NTA Level 5 • Semester 1 • PST05103

Introduction to Staphylococci

Pharmaceutical Microbiology • Source Session/Topic 6

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Session 6: Introduction to Staphylococci

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 Staphylococci (15 minutes)

• Staphylococcus is a genus of Gram-positive spherical bacteria (cocci)

which grow in grape-like clusters

• Staphylococci are catalase positive (this distinguishes them from

Streptococci which are catalase negative). The enzyme catalase breaks

down hydrogen peroxide into water and oxygen.

• Staphylococci are widely distributed; some are normal flora while

others are pathogenic to humans causing many forms of infections.

• Staphylococcus aureus colonizes the nasal passage and axillae while

Staphylococcus epidermidis is a common human skin commensal. Other

species of staphylococci are infrequent human commensals and other

animals.

• Staphylococci are salt tolerant and often hemolytic

• S. aureus and Staphylococcus intermedius are coagulase positive.

Coagulase enzyme clots blood plasma

• All other staphylococci are coagulase negative

STEP 3: Human Staphylococcal Pathogens (10 minutes)

• Most staphylococci are not pathogenic to humans

• Human pathogens include;

o S. aureus

▪ which is the most pathogenic of the staphylococci

▪ leading cause of nosocomial infections

o S. epidermidis

▪ Causes infections of prosthetic heart valves and hips

▪ It is a common member of the skin normal flora

o S. saprophyticus

▪ Which causes urinary tract infection

STEP 4: Epidemiology and Pathogenesis of the Staphylococci (20 minutes)

• Infections caused staphylococci include;

o Skin infections, pneumonia, endocarditis, osteomyelitis and septic

arthritis which are due to direct tissue invasion by the bacteria

o Toxic shock syndrome, staphylococcal scalded skin syndrome,

staphylococcal food poisoning which are toxin-mediated

• S aureus causes many forms of infection in humans;

o Superficial skin lesions (boils, styes) and more serious skin

infections e.g. furunculosis

o Toxin-mediated infections e.g. food poisoning

o Localized abscesses

o Deep-seated infections, such as osteomyelitis and endocarditis

• S. aureus expresses many potential virulence factors

o Surface proteins that promote colonization of host tissues

o Factors that probably inhibit phagocytosis e.g. capsule,

immunoglobulin binding protein

o Toxins that damage host tissues and cause disease symptoms

• Coagulase-negative staphylococci are normally less virulent and

express fewer virulence factors

o S. epidermidis are skin normal flora that readily colonize implanted

devices e.g. prosthetic heart valves

• Pathogenic staphylococci are transmitted by shedding from human

lesions and contaminated formites such as clothing and bed linens.

Heavily contaminated environment and compromised immunity favour

infection by members of the genus

• Manifestations of disease caused by Staphylococci are inflammatory and

toxin-mediated

o Inflammatory manifestations range from superficial skin lesions to

deep osteomyelitis to septicaemia

• Multiple antibiotic resistance is increasingly common in S. aureus and

S epidermidis

• Methicillin resistance indicates multiple resistance

• Methicillin-resistant S aureus (MRSA) causes outbreaks in hospitals

and can be epidemic

• Infections acquired outside hospitals can usually be treated with

penicillinase-resistant β-lactams

• Hospital acquired infections are often caused by antibiotic resistant

strains and can only be treated with vancomycin

STEP 5: Key Points (5 minutes)

• Staphylococci can cause many forms of infection

• Staphylococci are Gram-positive cocci 1μm in diameter and grown in

grape-like clusters

• Staphylococci are catalase positive

• S. aureus and S. intermedius are coagulase positive while all other

staphylococci are coagulase negative

STEP 6: Evaluation (5 minutes)

• Mention four characteristics of staphylococci

• S. causes which diseases in humans?

• How are staphylococcal infections acquired?

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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