta hemolysis at the juncture of the two organisms o Negative

 No enhancement of hemolysis S. pneumoniae  Susceptibility to ethylhydroxycupreine hydrochloride (optochin/P disk/Taxo P) o Optochin test  Principle  Optochin impregnated disk (Taxo P) is placed on a lawn of organism on a SBA plate  Result  Positive o Susceptible  Zone of inhibition ≥14 mm in diameter with 6-mm disk  Negative o resistant  No zone of inhibition  Positive for bile solubility  Alpha-hemolytic  Colonies are mucoid or flattened with a depressed center  Quellung test o Capsular swelling Viridans





Alpha hemolytic streptococci o Optochin resistant o PYRase negative Gamma hemolytic streptococci o PYRase negative o Do not grow in 6.5% of NaCl o Caramel odour 

Associated with milleri streptococci

Enterococci -

-

-

Group D Streptococci o Former name o But they have their own genus now Gram positive cocci Occurs singly, in pairs, or in short chains Facultative anaerobic Alpha or gamma hemolytic on blood agar o Some may exhibit Beta-hemolysis Common cause of urinary tract infection in hospitalised persons Common species o Enterococcus faecium o Enterococcus Faecalis Biochemical test o PYRase positive o Grow in the presence of 6.5% NaCl  Salt tolerance test  Principle o Heart infusion broth containing 6.5% NaCl is used as the test medium  Also contains  Small amount of glucose (for sugar) and bromcresol purple (pH indicator) o Indicator for acid production Result o Positive  Visible turbidity of the brotg  With or without a colour change from purple to yellow o Negative  No turbidity  No colour change Hydrolyse esculin in the presence of bile 

o



Causing visible growth and blackening of agar

Characteristics Differentiating Enterococcus and Interfering Organisms (Areococcus, Leuconostoc, and Pediococcus)

Gram stain

Hemolysis Bile esculin Growth in 6.5% NaCl PYR LAP Vancomycin susceptibility

Enterococcus Pairs and short chains

Aerococcus Tetrads

Beta/alpha/gamma + +

Alpha or gamma V +

Leuconostoc Cocci, coccobacilli, and rods; pairs and chains Alpha or gamma V V

+ + S/R

* * S

R

Pediococcus Tetrads and pairs; spherical cells

+ R

Alpha or gamma V...