Streptococci assist. Prof. - PowerPoint Presentation

Slide1

Streptococci

assist. Prof.

Zainab

Abdul

jabar

Aldhaher

Slide2

Streptococcus

is a

genus

of

spherical

Gram-positive

bacteria

belonging to the

phylum

Firmicutes

]

and the

lactic acid bacteria

group.

Cellular division

occurs along a single

axis

in these bacteria, and thus they grow in chains or pairs, hence the name. Contrast this with

staphylococci

, which divide along multiple axes and generate grape-like clusters of

cells

.

Slide3

Streptococci comprise a diverse group of Gram-positive

cocci

, which continuously undergo taxonomic revision.

They are distributed widely in humans and animals, mostly forming part of their normal flora. A few species cause significant human morbidity. The

oral streptococci

, which include the cariogenic

mutans

group, are important members of the

genus.

Streptococci

General properties

Characteristics

They are catalase-negative, Gram-positive spherical or oval

cocci

in pairs and chains; 0.7–0.9

μm

in diameter. Chain formation is best seen in liquid cultures or pus

.

Slide4

Streptococci

Characters of Streptococci

Gram positive

cocci

Chains

or pairs

Usually capsulatedNon motileNon spore formingFacultative anaerobesFastidiousCatalase negative (Staphylococci are catalase positive)

Slide5

Classification of Streptococci

Streptococci can be classified according to:

Oxygen requirements

Anaerobic (

Peptostreptococcus

)

Aerobic or facultative anaerobic (Streptococcus)Serology (Lanciefield Classification)Hemolysis on Blood Agar (BA)

Slide6

Optochin

Susceptibility Test

Principle:

Optochin

(OP) test is presumptive test that is used to identify

S.

pneumoniaeS. pneumoniae is inhibited by Optochin reagent (<5 µ

g/ml) giving a inhibition zone ≥14 mm in diameter.

Procedure:

BAP inoculated with organism to be tested

OP disk is placed on the center of inoculated BAP

After incubation at

37oC for 18

hrs

, accurately measure the diameter of the inhibition zone by the ruler

≥14

mm zone of inhibition around the disk is considered as positive and ≤13 mm is considered negative

S.

pneumoniae

is positive (S) while

S.

viridans

is negative (R)

Slide7

Serology:

Lanciefield

Classification

Streptococci classified into many groups from A-K & H-V

One or more species per group

Classification based on C- carbohydrate antigen of cell wall

Groupable streptococciA, B and D (more frequent)C, G and F (Less frequent)

Non-

groupable

streptococci

S.

pneumoniae

(pneumonia)

viridans streptococcie.g. S. mutansCausing dental carries

Slide8

group A

includes the important human pathogen

Streptococcus

pyogenes

group

B

contains one species, Streptococcus agalactiae, an inhabitant of the female genital tract; it causes infection in neonatesgroup C mainly causes diseases in animalsgroup D includes the enterococci (Enterococcus faecalis, etc.) and ranks next to group A in causing human disease.

Slide9

Slide10

Classification of Streptococci Based on Hemolysis on Blood Agar

Hemolysis on BA

-hemolysis

Partial hemolysis

Green discoloration around the colonies

e.g. non-

groupable

streptococci (

S.

pneumoniae

&

S.

viridans

)

-hemolysis

Complete hemolysis

Clear zone of hemolysis around the colonies

e.g.

Group A & B (S. pyogenes & S. agalactiae)-hemolysisNo lysise.g. Group D (Enterococcus spp)

Slide11

Hemolysis on Blood agar

-hemolysis

-hemolysis

-hemolysis

Slide12

Transmission

Most streptococci are part of the normal flora of the human throat, skin, and intestines but produce disease when they gain access to tissues or blood.

Viridans

streptococci and 

S.

pneumoniae

 are found chiefly in the oropharynx;S. pyogenes is found on the skin and in the oropharynx in small numbers; S. agalactiae

 occurs in the 

vagina

 and colon; and both the enterococci and anaerobic streptococci are located in the 

colon

.

Slide13

Group A streptococci

Include only

S.

pyogenes

Group A streptococcal infections affect all ages peak incidence at 5-15 years of age

90% of cases of pharyngitis

Slide14

Pathogenesis and Virulence Factors

Structural components

M protein M, which interferes with

opsonization

and

lysis

of the bacteriaLipoteichoic acid & F protein adhesionHyaluronic acid capsule, which acts to camouflage the bacteriaEnzymes

Streptokinases

Deoxynucleases

C5a peptidase

Pyrogenic toxins that stimulate macrophages and helper T cells to release cytokines

Streptolysins

Streptolysin O lyse red blood cells, white blood cells, and plateletsStreptolysin S

facilitate the spread of streptococci through tissues

Slide15

Disease caused by

S.

pyogenes

Suppurative

Non-Invasive

Pharyngitis (

“strep throat”)-inflammation of the pharynxSkin infection, Impetigo

Invasive

Scarlet fever-rash that begins on the chest and spreads across the body

Pyoderma

-confined, pus-producing lesion that usually occurs on the face, arms, or legs

Necrotizing fasciitis-toxin production destroys tissues and eventually muscle and fat tissue

Non

SuppurativeRheumatic fever: Life threatening inflammatory disease that leads to damage of heart valves muscleGlomerulonephritits

Immune complex disease of kidney

inflammation of the glomeruli and nephrons which obstruct blood flow through the kidneys

Slide16

Differentiation between

-hemolytic streptococci

The following tests can be used to differentiate between

-hemolytic streptococci

Lanciefield

Classification

Bacitracin susceptibility TestSpecific for S. pyogenes (Group A)CAMP testSpecific for S.

agalactiae

(Group B)

Slide17

Bacitracin sensitivity

Principle:

Bacitracin test is used for presumptive identification of group A

To distinguish between

S.

pyogenes

(susceptible to B) & non group A such as S. agalactiae (Resistant to B)Bacitracin will inhibit the growth of gp A Strep.

pyogenes

giving zone of inhibition around the disk

Procedure:

Inoculate BAP with heavy suspension of tested organism

Bacitracin disk (0.04 U) is applied to inoculated BAP

After incubation, any zone of inhibition around the disk is considered as susceptible

Slide18

CAMP test

Principle:

Group B streptococci produce extracellular protein (CAMP factor)

CAMP act synergistically with staph.

-

lysin

to cause lysis of RBCs

Procedure:

Single streak of

Streptococcus

to be tested and a

Staph.

aureus

are made perpendicular to each other3-5 mm distance was left between two streaksAfter incubation, a positive result appear as an arrowhead shaped zone of complete hemolysisS.

agalactiae

is CAMP test positive while non

gp

B streptococci are negative

Slide19

CAMP test

Slide20

Differentiation between

-hemolytic streptococci

The following definitive tests used to differentiate between

S.

pneumoniae

&

viridans streptococciOptochin Test

Bile Solubility Test

Inulin Fermentation

Slide21

Optochin

Susceptibility Test

Optochin susceptible

S. pneumoniae

Optochin resistant

S. viridans

Slide22

Bile Solubility test

Principle:

S.

pneumoniae

produce a self-lysing enzyme to inhibit the growth

The presence of bile salt accelerate this processProcedure:Add ten parts (10 ml) of the broth culture of the organism to be tested to one part (1 ml) of 2% Na

deoxycholate

(bile) into the test tube

Negative control is made by adding saline instead of bile to the culture

Incubate at 37oC for 15 min

Record the result after 15 min

Slide23

Bile Solubility test

Results:

Positive test appears as clearing in the presence of bile while negative test appears as turbid

S.

pneumoniae

soluble in bile whereas

S. viridans insoluble

Slide24

Differentiation between

-hemolytic streptococci

CAMP test

Bacitracin

sensitivity

Hemolysis

Negative

Susceptible



S. pyogenes

Positive

Resistant



S.

agalactiae

Inulin Fermentation

Bile solubility

Optochin sensitivity

Hemolysis

Not ferment

Soluble

Sensitive (≥ 14 mm)



S. pneumoniae

Ferment

Insoluble

Resistant

(≤13 mm)



Viridans

strep

Differentiation between

-hemolytic streptococci

Slide25

STREPTOCOCCUS PNEUMONIAE

Diseases

Pneumococci cause pneumonia, bacteremia, meningitis, and infections of the upper respiratory tract such as otitis media and sinusitis.

Pneumococci

are gram-positive lancet-shaped

cocci

arranged in pairs (diplococci) or short chains. (The term “lancet-shaped” means that the diplococci are oval with somewhat pointed ends rather than being round.)

On blood agar they produce alpha-hemolysis. In contrast to

viridans

streptococci, they are lysed by bile or

deoxycholate

and their growth is inhibited by

optochin

.

Slide26

Pneumococci possess 

polysaccharide capsules

 of more than 85

antigenically

distinct types. With type-specific antiserum, capsules swell (

quellung

reaction), and this can be used to identify the type. Capsules are virulence factors; i.e., they interfere with phagocytosis and favor invasiveness. Specific antibody to the capsule opsonizes the organism, facilitates phagocytosis, and promotes resistance. Such antibody develops in humans as a result either of infection (asymptomatic or clinical) or of administration of polysaccharide vaccine. Capsular polysaccharide elicits primarily a B-cell ( i.e., T-independent) response.

Slide27

Another important surface component of 

S.

pneumoniae

 is a carbohydrate in the cell wall called 

C-substance.

 This carbohydrate is medically important, not for itself, but because it reacts with a normal serum protein made by the liver called 

C-reactive protein (CRP). CRP is an “acute-phase” protein that is elevated as much as a 1000-fold in acute inflammation.CRP appears to be a better predictor of heart attack risk than an elevated cholesterol level.

Slide28

Transmission

Humans are the natural hosts for pneumococci; there is no animal reservoir. Because a proportion (5–50%) of the healthy population harbor virulent organisms in the oropharynx, pneumococcal infections are not considered to be communicable. Resistance is high in healthy young people, and disease results most often when predisposing

factors

Slide29

 Pneumococci are a prominent cause of otitis media, sinusitis, purulent bronchitis, pericarditis, bacterial meningitis, and sepsis, especially in

immunocompromised

patients

.

Treatment

Most pneumococci are susceptible to

penicillins and erythromycin. In severe pneumococcal infections, penicillin G is the drug of choice, whereas in mild pneumococcal infections, oral penicillin V can be used. In penicillin-allergic patients, erythromycin or one of its long-acting derivatives, e.g., azithromycin

Slide30

Oral streptococci

Streptococci

have been isolated from all sites in the mouth

and comprise

a large proportion of the resident cultivable oral

microbiota

.

Oral streptococci are generally alpha-

haemolytic

(partial

haemolysis

) on

blood agar, and early workers called them

viridans streptococci

.

Oral streptococci can be divided into four main

species groups

as follows:

1. mutans group2. salivarius group3. anginosus group4. mitis group.Each of these groups comprises a number of species.

Slide31

Species

of oral streptococci isolated from humans

Slide32

Mutans

group (

mutans

streptococci)

potential

role in the

aetiology

of dental caries.

Streptococcus

mutans

was

originally isolated from carious human teeth by Clarke in

1924 and shortly afterwards, was recovered from a case of

infective endocarditis.

Mutans

streptococci are recovered

almost exclusively from

hard, non-shedding surfaces in the mouth, such as teeth or dentures, Mutans streptococci are regularly isolated from dental plaque at carious sites and can act as opportunistic pathogens, being isolated from cases of infective endocarditis.is generally a result of their entry into the blood stream during intraoral surgical procedures (e.g. tooth extraction), Treatment and preventionIn patients at risk of infective endocarditis (e.g. those with damaged or prosthetic heart valves), prophylactic antibiotic cover should always be given before dental procedures.

Slide33

Gelatinous

colonies of

mutans

streptococci mainly comprising

extracellular polysaccharides