eChapters

Aetiology
Classification of the causative agent • Ehrlichia ruminantium (formerly Cowdria ruminantium) Order Rickettsiales, Family Anaplasmataceae
• Small, Gram negative, pleomorphic coccus, and obligate intracellular parasite.
• Strains of E. ruminantium are very diverse and vary in virulence: while some strains are highly virulent, others appear to be less-pathogenic.
• E. ruminantium has a high level of genomic plasticity. Several different genotypes can co-exist in a geographical area, and may recombine to form new strains.
• E. ruminantium multiplies in vascular endothelial cells throughout the body to cause severe vascular compromise.
• It usually occurs in clumps of from less than five to several thousand organisms within the cytoplasm of infected capillary endothelial cells, and can be detected in brain smears by light microscopy.
Resistance to Physical and Chemical Action
Temperature
Heat labile and loses its viability within 12–38 hours at room temperature. Infective stabilities can be cryopreserved in DMSO (dimethyl sulphide) or better yet in sucrosepotassium phosphate-glutamate medium (SPG). Infective half-life of thawed stabilate kept on ice is only 20–30 minutes.
pH: Not applicable.
Disinfectants: Not applicable.
Survival:

Introduction
Q fever is a zoonotic bacterial infection caused by Coxiella burnetii, an obligate intracellular parasite, classified within the family Rickettsiaccae. Q fever (Q for “query”) was first used in 1937 to describe a mysterious febrile illness of packing house workers in Brisbane, Australia. The causative agent was isolated from infected workers and later was identified as Rickettsiae. Almost simultaneously the same organism was identified wood tick collected in Montana. Cox, an American, and Burnet, an Australian, where honored for their early work with this organism, hence the name “Coxiella burnetii”.
Host and Susceptibility
Coxiella burnetii is a well-established infectious agent that has reached a state of balanced pathogenicity in a plethora of host. Human are unnatural and usually dead-end-host. The microorganism generally maintained in a less pathogenic form in separate cycle existing independently among wild mammals and their haematophagus arthropods, principally tick and in domestic animals.
Morphology
It is an intracellular organism which is a polymorphic bacillus (0.2-0.4mm width, 0.4-1.0 mm length), which has a cell membrane, like Gram negative bacteria. However, it stains poorly with pigmented Gram stain, but gimenez staining is traditionally used to stain the Coxiella burnetii pathogen from pathological materials and crop. Coxiella burnetii has several distinctive characteristics, including a sporulationlike
process that protects the organism against the external environment, where it can survive for long periods. In mammals, the usual host cell of C. burnetii is the macrophage, which is unable to kill the bacterium. The other an important characteristic of C. burnetii is its antigenic variations, those called phase variation. This antigenic shift can be measured and is valuable for differentiating acute from chronic Q fever. Thus, it displays two antigenic phases those are phase-I and phase- II that are liable to the Lipopolysaccharide (LPS) of the membrane.

The mycoplasmas are microorganisms in the class Mollicutes. Of the nine genera in this class, five contain species of veterinary interest. The genus Mycoplasma, in which there are about 100 species, contains most of the animal pathogens. The first mycoplasma identified in 1890 was Mycoplasma mycoides subspecies mycoides, the cause of contagious bovine pleuropneumonia. Similar types of mycoplasmas which were subsequently identified were called pleuropneumonia- like organisms (PPLO).
Mycoplasmas, the smallest prokaryotic cells capable of self-replication, are pleomorphic organisms ranging from spherical (0.3 to 0.9 pm in diameter) to filamentous (up to 1.0 μm long). Because they cannot synthesize peptidoglycan or its precursors, they do not possess rigid cell walls but have flexible, triplelayged outer membranes.
Their flexibility allows them to pass through bacterial membrane filters of pore size 0.22 to 0.45 μm. Mycoplasmas are susceptible to desiccation, heat, detergents and disinfectants. However, they are resistant to antibiotics such as penicillin which interfere with the synthesis of bacterial cell walls. Based on 5s rRNA sequence analyses, the mycoplasmas have been shown to be linked phylogenetically to Gram-positive bacteria such as Clostridium species which have low guanine-cytosine content in their DNA. They require enriched media for growth, characteristically forming umbonate micro-colonies
when illuminated obliquely and microcolonies with a ‘fried egg’ dppearance in transmitted light. The dense central zone is due to extension of the microcolony into the agar. Mycoplasmas, which have relatively small genomes (approximately 800 genes) are fastidious in their growth requirements.
Most mycoplasmas are facultative anaerobes and some grow optimally in an atmosphere of 5 to 10% CO2. Nonpathogenic anaerobic mycoplasmas are found in the rumens of sheep and cattle. The genera Mycoplasma and Ureaplasma contain animal pathogens.

Five genospecies of intestinal spirochaetes have been isolated from pigs namely Brachyspira hyodysenteriae,B. pilosicoli, B. innocens, Serpulina intermedia and S. murdochii. The genera Serpulina and Brachyspira were recently combined. These anaerobic spirochaetes have six to fourteen spirals and are 0.1 to 0.5 μm in width.
Usual Habitat
Pathogenic Brachyspira species are found in the intestinal tract of both clinically affected and normal pigs. Carrier pigs can shed B.hyodysenteriae for up to three months and are the principal source of infection for healthy pigs.
Differentiation of Brachyspira Species
The differentiation of B.hyodysenteriae from other intestinal spirochaetes is based on its pattern of haemolysis on blood agar. Tests for detecting indole production or the hydrolysis of hippurate are also useful diagnostically. Restriction endonnclease analysis, restriction fragment length polymorphism, ribotyping using 16s rRNA analysis, PCR-based assays and multilocus enzyme electrophoresis have been developed both for differentiating species and for distinguishing strains of organisms within species. Brachyspira hyodysenteriae isolates can also he allocated to several serogroups and serotypes.
Pathogenesis
Most information on the pathogenesis of Brachyspira species derives from studies of B.hyodysenteriae. Motility in mucus is an essential virulence factor of thisorganism; mutant strains with altered motility are lesscapable of colonizing the pig intestine. Colonization may be enhanced by factors in mucuswith chemotactic activity for the organisms. Factors with such chemotactic activities have been demonstrated in vitro. Haemolytic activity,demonstrated in vitro, correlates with pathogenicity andthree genes encoding haemolytic and cytotoxic activityhave been cloned and sequenced.

Borreliae, which are longer and wider than other spirochaetes, have a similar helical shape. In addition to a linear chromosome, which is unique among bacteria, borreliae possess linear and circular plasmids. Although these spirochaetes can cause disease in animals and humans, subclinical infections are also common. Borreliae are transmitted by arthropod vectors.
Usual Habitat
Borreliae are obligate parasites in a variety of vertebrate hosts. Although these organisms persist in the environment for short periods, they depend on vertebrate reservoir hosts and arthropod vectors for long-term survival.
Differentiation of Borrelia Species
Borreliae can be differentiated from other spirochaetes by their morphology, by the low guanine and cytosine content of their genomic DNA and by ecological, cultural and biochemical characteristics. Identification of Borrelia species depends mainly on genetic analysis. At least nine genospecies or genomic groups of B.burgdorferi sensulato, have been identified using DNA-DNA hybridization, 16s rRNA sequencing and other molecular techniques.
Clinical Infections
The species of particular veterinary importance are B. burgdorferi sensu lato, the cause of Lyme disease in animals and humans, and B. anserina which causes avian borreliosis. The significance of two other species, B.theileri andB.coriaceae, as animal pathogens, is uncertain.
Lyme Disease
This condition, also known as Lyme borreliosis, was first identified in 1975 following investigation of a cluster of arthritis cases in children near the town of Old Lyme, Connecticut. The causative agent, a spirochaete, was named Borrelia burgdorferi.

Members of the genus Serpulina (Treponema) are host-associated spirochaetes found in the oral cavity, intestinal tract and genital region of animals and humans. The cells are wider, are not as tightly coiled as th e leptospires and can be stained by aniline dyes.
The species of veterinary significance are S. Hyodysenleriae (swine dysentery) and T. paraluiscunicllii (ventdisease of rabbits). S. innocens, present in the faecesof pigs and dogs, is thought to be non- athogenic,although some workers regard S. innocens as a strainof S. hyodysenteriae of lower virulence. S. hyodysenteriae and S. innocens are s imilarmorphologically, culturally as well as biochemicallyand can be grown on laboratory media. T. Paraluiscuniculi has not been cultured in vitro.
Normal Habitat
T. paraluiscliniculi produces a benign venereal disease of rabbits and is present in lesions in the genito-perineal area of rabbits. It causes latentin fection in mice, guinea- pigs and hamsters. The treponemes can be found in the lymph nodes of these animals. The reservoir of S. hyodysenteriae is the intestinal tract of pigs, wild rats and mice. Recovered, asymptomatic pigs can excrete these organisms in faeces for 3 months or more. Survival of S. hyodysenteriae in soil or voided pig faeces is short, about 24 48 hours. Infection is by the faecal-oral route.

The order Spirochaetales contains two families, Leptospiraceae and Spirochaetaceae. It comprises spiral or helical bacteria (spirochaetes) which share some unique morphological and functional features. Members of the order are motile by means of endoflagella which are located within the periplasm.
The spirochactes are slender, motile, flexuous, unicellular, helically coiled bacteria ranging rrom 0.1 -3.0 μm in width. The outer sheath, the outermost layer of a spirochaete cell, is a multi layered membrane that completely surrounds the peri plasmic flagella (axial filament) and the helical protoplasmic cylinder. The cylinder consists or the nuclear material, cytoplasm, cytoplasmic membraneand the peptidoglycan portion of the cell wall.
The periplasmic flagella are wrapped around the cylinder and are in the peri plasmic space of these Gram-negative bacteria. One end of each flagellum is inserted near a pole of the protoplasmic cylinder and attached by platelike structures called insertion discs. The distal end of each flagellum is not inserted and extends to the centre of the cell and may overlap the flagellum from the opposite end. The periplasmic flagella facilitate the motility of the bacteria in viscid environments.
Leptospira species
Members of this species (leptospires) are motile helical bacteria (0.1 x 6 to 12 μm) with hook-shaped ends. Although cytochemically Gram-negative, they do not stain well with conventional bacteriological dyes and are usually visualized using dark-field microscopy. Silver impregnation and immunological staining techniques are used to demonstrate leptospires in tissues. Leptospirosis, which can affect all domestic animals and humans, ranges in severity from mild infections of the urinary or genital systems to serious systemic disease.

Many non-spore-forming, anaerobic, Gram-negative bacteria cause opportunistic mixed infections, often in association with facultative anaerobes. Synergistic interactions between the organisms in these mixed infections are common. Fusobacterium species and bacteria formerly referred to as Bacteroides species account for more than 50%of the anaerobic organisms isolated from these infections.
Usual Habitat
Nan-spore-forming, Gram-negative anaerobes are often found on muwus membranes, particularly in the digestive tract, of animals and man. They are excreted in the faeces and they can survive for short periods in the environment. Dichelobacter nodosus, a primary pathogen of the epidermal tissues of the hoof region of ruminants, survives for less than 4 days in mud. Diagnostic Procedures
In order to ensure that isolates of anaerobes are aetiologically significant, specimens for isolation procedures should be obtained by direct sampling from discharges or lesions and by supra pubic puncture in urinary infections. Specimens should be processed promptly after collection. Commercial kits and transport media are available for specimens from suspected anaerobic infections. In the core of a tissue specimen over 2-3 cm, an anaerobic microenvironment is usually maintained. Samples of fluid in a syringe remain suitable for anaerobic culture if air is expelled from the syringe and the needle
is plugged.
Anaerobic jars with an atmosphere of hydrogen and 10%CO2 are used for incubating cultures at 37°C for up to 7 days.

Bacteroides spp are non-spore forming gram-negative bacilli that are part of the human resident flora. Microbiologically, they are distinguished from other genera by growth in 20% bile. At present, the Bacteroides fragilis group consists of ten species: B. fragilis (the most frequent isolate), B. distasonis, B. thetaiotaomicron, B. vulgatus, B. ovatus, B. eggerrthii, B. merdae, B. stercoris, B. uniformis, and B. caccae. Since 1990, many organisms previously designated as Bacteroides have been reclassified (see chapter on Anaerobes other than Bacteroides). Bacteroides, the predominant genus in the human
intestine, are important in numerous metabolic activities and may provide some level of protection from invasive pathogens. All 10 species are usually isolated from the colon, although infections caused by or associated with them can include virtually any organ.
Characteristics
The gram-negative Bacteroides spp. or closely related genera are capsulated obligatory anaerobic bacilli that are non-spore forming, pale-staining, and some are motile by peritrichous flagella, while other taxa are non-motile. Bacteroides, Parabacteroides, Odoribacter are generally bile resistant, distinguished from genera which are bile sensitive. They are normally commensal, found in the
intestinal tract of humans (mouth, colon, urogenital tract) and other animals. Many cultures of Bacteroides strains display brown to black pigmentation on blood agar media caused by esculin hydrolysis.
Morphology
In general, all strains were stained poorly with safranin, but well with dilute carbolfuchsin. Motility was not observed in any strains. The morphology of Bacteroides fragilis in fresh cultures and in pus is not
especially characteristic. In this form, the bacillus measures 0.5 by 2.0 to 2.5 micra. Older cultures tend to develop larger forms (0.6 to 0.8 by 2.0 to 9.0 micra) but even in this state the organism cannot be distinguished from aerobic Gram-negative bacilli, by its morphology.

Moraxella bovis occurs as short (1.0 to 1.5 x 1.5 to 2.5 μm), plump Gramnegative rods or, occasionally, cocci which typically occur in pairs. This organism is non-motile, aerobic and usually catalase-positive and oxidasepositive. Although proteolytic, it is unable to utilize sugars. Growth, which is enhanced by the addition of blood or serum to media, does not occur on MacConkey agar. The optimal temperature for growth is 33-35°C. Most M.phenylpyruvica strains will grow on MacConkey agar. But M.bovis and M.lacunata are unable to do so.
Virulent strains, when isolated from cases of infectious bovine keratoconjunctivitis, are fimbriate, haemolytic and grow into the agar. Species, other than M.bovis, which are periodically isolated from clinical specimens, are generally regarded as non-pathogenic.
Usual Habitat
Moraxella bovis is found on mucous membranes of carrier cattle. The organism is susceptible to desiccation and is short-lived in the environment. It can survive for up to 72 hours in the salivary organs and on the body surface of flies, which can act as vectors.
Colonial Appearance
On blood agar after 48 hours’ incubation the colonies of M.bovis are flat, round, small (1 mm diameter), greyish-white and friable, surrounded by a narrow zone of complete haemolysis. The appearance is not unlike that of a beta-haemolytic streptococcus. New isolates are often piliated and erode the agar, sinking into it. Colonial growths will autoagglutinate when suspended in saline. On subculture, colonial variation is common, pili are no longer formed and the colonies are butyrous and less likely to autoagglutinate. Some colonies can become non-haemolytic. The strains of M. hovis (M.equi) isolated from
horses are non-haemolytic even on primary isolation. M.lacunata and M. phenylpyruvica are non-haemolytic on blood agar and some strains of M. phenylpyruvica will grow on MacConkey agar.

to be coccobacillary.They are strict aerobes and do not attack carbohydratesbut derive energy by the oxidation of amino acids. B. avium and B. bronchiseptica are motile by peritricholls flagella but B. pertussis and B. parapertussis are non-motile. All are catalase-positive and oxidase-positive. B. bronchiseptica and B. aium willgrow on MacConkey agar.
The genus Bordetella contains four species, B.pertussis, B.parapertussis, B. bronchiseptica and B. avium. Bordetella pertussis, the type species, and B.parapertussis are human pathogens associated with whooping cough in children. Bordetella bronchiseptica infects a wide range of animal species including man, while B.avium is a pathogen of avian species. The bordetellae are occasional pathogens which have an affinity for ciliated respiratory epithelium.
Bordetella bronchiseptica and B.avium are small (0.2 to 0.5 x 0.5 to 1.5 pm), Gramnegative rods with a coccobacillary appearance. They are catalasepositive, oxidase-positive aerobes and are motile peritrichous bacteria. Because they cannot utilize carbohydrates, they derive their energy mainly from the oxidation of amino acids and have no special growth requirements. They grow on MacConkey agar.
Natural Habitat
The bordetellae are inhabitants primarily of the upper respiratory tract of healthy and diseased humans, animals and birds. B. pertussis and B. parapertussis are human pathogens causing whooping cough and a mild form of whooping cough, respectively. B. bronchiseptica can be present in the upper respiratory tract of pigs, dogs, cats, rabbits, guinea-pigs, rats, horses and possibly other animals. B. avium inhabits the respiratory tract of infected poultry, principally turkeys. Mammalian infections are mainly transmitted by aerosols but in turkeys indirect spread can occur via water and litter.

Campylobacter species are slender, curved motile Gram negative rods (0.2 to 0.5 pm wide) with polar flagella. Daughter cells which remain joined have a characteristic gull-winged appearance and long spirals formed by joined cells also occur. These microaerophilic organisms grow best on enriched media in an atmosphere of increased CO2 and decreased oxygen tension. Many Campylobacter species grow on MacConkey agar. They are non-fermentative and oxidase-positive and have variable catalase reactions.
Usual Habitat
Many Campylobacter species are commensals in the intestinal tracts of warm-blooded animals. Campylobacter jejuni and C. lari (formerly C. laridis) colonize the intestines of birds, which can result in faecal contamination of water courses and stored food. A number of Campylobacter species are excreted in the faeces of pigs. Campylobacter fetus subspecies venerealis appears to be adapted principally to bovine preputial mucosa.
Differentiation of Campylobacter Species
Campylobacter species are strictly microaerophilic, requiring an atmosphere of 5 to 10% oxygen and 1 to 10% CO2 for growth. A selective enriched medium such as Skirrow agar is usually used for primary isolation. Differentiation of isolates is based on colonial morphology and certain cultural, biochemical and antibiotic-susceptibility characteristics.
Colonial Morphology
• Campylobacter fetus subspecies venerealis and C.fetus subspecies fetus have small, round, smooth, translucent colonies with a dewdrop appearance.
• Campylobacter jejuni produces small, flat, grey colonies with a spreading, watery appearance.

Introduction
Vibrios are Gram-negative, rigid, curved rods that are actively motile by means of a polar flagellum. The name ‘Vibrio’ is derived from the characteristic vibratory motility (from vibrare, meaning to vibrate). They are asporogenous and noncapsulated. Vibrios are present in marine environments and surface waters worldwide. The most important member of the genus is Vibrio cholerae, the causative agent of cholera. It was first isolated by Koch (1883) from cholera patients in Egypt, though it has been observed earlier by Pacini (1884) and others.
Natural Habitat
Vibrio spp. can be present in both freshwater and seawater as well as in the alimentary tracts of animals and man. At least five Vibrio spp. are human pathogens including V. cholerae, the cholera bacillus, and V.parahaemolyticus which causes food poisoning. Only V. metschnikovii is associated with disease in domestic animals. It causes a cholera-like disease in chickens and other birds but its geographical distribution is very limited. V. anguillarum causes infections in many species of fish especially in salt or brackish water. It causes high mortality in salt water eels.
Vibrio Cholerae
Morphology
The cholera vibrio is a short, curved, cylindrical rod, about 1.5 × 0.2-0.4 mm in size, with rounded or slightly pointed ends. The cell is typically comma shaped (hence the old name V comma) but the curvature is often lost on subculture. S-shaped or spiral form may be seen due to two or more cells lying end to end. Pleomorphism is frequent in old cultures. In stained films of mucus flakes from acute cholera cases, the vibrios are seen arranged in parallel rows,

Brucella species are small (0.6 x 0.6 to 1.5 pm), nonmotile, coccobacillary, Gram-negative bacteria. As they are not decolourized by 0.5% acetic acid in the modified Ziehl-Neelsen (MZN) staining technique, they are classed as MZN-positive. In MZN-stained smears of body fluids or tissues, they characteristically appear as clusters of red coccobacilli. For taxonomic purposes, all Brucella species should be classified as Brucella melitensis as DNA hybridization studies have shown that the genus contains only one species.
Brucella species are aerobic, capnophilic and catalase-positive. Apart from B.ovis and B.neotomae, they are oxidase-positive. All Brucella species are urease-positive except B.ovis. Brucella ovis and some biotypes of B.abortus require 5 to 10% CO2 for primary isolation. Moreover, the growth of other Brucella species is enhanced in an atmosphere of CO2. Media enriched with blood or serum is required for culturing B.abortus biotype 2 and B.ovis. Recently, brucellae have been detected in sea-mammals. Smears are made from specimens and stained by the modified Ziehl- Neelsen (MZN) stain. Brucellae appear as small, red-staining coccobacilli in clumps because of their intracellular growth.
Isolation
The brucellae grow well on 5-10 per cent blood agar. However, other than foetal abomasal contents and colostrum, the specimens are likely to contain many contaminating bacteria and fungi, so selective media are usually required. The selective media contain a nutritive blood agar base with 5 per cent sterile seronegative equine or bovine serum and an antibiotic supplement. The antibiotic
supplement used in selective media for B.ovis usually differs from that for B. abortus. Skirrow agar is a satisfactorymedium for both the Campylobacter fetus subspecies and for brucellae, including the most fastidious species such as B. abortus biotype 2, B.canis and B.ovis.

Introduction
The genus Haemophilus contains small, nonmotile, nonsporing, oxidase positive, pleomorphic, gram negative bacilli that are parasitic on human beings or animals. Haemophilus means blood loving organisms.

Haemophilus species are small (less than 1 pm x 1 to 3 μm), Gram-negative rods, which often appear coccobacillary and may occasionally form short filaments. These motile organisms, which are facultative anaerobes with variable reactions in catalase and oxidase tests, do not grow on MacConkey agar. They are fastidious bacteria requiring one or both of the growth factors X (haemin) and V (nicotinamide adenine dinucleotide, NAD). Optimal growth occurs in an atmosphere of 5-10% CO2 on chocolate agar which supplies both X and V factors. Small, transparent, dewdrop-like colonies are formed by most Haemophilus species after incubation for 48 hours.

Colonies of H.somnus have a yellowish hue and some isolates are haemolytic on sheep blood agar. The main pathogens in the genus are H.somnus in cattle and sheep, H.parasuis in pigs and H.paragallinarum which is responsible for infectious coryza of chickens.

The haemophili are motile, facultative anaerobes, produce acid from glucose, reduce nitrates and are variable in the oxidase and catalase tests. They are nutritionally fastidious, will not grow on MacConkey agar and grow best on chocolate agar (supplying the X and V factors) under 5- 10 per cent CO2 at 37°C.

The growth of many of the Haemaphilus species is enhanced by 10 per cent CO2, As this is not inhibitory for any of them, CO2 should be used for routine isolation.The inoculated chocolate agar plates are incubated under 10 per cent CO2 at 35-37°C for 3-4 days, although some growth may be seen after 24 hours.

Actinobacillus species are non-motile, Gram-negative rods (0.3 to 0.5 x 0.6 to 1.4 μm) which occasionally have a coccobacillary appearance. They are non-motile, non-sporeformingand non-acid-fast. A surface slime is presentin the three major species (A. ligllieresii. A. equuli andA. suis) and may be related to the stickiness of theircolonies on agar. Surface cultures have low viabilityand die in 5-7 days. The actinobacilli ferment carbohydrates, without the production of gas, within 24 hours and most species produce urease and grow on MacConkey agar. Most species are urease and oxidase positive. The
reactions in the oxidase andcatalase tests are variable. The genus is still in a stateof flux, mainly because of the close similaritiesbetween actinobacilli and species in the genera Pasteurella and Haemophilus.
These facultative anaerobes ferment carbohydrates producing acid but not gas. Actinobacilli exhibit some host specificity and are mainly pathogens of farm animals.
Usual Habitat
Actinobacilli are commensals on mucous membranes of animals particularly in the upper respiratory tract and oral cavity. As actinobacilli cannot survive for long in the environment, carrier animals play a major role in transmission.
Colonial Appearance
• A. lignieresii: small, glistening colonies develop in 24 hours. They are usually slightly sticky (viscid) on primary isolation but lose th is characteristic on subculture. The colonies are non-haemolytic and develop to about 2 mm in diameter in 48 hours. The organism grows well on MacConkey agar, the colonies are at first pale but become pinkish as A. lignieresii is a late lactose-fermemer.
• A. equuli: some strains are haemolytic and the colonies are sticky with this feature remaining on subculture. I t is a lactose-fermenter onMacConkey agar.

Pasteurella and Mannheimia species are small (0.2 x 1-2 μm) non-motile, Gramnegative rods or coccobacilli. They are oxidase-positive facultative anaerobes, and most species are catalase-positive. Although non-enriched media will support their growth, these organisms grow best on media supplemented with blood or serum. They usually remain viable for only a few days on culture plates.
Some species, such as Mannheimia haemolytica, Pasteurella trehalosi and P. aerogenes can tolerate the bile salts in MacConkey agar. In smears from infected tissues stained by the Giemsa method, pasteurellae exhibit bipolar staining.
The family Pasteurellaceae comprises five genera, Actinobacillus, Haemophilus, Mannheimia, Pasteurella and Lonepinella. These genera share a number of common features and some organisms have been reclassified within these genera following deoxyribonucleic acid hybridization studies and 16s rRNA sequencing.
The pasteurellae are small (0. 2 μm by up to 2.0 μm), Gram-negative rods or coccobacilli. They are nonmotile,non-sporing, facultatively anaerobic, fermentative(except for P. anatipesrijer), oxidase-positive andcatalase - positive (except for P. caballi). Althoughunenriched media support their growth, they grow beston media supplemented with serum or blood.
Recent Changes in Nomenclature
Previous name Present name
Pasteurella ureae Actinobacillus ureae
Haemophilus avium Pasteurella avium
Pasteurella pneumotropica Pasteurella dogmatis
(Henriksen biotype)

History
Pseudomonas is comprised of two Greek words-Pseudo meaning false and Monas meaning unit, so literally the term means “false unit”. However Pseudomonas is a real bacteria so we really do not know the basis of the nomenclature by Walter Migula. A scientist by the name of Migula gave the Genus name of Pseudomonas in 1894 to these bacteria. Classification
The classification of Pseudomonas is given below:
• Class : Gamma Proteobacteria
• Order : Pseudomonadales
• Family : Pseudomonadaceae
• Genus : Pseudomonas
• Eight groups : P. aeruginosa ; P. chlororaphis; P. fluorescens;
P.pertucinogena; P.putida; P. stutzeri; P. syringae; P.
incertae sedis.
The family has 191 valid species. These include bacteria which are saprophytic, free living, and human, animal and plant pathogens. The type species is Pseudomonas aeruginosa.
Usual Habitat
Pseudomonas species are environmental organisms which occur worldwide in water and soil, and on plants. Pseudomonas aeruginasa is also found on the skin, on mucous membranes and in faeces. Burkholderia pseudomallei, which is found in soils, occasionally infectsanimals and man. Wild rodents can act as reservoirs of this organism. It is widely distributed in some tropical and subtropical regions of Southeast Asia and Australia.Although B.mallei can survive in the environment for upto 6 weeks its reservoir is infected Equidae.

The genera Proteus and Providencia belong to the tribe Proteae of the family Enterobacteriaeceae. The members of both these genera are gram negative, motile bacilli, aerobes and facultative anaerobes and can grow on basic media. A characteristic feature which distinguishes tribe Proteae from other members of Enterobactereaceae is the presence of the enzyme phenylalanine-deaminase which converts phenylalanine to phenylpyruvic acid (PPA reaction).They also produces a powerful urease enzyme which rapidly hydrolyses urea to ammonia.
Genus Proteus
They are gram-negative bacilli, 1-3 μm long and 0.6 μm wide. They are noncapsulated and are actively motile by peritrichous flagella. The name ‘Proteus’ refers to their pleomorphism, after the Greek God Proteus who could assume any shape. Four species: Proteus mirabilis, P.vulgaris, P.penneri and P.myxofaciens are recognized. Proteus mirabilis, P.vulgaris are widely recognised as human pathogens.
Culture Characteristics
These can grow on ordinary media like nutrient agar with a characteristic fishy or seminal odour. On MacConkey and Teepol lactose agar, lactose nonfermenting pale colonies, around 2-3 mm in size are formed. On non-inhibitory solid media such as blood and nutrient agar Proteus mirabilis and P vulgaris show characteristic swarming growth in the form of a uniform film, which spreads over the whole surface of the plate. In young swarming cultures, many of the bacteria are long, curved and filamentous, sometimes reaching upto 80 μm in length. When two different strains of swarming proteus mirabilis encounter one another on an agar plate, swarming ceases and a visibile line of demarcation forms. This is known as the Dienes phenomenon. In liquid medium (peptone water, nutrient broth), Proteus produces uniform
turbidity with a slight powdery deposit and an ammoniacal odour.

Yersinia species are non-lactose fermenters and, with the exception of Y. pestis are motile. Although there are more than 10 Yersinia species, only Y. pestis, Y. enterocolitica and Y. pseudotuberculosis are pathogenic for animals and man. Yersinia ruckeri causes perioral haemorrhagic inflammation in some species of fish. Growth of yersiniae tends to be less rapid than other members of the
Enferobacteriaceae. They characteristically demonstrate bipolar staining in Giemsa-stained smears from animal tissues
Natural Habitat
Y. pestis, the cause of bubonic plague in man and a sylvatic cycle in animals, is transmitted mainly by fleas from tolerant rodents. Human infections through cuts, bites, scratches and aerosols can also occur. Cats are susceptible to Y.pestis and naturally infected cats can pose a health hazard for humans in endemic areas. Y. pseudotuberculosis persists in wild rodents and birds as well as in the environment. The intestinal tract of wild and domestic animals appears to be the reservoir for Y. enterocolitica. Pigs, particularly, are carriers of Y. enterocolitica strains pathogenic for humans.
Isolation
Yersinia species grow on nutrient, blood and MacConkey agars but the colonies, after 24 hours incubation, tend to be smaller than those of the other members of the Enterobacteriaceae. Y. pestis grows poorly on agars containing desoxycholate whereas Y. enterocolitica and Y. pseudotuberculosis grow well on these media. Yersinia selective medium (CIN agar) containing the antibiotic supplement cefsulodin (15mg/litre), irgasin (4 mg/litre) and novobiocin (2.5 mg/litre) is designed for the isolation of Y. enrerocolitica from faeces.