An AssignmentOnGRACILICUTES (Gram –negative Bacteria)SUBMITTED BY:ROUF AHMADM.Sc.MicrobiologyL-2011- BS-249-MSUBMITTED TO:Prof.Dr.(Mrs.) Urmila PhutelaDepartment of MicrobiologyPUNJAB AGRICULTURAL UNIVERSITY,LUDHIANA 141004
INTRODUCTION OF GRAM-NEGATIVE BACTERIA:Chemoheterotrphic eubacteria, many of which have clinical,industrial or agricultural importance.Most of the Gram-negative organisms have a relatively simplemorphology and cellular arrangement.Do not form complex structures such as prosthecae (semirigidextensions of the cell wall and cytoplasmic membrane), sheaths(hollow tubes that enclose chains or trichomes) or with rareexceptions, endospores and cysts.Cells not arranged in trichomes.Reproduce mainly by transverse binary fission rather than bybudding, fragmentation or spore formation.Motility if present is of free swimming type rather than thegliding type.Mainly heterotrophic but some can grow autographically in thepresence of H2.Some are saprophytes, parasites. Some highlypathogenic and others may be opportunistic pathogens (causedisease only in a patient whose defense mechanisms againstinfection have been weakened or compromised).
BERGEY’S MANUAL OF SYSTEMATIC BACTERIOLOGY, VOLUME 1Each volume of Bergey’s Manual is divided into a number of major sections, and eachbearing a descriptive common name rather than formal taxonomic name.The major sectionsof Volume 1 are listed below:The SpirochetesAerobic/Microaerophillic, Motile, Helical/Vibriod,Gram-negative BacteriaNon-motile or rarely motile, Gram-negative curvedBacteriaAerobic Gram-negative Rods and CocciFacultative anaerobic Gram-negative RodsGracilicutesAnaerobic Gram-negative straight, curved and helicalRodsDissimilatory sulphate or sulphur-reducing bacteriaAnaerobic Gram-negative cocciThe Rickettsias and ChlamydiasThe MycoplasmasEndosymbionts
1. THE SPIROCHETES:Distinguishing features:A helical shapeAn ability to twist or contort their shape(i.e., flexibility)The occurrence of a special kind of flagella termed periplasmic flagella(alsocalled axial fibrils or endoflagella)The major difference in structure from other Gram-negative eubacteria is in thelocation of the periplasmic flagella. They are located between the outer membrane(often termed outer sheath in spirochetes) and the protoplasmic cylinder (i.e., theprotoplast plus the overlying peptidoglycan layer); thus they are located in theperiplasmic space of the cell.Periplasmic flagella have an ultrastructure similar to that of an ordinary flagella,including a basal body with disks, and they are responsible for the swimmingmotility of spirochetes.Spirochetes swim best in media of high viscosity; whereas bacteria with ordinaryflagella swim best in media of low viscosity.Spirochetes can also exhibit creeping or crawling motility when in contact with solidsurfaces.Most spirochetes are so thin that they cannot be easily seen by lightmicroscopy,even when Gram-stained.SPIROCHETESORDER: SPIROCHAETALESFAMILY:SPIROCHAETACEAE LEPTOSPIRACEAEGENUS:LeptospiraSpirochaeta Cristispira Treponema Borrelia
THE FAMILY SPIROCHAETACEAE:They are stringent anaerobes, facultative anaerobes, or microaerophiles.Amino acids and carbohydrates are used as energy and carbon sources.Genus SPIROCHAETA:Harmless inhabitants of water,mud,and sediments of marine and freshwaterenvironments.Anaerobic and facultatively anaerobic.Use carbohydrates but not amino acids as carbon and energy sources.Genus CRISTISPIRA:Harmless parasites of freshwater and marine molluscs.Have never been isolated.Have unusually large number of periplasmic flagella(>100)Genus TREPONEMA:Inhabit mouth, intestinal tract, and genital areas of humans; some are pathogenic.Anaerobic and microaerophillic.Use carbohydrate and amino acids as carbon and energy sources. Some have beencultivated in vitro (on nonliving media) and are stringent anaerobes; these aremainly harmless parasites, but one species,T.hyodysenteriae, causes hog dysentery.Some species have not been cultivated invitro,e.g.,T.pallidum subsp. Pallidum whichcause syphills in humans and is microaerophillic.Genus BORRELIA:Parasites of wild rodents and small mammals, and also of the arthropods associatedwith these animals.Micaerophillic in nature.Pathogenic,causing louseborne or tickborne relapsing fever in humans.THE FAMILY LEPTOSPIRACEAE:They are aerobes.Long chain fatty acids are used as the source of carbon and energy.Genus LEPTOSPIRA:Some (L.biflexa) are harmless inhabitants of freshwater environments; others(L.interrogens) are parasites of wild and domestic animals.Aerobic in nature.L.interrogens is pathogenic and causes leptospirosis in animals and humans.
2.AEROBIC/MICROAEROPHILIC,MOTILE,HELICAL/VIBRIOID,GRAM NEGATIVE BACTERIAImportant characteristics are as:The cells are rigid (unlike spirochetes) and range from vibrioid (having less than oneturn or twist) to helical ( having one to many turns or twists).Swim by means of polar flagella.These are aerobic or microaerophillic.They attack few or no carbohydrates.Give usually positive oxidase test.Most of the organisms harmless saprophytes and occur in freshwater or marineenvironments, but a few are parasitic and can be pathogenic for humans and animalsor for other bacteria.IMPORTANT GENERA IN THIS SECTION ARE AS:GENUS CHARACTERISTICS1. AQUASPIRILLUMHelical or vibrioid.Typically possess bipolar tufts of flagella.These are harmless saprophytes,aerobic tomicroaerophillic.Occur in stagnant stream or pond.No growth occurs in the presence of 3%NaCl or seawater.
GENUS CHARACTERISTICS2. AZOSPIRILLUMCells are plump and vibrioid with a single polar flagellumand if grown on solid media, with numerous lateral flagellaas well.Occur within roots of grasses,wheat,corn and many otherplants or as free living soil organisms.Fix N2 within plant roots or in laboratory cultures.Under nitrogen fixing conditions they are microaerophillic,but they are aerobic if supplied with a source of fixednitrogen such as ammonium salt.One species A.lipoferum can grow autotrophically withhydrogen gas as the source of energy.Fig. Of Azospirillum3.OCEANOSPIRILLUMCells are helical, usually with bipolar tufts of flagella.Oceanospirilla aerobic and harmless saprophytes.Occur in coastal marine waters.Sea water is required for their growth.4.CAMPYLOBACTERThese are vibrioid cells having a single flagellum at one orboth poles.Microaerophillic parasites.Occur in the reproductive organs, intestinal tract and oralcavity of humans and other mammals.
Some species are pathogenic,e.g.,C.jejuni,causes diarrheain humans, or C.fetus subspecies venerealis,causesabortion in cattleFig. Campylobacter jejuni5.BDELLOVIBRIOThese are aerobic, vibriod cells.Possess single polar flagellum.Have unique property of being parasitic on other Gram- negativebacteria.After penetration of the outer membrane of the cell wal, theygrow within the periplasmic space.The host cell becomes anempty “ghost” cell.Occur in soil,sewage, and in freshwater and mrine environments.NOTE: The genus Vampirovibrio has certain similarities tothe genus Bdellovibrio, but the organisms attack eukaryoticalgae, not bacteria.
3.NON-M0TILE (0R RARELY MOTILE),GRAM-NEGATIVE, CURVED BACTERIA:Important characteristics of the bacteria in this section are as follows:Rigid cells that are curved to various degrees, forming coils, helical spirals, andsometimes rings ( i.e.,cells that are curved around so that the ends overlap).Non motile in nature.These are harmless saprophytes and occur mainly in soil, freshwater, and marineenvironments.This section contains the family SPIROSOMACEAE .It contains three genera whose cells are;AerobicForm no intracellular gas vacuoles, are catalase and oxidase-positiveForm colonies that are yellowFAMILY SPIROSOMACEAEGENUS (1, 2,3)1. SPIROSOMA 2. RUNELLA 3.FLECTIBACILLUS(form yellow colonies) (form pink colonies) (form pink colonies)
4. AEROBIC, GRAM – NEGATIVE RODSAND CONES:This section forms one of the largest and most diverse groups of bacteria. Two generalfeatures are as follows:1. The cells are mainly straight or slightly curved (but not helical) rods, but some arecocci.2. They have a strictly respiratory type of metabolism.Several families and some additional genera that are not assigned to any family arerepresented.FAMILIES GENERAPSEUDOMONASPSEUDOMONADACEAE XANTHOMONASZOOGLOEAAZOTOBACTERCEAE AZOTOBACTERRHIZOBIUMAerobic RHIZOBIACEAE BRADYRHIZOBIUMGram-Negative AGROBACTERIUMRods and METHYLOCOCCACEAE METHYLOCOCCUSCocci METHYLOMONASACETOBACTERACEAE ACETOBACTERGLUCONOBACTERLEGIONELLACEAE LEGIONELLANEISSERIACEAE NEISSERIAACINETOBACTER
THE FAMILY PSEUDOMONACEAE:- The features of this family include the following:-1. Straight or slightly curved rods.2. Motile by polar flagella.3. Catalase-positive and usually oxidase-positive.Some of the genera included in this family are described here.1.PSEUDOMONAS:-Characteristics of pseudomonas:-Widely distributed in soil and water.All pseudomonas can grow aerobically but some can also grow anaerobically byusing nitrate as an electron acceptor.Several species are pathogenic for humans and animals; others are important plantpathogens.Some cause spoilage of meats and other foods.Identification of species is based on many physiological and nutritionalcharacteristics, such as ability to use certain compounds as carbon sources forgrowth.(FIG: - Pseudomonas strain)A few examples of Pseudomonas are listed below:-Pseudomonas aeruginosa: - Important features;Produces water soluble blue pigment, pyocyanin, and a water soluble fluorescentpigments, pyoverdin.It is mainly a soil and water saprophyte, but it is also frequently and opportunisticpathogen and can often be isolated from wound, burn and urinary tract infection.Pseudomonas maltophilia:-It is a non-fluoroscent species that also frequently isolated from clinical specimens.
Pseudomonas fluorescens:-It is a common saprophytic soil and water organism that makes only a fluorescentpigment.Pseudomonas syringae:-This and several other species are important plant pathogens, causing diseases suchas leaf spot, leaf strip, wilt and necrosis.Pseudomonas mallei:-It is the causative agent of glanders and farcy, diseases of horses and donkeys thatare transmissible to humans.Pseudomonas pseudomallei:-Causes melioidosis in humans and animals.2.XANTHOMONAS:-Characteristic features:-Forms characteristics yellow pigments called xanthomonadins.All species are pathogenic for plants, causing diseases such as spots, streaks, cankers,wilts, and rots.Make viscous exocellular polysaccharides (xanthan gums) which are useful forindustrial application such as stabilizers in foods and anti drip in paints.3.ZOOGLOEA:-Important features:-An outstanding characteristic of this genus is the embedment of the cells in agelatinous matrix to form slimy masses with a finger like morphology.Saprophytic in nature and commonly found coating the rocks on trickling filer beds insewage treatment plants, where they are oxidise the soluble organic components ofthe sewage.Fig.of zoogloea
THE FAMILY AZOTOBACTERACEAE:-Important features of this family are as follows:The cells are blunt rods , oval cells or cocci.Their motility and flagellar arrangement vary; some are non- motile.They are saprophytes that occur in soil, water, and sometimes the plantrhizosphere(soil region subjected to the influence of plant roots).Organisms fix N2 under aerobic conditions.Have unusually high respiratory rate, which serves to use up oxygen rapidly at thecell surface and maintain an anaerobic cell interior; this protects the oxygen sensitivenitrogenase complex(responsible for nitrogen fixation) from being inactivated underan air atmosphere.It contains one genus namely AZOTOBACTER- forms dessication resistant cysts.THE FAMILY RHIZOBIACEAE:-This famaliy contains rod shaped cells that incite hypertrophies on plants ( root nodules,leaf nodules, or tumors).It contains three genera as follows:-1.and 2.RHIZOBIUM AND BRADYRHIZOBIUM:-Important characteristics:-These fix N2 by means of a complex , highly evolved symbiosis with the roots ofleguminous plants.These bacteria to the roots hairs, penetrate the root, and induce proliferation of theroot cells.Within the resulting root nodules the bacteriaexist as highly pleomorphic N2 fixingforms called bacteriods.Leghaemoglobin protects the nitrogenase enzyme complex from being destroyed byexcess oxygen.Species and strains of rhizobia and bradyrhizobia exhibit a range of specificities forvarious legumes.3.AGROBACTERIUM:-Characteristics:-Agrobacteria do not fix nitrogen.The organisms are plant pathogen died inside tumors when they invade the crown,roots, and stems of a great variety of dicotyledonous and some gymnosperms plants.Induction of tumor is because of the presence of a paricular plasmid (Ti plasmid).
THE FAMILY METHYLOCOCCACEAE:-Important characteristic features:-Consists of a diverse group of rods, vibrios, and cocci having in common the abilty touse methane gas a sole carbon and energy source under aerobic or microaerophilicconditions.These are harmless organisms and occur in soil, mud or water adjacent to oroverlying the anaerobic environment where methane is formed.Some of the members of this family fix nitrogen under microaerophilic cndition.Some of the members form azotobacter like cysts.It includes two genera namely;1.MethylococcusAre all obligate methane oxidizers (that is carbon sources suchglucose can not be used for growth).2.MethylomonasTHE FAMILY ACETOBACTERACEAE:-Important features:-Contents ellipsoidal to rod shaped cells that oxidized ethanol to acetic acid in neutralor acidic (pH 4.5) media.Two genera included:-1.AcetobacterBoth are differentiated by certain biochemical characteristicsand by the occurance of peritrichous flagella (Acetobacter)or polar flagella.2.GluconobacterCharacteristic features of Acetobacter and Gluconobacter:-Members of this two genera are saprophytes that occur in sugar or alcohol enriched,acidic environments such as flowers, fruits , beer, wine, cedar, vinegar, souring fruitjuices, bees, and honey.These are industrially very important:Acetobacters are used to make vinegar.
Gluconobacters are involved in the manufacter of chemicals such asdihydroxyacetone, sorbose and 5-ketogluconic acid.Some of the strains of Acetobacter have the highly unusual ability to makeexocellular fibrils that accumulate around the cells.THE FAMILY LEGIONELLACEAE:-Include rod shaped bacteria which require L-Cystine, iron, salts, and activated powdercharcoal for growth. The charcoal destroys toxic hydrogen peroxide in the medium.It contains a single genus, LEGIONELLA.Features of Legionella:-Motile by polar or lateral flagella.Occur in surface water, thermally polluted lakes and streams, water from airconditioning cooling towers and evaporative condensers and in moist soil adjacentto a body of water.All species are opportunistics pathogens of human, causing Legionellosis.THE FAMILY NEISSERIACEAE:-This family contains:-Non-motile rods and cocci.Catalase positive.Oxidase positive organisms.It includes two genera namely:-1.Neisseria:- It consists of;Oxidase and catalase positive cocci that occur most often in pairs with the adjacentsites flattened.
(FIG:- Neisseria gonorrheae)Neisseria elongate is included because of its relatedness.The neisseria are parasites that inhabit the mucous membranes of humans andanimals.Two species are highly pathogenic for humans,e.g.,N.gonorrheae,the causative agentof gonorrhea, and N. Meningitidis , the causative agent of epidemic cerebrospinalmeningitis.2.ACINETOBACTER:-These are diplobacilliCatalase positive but oxidase negative.Saprophytes that occur in soil, water, and sewage.Opportunistic human pathogens that can a variety of infections particularly inhospitalized patients.Example; Acinetobacter baumanni, Acinetobacter bacteria
Other Genera of Aerobic Gram-Negative Rod and Cocci Not Assigned toAny Family:-Beijerinckia and DerxiaXanthobacterThermus and ThermomicrobiumAlteromonasFlavobacterium F.meningosepticum causes severeAlcaligenes meningitis in new born infants.Brucella causing BrucellosisBordetella B.pertusis occurs in humans causing whooping cough.Francisella F.tularensis parasite of wild animals can causeLampropedia tularaemia in humans.Fig. of BRUCELLA
5. FACULTATIVELY ANAEROBIC GRAM-NEGATIVE RODS:Organisms in this section form a diverse group of straight or curved rods.Organisms can grow aerobically or also under anaerobic conditions byfermenting various carbohydrates.Most genera are associated with animals or plants, but some occur in soil andwater.Facultatively anaerobic Gram negative rodsFamily:ENTEROBACTERIACEAE VIBRIONACEAE PASTEURALLACEAEGE VIBRIO AEROMONASNERA PASTEURELLA HAEMOPHILUS ACTINOBACILLUSEscherichia Shigella Salmonella Enterobacter Erwania Serratia Proteus Yersinia
THE FAMILY ENTEROBACTERIACEAE:-Some important features are:-Cell diameter is 0.3 to 1.5 µm.Cell shape is that of a straight rod.Motility, if present, is by means of lateral flagella.They are oxidase-negative.Cells contain a characteristic antigen, called the enterobacterial common antigen.The familt contains a large number of genera that are biochemically and genetically relatedto one another. Some selected genera are listed below:-1.ESCHERICHIA:-E. Coli occurs in the lower portion of the intestine of humans and warm bloodedanimals.Some strains can cause gestroenteritis; others can cause urinary tract infections.Fig.of E.coli2.SHIGELLA:-All strains are pathogenic.Causing bacillary dysentery in humans.3.SALMONELLA:-All strains are pathogenic.Causing enteric fevers (such as typhoid and paratyphoid fevers), gasteroenteritis,and septimecia.Many strains also infect a variety of animals.
Over 2,000 antigenic types of salmonellae occur.Fig. of Salmonella4. ENTEROBACTER:-Enterobacter species grow best at 30˚C rather than at 37˚C.They occur mainly in water, sewage, soil, meat, plants, and vegetables.Some species also occur in human and animal feces, and some can be opportunistichuman pathogens.5. ERWINIA:-They mainly associated with plants.They are often plant pathogens.They are causing diseases such as blights, cankers, die back, leaf spot, wilts,discoloration of plant tissues, and soft rots.They are seldom isolated from animals or humans.6. SERRATIA:-They are widely distributed in soil, in water, and on plant surfaces.Many strains produce pink or red colonies.They are opportunistic human pathogens and are particularly prone to infecthospitalized patients.7. PROTEUS:-These organisms can swarm on agar media.Proteus strains occur in the intestine of humans and a wide variety of animals, inpolluted waters, and in soil.They can be opportunistic human pathogens.Like E. Coli, P. mirabilis is one of the leading causes of urinary tract infections inhumans.
8. YERSINIA:-These are parasites of animals but can also cause infections in humans.For example, Y. Pestis is the causative agent of plague, and Y. enterocolitica is afrequent cause of gastroenteritis in children.THE FAMILY VIBRIONACEAE:-Some important features are:-Cell diameter is 0.3 to 1.3 nm.Cell shape is that of curved or straight rod.The cells are motile by means of polar flagella.They are usually oxidase positive.Cells do not contain the enterobacterial common antigen.The vibrionaceace occur in marine and fresh water environments or in associationwith animals living in thise environments.Two genera are described below:-VIBRIONACEAEVIBRIO AEROMONASDistinguished from other members i. Cells are straight rods that have noOf the family by having sheathed flag- sheathed flagella.-ella. ii. Organisms occur in fresh water sour-Occur in aquatic habited with a wide -ces and sewage.range of salinities. iii. Some species are pathogenic forSome show bioluminescence, an oxygen frogs and fish (e.g. ,A. Salmonicidadependant reaction catalyzed by the is the causative agent of Furunculosisenzyme luciferase. In salmon and trout.Example: V. FischeriMost of the vibrio species are harmlessSaprophytes but some are pathogenic.Example: V. Cholera (cholera).V. parahaemolyticus (gastroenteritis inHumans).V. anguillarum (pathogen of marine fish and eels)
THE FAMILY PASTEURELLACEAE:-Some important features of this family are:-The cell diameter is small (0.2 to 0.4 µm).Cell shape is that of a straight rod.The cells are nonmotile.They are usually oxidase-positive.Cells do not contain the enterobacterial common antigen.The family occurs as parasites of vertebrates.Na+is not required or stimulatory for growth.Organisms often have complex nutritional requirements.Some genera included in the family are described below:-1.PASTEURELLA:-These organisms are parasitic on the mucous membranes of the upper respiratorytract of mammals (rarely humans) and birds.The major pathogen is P. multocida, which causes hemorrhagic septicaemia in cattleand fowl cholera in domestic and wild birds.2. HAEMOPHILUS:-Haemophilus species occur as parasites of the mucous membranes of humans andanimals.Some are pathogenic for humans; for example, H. Influenza is a leading cause ofmeningitis in children.Fig.of Haemophilus influenza3.ACTINOBACILLUS:-These bacteria are also parasitic on mammals and birds.The organisms are only occasionally pathogenic for humans, but several species arepathogenic for animals, e.g., A. lignieressii, which causes granolomatous lesion incattle and sheep, and A. suis, which causes septicaemia, pneumonia, and arthritis inpigs.
Other Genera Of Facultatively Anaerobic Gram-Negative Rods NotAssigned To Any Family:-1. ZYMOMONASSaprophytic rods that occur in honey and as spoilage organisms in beer andcider.Have the capability of production of ethanol from glucose.2. CHROMOBACTERIUMThese are motile, rod – shaped organisms.Form violet colonies due to a pigment called violacein.C.violaceum occurs as a saprophyte in soil and water but can occasionallycause infections of humans and other mammals.3. GARDNERELLANonmotile ,pleomorphic rods which stain Gram-negative to gram-variable.G.vaginalis occurs in the human genito-urinary tract and is major cause ofbacterial “nonspecific” vaginitis.4. STREPTOBACILLUSThese are pleomorphic in shape.During cultivation ,L- phase variants may occur spontaneously; these have adefective cell wall,and more or less spherical in shape and form tiny fried-egg colonies similar to those of formed by mycoplasmas.S.monoliformis,is a parasite of rats and causes one form of rat-bite fever inhumans.6. ANAEROBIC, GRAM NEGATIVESTRAIGHT, CURVED, AND HELICAL RODS:-This section consists of a single family namely Bacteroidaceae.THE FAMILY BACTEROIDACEAE:-The organisms in this family exhibit the following characters:-They are anaerobic organisms that do not form endospores.They may be motile or nonmotile.They do not respire anaerobically by using inorganic sulfur compounds as electronacceptors; some do anaerobically with nitrate or fumarate; most have only afermentative type of metabolism.
Most species produce detectable amounts of organic acids as the result of theirfermentative metabolism.The organisms occur in the oral cavity and intestinal tract of humans and animals, inthe rumen of cattle, sheep, and other ruminant animals, or in other anaerobicenvironments.Some genera contain species that are pathogenic for humans; e.g, Bacteroidesfragilis is the most common anaerobic bacterium isolated from human soft tissueinfections and anaerobic blood infections.It includes below mentioned genera, these genera are differentiated mainly on the basisof their morphology and the kinds of organic acid end products they produced.GENUS MORPHOLOGY MAJOR ORGANIC ACID ENDPRODUCTS OF FERMENTATIONBacteroides Straight rods; nonmotile or motileby peritrichous flagella.Mixtures including succinate,acetate, formate, lactate,propionate; butyrate is either notformed or, if produced isaccompanied by isobutyrate andisovalerate.Fusobacterium Straight rods; nonmotile. Butyrate.Succinimonas Short rods or coccobacilli; motileby a single polar flagellum.Acetate and Succinate.Wolinella Helical, curved, or straight rods;motile by a single polar flagellum.Do not have a fermentative typeof metabolism; respireanaerobically with H2 or formateas electron donors and fumarateor nitrate as electron acceptors;the formate is oxidized to CO2,and the fumarate is reduced tosuccinate.Selenomonas Crescent shaped cells; motile by atuft of flagella located at themiddle of the concave side.Acetate, propionate, andsometimes lactate.Anaerovibrio Slightly curved rods; motile by asingle polar flagellum.Propionate and acetate.
7. DISSIMILATORY SULFATE OR SULFURREDUCING BACTERIA:-Important characteristic features of this section are:-Rigid.Anaerobic bacteria which respire an aerobically by using inorganic sulfur aselectron acceptors with the consequent formation of large amounts of H2S.Occur in mud from fresh water, marine or brackish environments and in theintestinal tract of humans and animals.One genus Desulfuromonas can respire with elemental sulfur as the electronacceptor; the other genera can not use sulfur but can use sulfate, thiosulfate orother oxidized sulfur compounds.Some genera are differentiated mainly on the basis of morphology, e.g.,Desulfovibrio (Vibrioid or helical cells), Desulfococcus (spherical cells), etc.8. AEROBIC GRAM-NEGATIVE COCCI:-It consists of a single family, VEILLONELLACEAE:-Consists of nonmotile cocci, typically occuring in pairs, often with adjacent sideflattened.Family VEILLONELLACEAE contains three genera which differ with regerd to their size andtheir energy sources and fermentation products.VEILLONELLACEAEVEILLONELLA ACIDAMINOCOCCUS MEGASPHAERAAll are inhabitants of the oral cavity,respiratory tract or intestinal tract ofhumans, ruminants, rodents and pigs
9. THE RICKETTSIAS AND CHLAMYDIASThese are tiny, nonmotile Gram-negative bacteria.Most of these re obligate prasites, able to grow only within the host cells.In some instances their size approaches to that of some large viruses which are alsoobligate parasites.The RICKETTSIAS comprises the order RICKETTSIALES and the CHLAMYDIAS includesthe order CHLAMYDIALES. The order RICKETTSIALES differ from the CHLAMYDIALESby:Having a more complex metabolism that allows them to synthesize ATP.Lacking a complex developmental cycle.The order RICKETTSIALES :-Rickettsias are associated with various arthropods which may serve as major hostsor which can act as vectors for transmission of the rickettsias to vertebrates.Rickettsias which are capable of multiplying within vertebrates grow within thereticuloendothelial cells,vascular endothelial cells ,or erythrocytes of these animaOrder RICKETTSIALESFAMILIES:BARTONELLABCEAE RICKETTSIACEAE ANAPLASMATACEAETRIBES:RICKETTSIEAE EHRLICHIEAE WOLBACHIEAE(Pathogenic for humans) (Pathogenic for vertebrate host (not pathogenic forOther than humans.) vertebrates;infectGenera; arthropods)RICKETTSIA ROCHALIMAEA COXIELLA
THE FAMILY RICKETTSIACEAE:-Consists of small rod-shaped or coccoid rickettsiasAre often pleomorphicThe family is subdivided into three tribes namely;a) The tribe RICKETTSIEAEb) The tribe EHRLICHIEAEc) The tribe WOLBACHIEAEThe tribe RICKETTSIEAE contains three genera,which are described below:1). RICKETTSIA:-The features of this genus are as follows:Transmission to humans occurs via arthropod vector(lice, fleas, ticks, mites,depending on the species).The organisms multiply within the cytoplasm , and sometimes within nucleus of hostcells.In the laboratory they are cultured ina) host animals , such as guinea pigs or miceb) embryonated chicken eggs ,particularly within the cells of the yolk sac membranec) tissue cell cultures,usually cells from 10-day old chicken embryos.Disease caused by RICKETTSIA species, and the arthropod vectors which transmit them are:a). Rocky Mountain Spotted Fever (ticks)b). Classical Typhus Fever (lice)c). Murine Typhus Fever (fleas)d). Rickettsialpox (mites)e). Scrub Typhus (mites)2.ROCHALIMAEA:-This genus is similar to RICKETTSIA except the following features:Mainly parasites of humans and human body lice and can be cultivated in vitro onlaboratory media (blood based agar).Grow epicellulary (i.e.,on the surface of host cells) rather than in the cytoplasm ornucleus.EXAMPLE: R. quintana causes a louse born disease, trench fever, in humans.
3. COXIELLA:- This genus is distinguished by several unusual properties:-Growth occurs preferentially within membrane-bounded vacuoles of host cells rather thanfree in the cytoplasm or nucleus.The organisms have an unusually high resistance to heat ( may survive a temerature of 62˚C/143˚F for 30 min.), probably due to the occurance of endospore-like structures in the cells.Although transmission to vertebrates can occur via an arthropod vector, it occurs mainly byinhalation of airborne infectious dust. The organisms can also be acquired by drinkingcontaminated unpasteurized milk.The single species of the genus, Coxiella burnetii, is the causative agent of Q fever, a type ofpneumonia.THE FAMILY BARTONELLACEAE:-Consists of parasites of the red blood cells of humans and other vertebrates.The organisms can be cultivated on nonliving laboratory media.The genus Bartonella causes Oroya fever in humans and is transmitted by biting fliesthat occur along the western slopes of the andes mountains in south America.THE FAMILY ANAPLASMATACEAE:-These organisms grow within or on erythrocytes or occur free in the plasma ofvarious wild and domestic animals.Have not yet been cultivated on nonliving laboratory media.THE ORDER CHLAMYDIALESSingle family CHLAMYDIACEAESingle genus CHLAMYDIASpecies; C. trachomatis, C. psittaciTHE ORDER CHLAMYDIALES:-This order contains the chlamydias, intracellular parasites that are distinguished fromrickettsias by-
1. An ability to make ATP (they have an absolute reliance on host cells for thiscompound and are sometimes termed “energy parasites”), and2. Occurance of a characteristic developmental cycle.In the laboratory, chlamydias are cultivated in the yolk sac membrane of embryonatedchicken eggs or in tissue cultures of mammalian cells, such as McCoy and HeLa cells.REPRODUCTION OF CHLAMYDIAS:-An infectious small particles, or elementary body (having electron dense nucleoid) istaken in to the host cell by phagocytosis.The elementary body is enclosed within a membrane bounded vacuole in thecytoplasm of the host cell.Within the vacuole the elementary body is reorganized into reticulate body (alsoknown as initial body).The reticulate body undergoes by binnary fission until a number of reticulate bodiesare formed, which then undergo reorganization of elementary bodies. This aggregateof reticulate bodies and elementary bodies within the vacuoles of the host cell formsa host cell inclusion (which can be seen by light microscopy).Some strains of Chlamydia trachomatis cause a type of keratoconiuntivitis, trachoma, thatoften results in blindness.Other strains cause nongonococcal urethritis, which is the most prevalent sexuallytransmitted disease in the United States today.Still other strains cause the sexually transmitted disease lymphogranuloma venereum.The species Chlamydia psittaci is mainly a pathogen of birds and domestic and wildmammals but can also cause psittacosis in humans.10. THE MYCOPLASMASImportant features of mycoplasmas are as follows:They lack cell wall, the outer boundary of the cells being the cytoplasmic membrane.Due to lack of cell wall, the cells have plasticity and can assume many differentshapes ranging from spheres to branched filaments.The cells are susceptible to lysis by osmotic shock caused by sudden dilution of themedium with water.Due to lack of cell wall, mycoplasmas are not inhibited by even high levels ofpenicillin;but they can be inhibited by antibiotics that affect protein synthesis,such astetracyclines or chloramphenicol.
Mycoplasmas can be cultivated in vitro on nonliving media(of rich composition) asfacultative anaerobes or obligate anaerobes.Genome is about one-fifth to one half the size of those bacteria capable of growthon nonliving media (this explains why these organisms have complex nutritionalrequirements and limited biosynthetic abilities.)Colonies on agar plates are usually tiny and have a characteristic fried-eggappearance.At present are placed in the taxonomic class, MOLLICUTES.Class MOLLICUTESOrder MYCOPLASMATALESFamiliesMYCOPLASMATACEAE ACHOLEPLASMATACEAE SPIROPLASMATACEAGeneraMYCOPLASMA UREAPLASMA ACHOLEPLASMA SPIROPLASMA
THE FAMILY MYCOPLASMATACEAE:-These are parasites of the mucous membranes and joints of humans or animals andrequire cholesterol for growth.Many species of the genus Mycoplasma are pathogenic for animals; the speciesMycoplasma pneumonia has the most significance for humans and is the causativeagent of primary atypical pneumonia.Members of the genus Ureaplasma require urea for growth and cause urethritis inhumans, pneumonia in cattle, and urogenital disease in cattle and other animalspecies.THE FAMILY ACHOLEPLASMATACEAE:-These mycoplasmas do not require cholesterol for growth.They are widely distributed in vertebrates, in sewage and soil, and possibly onplants.Their pathogenicity is unknown. Only a single genus, Acholeplasma, occurs.THE FAMILY SPIROPLASMATACEAE:-These organisms are unusual in that they are helical and exhibit a swimming motility.The family contains a single genus, Spiroplasma.The organisms are pathogenic for citrus and other plants.They can be isolated from plant fluids and plant surfaces and from arthropods thatfeed on plants.11. ENDOSYMBIONTSEndosymbionts are bacteria like forms that have been observed within the cells ofprotozoa, insects, fungi, sponges, coelenterates, helminths and annelids.Most of this bacteria like forms have not been cultivated in laboratory.Most endosymbionts do not harm their host, indeed many appear to be beneficialeven necessary for the growth and development of their hosts. A vast amount ofinformation has been obtained for endosymbionts of protozoa, even to the point ofclassifying many of them by separating their DNA from that of their host cell andperforming base composition and homology experiments with the DNA.Many of the protozoan endosymbionts now bear formal genus and species name.For example, Lyticum flagellatum is an endosymbiont carried by certain strains ofthe protozoan Paramecium tetraurelia.
One function of Lyticum flagellatum is to synthesize the vitamin folic acid for itshost; symbiont free lines of the same strains of the protozoan need to be suppliedwith this vitamin.Another function of Lyticum flagellatum is to produce a toxin that is liberated intothe culture medium: when an endosymbiont-bearing strain of Parameciutetraurelia(called a killer strain) is mixed with certain strains lacking it (called sensative strain),the latter protozoa are rapidly killed and lysed. The endosymbiont-bearing strainsare resistant to this toxin.