Preface Veterinary Bacteriology, a branch of Veterinary Microbiology has major importance in diagnosis and treatment of animal diseases. It also provides the basic knowledge for biotechnology related work. During my initial attachment with this subject as a post graduate student and latter as a teacher, I felt the necessity of a comprehensive book with update which motivates me to write the present manuscript.              The book is written following the syllabus framed by Veterinary Council of India (VCI). It comprises historical introduction, morphology, classification, resistance, natural habitat, genome, isolation and colony characteristics, biochemical and antigenic properties, pathogenesis, disease produced and diagnosis of each bacterial genus associated with animal and human health. The book is intended to help BVSc and Post Graduate students of Veterinary Microbiology as well as the aspirants of ICAR-JRF, ICAR-NET/ARS examinations. Further, it will also help the person engaged as Veterinarian or in the laboratory for the diagnosis of animal diseases. As the book comprises the diagnostic technique for each bacterial genus ranging from staining parameters to molecular tools.

Sir Alexander Ogston (1880) first isolated Micrococci in pus and in 1883 he subdivided them into two groups i.e. Staphylococcus and Streptococcus. He also first proposed the name ‘Staphylococcus’ (Greek ‘staphyle’ means bunch of grapes and ‘kokkos’ means berry). Experiments of Bumm (1885), Garre (1885) and Bockhart (1887) established its relationship with human infections. As well as Nocard (1887) first isolated Staphylococcus from mastitis in sheep and found its pathogenic significance in animals. Properties of Genus Morphology : Staphylococci are gram positive cocci, capsulated, non-sporing and non-motile. Each coccus cell is 1µm in diameter.  They are arranged in a group or grape like cluster as cell division occurs in more than one plane. During preparation of smear and staining the cluster is sometimes broken and cocci are seen in pair or single (Fig. 1). Staphylococcal capsule is polysaccharide in nature. The capsule can inhibit phagocytosis and helps in virulence.  Staphylococcal cell wall contains three major components i.e. peptidoglycan (PG), teichoic acid (TA) and surface proteins.

Rivolta (1873) first described the chain forming cocci in pus collected from the equine infection. Later Rosenbach established the genus ‘Streptococcus’. Nocard and Mollereau (1887) first observed the relationship between the bovine mastitis and Streptococcus agalactiae. Properties of genus 1. Morphology : Streptococci are gram positive cocci, capsulated, non-sporing and non-motile. Each coccus cell is 1µm in diameter.  They are arranged in a pair or chain of cells as the cell division occurs in one plane (Fig. 1). The chain formation and the chain length are variable. Streptococcus equi ssp equi is a constant chain producer, other species are not. The chain length is shorter in artificial media than natural one. Young cultures are gram positive whereas the bacteria present in the pus and older cultures in the laboratory are often stained as gram negative.  Streptococcal capsule is polysaccharide in nature. It can be subdivided into different antigenic types (e.g. S. agalactiae, S. pneumonae). However capsules of S. equi, S. pyogenes are made of nonantigenic hyalu-ronic acids containing repeating units of glucuronic acid and N-acetyl-glucosamine. Synthesis of the polymer involves the products of three genes, hasA, hasB, and hasC, which are all in the same operon.

In 1850, Bacillus anthracis was first reported by three individuals in two different countries i.e. Delafond (who may have found them as early as 1838) and Davaine in France, Pollender in Germany. However, they could not establish the relationship between the disease and the bacterium. Absolute proof of the anthrax etiology as B. anthracis was established by Robert Koch in 1876-77. The name Bacillus anthracis was first coined by Cohn (1875) and the disease ‘anthrax’ was first named by Hippocrates (5th century B.C.). In Greek language meaning of anthrax is ‘coal’ referring to the black coloured skin or blood in affected animals. B. anthracis organism has certain historical importance: a)   Anthrax is the first disease identified to be caused by a bacterium. b)   Robert Koch first isolated the organism and reproduced the disease in experimental animals. He proposed his postulates (Koch’s postulate, 1876) based on his experiments related to this organism. It later became a fundamental milestone of all microbiological works related to the infectious diseases. c)   Louis Pasteur first used heat attenuated culture of B. anthracis as vaccine in a group of sheep in 1881 at Pouilly-le-Fort. He cultured the organism at 42-43oC in presence of oxygen. The bacteria did not produce spores and became attenuated. d)         First concept of bacterial antagonism was provided by Louis Pasteur and Joubert based on their work on this organism. Injection of other unidentified bacteria along with B. anthracis can prevent anthrax in animals .

The genus Clostridium belongs to the family Clostridiaceae. The genus name was originated from the Greek word ‘kloster’ means spindle, referring to their individual rod shape. Clostridia are gram positive, large, sporulating anaerobic rods (except C. piliforme which is gram negative). At present, there are more than 200 numbers of species under the genus Clostridium. Among them, 15 species can produce potent toxins and are considered as pathogenic for animals and human. The animal pathogenic Clostridia can be classified as neurotoxic, histotoxic and enteric.

In 1882, Robert Koch first isolated the organism, stained with alkaline methylene blue and vesuvin as counter stain and proved its etiologic relationship with Tuberculosis.  Ehrlich first developed acid fast stain in 1882 and used for better staining of the bacteria which was adopted by Robert Koch. Later this staining technique was modified by Ziehl-Neelsen, accordingly it is now a day known as Z-N staining. In 1890, Koch prepared a glycerine broth extract of the tubercle bacillus, known as ‘tuberculin’.       He tried to prepare it as a curative agent; however, it was used later in diagnosis. In 1895, Johne and Frothingham described the first case of paratuberculosis in cattle, later known as ‘Johne’s disease’. Although, the causative agent was first isolated by Twort and Ingram in 1910.             In India, bovine Tuberculosis was reported from several states since 1959 (Dhanda and Lal, 1959). Whereas bovine paratuberculosis was first reported by Nanda and Singh (1940) in Hissar, Haryana.

This family Enterobacteriaceae belongs to the order Enterobacteriales. The family comprises 25 genera. Among them there are 10 genera consistently found pathogenic for animals, birds and human. These genera are mentioned below (first 10 are consistent pathogenic).

In 1886, Escherich observed Campylobacter like organisms in stool samples of children with diarrhoea. In 1913, McFaydean and Stockman first confirmed them as Campylobacter in foetal tissues of aborted sheep. Confirmatory tests were also carried out by Smith in 1918 when similar organisms were isolated from aborted bovine foetuses. The organism was then known as Vibrio foetus. In 1963, due to certain differentiating characteristics, the organisms were separated from Vibrionaceae family and the new genus Campylobacter (means ‘curved rod’) under Campylobacteriaceae family was proposed.  Properties of genus 1.   Morphology :  Campylobacter is gram negative, comma shaped rods specially in infected tissues and young cultures. The size is 1.5-4 µm by 0.5 µm. When two bacterial cells are found together in a microscopic field, it looks like ‘S’ or ‘wing of gull’ (‘flying seagull’). However in older cultures, the chains of organism appear as long spirals. They are motile by single unipolar/ bipolar unsheathed flagella. Motility is darting or corkscrew type, best observed by dark field microscopy. They are non-sporing. Some species contains S-layer (surface layer), a paracrystalline protein structure composed of S-layer proteins (SLPs). It is external to the outer membrane. It helps the bacteria in immune evasion.

Clinical conditions similar to Brucellosis have been described since the time of Hippocrates (450 BC). J. A. Marston first described brucellosis as gastric remittent fever in 1861 at Malta (Marston, 1861). Sir David Bruce in 1886 first isolated little coccobacillus from an infected soldier’s spleen. However he isolated the bacteria in a pure culture in 1887 and named Micrococcus melitensis (Bruce, 1889). Later the genus was renamed as Brucella in his honour. Similarly, Bang and Stribolg first isolated Brucella abortus from abortion material of a cow (Bang, 1897). Traum in 1914 isolated the Bacillus abortus suis. Presently we know it as Brucella suis. In 1953, Brucella ovis was first isolated in New Zealand (Budlle and Boyes, 1953) from the aborted material of sheep. Carmichael and Bruner in 1968 first isolated B. canis from the aborted placenta of a dog.             In India first report of ‘Contagious abortion’ by Brucella was found from annual report of Imperial Veterinary Research Institute (presently Indian Veterinary Research Institute), Mukteswar, Uttarakhand (Anonymous, 1918). Seroprevalence of Brucellosis is reported from various states of India afterward (Polding, 1942; Sethi et al., 1971 etc.).

Pasteurella and Mannheimia species are gram negative small coccobacilli under family Pasteurellaceae. Trevisan (1887) coined the generic name Pasteurella for the first time and it was accepted worldwide. Lignieres (1900) proposed the specific name for each organism according to the species of animal host: Pasteurella aviseptica for fowls; P. suiseptica for pigs; P. boviseptica for bovines; P. oviseptica for ovines and P. leptiseptica for rabbits. Finally, Rosenbuch and Merchant (1939) proposed a single species Pasteurella multocida and it is in use till date.        Mannheimia haemolytica was earlier known as Pasteurella haemolytica, but because of variations in cultural, pathological and 16S rRNA sequence, it is placed in separate genus. Properties of genus Morphology : P. multocida is a non motile, non spore-forming short rod or coccobacillus, 0.2-0.4 by 0.6-2.5 µm in size. Repeated laboratory subcultures or cultures grown under unfavourable conditions tend to be pleomorphic and longer rods or filamentous forms appear. In tissues, exudates and recently isolated cultures, the organism shows the typical coccobacillary forms. It is a gram-negative organism and, in fresh cultures and animal tissues, gives typical bipolar staining (Fig.1), particularly with Leishman or methylene blue stain.

Lucke (1862) first described that the bluish green discolouration of surgical dressing is associated with the presence of small vibrio like organisms. Latter Gessard first isolated the organism as Pseudomonas in 1882. Properties of Genus Morphology : They are Gram negative straight or curved rod, motile by one or more polar flagella. Usually it is 1.5 µm in length and 0.5 µm in width. Longer filamentous forms are sometimes observed. The bacteria are non- acid fast, non- sporulating and uncapsulated. Pili on the bacterial surface are detected. Environmental and strains present within tissue can produce slime. The slime is composed of glycolipoprotein (GLP) and polysaccharide of LPS.   They are strict aerobe. Classification : Pseudomonas belongs to class Gamma-Proteobacteria, order- Pseudomonadales, family- Pseudomonadaceae.  Previously Pseudomonas included two group of bacteria viz. Fluorescent group and Pseudomallei group. Recent classification system included this Pseudomallei group into a new genus known as Burkholderia. Important species of Pseudomonas are:

The genus was named after Morax who first isolated the organisms from human conjunctivitis in 1896. Properties of genus 1.   Morphology :  Moraxella are gram negative, small rods occurring in pair (diplobacilli). The aged cultures exhibit pleomorphism, occurring in pairs or chains as short, plump rods with rounded ends. Some strains may appear as cocci. The capsule is present in fresh isolates of some species (except Moraxella catarrhalis). They are non-motile and non-sporing. Moraxella bovis contains numerous type IV fimbriae on its surface. 2.   Moraxella is aerobic, fastidious and non-fermenting in nature. However, some strains prefer anaerobic condition for their growth.     3.   Classification : The genus Moraxella belongs to the Moraxellaceae family. Previously it was known as Branhamella. Most of the species are commensal except a few, which have disease producing capabilities. Important species are M. bovis, M. ovis, M. catarrhalis, M. boevrei, M. canis, M. caprae, M. caviae, M. cuniculi, M. phenylpyruvica. 4. Resistance : Resistance to physical and chemical agents is not remarkable. They are susceptible to desiccation and do not survive long outside the host. The beta- lactam antibiotic resistance is observed among M. catarrhalis isolates from clinical cases. This resistance is associated with the production of beta-lactamase enzyme.

Pfeiffer first isolated and described Haemophilus influenzae as a cause of human influenza (1892). So it is also known as ‘Pfeiffer’s bacillus’. Later other workers isolated and described different species of the genus Haemophilus from animals and birds. In 1903, Friedberger, a research assistant of Pfeiffer, isolated similar kind of organism from prepuce of the dogs. In 1922, Rivers described it as Haemophilus canis. In 1925, Mitchell isolated Haemophilus ovis from the respiratory tract of sheep. In 1931, Lewis and Shope first isolated and illustrated Haemophilus suis from the infected pigs. Glasser found an association between fibrinous serositis, polyarthritis in pigs (Glasser’s disease) and a small gram negative rod as early as 1910, latter became known as Haemophilus parasuis. It was first isolated by Hjarre and Wramby in 1943.  The first recorded isolation of a hemophilic organism from the birds was in 1931 by De Blieck and he called them as Bacillus haemoglobinophilus coryzae gallinarum. He isolated them from the chickens suffering a disease, now known as ‘infectious coryza’.

Taylorella was first isolated by Taylor et al. (1978) as a causative agent of contagious equine metritis (CEM), a venereal disease of horses. The disease (CEM) was first reported in the mares of thoroughbred horses in UK in 1977 breeding season (Crowhurst, 1977). Initially the causative agent was assumed as Haemophilus equigenitalis. Later on the basis of numerical taxonomic characteristics, genomic G+C contents, DNA-DNA hybridisation studies, the new genus Taylorella was proposed in 1983 (Sugimoto et al., 1983). It was approved by the International Committee on Systematic Bacteriology. Properties of genus 1.   Morphology :  Taylorella are gram negative, small rods or coccobacilli, measuring 5-6 µm by 0.8 µm. They are pleomorphic, piliated, encapsulated, non-sporing and non-motile. 2.   They are microaerophilic (require low O2 tension for growth), non-fermentative, and non-proteolytic in nature. 3.         Classification : Taylorella belongs to β- subclass of class Proteobacteria (whereas, Haemophilus belongs to the γ- subclass of Proteobacteria). Major important species is Taylorella equigenitalis. The genus was considered as a ‘single species genus’ for a long time. Latter in   1997, National Veterinary Services Laboratories confirmed the identity of another Taylorella species, isolated from a donkey jack (Equus asinus) in California. It was named as T. asinigenitalis. The new species has minor difference in 16S rDNA sequence (97.6% similarity), DNA–DNA hybridization (23% similarity) and (G + C) composition with T. equigenitalis (Matsuda and Moore, 2003) .

Listeria Murray et al. (1926) first described about Listeria which was followed by Pirie et al. (1927). In India Listeriosis was first reported by Mahajan (1936) in sheep from Andhrapradesh. He recognized it as ‘circling disease’. Latter a number of reports are available from various parts of India.

Lignieres and Spitz first isolated the bacteria from the cattle with Actinomycosis like condition in Argentina in 1902. They referred them as ‘Actinobacilllus’. These findings were also confirmed by Nocard in 1902. Latter, the isolated bacterium from the cattle was named as Actinobacillus lignieresii, in memory of Lignieres.  Properties of genus 1.   Morphology :  Actinobacillus are gram negative small rods, measuring 1.5 µm in length and 0.4 µm in width, occurring singly, in pairs or more rarely in chains. After isolation in the laboratory they may show pleomorphism varying from coccobacilli to filamentous forms. In gram stained smear they may show both bacillus and coccus form together, known as ‘morse code’ appearance (dots and dashes appearance, Fig.1). They are non-motile (both at room temperature and 37oC), non-sporing and non-acid fast. The pili are found in A. pleuropneumoniae.       Some of them (A. pleuropneumoniae) are capsulated. Whereas, slime layer is found in the surface of other species like A. lignieresii, A. suis, A. equuli.  This slime layer is related with stickiness of the colonies in the agar, enhanced resistance of the colonies to the chemical disinfectants, as well as, resistance of the bacterial cell to the antibiotics and desiccation. 2.         Actinobacillus are aerobic, microaerophilic or facultative anaerobic in nature. They are chemoorganothrophic having both respiratory and fermentative types of metabolism.

Cohn (1875) first observed and described a branching filamentous micro-organism in the concretions (coagulated mass) taken from a lacrimal canal, latter identified as Actinomyces israelii. Bollinger first reported the yellow granules in jaw tissues of the cattle in 1877 and established the significance of the organisms as an etiological agent. In 1878, Israel described the first human case. In 1879, Hartz observed the microscopic appearance of granules of Actinomyces infection and suggested the name Actinomyces bovis. Mosselman & Lihnaux (1890) and Wolf &Israel (1891) first isolated the bacteria in artificial laboratory media from lumpy jaw cases of cattle and human Actinomycosis, respectively. Properties of genus 1.         Morphology :  Actinomyces are gram positive filamentous organisms with branching rods. In artificial media, short bacilli or cocci forms are also observed. During infection, they can produce yellow coloured granules (sulphur granule), commonly found in the pus as ‘opaque speck’ and are visible under naked eye (1-2 mm in diameter). The granules are usually soft and easily broken under light pressure, but they may occasionally be tough or even calcified. They are composed of club shaped bodies, arranged radially with their narrow ends towards the centre. So the organisms are also known as ‘ray fungus’. In the centre of the club, filamentous masses of gram positive organisms with some bacilli or cocci form are found. Together the club like processes and bacterial masses are known as ‘rosette’ (Fig.1). This club is composed of calcium phosphate and inflammatory debris .

The genus Arcanobacterium was first described to include the bacteria originally isolated as Corynebacterium haemolyticum from American wounded soldiers (Collins et al., 1982). The bacteria had different cell wall and lipid composition in comparison to the other members of the genus Corynebacterium. So the new genus Arcanobacterium was created. Properties of genus 1.         Morphology : Arcanobacterium pyogenes is a Gram positive, non-motile, non- spore forming, short, rod-shaped bacterium, measuring 0.5µm by 2 µm. They are non-capsulated and do not contain any metachromatic granule. Initially (during first 18 hour of growth) the bacterial cells may show characteristic ‘V’-arrangement like Corynebacterium, latter as the growth proceeds, the organisms become granular and segmented so that they resemble small and irregular cocci (whereas, A. hippocoleae and A. pluranimalium appear to be less coccoid). The cell wall is devoid of mycolic acid, arabinogalactan unlike ‘coryneform’ bacterial group (Mycobacterium, Corynebacterium, Rhodococcus, Nocardia). Cell wall peptidoglycan is composed of N-acetyl muramic acid, lysine. Being gram positive in nature, some strains exceptionally possess fimbriae.

Corynebacterium diptheriae was first observed by Klebs in 1883 and described in details by Loeffler in 1884. So it is also known as ‘Klebs-Loeffler bacillus’. In 1888, Nocard isolated a similar type of bacteria from cases of bovine farcy. In 1894, Preisz described it completely and revealed its similarities with the diphtheria bacilli. Latter it was named as Corynebacterium pseudotuberculosis (Preisz-Nocard bacillus). Bollinger (1890) first reported C. renale from the cases of pyelonephritis in cows. Magnusson (1923) first described C. equi (Rhodococcus equi) form suppurative pneumonia of a foal. Properties of genus 1.   Morphology Corynebacterium are gram positive, pleomorphic bacteria ranging from coccoid to filamentous rods. The size varies from 0.5-0.6 µm by 1.0- 3.0 µm. Some of the species appear as packets of parallel cells (palisade arrangement) or show ‘V’ shaped form (Chinese letter arrangement) in the microscopic field (Fig.1and Fig.2). The cell wall peptidoglycan contains meso-diaminopimelic acid (meso-DAP). The arabinose and galactose are major cell wall sugars. Short-chain mycolic acids (corynomycolic acids, 22–36 carbon atoms) are present. This kind of cell wall structure is impermeable to the hydrophilic compounds. However, the ‘porin’ present in the cell wall sometimes helps in import of the hydrophilic substances. Mycolic acid containing cell wall helps in intracellular survival within the macrophages. Corynebacterium is non acid fast, non-sporulating, non-capsulated and non-motile bacteria (except C. aquaticum) .

Edmond Nocard (French Veterinarian) first isolated filamentous aerobic bacteria from clinical cases of ‘bovine farcy’ in 1888. In 1889, the genus Nocardia was formed by Trevisan, and the organism described by Nocard was named as Nocardia farcinica. In 1891 another similar organism (Nocardia asteroides) was isolated by Eppinger from a human brain abscess. Initially it was thought that they are the same organisms. Latter on the basis of the molecular studies their separate entity is established.             However, 80 years later, re-examination of Nocard’s original isolate revealed two different filamentous organisms, one of which was Mycobacterium and the other was Nocardia. The cause of ‘bovine farcy’ has been subsequently attributed to Mycobacterium. Latter, it is proved that Mycobacterium farcinogenes is the actual causative agent of ‘bovine farcy’.

Dermatophilus congolensis was first described from clinical case of exudative dermatitis in cattle in Congo by Van Saceghem (Van Saceghem, 1915). It is primarily known as an animal pathogen causing acute, sub acute or chronic skin disease. The first cases of human infection with D. congolensis were reported in 1961 in four people who developed skin infection after handling an infected deer in a wildlife reserve in USA (Dean et al., 1961). Properties of genus 1.   Morphology Dermatophilus is a gram positive, non-acid fast, unusual bacterium having branched filaments. It follows a life cycle with different morphological features. It can be found in smears prepared from clinical samples in any form of its life cycle. Young filaments are 0.5 to 1.5 μm in diameter.  They enlarge within epidermis as they produce layers of transverse and longitudinal septations and reach 5 to 8 μm in diameter, surrounded by a mucoid capsule. The septations result in the formation of a sporangia (a kind of fungal fruiting body, sac like structure with spores) containing up to eight cocci cells. In the presence of liquid, the cocci are released and converted into flagellated motile zoospores, the infective form of the organism. It can infect the new site in the same animal or new host. These zoospores become visible in smear as parallel lines forming a ‘railway-track’ or ‘trum-track’ appearance (Fig.1). Under favourable conditions, the zoospores form germ tubes that develop into branching filaments. These filaments are the invasive form of the organism and the cycle is repeated.

Leptospira  Antony Van Leeuwenhoek (1681) first observed the Spirochaetes under the microscope and described them. In 1833, Ehrenberg used the name Spirochaeta for free living spiral shaped organisms. Obermeir (1873) first described a Spirochaete of pathogenic significance isolated from human patients of relapsing fever. Inada et al. (1916) first isolated Leptospira icterohaemorrhagiae from human patients of Weil’s disease. In 1980, Nogochi proposed the name Leptospira.       In India, Taylor and Goyale (1931) first reported Leptospira from human patients suffering from jaundice in Andaman Islands (Srivastava, 2006). Ayyar (1932) first reported Leptospira from dogs in Chennai city.  Properties of genus 1. Morphology : Leptospira are gram negative, spiral shaped organisms with hooked ends. Length varies from 6-20 µm with 0.1-0.2 μm diameter (Fig.1). They have a typical double membrane covering. The cytoplasmic membrane and peptidoglycan cell wall are closely associated and are surrounded by an outer membrane. Two periplasmic flagella (endoflagella) are found within the cell and are responsible for the motility. No flagella are present as extracellular appendages. One end of the flagella is attached with the pole of the bacterial cell by insertion disc. Other end extends towards the centre of the cell and may overlap the flagella coming from the opposite end. The endoflagella consists of a solid inner core surrounded by tubular sheaths. The FlaA and FlaB proteins constitute these flagellar sheath and core, respectively.

Properties Bacteroides, Dichelobacter and Fusobacterium are major gram negative anaerobes isolated from human and animals. Other gram negative anaerobes are listed below (Table-1).        2.   They are tolerant to oxygen in comparison to strict anaerobes. They do not die after oxygen exposure        3.         They naturally inhabit the intestine and mucosal surfaces of human and animals. Majority of them are opportunistic pathogens. Often they cause mixed bacterial infection along with aerobes. Aerobes remove oxygen and create an anaerobic condition favourable for their growth. Aerobes may also supply other growth requirements. For e.g. Porphyromonas asaccharolytica requires vitamin K for its growth, supplied by another bacterium, not the host.

The name Mycoplasma is originated from the Greek word mykes (fungus) and plasma (formed). It was first used by Albert Bernhard Frank, a German Biologist in 1889. He thought it was a fungus. An older name for Mycoplasma was Pleuropneumonia-Like Organisms (PPLO), referring to organisms similar to the causative agent of contagious bovine pleuropneumonia (CBPP). It was later found that the fungus-like growth pattern of M. mycoides is unique to that species. It was first isolated in 1898 by Edmond Nocard and E. Roux from bovine lungs. Whereas, Mycoplasma pneumoniae was considered as a virus previously. Eaton and his co-workers cultured the causative agent of human primary atypical pneumonia (PAP) or "walking pneumonia." It was known as "Eaton's agent." In the early 1960s, Leonard Hayflick, in Philadelphia, was first to isolate and cultivate the causative agent of primary atypical pneumonia and identified the agent as a Mycoplasma and named it Mycoplasma pneumoniae.

History of Rickettsial infections went back to 16th century and it has long been associated with famine and war. Thus Rickettsial infections played a significant role in the history of Western civilization. Epidemic typhus had major impact to decide over the outcome of several wars. This epidemic alone killed or caused great suffering to over 100,000 people in the two World Wars.  However, the causative agent was not determined until the early part of the 20th century. Rocky Mountain Spotted Fever (RMSF) was the first detected Rickettsial infection as early as in 1896 in Idaho Valley, USA.  It was originally known as ‘Black Measles’ because of its clinical appearance in the form of characteristic spotted rash appearance throughout the body of the patients. Howard Taylor Ricketts, an American pathologist for the first time described the causative agent of Rocky Mountain spotted fever and was able to isolate it in the laboratory animals during 1902-1909. He was a dedicated scientist and, on several occasions, injected himself with a pathogen for experiment. The causative pathogen of Rocky Mountain spotted fever, Rickettsia rickettsii was named after him. Later, the family Rickettsiaceae as well as the order Rickettsiales was named after him. Ernest William Goodpasture, an American pathologist and physician, invented the methods of isolation and culturing the rickettsial pathogens in chicken embryos and fertilized chicken eggs.

The word ‘chlamydia’ comes from the Greek word ‘chlamys’ which means, “cloak draped around the shoulder”. This describes how the intracytoplasmic inclusions caused by the bacterium are “draped” around the infected cell’s nucleus. Chlamydia was first discovered by a Czech zoologist and parasitologist, Stanislaus von Prowazek in 1907 in Berlin, but scientists believe it was actively infecting people for centuries before its discovery. Because the symptoms of Chlamydia are similar to some other infections it was not identified as a sexually transmitted disease. Originally, because of its structure it was thought to be a virus. In 1963 it was recognized as bacteria rather than a virus. Properties of genus            They are poorly stained by Gram’s stain. Chlamydiae are readily stained by Castaneda (blue in appearance), Giemnez and Macchiavello (red in appearance) methods. However, Giemsa staining is preferable to stain the inclusions (Chlamydial micro colony) in the cell culture. Inclusion bodies of the Chlamydiae are basophilic in nature. Again, the staining of the inclusion bodies may differ depending on the species. In C. trachomatis, the inclusion bodies contain glycogen matrix and can be easily stained with iodine solution.

A abattoir, 354, 355 abortion, 24, 25, 110, 147, 148, 170, 180, 181, 185, 191, 192, 193, 195, 238, 246, 253, 258, 267, 283, 298, 312, 313, 321, 333, 341, 356, 361, 373, 374 Abscesses, 12 acid fast, 101, 112, 116, 185, 209, 249, 255, 261, 272, 285, 286, 301 Actinobacillus, 197, 200, 215, 227, 238, 240, 241, 261, 262, 263, 265, 267, 268, 269, 270 Actinomyces, 269, 271, 272, 273, 274, 275, 277, 279, 284, 295 Afu-A, 265 agalactia, 23, 313, 341 agglutination, 4, 14, 91, 97, 115, 123, 134, 135, 149, 167, 183, 193, 194, 204, 205, 222, 226, 234, 240, 247, 254, 315, 353, 357, 362 Alpha toxin, 44, 49, 89, 90, 99 Amies, 182 Anaplasma, 348, 358, 359, 360, 362, 366 anthracoid, 29, 39 anthrax, 27, 32, 34, 35, 36, 39, 40, 55, 81 antimicrobial, 29, 145, 150