This document provides an introduction and overview of gram-negative bacteria. It discusses their key characteristics and classification. Specifically, it summarizes several genera of gram-negative bacteria, including Pseudomonas, Xanthomonas, Azotobacter, Rhizobium, Methylococcus, Acetobacter, and Legionella. It also describes the families they belong to, such as Pseudomonadaceae, Azotobacteraceae, and Legionellaceae.

1. An Assignment
On
GRACILICUTES (Gram –negative Bacteria)
SUBMITTED BY:
ROUF AHMAD
M.Sc.Microbiology
L-2011- BS-249-M
SUBMITTED TO:
Prof.Dr.(Mrs.) Urmila Phutela
Department of Microbiology
PUNJAB AGRICULTURAL UNIVERSITY,LUDHIANA 141004

2. 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).

3. 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

4. 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

5. 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.

6. 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.

7. 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.

8. 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.

9. 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)

10. 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
Aerobic RHIZOBIACEAE BRADYRHIZOBIUM
Gram-Negative AGROBACTERIUM
Rods and METHYLOCOCCACEAE METHYLOCOCCUS
Cocci METHYLOMONAS
ACETOBACTERACEAE ACETOBACTER
GLUCONOBACTER
LEGIONELLACEAE LEGIONELLA
NEISSERIACEAE NEISSERIA
ACINETOBACTER

11. 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.

12. 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

13. 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).

14. 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.

15. 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.

16. (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

17. 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.
Fig. of BRUCELLA

18. 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 rods
Family:
ENTEROBACTERIACEAE VIBRIONACEAE PASTEURALLACEAE
G
E VIBRIO AEROMONAS
N
E
R
A PASTEURELLA HAEMOPHILUS ACTINOBACILLUS
Escherichia Shigella Salmonella Enterobacter Erwania Serratia Proteus Yersinia

19. 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.

20. 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.

21. 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 Furunculosis
enzyme 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)

22. 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.

23. 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.

24. 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;
motile by a single polar flagellum.
Do not have a fermentative type
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.

25. 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

26. 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

27. 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 RICKETTSIEAE
b) The tribe EHRLICHIEAE
c) 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 mice
b) embryonated chicken eggs ,particularly within the cells of the yolk sac membrane
c) 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.

28. 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-

29. 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.

30. 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

31. 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.

32. 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.