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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