Classification of microorganisms Presented by R.Parthasarathy
INTRODUCTION:Classification of organism.Difference between the bacteria, archaea, Eukarya.Fungi, Alagae, Protozoa, Virus, Bacteria.Identification of bacteria.General characteristics features used for classification of bacteria.
BINOMINAL NOMENCLATURE:In the 18th century, Carolus Linnaeus, a Swedish scientist,began identifying living organisms according to similarities inresemblances and placing organisms in one of two“kingdoms”Vegetalia and Animalia.Genera named after individuals:Escherichia coli: Theodore escherich invented the bacteriawhich causes disease in colon.Neisseria gonorrhoea: Albert Neisser discovered the bacteriawhich causes gonorrhoea.
Binominal nomenclature: cont..Genera named after Microbe’s shape:Vibrio chlerae: Bacteria is comma shaped which causes cholera.Staphyococcus epidermidis: Staphylo means clusters; coccus means spheres.Genera named after Attribute of the Microbe:Saccharomyces cerevisiae: Saccharo means sugar; Myces means fungus; cerevisiae meansbeer. Bacteria which converts sugar in the sample into Alcohol.
WOESE’S THREE-DOMAIN SYSTEM:In Woese’s three-domain system, one branch of the phylogenetic tree includes theformer archaebacteria and is called the domain Archaea ( FIGURE ). The secondencompasses all the remaining true bacteria and is called the domain Bacteria. The thirddomain, the Eukarya,includes the four remaining kingdoms (Protista, Plantae, Fungi, andAnimalia).
FUNGI• Fungi exist in either yeast or mold forms.• The smallest of yeasts are similar in size to bacteria, but most are larger (2 to 12 m) and multiply by budding.• Molds form tubular extensions called hyphae, which, when linked together in a branched network, form the fuzzy structure seen on neglected, bread.• Fungi are eukaryotic, and both yeasts and molds have a rigid external cell wall composed of their own unique polymers, called glucan, mannan, and chitin.• Their genome may exist in a diploid or haploid state and replicate by meiosis or simple mitosis.• Most fungi are free-living and widely distributed in nature.• Generally, fungi grow more slowly than bacteria, although their growth rates sometimes overlap.• The fungi probably represent an evolutionary offshoot of the protozoa; they are unrelated to the actinomycetes, mycelial bacteria that they superficially resemble.• The major subdivisions (phyla) of fungi are: Chytridiomycota, Zygomycota (the zygomycetes), Ascomycota (the ascomycetes), Basidiomycota (the basidiomycetes), and the "deuteromycetes" (or imperfect fungi).
ALGAE• The term "algae" has long been used to denote all organisms that produce O2 as a product of photosynthesis.• One major subgroup of these organisms—the blue-green bacteria, or cyanobacteria—are prokaryotic and no longer are termed algae.• This classification is reserved exclusively for photosynthetic eukaryotic organisms.• All algae contain chlorophyll in the photosynthetic membrane of their subcellular chloroplast.• Many algal species are unicellular microorganisms. Other algae may form extremely large multicellular structures.• Kelps of brown algae sometimes are several hundred meters in length.• A number of algae produce toxins that are poisonous to humans and other animals.• Dinoflagellates, a unicellular algae, cause algal blooms, or red tides, in the ocean. Red tides caused by the dinoflagellate Gonyaulax species are serious as this organism produces neurotoxins such as saxitoxin and gonyautoxins, which accumulate in shellfish (eg, clams, mussels, scallops, and oysters) that feed on this organism.• Ingestion of these shellfish by humans results in symptoms of paralytic shellfish poisoning and can lead to death.
PROTOZOA• Protozoa are unicellular nonphotosynthetic protists.• The most primitive protozoa appear to be flagellated forms that in many respects resemble representatives of the algae.• It seems likely that the ancestors of these protozoa were algae that became heterotrophs—the nutritional requirements of such organisms are met by organic compounds. Adaptation to a heterotrophic mode of life was sometimes accompanied by loss of chloroplasts, and algae thus gave rise to the closely related protozoa.• From flagellated protozoa appear to have evolved the ameboid and the ciliated types; intermediate forms are known that have flagella at one stage in the life cycle and pseudopodia (characteristic of the ameba) at another stage.• A fourth major group of protozoa, the sporozoa, are strict parasites that are usually immobile; most of which reproduce sexually and asexually in alternate generations by means of spores.
VIRUS• Viruses are strict intracellular parasites of other living cells, not only of mammalian and plant cells, but also of simple unicellular organisms, including bacteria (the bacteriophages).• Viruses are simple forms of replicating, biologically active particles that carry genetic information in either DNA or RNA molecules enclosed in a protein coat or capsid.• Proteins—frequently glycoproteins—in the capsid determine the specificity of interaction of a virus with its host cell.• The capsid protects the nucleic acid and facilitates attachment and penetration of the host cell by the virus.• Inside the cell, viral nucleic acid redirects the hosts enzymatic machinery to functions associated with replication of the virus. In some cases, genetic information from the virus can be incorporated as DNA into a host chromosome.• In other instances, the viral genetic information can serve as a basis for cellular manufacture and release of copies of the virus. This process calls for replication of the viral nucleic acid and production of specific viral proteins.
BACTERIA• Bacteria are the smallest (0.1 to 10 m) living cells.• They have a cytoplasmic membrane surrounded by a cell wall; a unique interlinking polymer called peptidoglycan makes the wall rigid.• The simple prokaryotic cell plan includes no mitochondria, lysosomes, endoplasmic reticulum, or other organelles .• In fact, most bacteria are about the size of mitochondria.• Their cytoplasm contains only ribosomes and a single, double-stranded DNA chromosome.• Bacteria have no nucleus, but all the chemical elements of nucleic acid and protein synthesis are present.• Although their nutritional requirements vary greatly, most bacteria are free-living if given an appropriate energy source.• They divide by binary fission and can be grown in artificial culture, often in less than 1 day.• Archaebacteria differ radically from other bacteria in structure and metabolic processes; they live in environments humans consider hostile (eg, hot springs, high salt areas) but are not associated with disease.
IDENTIFICATION OF BACTERIABiochemical Tests• A large number of biochemical tests exist and often a specific test can be used to eliminate certain groups from the identification process.• Among the more common tests are: fermentation of carbohydrates, the use of a specific substrate, and the production of specific products or waste products. But, as with the physical characteristics, often several biochemical tests are needed to differentiate between species.
SEROLOGICAL TESTS• Microorganisms are antigenic, meaning they are capable of triggering the production of antibodies.• Solutions ofsuch collected antibodies, called antisera, are commercially available for many medically important pathogens. For example, mixing a Salmonella antiserum with Salmonella cells will cause the cells to clump together or agglutinate. If a foodborne illness occurs, the antiserum may be useful in identifying if Salmonella is the pathogen.• In recent years, a number of miniaturized systems have been made available to microbiologists for the rapid identification of enteric bacteria.• One such system is the Enterotube II, a self-contained, sterile, compartmentalized plastic tube containing 12 different media and an enclosed inoculating wire. This system permits the inoculation of all media and the performance of 15 standard biochemical tests using a single bacterial colony. The media in the tube indicate by color change whether the organism can carry out the metabolic reaction. After 24 hours of incubation, the positive tests are circled and all the circled numbers in each boxed section are added to yield a 5-digit ID for the organism being tested. This 5-digit number is looked up in a reference book or computer software to determine the identity of the bacterium.