W12 Infectious agents Flashcards
5 Kingdom system
Protista Plantae Animalia Fungi Monera
Three Domain System
Multiple Kingdoms
Modern DNA analysis
Distinctive biological characteristics
All organisms are cells not viruses! Membranes Cellular and genome organisation Single cells Multiple stages –life cycles Multicellular - parasites
Prokaryotic
No nucleus
No mitochondria
Mainly circular DNA
e.g. bacteria
Eukaryotic
Chromosome
Nucleus
Identification essential to understand:
Biology and microbiology Evolution and phylogenetics Pathogenesis of infectious diseases Life cycles Accurate diagnosis Effective treatment Public health control of infectious diseases
Criteria: (Systems of Classification of Pathogenic Organisms)
Structural and functional and metabolic observations
Molecular and genetic and genome analysis
Sub-species classification:
Differentiate pathogenic and non-pathogenic strains
- different disease patterns and clinical outcomes
Linnaean Classification - Hierarchical
Domain - Eubacteria
Kingdom - Procaryote
Phylum - Gram +ve
Class - Actinobacteridae
Order - Actinomyceteales
Family - Mycobacteriaceae
Genus - Mycobacterium
Species - Mycobacterium tuberculosis
Strain - Beijing W1
Isolate - Mr Bloggs (12/02/2004)
Visualisation of Microbes - Viruses
Can be seen with
electron microscope
x100,000
20 – 300nm
Viruses - size
20nm - 300nm
Viruses - structure
DNA or RNA genome
- linear, segmented, single or double stranded genome size 9Kb- 300Kb
- protein nucleocapsid - individual capsomeres Helical, cubic or complex arrangement
No cytoplasm
Enveloped or non-enveloped
- may have components derived from host cell
obligate intracellular organism
Virus life cycle
Recognition Attachment Penetration Fusion Uncoating Transcription Protein synthesis Replication Envelopment Budding and release Lysis and release
Common viral infections in the UK - Community
Upper respiratory tract infection - rhinovirus, influenza, RSV
Gastroenteritis e.g.
Norovirus (SRSV), adenovirus, rotavirus
Rashes e.g. varicella zoster virus (chickenpox), measles
Meningitis e.g. enterovirus
Hepatitis virus e.g. HepB
Human Papilloma virus (HPV) - genital warts
Common viral infections in the UK - Healthcare-associated Infection (Hospital Acquired)
Norovirus, flu
adenovirus
Non-enveloped
DNA virus
What virus causes muco-cutaneous lesions ?
Human Herpes simplex Type 1
Herpes viruses
Icosahedral nucleocapsid
Envelope
Influenza virus
e.g. H3N2
Surface Haemagglutinin
Enveloped pleomorphic Segmented RNA genome Mutation and recombination Epidemics and pandemics Vaccine component H and N
Bacteria - size
1/1000th of a mm
0.5 μm to 3 μm
Bacteria - structure
Prokaryotic
Haploid DNA, circular genome
no nucleus
usually have rigid cell wall outside cytoplasmic membrane
no mitochondria
Binary fission
Visualisation of Bacteria
Unstained at x400
Motile bacteria with flagella move rapidly
Non-motile bacteria also move “on the spot”
i.e. Brownian motion
Gram Staining Bacteria
All purple = iodine + crystal violet
G+ purple = alcohol
G- colourless = alcohol
G+ purple = safranin
G- red = safranin
Morphology
cocci, rod/bacilli, coccobacilli, spirochetes
- atypicals e.g. mycoplasma (no cell wall), chlamydia (biphasic)
Gram stain
positive or negative, acid fast, variable
Growth requirements
aerobic vs anaerobic
Biochemical reactions
e.g. lactose fermenting or non-fermenting
Serotype groups
e.g. Streptococcus group A or B; meningococcus B or C
Antibiotic resistance
e.g. MSSA or MRSA
Other classification criteria for bacteria
rRNA sequencing
Genome sequencing
MLST or RFLP typing – genetic variation typing methods
The presence of beta-hemolytic colonies indicates
indicates the possibility of Streptococcus pyogenes infection
Selective Atmosphere - anaerobic culture
eg. Clostridium tetani, Clostridium botulinum, Clostridium difficile
GRAM POSITIVE
SPORE FORMING
ANAEROBIC
ROD/BACILLUS SHAPED
Clostridium perfringens on Blood agar
Grown in ANAEROBIC atmosphere
Haemophilus influenzae
Genome = 1.83Million bases (Mb)
First genome of a free-living organism sequenced was that of HI - 1995
The genome encodes more than 1700 proteins + 70 RNA molecules
Functions of ~ 50% of proteins were determined by comparison w/other species
Fungi - Mycoses size
over 2 μm
Fungi - Mycoses structure
Eukaryotic
Haploid or diploid DNA
Single or multiple nuclei
Rigid chitinous cell wall outside cytoplasm Single or multicellular
Single or multicellular e.g.
- yeast (spheroid single cells budding and division)
or - Filamentous form/moulds. – hyphae (e.g. Aspergillus spp) multinucleate branching hyphae forming mycelium
Classification is complex and is based on morphology (growth form), mode of reproduction (sexual or asexual) and disease caused: 70,0000species ~300 human pathogens
Superficial mycoses
Skin, nail hair and mucous membranes (dermatophytes) or thrush (Candida albicans)
Cutaneous mycoses
e.g. Tanea – aka ringworm
Systemic mycoses
e.g Histoplasmosis
Histoplasma capsulatum
Dimorphic
microconidia and hyphae,
yeast like and spores
Oral Candidiasis / Candidosis
most common oral fungal infection
carriage rates 20% - 75% without any symptoms.
Usually Candida albicans
Yeast
normal constituent of the digestive and vaginal tracts
Generally no problems in healthy people
Opportunistic pathogens
Cryptococcus neoformans
Fungal yeast like form – encapsulated – large capsule
Pneumocystis carinii (now jiroveci)
Previously classified as a protozoan
PCP in AIDS
Single cells (amoeboid)
forms cysts containing spores
Athletes foot - Tinea pedis
Dermatophytes
multiple septate branching hyphae on microscopy
Ringworm (Dermatophytosis)
40 types of fungi can cause ringworm.
DO NOT confuse with pinworm, round worm
Tinea unguium
of the nails is termed onychomycosis
Protozoa
Single cells 5 to 300 μm Single or multiple nuclei Haploid DNA. Morphology varies throughout life cycle` May have flagella
complex life cycles
Trophozoites, cysts and other morphotypes
Giardia lamblia
Trophozoite stage
Cyst stage
Protozoa - structures
e.g Plasmodium falciparum (malaria)
Uninfected erythrocytes
Schizont
Trophozoites (ring forms)
Entamoeba histolytica
50 Million people infected
Liver abscess + diarrhoea
Faecal cyst
Trichomonas vaginalis
Common STI
trophozoite
Trypanosoma brucei
Trypanosomaa spp – vector tetse fly or reduviid bug
(Chagas disease; Sleeping sickness)
Blood stage
Helminths
These are multicellular parasitic worms
Different morphology and sizes at different life cycle stages
They can be microscopic or visible to the eye
Multicellular
3 Groups of parasites
Cestodes are tapeworms e.g. Taenia saginata, the beef tapeworm;
Trematodes are flatworms or flukes and include Schistosoma haematobium the cause of bilharzia or schistosomiasis filarial worm Onchocerca volvulus – River Blindness
Nematodes which are roundworms e.g. Ascaris lumbricoides
River Blindness- Oncocerciasis
microfilariae migrate to eyes
Schistosomiasis
microfilariae
Helminths- Cestode
Tape worm -Taenia saginata
Egg shed in faeces (human)
Cysts in muscle (beef)
Adult tapeworm (human) 2 – 4 metres long 700- 1000 segments
Helminths- Trematoda
Schistosoma haematobium
Egg shed in urine (human) (via snails)
Metacercaria in water
(burrow into skin)
Adult fluke in human
Helminths - nematodes
Ascaris lumbricoides
Egg shed in faeces
Adult worm
Enterobious virmicularis
a nematode – common in UK children
threadworm or pinworm
Asymmetical shape (50 uM)
Sticky tape mount to pinworm eggs
