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