gracilicutes (2)

An Assignment

On

GRACILICUTES (Gram –negative Bacteria)

SUBMITTED BY:

ROUF AHMAD

M.Sc.Microbiology (Ist sem.)

L-2011- BS-249-M

SUBMITTED TO:

Prof.Dr.(Mrs.) Urmila Phutela

Department of Microbiology

PUNJAB 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 simple morphology and cellular arrangement.

Do not form complex structures such as prosthecae (semirigid extensions of the cell wall and cytoplasmic membrane), sheaths (hollow tubes that enclose chains or trichomes) or with rare exceptions, endospores and cysts.

Cells not arranged in trichomes. Reproduce mainly by transverse binary fission rather than by

budding, fragmentation or spore formation. Motility if present is of free swimming type rather than the

gliding type. Mainly heterotrophic but some can grow autographically in the

presence of H2.Some are saprophytes, parasites. Some highly pathogenic and others may be opportunistic pathogens (cause disease only in a patient whose defense mechanisms against infection have been weakened or compromised).

BERGEY’S MANUAL OF SYSTEMATIC BACTERIOLOGY, VOLUME 1 Each volume of Bergey’s Manual is divided into a number of major sections, and each bearing a descriptive common name rather than formal taxonomic name.The major sections of Volume 1 are listed below:

The Spirochetes

Aerobic/Microaerophillic, Motile, Helical/Vibriod, Gram-negative Bacteria

Non-motile or rarely motile, Gram-negative curved

Bacteria

Aerobic Gram-negative Rods and Cocci

Facultative anaerobic Gram-negative Rods

Gracilicutes

Anaerobic Gram-negative straight, curved and helical

Rods

Dissimilatory sulphate or sulphur-reducing bacteria

Anaerobic Gram-negative cocci

The Rickettsias and Chlamydias

The Mycoplasmas

Endosymbionts

1. THE SPIROCHETES:

Distinguishing features:

A helical shape

An ability to twist or contort their shape(i.e., flexibility) The occurrence of a special kind of flagella termed periplasmic flagella(also

called axial fibrils or endoflagella) The major difference in structure from other Gram-negative eubacteria is in the

location of the periplasmic flagella. They are located between the outer membrane (often termed outer sheath in spirochetes) and the protoplasmic cylinder (i.e., the protoplast plus the overlying peptidoglycan layer); thus they are located in the periplasmic 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 swimming motility of spirochetes.

Spirochetes swim best in media of high viscosity; whereas bacteria with ordinary flagella swim best in media of low viscosity.

Spirochetes can also exhibit creeping or crawling motility when in contact with solid surfaces.

Most spirochetes are so thin that they cannot be easily seen by light microscopy,even when Gram-stained.

SPIROCHETES

ORDER: SPIROCHAETALES

FAMILY:

SPIROCHAETACEAE LEPTOSPIRACEAE

GENUS:

Leptospira

Spirochaeta 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 freshwater

environments. 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 been

cultivated in vitro (on nonliving media) and are stringent anaerobes; these are mainly harmless parasites, but one species,T.hyodysenteriae, causes hog dysentery.

Some species have not been cultivated invitro,e.g.,T.pallidum subsp. Pallidum which cause syphills in humans and is microaerophillic.

Genus BORRELIA: Parasites of wild rodents and small mammals, and also of the arthropods associated

with 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 BACTERIA

Important characteristics are as:

The cells are rigid (unlike spirochetes) and range from vibrioid (having less than one turn 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 marine

environments, but a few are parasitic and can be pathogenic for humans and animals or for other bacteria.

IMPORTANT GENERA IN THIS SECTION ARE AS:

GENUS CHARACTERISTICS

1. AQUASPIRILLUM Helical or vibrioid. Typically possess bipolar tufts of flagella. These are harmless saprophytes,aerobic to

microaerophillic. Occur in stagnant stream or pond. No growth occurs in the presence of 3%NaCl or sea

water.

GENUS CHARACTERISTICS

2. AZOSPIRILLUM Cells are plump and vibrioid with a single polar flagellum

and if grown on solid media, with numerous lateral flagella as well.

Occur within roots of grasses,wheat,corn and many other plants 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 fixed nitrogen such as ammonium salt.

One species A.lipoferum can grow autotrophically with hydrogen gas as the source of energy.

Fig. Of Azospirillum

3.OCEANOSPIRILLUM Cells 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.CAMPYLOBACTER These are vibrioid cells having a single flagellum at one or

both poles. Microaerophillic parasites. Occur in the reproductive organs, intestinal tract and oral

cavity of humans and other mammals. Some species are pathogenic,e.g.,C.jejuni,causes diarrhea

in humans, or C.fetus subspecies venerealis,causes abortion in cattle

Fig. Campylobacter jejuni

5.BDELLOVIBRIO These are aerobic, vibriod cells. Possess single polar flagellum. Have unique property of being parasitic on other Gram- negative

bacteria.

After penetration of the outer membrane of the cell wal, they grow within the periplasmic space.The host cell becomes an empty “ghost” cell.

Occur in soil,sewage, and in freshwater and mrine environments.

NOTE: The genus Vampirovibrio has certain similarities to the genus Bdellovibrio, but the organisms attack eukaryotic algae, 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, and sometimes 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 marine

environments.

This section contains the family SPIROSOMACEAE .It contains three genera whose cells are;

Aerobic Form no intracellular gas vacuoles, are catalase and oxidase-positive Form colonies that are yellow

FAMILY SPIROSOMACEAE

GENUS (1, 2,3)

1. SPIROSOMA 2. RUNELLA 3.FLECTIBACILLUS(form yellow colonies) (form pink colonies) (form pink colonies)

4. AEROBIC, GRAM – NEGATIVE RODS AND CONES:

This section forms one of the largest and most diverse groups of bacteria. Two general features are as follows:

1. The cells are mainly straight or slightly curved (but not helical) rods, but some are cocci.

2. They have a strictly respiratory type of metabolism.

Several families and some additional genera that are not assigned to any family are represented.

FAMILIES GENERA

PSEUDOMONAS

PSEUDOMONADACEAE XANTHOMONAS

ZOOGLOEA

AZOTOBACTERCEAE AZOTOBACTER

RHIZOBIUM

Aerobi c RHIZOBIACEAE BRADYRHIZOBIUM

Gram-Negative AGROBACTERIUM

Rods and METHYLOCOCCACEAE METHYLOCOCCUS

Cocci METHYLOMONAS

ACETOBACTERACEAE ACETOBACTER

GLUCONOBACTER

LEGIONELLACEAE LEGIONELLA

NEISSERIACEAE NEISSERIA

ACINETOBACTER

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 by

using nitrate as an electron acceptor. Several species are pathogenic for humans and animals; others are important plant

pathogens. Some cause spoilage of meats and other foods.

Identification of species is based on many physiological and nutritional characteristics, such as ability to use certain compounds as carbon sources for growth.

(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 fluorescent pigments, pyoverdin.

It is mainly a soil and water saprophyte, but it is also frequently and opportunistic pathogen 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 fluorescent

pigment.

Pseudomonas syringae:- This and several other species are important plant pathogens, causing diseases such

as leaf spot, leaf strip, wilt and necrosis.

Pseudomonas mallei:- It is the causative agent of glanders and farcy, diseases of horses and donkeys that

are 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 for

industrial 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 a gelatinous matrix to form slimy masses with a finger like morphology.

Saprophytic in nature and commonly found coating the rocks on trickling filer beds in sewage treatment plants, where they are oxidise the soluble organic components of the 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 plant

rhizosphere(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 the

cell surface and maintain an anaerobic cell interior; this protects the oxygen sensitive nitrogenase complex(responsible for nitrogen fixation) from being inactivated under an 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 of leguminous plants.

These bacteria to the roots hairs, penetrate the root, and induce proliferation of the root cells.

Within the resulting root nodules the bacteriaexist as highly pleomorphic N2 fixing forms called bacteriods.

Leghaemoglobin protects the nitrogenase enzyme complex from being destroyed by excess oxygen.

Species and strains of rhizobia and bradyrhizobia exhibit a range of specificities for various 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 to use methane gas a sole carbon and energy source under aerobic or microaerophilic conditions.

These are harmless organisms and occur in soil, mud or water adjacent to or overlying 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.Methylococcus

Are all obligate methane oxidizers (that is carbon sources such glucose can not be used for growth).

2.Methylomonas

THE FAMILY ACETOBACTERACEAE:- Important features:-

Contents ellipsoidal to rod shaped cells that oxidized ethanol to acetic acid in neutral or acidic (pH 4.5) media.

Two genera included:-

1.Acetobacter

Both are differentiated by certain biochemical characteristics and by the occurance of peritrichous flagella (Acetobacter) or polar flagella.

2.Gluconobacter

Characteristic 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 fruit juices, bees, and honey.

These are industrially very important:Acetobacters are used to make vinegar.Gluconobacters are involved in the manufacter of chemicals such as dihydroxyacetone, sorbose and 5-ketogluconic acid.

Some of the strains of Acetobacter have the highly unusual ability to make exocellular fibrils that accumulate around the cells.

THE FAMILY LEGIONELLACEAE:-Include rod shaped bacteria which require L-Cystine, iron, salts, and activated powder charcoal 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 air conditioning cooling towers and evaporative condensers and in moist soil adjacent to 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 adjacent

sites flattened.

(FIG:- Neisseria gonorrheae)

Neisseria elongate is included because of its relatedness. The neisseria are parasites that inhabit the mucous membranes of humans and

animals. Two species are highly pathogenic for humans,e.g.,N.gonorrheae,the causative agent

of gonorrhea, and N. Meningitidis , the causative agent of epidemic cerebrospinal meningitis.

2.ACINETOBACTER:-

These are diplobacilli Catalase positive but oxidase negative. Saprophytes that occur in soil, water, and sewage. Opportunistic human pathogens that can a variety of infections particularly in

hospitalized patients.

Example; Acinetobacter baumanni, Acinetobacter bacteria

Other Genera of Aerobic Gram-Negative Rod and Cocci Not Assigned to Any Family:-

Beijerinckia and Derxia

Xanthobacter

Thermus and Thermomicrobium

Alteromonas

Flavobacterium F.meningosepticum causes severe

Alcaligenes meningitis in new born infants.

Brucella causing Brucellosis

Bordetella B.pertusis occurs in humans causing whooping cough.

Francisella F.tularensis parasite of wild animals can cause

Lampropedia tularaemia in humans.

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 by

fermenting various carbohydrates. Most genera are associated with animals or plants, but some occur in soil and

water.

Facultatively anaerobic Gram negative rodsFamily:

ENTEROBACTERIACEAE VIBRIONACEAE PASTEURALLACEAE

G

E VIBRIO AEROMONAS

N

E

R

A PASTEURELLA HAEMOPHILUS ACTINOBACILLUS

Escherichia 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 related to one another. Some selected genera are listed below:-

1.ESCHERICHIA:-

E. Coli occurs in the lower portion of the intestine of humans and warm blooded animals.

Some strains can cause gestroenteritis; others can cause urinary tract infections.

Fig.of E.coli

2.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 Salmonella

4. 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 opportunistic

human 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 infect

hospitalized patients.

7. PROTEUS:- These organisms can swarm on agar media. Proteus strains occur in the intestine of humans and a wide variety of animals, in

polluted 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 in

humans.

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 a

frequent 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 association

with animals living in thise environments.

Two genera are described below:-

VIBRIONACEAE

VIBRIO AEROMONAS

Distinguished from other members i. Cells are straight rods that have no Of 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 for

Some show bioluminescence, an oxygen frogs and fish (e.g. ,A. Salmonicida dependant reaction catalyzed by the is the causative agent of Furunculosisenzyme luciferase. In salmon and trout.Example: V. Fischeri

Most of the vibrio species are harmless Saprophytes but some are pathogenic.Example: V. Cholera (cholera).V. parahaemolyticus (gastroenteritis in Humans).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 respiratory

tract of mammals (rarely humans) and birds. The major pathogen is P. multocida, which causes hemorrhagic septicaemia in cattle

and fowl cholera in domestic and wild birds.

2. HAEMOPHILUS:- Haemophilus species occur as parasites of the mucous membranes of humans and

animals.

Some are pathogenic for humans; for example, H. Influenza is a leading cause of meningitis in children.

Fig.of Haemophilus influenza

3.ACTINOBACILLUS:-

These bacteria are also parasitic on mammals and birds. The organisms are only occasionally pathogenic for humans, but several species are

pathogenic for animals, e.g., A. lignieressii, which causes granolomatous lesion in cattle and sheep, and A. suis, which causes septicaemia, pneumonia, and arthritis in pigs.

Other Genera Of Facultatively Anaerobic Gram-Negative Rods Not Assigned To Any Family:-

1. ZYMOMONAS Saprophytic rods that occur in honey and as spoilage organisms in beer and

cider. Have the capability of production of ethanol from glucose.

2. CHROMOBACTERIUM These 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 occasionally

cause infections of humans and other mammals.

3. GARDNERELLA Nonmotile ,pleomorphic rods which stain Gram-negative to gram-variable. G.vaginalis occurs in the human genito-urinary tract and is major cause of

bacterial “nonspecific” vaginitis.

4. STREPTOBACILLUS These are pleomorphic in shape. During cultivation ,L- phase variants may occur spontaneously; these have a

defective 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 in humans.

6. ANAEROBIC, GRAM NEGATIVE STRAIGHT, 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 electron

acceptors; some do anaerobically with nitrate or fumarate; most have only a fermentative type of metabolism.

Most species produce detectable amounts of organic acids as the result of their fermentative metabolism.

The organisms occur in the oral cavity and intestinal tract of humans and animals, in the rumen of cattle, sheep, and other ruminant animals, or in other anaerobic environments.

Some genera contain species that are pathogenic for humans; e.g, Bacteroides fragilis is the most common anaerobic bacterium isolated from human soft tissue infections and anaerobic blood infections.

It includes below mentioned genera, these genera are differentiated mainly on the basis of their morphology and the kinds of organic acid end products they produced.

GENUS MORPHOLOGY MAJOR ORGANIC ACID END PRODUCTS OF FERMENTATION

Bacteroides Straight rods; nonmotile or motile by peritrichous flagella.

Mixtures including succinate, acetate, formate, lactate, propionate; butyrate is either not formed or, if produced is accompanied by isobutyrate and isovalerate.

Fusobacterium Straight rods; nonmotile. Butyrate.Succinimonas Short rods or coccobacilli; motile

by a single polar flagellum.Acetate and Succinate.

Wolinella Helical, curved, or straight rods; Do not have a fermentative type

motile by a single polar flagellum. of metabolism; respire anaerobically with H2 or formate as electron donors and fumarate or nitrate as electron acceptors; the formate is oxidized to CO2, and the fumarate is reduced to succinate.

Selenomonas Crescent shaped cells; motile by a tuft of flagella located at the middle of the concave side.

Acetate, propionate, and sometimes lactate.

Anaerovibrio Slightly curved rods; motile by a single polar flagellum.

Propionate and acetate.

7. DISSIMILATORY SULFATE OR SULFUR REDUCING BACTERIA:-Important characteristic features of this section are:-

Rigid. Anaerobic bacteria which respire an aerobically by using inorganic sulfur as

electron acceptors with the consequent formation of large amounts of H2S. Occur in mud from fresh water, marine or brackish environments and in the

intestinal tract of humans and animals. One genus Desulfuromonas can respire with elemental sulfur as the electron

acceptor; the other genera can not use sulfur but can use sulfate, thiosulfate or other 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 side flattened.

Family VEILLONELLACEAE contains three genera which differ with regerd to their size and their energy sources and fermentation products.

VEILLONELLACEAE

VEILLONELLA ACIDAMINOCOCCUS MEGASPHAERA

All are inhabitants of the oral cavity,

respiratory tract or intestinal tract of

humans, ruminants, rodents and pigs

9. THE RICKETTSIAS AND CHLAMYDIAS These 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 also

obligate parasites.

The RICKETTSIAS comprises the order RICKETTSIALES and the CHLAMYDIAS includes the order CHLAMYDIALES. The order RICKETTSIALES differ from the CHLAMYDIALES by:

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 hosts or which can act as vectors for transmission of the rickettsias to vertebrates.

Rickettsias which are capable of multiplying within vertebrates grow within the reticuloendothelial cells,vascular endothelial cells ,or erythrocytes of these anima

Order RICKETTSIALES

FAMILIES:

BARTONELLABCEAE RICKETTSIACEAE ANAPLASMATACEAE

TRIBES:

RICKETTSIEAE EHRLICHIEAE WOLBACHIEAE(Pathogenic for humans) (Pathogenic for vertebrate host (not pathogenic for

Other than humans.) vertebrates;infect

Genera; arthropods)

RICKETTSIA ROCHALIMAEA COXIELLA

THE FAMILY RICKETTSIACEAE:-

Consists of small rod-shaped or coccoid rickettsias Are often pleomorphic

The family is subdivided into three tribes namely;

a) The tribe RICKETTSIEAEb) The tribe EHRLICHIEAEc) The tribe WOLBACHIEAE

The 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 host cells.

In the laboratory they are cultured in a) 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 on laboratory media (blood based agar).

Grow epicellulary (i.e.,on the surface of host cells) rather than in the cytoplasm or nucleus.

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 than free 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 by inhalation of airborne infectious dust. The organisms can also be acquired by drinking contaminated unpasteurized milk.

The single species of the genus, Coxiella burnetii, is the causative agent of Q fever, a type of pneumonia.

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 flies

that 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 of various wild and domestic animals.

Have not yet been cultivated on nonliving laboratory media.

THE ORDER CHLAMYDIALES

Single family CHLAMYDIACEAE

Single genus CHLAMYDIA

Species; C. trachomatis, C. psittaci

THE ORDER CHLAMYDIALES:-

This order contains the chlamydias, intracellular parasites that are distinguished from rickettsias by-

1. An ability to make ATP (they have an absolute reliance on host cells for this compound and are sometimes termed “energy parasites”), and

2. Occurance of a characteristic developmental cycle.

In the laboratory, chlamydias are cultivated in the yolk sac membrane of embryonated chicken 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) is

taken in to the host cell by phagocytosis. The elementary body is enclosed within a membrane bounded vacuole in the

cytoplasm of the host cell. Within the vacuole the elementary body is reorganized into reticulate body (also

known as initial body). The reticulate body undergoes by binnary fission until a number of reticulate bodies

are formed, which then undergo reorganization of elementary bodies. This aggregate of reticulate bodies and elementary bodies within the vacuoles of the host cell forms a host cell inclusion (which can be seen by light microscopy).

Some strains of Chlamydia trachomatis cause a type of keratoconiuntivitis, trachoma, that often results in blindness.

Other strains cause nongonococcal urethritis, which is the most prevalent sexually transmitted 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 wild mammals but can also cause psittacosis in humans.

10. THE MYCOPLASMAS

Important 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 different

shapes ranging from spheres to branched filaments. The cells are susceptible to lysis by osmotic shock caused by sudden dilution of the

medium with water. Due to lack of cell wall, mycoplasmas are not inhibited by even high levels of

penicillin;but they can be inhibited by antibiotics that affect protein synthesis,such as tetracyclines or chloramphenicol.

Mycoplasmas can be cultivated in vitro on nonliving media(of rich composition) as facultative anaerobes or obligate anaerobes.

Genome is about one-fifth to one half the size of those bacteria capable of growth on nonliving media (this explains why these organisms have complex nutritional requirements and limited biosynthetic abilities.)

Colonies on agar plates are usually tiny and have a characteristic fried-egg appearance. At present are placed in the taxonomic class, MOLLICUTES.

Class MOLLICUTES

Order MYCOPLASMATALES

Families

MYCOPLASMATACEAE ACHOLEPLASMATACEAE SPIROPLASMATACEA

Genera

MYCOPLASMA UREAPLASMA ACHOLEPLASMA SPIROPLASMA

THE FAMILY MYCOPLASMATACEAE:-

These are parasites of the mucous membranes and joints of humans or animals and require cholesterol for growth.

Many species of the genus Mycoplasma are pathogenic for animals; the species Mycoplasma pneumonia has the most significance for humans and is the causative agent of primary atypical pneumonia.

Members of the genus Ureaplasma require urea for growth and cause urethritis in humans, pneumonia in cattle, and urogenital disease in cattle and other animal species.

THE FAMILY ACHOLEPLASMATACEAE:-

These mycoplasmas do not require cholesterol for growth. They are widely distributed in vertebrates, in sewage and soil, and possibly on

plants. 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 that

feed on plants.

11. ENDOSYMBIONTS

Endosymbionts are bacteria like forms that have been observed within the cells of protozoa, 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 beneficial

even necessary for the growth and development of their hosts. A vast amount of information has been obtained for endosymbionts of protozoa, even to the point of classifying many of them by separating their DNA from that of their host cell and performing 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 of the protozoan Paramecium tetraurelia.

One function of Lyticum flagellatum is to synthesize the vitamin folic acid for its host; symbiont free lines of the same strains of the protozoan need to be supplied with this vitamin.

Another function of Lyticum flagellatum is to produce a toxin that is liberated into the 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 strains are resistant to this toxin.