NTA Level 5 • Semester 1 • PST05103

Introduction to Bacilli

Pharmaceutical Microbiology • Source Session/Topic 13

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Session 13: Introduction to Bacilli

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:

• Describe medical bacilli

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 Bacilli (10 minutes)

• Bacilli are rod shaped bacteria. They are not spherical as cocci.

• Bacilli should not be confused with bacillus which is a genus in the

spore forming gram positive bacilli

• Bacilli are groped into two major groups depending on their staining

properties with Gram stain

o Gram postive bacilli

o Gram negative bacilli

• Bacilli consist of a large number of bacteria some of which cause serious

diseases in humans and others are normal flora of humans

STEP 3: Classification of Gram Positive Bacilli (25 minutes)

• Spore forming Gram Positive Bacilli

o These bacilli are ubiquitous, and because they form spores, they can

survive in the environment for many years

o The gram-positive spore-forming bacilli are the Bacillus and

Clostridium species

▪ Genus Clostridium

• Anaerobic spore-forming bacilli

• Members of the genus Clostridium are obligate anaerobic to

spore forming bacilli

• Found in soil as well as in normal intestinal flora of man and

animals

• There are both gram-positive and gram-negative species,

although the majority of isolates are gram-positive

• Produce exotoxin(s) which play an important role in disease

production

• Pathogenic members include;

o Corynebacterium perfringes which causes gas gangrene

o Clostridium tetani which causes tetanus

o Clostridium botulinum which causes botulism

o Clostridium difficile which causes pseudomembraneous colitis

o Clostridium perfringes which causes food poisoning and

necrotizing enteritis

▪ Genus Bacillus

• Consists of aerobic or facultatively anaerobic gram positive

spore-forming bacilli

• Some may turn Gram negative with age

• Most members of the genus bacillus are saprophytic

• They are able to survive in harsh environment

• They include thermophilic, psychrophilic, acidophilic,

alkaliphilic, halotolerant, and halophilic representatives,

which are capable of growing at temperatures, pH values, and

salt concentrations at which few other organisms could survive

• Pathogenic bacteria in this genus include

o Bacillus anthracis which causes anthrax

o Bacillus cereus which causes bacillus food poisoning

• The non–spore-forming gram-positive bacilli are a diverse group of

aerobic and anaerobic bacteria

o They are grouped into acid-fast bacilli and non-acid fast bacilli

o The acid fast bacilli include Mycobacterium and Nocardia

▪ Mycobacterium e.g. Mycobacterium tuberculosis that cause

tuberculosis, Mycobacterium leprae that causes leprosy

• The non-acid fast bacilli include regular bacteria and pleomorphic

bacteria

o The regular acid fast bacilli include Lactobacillus and Listeria

▪ Listeria e.g. Listeria monocytogenes which causes meningitis and

sepsis

o The pleomorphic acid fast bacilli include Corynebacterium and

Propionibacterium

▪ Corynebacterium e.g. Corynebacterium diphteriae causes Diphtheria

▪ Propionibacterium acnes is associated with acne vulgaris

STEP 4: Classification of Gram Negative Bacilli (15 minutes)

• The Gram negative bacilli are grouped into two groups; the aerobic non

enteric bacilli and the enteric bacilli

• Aerobic Gram-Negative Nonenteric Bacilli

o Do not ferment sugars

o They include

▪ Pseudomonas e.g. Pseudomonas aeruginosa, a dangerous

opportunistic pathogen

▪ Brucella e.g. Brucella species which cause brucellosis

▪ Francicella e.g. Francicella tularensis which causes Tularemia

▪ Bordetella e.g. Bordetella pertussis which cause whooping cough

▪ Legionella e.g. Legionella pneumophilia which causes

legionnaire’s disease

• Enteric Gram-Negative Bacilli (Enterobacteriaceae)

o These are gram negative rods

o They ferment glucose with acid production

o Reduce nitrates into nitrites

o They are oxidase positive

o They are catalase positive

o They are facultative anaerobic

o They are motile except Shigella, Klebsiella, and Yersinia

o They are non-capsulated except Klebsiella

o They are non-fastidious

o They grow on bile-containing agar (MacConkey agar)

o Most members are opportunistic or cause secondary infections of

wounds, the urinary tract and the circulatory system

o They are grouped into two groups

▪ Lactose fermenters e.g. E. coli

▪ Lactose non fermenters e.g. Salmonella, Shigella, Proteus,

Yersinia

STEP 5: Key Points (5 minutes)

• Gram positive bacilli are grouped into spore forming and non spore

forming

• The spore forming gram positive bacilli are grouped into bacillus and

clostridia, all are pathogenic to humans

• The non-spore forming are grouped into acid fast and non acid fast

• Gram negative bacilli are grouped into two groups namely non enteric gram

negative bacilli and the enterics (enterobacteriaceae)

• Non enteric gram negative bacilli do ferment any sugar while the

enterobacteriaceae ferment a varieties of sugar

STEP 6: Evaluation (5 minutes)

• What are the features of gram positive bacilli?

• List some bacteria that are gram positive bacilli

• Mention some diseases caused by gram positive bacilli

• Differentiate non enteric gram negative bacilli from the enteric gram

negative bacilli

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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