UNIT 4 OTHER PATHOGENS Structure 4.0 Objectives 4.1 Introduction 4.2 Spirochaetes 4.2.1 Biological Position 4.2.2 Characteristics 4.2.3 Size and Shape 4.2.4 Structure and Reproduction 4.3 Pathogenic Spirochaetes 4.3.1 Venereal Treponeme — T. pallidum 4.3.2 Non-Venereal Treponemes 4.3.3 Borrelia 4.3.4 Leptospira 4.4 Rickettsiae 4.4.1 Historical Background 4.4.2 Biological Position 4.4.3 Characteristics 4.4.4 Size and Shape 4.4.5 Morphology 4.5 Pathogenic Rickettsiae 4.5.1 Typhus Fever Group 4.5.2 Spotted Fever Group 4.5.3 Scrub Typhus (Mite Typhus) Fever Group 4.5.4 Q Fever Group 4.5.5 Trench Fever Group 4.6 Chlamydias 4.6.1 Biological Position 4.7 Pathogenic Chlamydias 4.7.1 Trachoma 4.7.2 Inclusion Conjunctivis (Paratrachoma) 4.7.3 Lymphogranuloma Venereum (LGV) 4.7.4 Nongonococcus Urethritis 4.7.5 Psittacosis 4.8 Mycoplasma 4.8.1 Characteristics 4.8.2 How Do they Differ from Virus? 4.8.3 Mycoplasma pneumoniae 4.8.4 Parasitic Mycoplasma 4.9 Bacteriodes and Fusobacteria 4.9.1 Bacteriodes 4.9.2 Fusobacteria 4.10 Let Us Sum Up 4.11 Key Words 4.12 Answers to Check Your Progress 57 Microbiology-I 4.0 OBJECTIVES After studying this unit, you should be able to: l state the biological position and characteristics of Spirochaetes and Rickettsiae; l identify Spirochaetes: Treponema pallidum, Borrelia and Leptospira; l describe the venereal disease, ‘Syphilis’; l discuss some non-venereal Treponemes; l enumerate different typhus fever groups; l differentiate between epidemic and endemic typhus fever; l learn the groups chlamydias and mycoplasma; l describe trachoma, inclusion conjuncivitis and lymphogranuloma venereum (LGV) diseases; and l define the anaerobic bacteroides and fusobacteria. 4.1 INTRODUCTION In Unit 3, you have learnt about Pathogenic Gram Positive, Gram Negative bacteria and Mycobacteria. In this unit, you will study some other pathogens, viz. i) Spirochaetes, ii) Rickettsiae, iii) Chlamydias, iv) Mycoplasmas, v) Bacteroides, and vi) Fusobacteria. Each of these six pathogens, on account of some special characters and peculiarities of its own, occupies an independent position in the classification of microbes. We will briefly highlight all these six types of pathogens. In this unit, you will also become familiar with one of the very well known venereal disease ‘syphilis’ caused by a type of spirochaete Treponema pallidum. Several types of typhus fevers caused by Rickettsiae will also be discussed. You will also learn a very serious type of eye disease ‘Trachoma’ which is caused by a type of chlamydia. The special bacterial group ‘Mycoplasma’ the members of which have no cell walls is also included in this unit. At the end, we will briefly describe the anaerobes, viz. Bacteroides and Fusobacteria often responsible for mixed infections. 4.2 SPIROCHAETES The word spirochaete means coil of hair (speira means ‘coil’ and chaete means ‘hair’). Spirochaeates are flexible spiral shaped organisms with several coils. Different types of spirochaetes are distinguished from each other by the number and character of their spirals and the manner of their movements. Many spirochaetes are free-living found in mud, water, soil and decaying organic matter. Others occur as commensals in the mouth and genitalia of human beings, while some are pathogenic in the body of animals and human beings. Spirochaetes differ from all other pathogenic organisms in being able to wriggle, flex and bend themselves like coiled steel springs. One of the most important pathogenic spirochaete is Treponema pallidum which causes the venereal disease syphilis in human beings. 4.2.1 Biological Position Most authorities classify spirochaetes under order spirochaetales, one of the division of class “Fungi”. Other authors consider them an independent group between the lowest plants (Bacteria) and lowest animals (Protozoa). The order spirochaetales is divided into two families Spirochaetaceae and Treponemataceae. Family Spirochaetaceae includes harmless non-pathogenic spirochaetes and Family Treponemataceae includes non- pathogenic as well as pathogenic spirochaetes. They are slender spirochaetes with fine spirals and pointed or rounded ends. The non-pathogenic spirochaetes occur as commensals in mouth gums and genitalia of human beings and can be grown in artificial media. On the other hand most of the pathogenic forms are saprophytic and do not grow in artificial media or chick embryo or tissue culture. However, we will deal here only with those spirochaetes which are pathogenic to human beings. Pathogenic Treponemes belong to 58 Table 4.1: Three Genera of Pathogenic Treponemes Other Pathogens Order: Spirochaetales Family: Spirochaetaceae Family: Treponemataceae Non-pathogenic Pathogenic and Non-pathogenic Genus Treponema Genus Borrelia Genus Leptospira L. icterohaemorrhagiae Venereal Non-venereal Disease: Weil (Spirochaetal jaundice) T. pallidum i) T. pertenue Disease: Syphilis Disease: Yaw’s ii) T. cereteum Disease: Pinta B. rccurrentis B. vincentii Disease: Diseases: i) Epidemic Relapsing Fever i) Vincent’s stomatitis ii) Endemic Relapsing Fever ii) Vincent’s gingivitis three genera, viz. Treponema, Borrelia and Leptospira (See Table 4.1). 4.2.2 Characteristics 1) Protozoa like Characters a) Cell wall of Spirochaetes is extremely thin elastic flexible more or less resembling the cell membrane of Protozoa. b) Some spirochaetes are readily filterable through filters, which hold back ordinary bacteria. c) Like protozoa, spirochaetes require special media and stain for cultivation and staining respectively. d) Spirochaetes possess fine contractile fibres between cell wall and cytoplasmic membrane. In some cases the fibres are present round the central axial filament and are responsible for contraction, relaxation and various rotary movements of the body. These fibres consist of a material characteristic of Protozoa. 2) Bacteria like Characters Spirochaetes resemble bacteria in: a) size, b) lack of definite nuclear structure, c) method of nutrition, and d) multiplication. 4.2.3 Size and Shape The size and shape of spinchaetes is described below. Size Spirochaetes vary widely in shape ranging from 0.5 micron to 2.0 micron in diameter and 5.0 microns to 50.0 microns in length. Some species attain a length of 500 microns. 59 Microbiology-I Shape Spirochaetes are spiral shaped and motile organisms but they do not possess flagella. They are best studied in living organisms freshly obtained from the body under dark field microscope where they look as silvery-coiled threads. Different varieties of spirochaetes are distinguished from each other by the number of characters of their spirals and the manner of their movements. 4.2.4 Structure and Reproduction The spirochaetes are unicellular organisms with a distinctive form. The cell is helicoidal in shape and always very long as compared to its width. It is surrounded by a delicate thin elastic flexible cell wall which lies external to the cytoplasmic membrane. Spirochaetes possess long fine contractile fibres between the cell wall and cytoplasmic membrane forming axial filament. The axial filament is formed of two overlapping sets of fibrils. Spirochaetes multiply by binary fission. 4.3 PATHOGENIC SPIROCHAETES The pathogenic spirochaetes belong to the family Treponemateceae and include organisms belonging to three genera, viz. Treponema, Borrelia and Leptospira (Fig. 4.1). We shall discuss each one of them as follows. Treponema Borrelia Leptospira Fig. 4.1: Types of spirochaetes 4.3.1 Venereal Treponeme–Treponema pallidum Treponema pallidum causes venereal disease syphilis in human beings. The name pallidum refers to its pale staining as it does not stain well with the usual ordinary bacteriological dyes and appears as transparent wavy lines. Instead these organisms require silver impregnation staining methods where they appear black against a yellowish background. T. pallidum is a thin, delicate, actively motile, slender and highly coiled spirochaete with tapering ends terminating in long fibrils. It is 4 to 14 microns in length and 0.1 to 0.2 microns in diameter. It has 8 to 15 sharp angular spirals at regular intervals of about 1 micron. These organisms are actively motile and can rotate on the long axis. We shall now discuss the disease-syphilis very briefly. Syphilis It is a venereal disease which may be inherited from the mother (congenital syphilis) or it 60 may be acquired by sexual intercourse. The spirochaetes Treponema pallidum enter the body through minute abrasions of the skin or mucosa. They multiply at the site of entry and Other Pathogens after an incubation period of about a month, a chancre develops which leads to primary, secondary, tertiary, latent and congenital syphilis. Primary syphilis begins with a painless rash or chancre which develops on genitalia especially on labia or uterus in female and penis in male. It may also develop on lip or hand. The organisms from the chancre quickly spread through the blood stream. Secondary syphilis begins with 5 to 6 weeks after the appearance of the chancre if the disease is not treated in the primary stage. The patient is highly infectious during secondary stage. Tertiary syphilis may follow the secondary stage and the internal organs most commonly the cardiovascular system and the central nervous system are affected leading to cardiovascular syphilis and neurosyphilis respectively. In neurosyphilis the germs attack meninges of the brain and spinal cord and result in general paralysis or even insanity. It may be mentioned here that sometimes the secondary syphilis may not immediately lead to tertiary syphilis but it may lead to latent syphilis during which the patient shows no symptoms of the disease and the infection is recognized only by serological tests. Latent stage may last for few months to few years and then suddenly gives rise to tertiary syphilis. Congenital Syphilis (Prenatal Syphilis) is mostly acquired before birth. The infection is transmitted from the blood stream of the pregnant mother to the developing child. A syphilitic father can transmit the infection to his child only indirectly by infecting the mother and usually it leads to miscarriage.