15.Medically important groups of bacteria

Spirochaetes: Treponema, Borrelia, Leptospira Spiral and curved bacteriaGram negative aerobic rods and cocci Pseudomonas, Brucella, Bordetella,

Francisella

Gram negative facultatively anaerobic rods Enterobacteriaceae : Escherichia,

Salmonella, Shigella, Klebsiella, Proteus, Serratia, Yersinia, Erwinia, Enterobacter.

Vibrionaceae : Vibrio, Aeromonas Haemophilus

Gram negative anaerobic bacteria:FusobacteriumGram negative cocci and coccobacilli Neisseria , Moraxella

Gram negative anaerobic cocci: Veillonella

Gram positive cocci :Staphylococcus, StreptococcusEndospore-forming rods: Bacillus, ClostridiumGram positive non-spore forming rod shaped bacteria : Lactobacilli

Actinomycetes and related organism : Mycobacterium, Actinomyces, Streptomyces, Nocardia, CorynebacteriumRickettsiaes, Chlamydias, Mycoplasmas

Fungi

General properties of fungi : eucaryotic, filamentous/unicellular, vegetative growth by apical elongation of filament or by budding. Reproduction by asexual /sexual spores. Cell walls composed of chitin/polysaccharides. Unicellular – yeast; multicellular – molds.Vegetative structures of fungi hyphae : long filament of cells join together.

a. Coenocytic: protoplasm streams through hypae, uninterrupted by cell walls with many nuclei

b. Septate: cross walls with either single/multiple pores. mycelium : hyphae that has grown and form

filamentous mass a. vegetative : the portion of hyphae that obtain nutrientb. reproductive/ aerial : portion that concern with

reproduction, bear reproductive spores, projects above the surface of medium on which the fungus is growing.

Dimorphism: the property having 2 forms of growth. YM shift – change from mold to yeast vice versa.

reproductive structure of fungi (spore formation) asexual spores : occurs in an individual

fungus through mitosis and subsequent cell division. arthrospore chlamydospore sporangiopore conidiospore blastophore

sexual spore : haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (-). (+) and (-) nuclei fuse to form a diploid zygote nucleus. By meiosis, the diploid nucleus gives rise to haploid nuclei (sexual spores). zygospore ascospore basidiospore

medically important phyla of fungi Zygomycota : rhinocerebral zygomycosis (nose –

brain); extensive cellulitis with rapid tissue destruction

Ascomycota : causes ergotism- toxic condition in human/animal after eating infected grain with fungus

Basidiomycota : disease called cryptococosis, a systemic infection primary involving the lungs and central nervous system

Deuteromycota (Fungi Imperfecti) : lacks of sexual phase, cause athlete’s foot, ringworm.

Fungal diseases (mycoses) : mycoses are generally chronic (long-lasting) infections, because they are slow growers. Note : transmission, epidemiology, diagnosis, treatment, examples of fungus involved.

superficial mycoses : fungal infection on the skin, confined to the outmost layer, seldom invade deeper tissue, Eg. Athlete’s foot ringworm;transmission:indirect/direct;eg:dermatophytes treatment:topical application of antifungal (Nizoral)

cutaneous mycoses (dermatomycoses) : fungus that infect only the epidermis, hair and nails. They secret keratinase, an enzyme that degrades keratin ( protein found in hair, skin, nails);transmission:human to human,animal to human. Treatment &eg similar to the above

subcutaneous mycoses : fungal infection beneath the skin. Eg: Norcadia, Streptomyces;direct implantation of spores/mycelial into wounds in the skin;fungi that live in soil and on vegetation;wear shoes (workers);localised swollen lesions;collect pus /biopsy;surgery of lesions,rifampicin,sulphonamides

systemic (deep) mycoses : fungal infection deep within the body. Eg. Histoplasmosis, coccidioidomycosis;examine sputum, pus, inoculate on culture and identify the colony morphology;found in soil,birds’droppings, inhalation of spores;Ketoconazole

opportunistics fungal infections : harmless in its normal habit but become pathogenic in a host who is seriously debilitated/traumatized, under treatment with broad spectrum antibiotic/suppressed by drug.

candidiasis : found in vaginal, oral thrush, skin infection, produce yeast like fungus, rarely spread throughout the body

aspergillosis : grow in preexisting lesions in the lungs and bronchioles

mucormycosis : affecting external ear, skin nose/brain

mycotic diseases in AIDS patients : candidiasis, coccidioidomycosis, histoplasmosis

Viruses

General properties and structure of viruses: infectious agents( non-cellular). Conatin a single type of nucleic acid either DNA/ RNA. Contain protein coat (lipid/ CHO),

multiply inside living cells. Virion : complete virus particle (consist DNA/RNA

enclosed in a coat of protein) Nucleocapsid : composed of a nucleic acid, held

within a protein coat Capsid : A protein coat which protects viral genetic

material and aids in its transfer between host cells Capsomers: each capsid is composed of protein

subunits.

4 general morphological types of capsid: icosahedral - regular polyhedron helical – cylinders envelope – outer layer surrounding the capsid,

roughly spherical complex – possess tails, multilayer walls.

General features of virus replication Attachment/adsorption Penetration ‘uncoating’ synthesis of viral protein/nucleic acid assembly release

T phage replicationLysogenyMultiplication of animal viruses difference between animal virus

multiplication vs bacteriophage multiplication of DNA viruses vs RNA

viruses

cultivation of viruses cell cultures - need:suitable living host

tissue; suitable nutrient fluid; tissue is inoculated and agitated; virus is inoculated into tissue;further incubation;virus harvest from fluid.

Cell culture are prepared: 1. Digest tissue with trypsin 2. Cells allow to grow as single sheet on

the surface of flask

3. Virus inoculated into monolayer culture produces plagues of lysed cells, similar to phage plagues / local cytopathogenic (infected cells with various abnormalities)effects which are of diagnostic value.

Types of tissue culture: 1. Roller culture 2. Rocker culture

embryonated egg: whole host cultivation used for animal

viruses;uses a fertile hen’s egg after 7 to 12 days’ incubation;viruses being inoculated onto or into a suitable embryonic tissue or fluid (eg: chorio-allantois, vaccinia; allantoic fluid, influenza etc. After further incubation, the virus is harvested from the appropriate tissue and purified by differential centrifugation

Fluid from amniotic cavity of the infected embryo is titrated for its hemagglutinating activityInfluenza virus replication is detected by the particles to cause RBC to clump.Small pox virus is recognized by the formation of characterictics pock marks.

cultivation of bacteriophages assay of viruses

ID50 / LD50

Plague assay heamagglutination

Hemaglutination: eg:influenza-have surface heamaglutinins by which

they can attach themselves to RBC to form clumps If the test is performed in a tube, adhere irregularly

to the glass. Absence of virus, the cells settle to a button on the base of the tube.

Plague* assay: counting the # of plagues produced;seen as clear

zones * lysis of host destruction of bacteria growth on a

surface of a bacterium, areas of clearings

ID50/LD50 - The virulence of a microbe or potency of its toxin is often expressed as the LD50 (lethal dose for 50% of hosts)

- The # of microbes in a dose that will kill 50% of inoculated test animals under normal conditions- ID50 : infectious dose for 50% of hosts. The dose required to produce a demonstrable infection in 50% of the test animal.

effects of chemical and physical agents on viruses chemical agents

lipids solvents phenol formadehyde ethly alcohol, iodophors, sodium

hypochlorite, 2% glutaraldehyde

physical agents temperature radiation (uv, X-ray)