The world of Bacteria II:“Ordinary” Gram-Positive Bacteria

Anil ShresthaMsc Medical Microbiology

1) Aerobic/ Facultatively Anaerobic Cocci

• They possess cytochrome.• They are able to respire with oxygen, i.e., have

an oxidative type of metabolism.• Some can also obtain energy under anaerobic

conditions by fermentation (have a fermentative type of metabolism).

Deinococcaceae and Micrococcaceae is the family for this organism.

DEINOCOCCACEAE

• The cocci occur mainly in tetrads or cubical packets.

• The organisms have an unusually high resistance high resistance to gamma and ultraviolet radiation.

• Eg: Deinococcus radiodurans

MICROCOCCACEAE• The cocci occur mainly in clusters, tetrads, or cubical

packets of eight cells.• The cells donot exhibit any unusal resistance to gamma

and ultraviolet radiation.The genera included are Micrococcus:- 1) nonmotile, aerobic, oxidative, catalase positive.Planococcus:- 1) motile, aerobic, oxidative, catalase positive.Staphylococcus:- nonmotile, facultative anaerobes, fermentative, catalase positive.

2) Aerotolerant fermentative cocci

• They do not possess cytochromes.• They have only a fermentative type of metabolism

and do not respire; yet they can grow anaerobically or aerobically.

• The cells are arranged in pairs, chains, or tetrads.Streptococcus:- arranged in pair or chains, catalase negative, homofermentative.i.e, the predominant end product of sugar fermentation is lactic acid.

• Lancefield grouping is a method of grouping catalase-negative, coagulase-negative bacteria based on the carbohydrate composition of bacterial antigens found on their cell walls.

• Classification• Group A - Streptococcus pyogenes• Group B - Streptococcus agalactiae• Group C - Streptococcus equisimilis, Streptococcus equi, Streptococcus

zooepidemicus, Streptococcus dysgalactiae• Group D - Enterococci, Streptococcus bovis• Group E - Streptococcus milleri and mutans• Group F - Streptococcus anginosus• Group G - Streptococcus canis and Streptococcus dysgalactiae• Group H - Streptococcus sanguinis• Group L - Streptococcus dysgalactiae• Group M - Streptococcus fryi sp. nov• Group N - Lactococcus lactis• Group R&S - Streptococcus suis• other Streptococcus species are classified as 'non-Lancefield Streptococci'

• Though there are many groups of streptococcus, only five are known to commonly cause disease in immune-competent human beings: Group A, Group B, both members of Group D, and two groups that lack the Lancefield carbohydrate antigen: Streptococcus pneumoniae and Viridans streptococci.

Leuconostoc :- • Cocci are arranged in pairs and chains.• Catalase negative• Heterofermentative; produce CO₂ and ethanol or acetic acid in

addition to lactic acid.

Pediococcus :-• Cocci occur in pairs and tetrads.• Catalase negative.• Exhibit homolactic type of fermentation.Pediococci are saprophytes and are particularly noted for their ability to form capsular material that causes beer to become ropy and viscous.

3) Anaerobic Gram Positive Cocci

• These cocci have a fermentative type of metabolism. Some genera must be supplied with a fermentable carbohydrate in order to grow; others can ferment amino acids and do not require carbohydrates. Lactic acid is not a major fermentation product. Most genera form CO₂, H₂, short-chain fatty acids, and in some cases ethanol or succinic acid.

Genus Arrangement of Cells

Main Sources of Carbon and Energy

Occurrence

Peptococcus Pairs, clusters, tetrads, and short or long chains

Peptone or amino acids

Human intestine and respiratory tract; clinical specimens

Peptostreptococcus Pairs and short or long chains

Peptone or amino acids

Human clinical specimens

Ruminococcus Pairs and short or long chains

Carbohydrates Bovine and Ovine rumen

Coprococcus Pairs and short or long chains

Carbohydrates Human feces

Sarcina Cubical packets of eight cells

Carbohydrates Soil; mud; cereal grains; diseased human stomachs

Endospore-forming Gram-Positive bacteria

Aerobic/Facultatively Anaerobic Sporeforming Rods and Cocci

Bacillus• Rod-shaped bacteria.• Most species are harmless saprophytes occurring in soil,

freshwater, or sea water.• Many form exocellular enzymes that hydrolyze proteins or complex

polysaccharides, activities that are often important causes of food spoilage.

• Because of the heat resistance of endospores, Bacillus species may species may survive milk pasteurization or inadequate heat treatment during canning of foods.

• Eg:- B. stearothermophilus, B. polymyxa, B. thuringiensis, B. anthracis

Sporosarcina• Cocci arranged in tetrads or cubical packets of

eight cells• Widely distributed in fertile soil, where they

play an active role in the decomposition of urea.

Anaerobic spore-forming Rods

• Clostridium :- have fermentative type of metabolism– C. botulism– C. tetani– C. perfringens– C. thermosaccharolyticum

• Desulfotomaculum– Obtain energy by anaerobic respiration, with

sulfate serving as the terminal electron acceptor and organic substrates such as lactic or pyruvic acid serving as electron donor. Large amounts of H₂S are formed during growth.

Non spore forming Gram-Positive rods of Regular shape Genus Morphology and

MotilityOxygen Relationship

Catalase test

Lactobacillus Long to very short rods, often in chain; usually motile

Strictly fermentative organism, but can usually tolerate air; some strains are anaerobic

Negative

Listeria Very short rods, often in chains; motile by peritrichous flagella

Aerobic to microaerophilic

Positive

Erysipelothrix Filament-forming rods; nonmotile

Aerobic Negative

Non sporeforming Gram-positive rods of irregular shape

Aerobic/Facultatively anaerobic nonfilamentous rods

• Straight to slightly curved rods that exhibit swellings, club shapes, or other deviations from a uniform rod shape.

• An aerobic or facultatively anaerobic nature, being capable of a respiratory type of metabolism and in some instances also of a fermentative type of metabolism.

Eg:- Corynebacterium

Anerobic nonfilamentous or filamentous rods

• Actinomyces ( Facultative anaerobes)• propionibacterium

• Mycobacterium• Nocardia