Medical Microbiology

1st semester

2020-2021

Catalase Negative

Gram Positive Cocci

Genus: Streptococci

Prof. Dr. Amal Talib Al-Sa'ady

Streptococci

Gram -positive spherical bacteria

Pairs or chains.

Widely distributed in nature

members of normal human flora

Associated with serious human diseases.

Elaborate a variety of extracellular

substances and enzymes.

Streptococci

is a large and heterogeneous group of

bacteria. No one system suffices to

classify them,yet. understanding their

taxonomy is key to understanding their

medical importance.

Classification of Streptococci The classification of streptococci has been based on a

series of observations over many years:

1. Colonial Morphology &Microscopic examination

2. Hemolytic Reactions on blood agar

3. Serologic Specificity of the cell wall group-

specific substance (Lancefield antigens) or

capsular antigens.

4. Biochemical tests and resistance to physical

and chemical factors.

5. Ecologic Features.

6. Molecular Genetics have also been used to

study the streptococci.

Combinations of these five methods have permitted the

classification of streptococci for purposes of clinical and

epidemiologic convenience.

Depending On The Type Of

Hemolysis,

Streptococci Are Classified

into:

α, β, and γ.

α -Hemolytic Streptococci Partial hemolysis, the blood agar under the colony

is dark and greenish

hydrogen peroxide produced by this bacteria and

oxidizing Hemoglobin to green Met-hemoglobin. Streptococcus pneumoniae and Viridians

Streptococci display alpha hemolysis.

Strep. pneumoniae is:

capsulated,,, optochin sensitive,,, bile salt soluble

and have autolysis,,,

Viridans streptococci are no capsulated,,, no bile

salt soluble,,, no autolysis,,,and optochin resistant.

Pneumococcal Autolysis: a process is mediated

by cell wall-bound enzyme called Autolysin or

Amidase, which breaks down peptidoglycan in the

cell wall of Strep. pneumoniae

Strep. Pneumoniae

pneumococcus or pneumococci

lancet-shaped diplococci(elongated cocci with

a slightly pointed outer curvature).

pairs of cocci (diplococci).

Possessing anti-phagocytic capsule of

polysaccharide.

a part of the normal flora in upper respiratory

tract, but, as with many normal flora, it can

become pathogenic and spread to other

locations and cause disease.

The Respiratory Tract, Sinuses, and Nasal

Cavity are the parts of host body that are

usually infected with this bacteria.

pathogenesis of Strp. Pneumoniae • Pneumonia

• Bacteremia& Septicemia

• Otitis Media

• Sinusitis

• the main cause of Community Acquired Pneumonia

• Meningitis in children and the elderly

• Septicemia in HIV-patients.

methods of transmission

sneezing,

coughing

direct contact with an infected person.

Once pneumococci colonizes the alveoli, the body

responds by stimulating the inflammatory response.

This causes plasma, blood, and WBC's to fill the

alveoli, This condition is called “Pneumonia”

Virulence Factors of Strp. pneumoniae

1. Pneumolysin

is pore-forming toxin which has the ability of lysis of host cells

and form pores,

and interference with the function of cells and soluble molecules

of the immune system.

This action will aid the bacteria during colonization and

infection.

2. Anti-phagocytic Capsule

polysaccharide capsule prevents phagocytosis.

3. Hydrogen peroxide

causes damage to host cells and has bactericidal effects against

competing bacteria.

4. Pili

are hair-like structures that extend from the surface.

They contribute to colonization of upper respiratory tract.

Viridans Streptococci

The Viridans Streptococci are a large

group of commensal bacteria. In general,

it's pathogenicity is low. This bacteria are

most abundant in the mouth.

Strep. mutans is a member of this group

which is the etiologic agent of dental

caries in most cases and populations.

β-Hemolytic Streptococci

β -hemolytic streptococci

complete hemolysis On blood agar, wide clear zone

surrounding bacterial colonies.

Lancefield Classification: describes 20 serotypes

(Lancefield groups)from A-V (excluding I and J ).

Group A Streptococcus(GAS): Strep. Pyogenes is

Bcitracin sensitive, sodium hippurate hydrolysis(-)

CAMP test(-).

GAS is a part of the skin flora, it is clinically

important in human illness.

has several virulence factors that enable it to attach to

host tissues: bacterial Capsule, M Protein, Lipoteichoic

Acid, and Protein F.

Lancefield groups of β –Hemolytic Streptococci للاطلاع فقط

Group A – Strep. pyogenes

Group B – Strep. agalactiae

Group C – Strep. equisimilis, Strep. Equi, Strep. zooepidemicus, Strep.

dysgalactiae

Group D -Enterococcus faecalis, Enterococcus faecium, and Strep. bovis

Group E - 'Enterococci

Group F,G&L – Strep. anginosus

Group H – Strep. sanguis

Group K – Strep. salivarius

Group L – Strep. dysgalactiae

Group M&O – Strep. mitior

Group N - Lactococcus lactis

Group R&S – Strep. suis

other Streptococcus species are classified as 'non-Lancefield Streptococci'

2. Streptokinase(Fibrinolysin) is proteolytic enzyme digests the fibrin and other proteins.

3. Hyaluronidase facilitates the spread of the bacteria by breaking down hyaluronic

acid.

4. Streptodornase(DNase) depolymerizes DNA and protect the bacteria against the

digesting by neutrophils.

Pathogenesis of Strep. Pyogenes

Strep. pyogenes causes many human diseases, ranging from mild superficial skin

infections to life-threatening systemic diseases.

include pharyngitis (strep throat) and localized skin infection (impetigo, Erysipelas

and cellulitis.

can lead to necrotizing fasciitis, a life-threatening condition requiring surgery.

Throat infections associated with release of certain toxins lead to scarlet fever.

Streptococcal Toxic Shock Syndrome, which can be life-threatening.

also can cause non-pyogenic syndromes with out pus formation such as Rheumatic fever.

Strep. pyogenes remains acutely sensitive to penicillin. Failure of treatment with

penicillin is generally attributed to other local commensal organisms producing β-

lactamase.

Methods of Transmission

include Respiratory droplets, Hand contact with nasal discharge and skin contact with

skin infection.

Group B Streptococcus(GBS): Strep. agalactiae

is characterized by antigen group B of Lancefield grouping can be

detected directly using latex agglutination tests.

The CAMP(+) test is also another important test for identification of

GBS.

able to hydrolyze sodium hippurate(+)but it is Bcitracin resistant.

GBS is a part of the human flora in the gastrointestinal and

genitourinary tract as asymptomatic carriers, including pregnant

women.

causes severe invasive infections.

GBS has virulence factors: anti- phagocytosis capsule, and a pore-

forming toxin( β-hemolysin).

Pathogenesis of GBS

during pregnancy, it causes serious illness for the

mother(chorioamnionitis) and neonate.

GBS Urinary Tract Infection (UTI) may induce labor and cause

premature delivery.

the major cause of several bacterial infections of the neonate,

Septicemia, Pneumoniae, and Meningitis.

Early-Onset Disease (EOD) and Late-Onset Disease (LOD).

Group D streptococci, GDS(Enterococci):

common commensals in the intestines of humans: E. faecalis (90–95%) and E.

faecium (5–10%). Until 1984, classified as group D Streptococcus.

Enterococci have no hemolysis(gamma-hemolysis).

tolerant of a wide range of environmental conditions: extreme temperature(10–

45°C), pH (4.5–10.0), and high sodium chloride concentrations.

In 2004, Enterococci sp. took the place of faecal coliforms as the new federal

standard in USA for water quality at public saltwater beaches.

Because of it's tolerance of bile salt,and it's ability to ferment of lactose,

Enterococci can grow on MacConky agar with pink colonies.

E. faecalis causes life-threatening infections in the nosocomial environment.

E. faecalis survive very harsh environments :pH (9.6), high salt concentrations,

bile salts, detergents, heavy metals, ethanol, azide, and desiccation.

Pathogenesis of E. faecalis E. faecalis can cause endocarditis, septicemia, UTI, meningitis.

virulence factors : lytic enzymes, cytolysin(hemolysin), aggregation substance,

pheromones, lipoteichoic acid, and forming a biofilm.

E. faecalis is resistant to many commonly used antibiotics.

Resistance to vancomycin in E. faecalis is becoming more common.

Treatment options for vancomycin-resistant E. faecalis(VRE) include

nitrofurantoin (in the case of uncomplicated UTIs.

Group D Enterococci(GDE):

Enterococcus faecalis

Enterococcus faecium