NTA Level 5 • Semester 1 • PST05103

Introduction to Streptococci

Pharmaceutical Microbiology • Source Session/Topic 7

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Session 7: Introduction to Streptococci

Total Session Time: 60 minutes

Pre-requisites

• Human anatomy and physiology

Students Learning Tasks

By the end of this session students are expected to be able to:

• List characteristic of the medical Staphylococci

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Characteristics of Streptococci (15 minutes)

|Activity: Buzzing (5 minutes) |

| |

|ASK students to pair up and buzz on the following question for 2 |

|minutes |

| |

|What are the characteristics of Streptococci? |

| |

|ALLOW few pairs to respond and let other pairs to add on points |

|not mentioned |

| |

|WRITE their response on the flip chart/board |

| |

|CLARIFY and SUMMARIZE by using the content below |

• Streptococci belong to the genus Streptococcus

• Streptococci are Gram positive, non motile, non spore forming cocci

that grow in pairs or in chains

• They lose their Gram-positive character as the culture grow old

• Most are facultative anaerobic but some are obligate anaerobic

• Most require enriched media (e.g. blood agar) for their growth

• All Streptococci are catalase negative (this distinguish them from

Staphylococci which are catalase positive) i.e. Streptococci cannot

break down hydrogen peroxide

• Streptococci exhibit various degree of red blood cells haemolysis.

o Complete haemolysis –β-haemolytic streptococci

o Partial haemolysis –α-haemolysis

o No haemolysis –γ-haemolysis

STEP 3: Classification of Streptococci (15 minutes)

• Based on Haemolysis of red blood cells

o Three different types of streptococci are initially differentiated

by their appearance when they are grown on sheep blood agar

▪ β-haemolytic streptococci

• Produce zones of clear haemolysis around each colony

▪ α-haemolytic streptococci

• produce partial haemolysis or show green discoloration

resulting from incomplete haemolysis

▪ γ-haemolytic streptococci (also known as the Viridans

Streptococci)

• they are non-haemolytic.

• Based on the presence of a specific carbohydrate in their cell wall,

streptococci are subsequent classified into Lancefield groups A

through H and K through T

• Viridans streptococci form a separate group that is difficult to

classify by the Lancefield grouping method

• In the Lancefield classification, enterococci were initially included

among the group D streptococci but now have been classified as a

separate genus

[pic] Refer students to Figure 9.1: Medically important Streptococci for

detailed information on the classification of various Streptococci

into Lancefield classification

STEP 4: Human Streptococcal Pathogens (5 minutes)

• Various members of the Streptococci are normal flora of humans and

other animals

• Some Streptococci are pathogenic to humans causing acute and chronic

diseases

• Some pathogenic Streptococci include;

o Streptococcus pyogenes

o Streptococcus pneumoniae

o Streptococcus agalactiae -causes neonatal disease

o Viridans streptococci

▪ S. sanguis

▪ S. mutans

▪ S. milleri

STEP 5: Epidemiology and Pathogenesis of Streptococcal Infections (10

minutes)

• Pathogenic Streptococci cause diseases that range from subacute to

acute or even chronic

• In humans, diseases associated with the streptococci occur chiefly in

the respiratory tract, bloodstream, or as skin infections

• Most significant human diseases caused by streptococci are scarlet

fever, rheumatic heart disease, glomerulonephritis, and pneumococcal

pneumonia

• The most significant streptococcal pathogen is S. pyogenes, which is

beta-hemolytic and in Lancefield group A and is thus denoted as group

A beta-hemolytic streptococci (GABHS)????

o The most common acute diseases due to GABHS are

▪ Pharyngitis (or sore throat)

▪ Skin infections such as impetigo, cellulitis and necrotising

fasciitis

o In addition, delayed, nonsuppurative complications (rheumatic

fever, acute glomerulonephritis) sometimes occur ≥ 2 weeks after

infection

• Disease caused by other streptococcal species is less prevalent and

usually involves soft-tissue infection or endocarditis (Some non-GABHS

infections occur predominantly in certain populations (e.g. group B

streptococci in neonates and postpartum women)

• GABHS can spread through the affected tissues and along lymphatic

channels (causing lymphangitis) to regional lymph nodes (causing

lymphadenitis)

• GABHS can also cause local suppurative complications, such as

peritonsillar abscess, otitis media, sinusitis, and bacteremia

• Suppuration depends on the severity of infection and the

susceptibility of tissue.

• Other serious GABHS infections include septicemia, puerperal sepsis,

endocarditis, pneumonia, and empyema

• Streptococcal infections are transmitted through contact, droplets,

food or formites

• Portal of entry for the infections are generally the skin or pharynx

• Children are predominantly affected for cutaneous and throat

infections

• Systemic infections and progressive sequela are possible if local

infections are left untreated

STEP 6: Key Points (5 minutes)

• Streptococci are gram positive spherical bacteria (cocci) that occur

in chain

• Streptococci are catalase negative

• Streptococci are classified by their ability to haemolyse red blood

cells and presence of specific carbohydrate in their cell walls

• Pathogenic streptococci cause a variety of infections due to direct

invasion of tissues and toxin-mediated infections

• Many skin infections caused by Streptococci are also caused by

Staphylococci.

STEP 7: Evaluation (5 minutes)

• How are streptococci classified?

• How do streptococci differ from staphylococci?

Figure 9.1: Medically important Streptococci

[pic]

Source: Medical Microbiology. 4th edition. Baron S, editor.

Galveston (TX): University of Texas Medical Branch at Galveston,1996.

References

Hugo and Russell (2011), Pharmaceutical Microbiology 8th Edition, Willey-

Blackwel publications

Karen C. Carroll et al (2013); Jawetz, Melnick and Adelberg’s Medical

Microbiology 26th Ed. McGraw Hill Co. Inc.

Greenwood et al (2012); Medical Microbiology, 18th edition Churchill

Livingstone

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