Gram-positive bacteria

Gram-positive bacteria

Separated on basis of G + C content of chromosomal DNA

Low G + C Gram-positives = Firmicutes

High G + C Gram-positives = Actinobacteria

Firmicutes (Low G + C )

Divided into 3 classes:

Clostridia

Mollicutes

Bacilli

Further divided into 10 orders and 34 families

Class Mollicutes

Composed of 5 orders and 6 families

Commonly referred to as mycoplasmas

Are widespread and can be isolated from animals and the environment

Species can cause diseases in humans, animals and plants

e.g. Mycoplasm pneumoniae

Class Mollicutes

Lack cell walls and are unable to synthesize peptidoglycan

Cells are pleomorphic (variably-shaped)

Often require sterols

Class Clostridia

Divided into 3 orders and 10 families

Largest genus is Clostridium

Anaerobes that form endospores

Genus contains over 100 species (likely to be subdivided in the future)

Class Clostridia

Many species can ferment amino acids using the Stickland reaction

C. botulinum - food poisoning

C. tetani - tetanus (lockjaw)

C. prefringens - gas gangrene

Heliobacteria-Family Heliobacteriaceae

Comprised of genera Heliobacterium and Heliophilum

Anaerobic gram-positive photosynthetic bacteria

Stain gram-negative due to lower than normal levels of peptidoglycan

Genus Veillonella

Gram positive cocci with complex nutritional requirements

Parasites of warm-blooded animals

Some species are part of the normal microbiota (mouth and vagina)

Many species are not thoroughly understood

Class Bacilli

Divided into 2 orders

Bacillales

Lactobacillales

Further divided into 17 families and over 70 species

Order Bacillales

Genus Bacillus

Largest genus in the order

Endospore-forming rods

Many species placed in new genera due to rRNA analyses

Order Bacillales

Genus Bacillus

B. subtilis is the type species (chromosome has been sequenced)

B. anthracis - anthrax

B. cereus - food poisoning

B. thuringiensis - insecticide

Order Bacillales

Genus Thermoactinomycetes

Formally grouped with the actinomycetes

Thermophilic (optimum temperature 45-60 C)

Form aerial mycelium like actinomycetes

Commonly found in hay stacks and compost heaps

Order Bacillales

Genus Staphylococcus

Facultative anaerobic nonmotile cocci

Associated with skin and mucous membranes of animals

Order Bacillales

Genus Staphylococcus

S. epidermidis - human skin normal microbiota

S. aureus - abscesses, pneumonia, toxic shock syndrome, food poisoning

Order Lactobacillales

Sometimes referred to as lactic acid bacteria

Major or some fermentation product is lactic acid

Nonspore-forming and usually nonmotile

Order Lactobacillales

Genus Lactobacillus

Can carry out homolactic or heterolactic fermentation

Grow optimally under slightly acidic conditions

Order Lactobacillales

Genus Lactobacillus (over 100 species)

Many species used in the food and dairy industry (e.g. L. bulgaris used in yogurt production)

Some species are responsible for food spoilage

Order Lactobacillales

Genus Leuconostoc

Facultative gram-positive cocci

Many species used in wine production, the fermentation of vegetables and the production of dairy products

Some species are involved in food spoilage

Order Lactobacillales

Genus Streptococcus

Large complex genus

Many species have been placed in new genera (e.g. Enterococcus and Lactococcus)

Many species are the cause of disease

Order Lactobacillales

Genus Streptococcus

S. pyogenes - strep throat, rheumatic fever

S. pneumoniae - pneumonia, ear infections

S. mutans - dental caries

Order Lactobacillales

Genus Streptococcus

Classified based on type of hemolysis on blood agar plates

Lancefield grouping - grouping of -hemolytic streptococci based on antigenic properties

Actinobacteria (High G + C gram-positive bacteria)

Actinobacteria (High G + C)

Suborder Actinomycineae (Order Actinomycetales)

Irregularly-shaped aerobic or facultative nonspore-forming rods

Contain the genera Actinomyces, Arcanobacterium, and Mobiluncus

Suborder Actinomycineae

Genus Actinomyces

Inhabit mucosal surfaces of humans and other warm-blooded animals

Often found in the oral cavity

Some species and cause eye and gum infections (A. israelli)

Suborder Corynebacterineae (Order Actinomycetales)

Contains 7 families with several well-known genera

Corynebacterium

Mycobacterium

Nocardia

Suborder Corynebacterineae

Genus Corynebacterium

Aerobic and facultative curved rods

Some species are saprophytes and others are pathogens (e.g. C. diphtheriae)

Suborder Corynebacterineae

Genus Mycobacterium

Aerobic rods that sometimes branch or form filaments

Grow very slowly

Cell walls have a high lipid content and contain waxes (acid-fast)

Suborder Corynebacterineae

Genus Mycobacterium

Some species are human pathogens

M. tuberculosis - tuberculosis

M. leprae - leprosy

Suborder Corynebacterineae

Genus Nocardia

Found world-wide in soil and aquatic environments

Can form aerial mycelia

Suborder Corynebacterineae

Genus Nocardia

Can degrade hydrocarbons and waxes

Contribute to the deterioration of rubber joints in sewer pipes

Suborder Propionibacterineae (Order Actinomycetales)

Nonmotile nonspore-forming anaerobic or aerotolerant rods

Species of genus Propionibacterium found on skin and digestive tracts of animals

Some species used in the production of Swiss cheese

P. acnes involved in body odor and acne

Suborder Streptomycineae (Order Actinomycetales)

Contains 1 family and 3 genera

Most important genus is Streptomyces

About 500 species of Streptomyces

Genus Streptomyces

Strict aerobes that produce aerial hyphae

Found in soil (1-20 % of culturable population)

Play a major role in mineralization

Genus Streptomyces

Produce many important antibiotics (e.g. chloramphenicol, streptomycin, tetracycline)

A few are involved in causing diseases in plants and animals

Suborder Frankineae (Order Actinomycetales)

Spore-forming bacteria that form hyphae

Many species of the genus Frankia grow symbiotically in association with plant roots

Order Bifidobacteriales

Composed of 1 family and 10 genera

Nonmotile nonspore-forming rods

Can be found in the mouth and intestinal tracts of animals