Re-introduction to microbiology Flashcards
The properties of bacteria including: morphology, staining and culture; taxonomy; commensals and carriers. The properties of viruses including: characteristic features of viruses; elementary taxonomy; outlines of structure and replication; principles of latent viral infection. The properties of fungi and protozoa: features of medically important fungi; laboratory diagnosis of these infections. The properties of Prions: -relationship to spongiform encephalopathies; -practical difficulties for ste
The micro-organisms
Protozoa (eukaryotes) Fungi (eukaryotes) Bacteria (prokaryotes) Viruses Prions (infectious 'rogue' proteins)
Protozoa
Unicellular eukaryotes
2-100 μm
Many are free-living e.g. euglena (pond-water)
Several are important human pathogens (malaria)
Often affect the immunocompromised
Mainly a threat in developing countries
Protozoa examples
Trypanosomiasis (chagas disease) -South America kissing bug Malaria Cryptosporidium (causes diarrhoeic diseases in bad water) -chlorinated swimming pools Toxoplasma gondii -crazy cat lady
Fungi
Eukaryotic organisms with a variety of forms
Commercially important - baking, brewing and pharmaceuticals
External, rigid cell wall - containing chitin
Filamentous or yeast forms
Many display both - dimorphic e.g. Candida
Bacteria
Most numerous organisms on earth
Adapted to inhabit almost all habitats
-even those not based on sunlight - deep sea vents
Responsible for notable worldwide epidemics - PLAGUE
Prokaryotes - no internal membranous compartments
Specialised cell walls
Produce a range of toxins - virulence factors
Cellular forms
Cocci -cocci, diplococci, tetrads, sarcina, streptococci, staphylococci Bacilli Extended irregular rods Kidney bean Corkscrew Helical Gram positive and gram negative
Diplococci example
Neisseria
Sarcina
Gram positive cocci
Genus
Streptococci example
Streptococcus mutans
Staphylococci example
Staphylococcus aureus MRSA
Bacilli example
Bacillus subtilis
Extended irregular rods example
Fusobacterium
Kidney bean example
Vibrio spp.
Corkscrew example
Treponema spp.
Helical example
Campylobacter
Gram positive
Thick cell wall made of peptidoglycan
Retain crystal violet stain
Gram negative
Do not retain stain Coloured red or pink More resistant against antibodies because of impenetrable cell wall Thin (single-layered) cell wall Periplasmic space LPS on outside with porin in between
Peptidoglycan
A polymer of N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG)
Crosslinked via amino acid pentapeptides and anchored to cell wall
Surface structures
Flagellum
Pili and fimbriae
Pili and fimbriae
Proteinaceous filamentous structures Often used for attachment to host-cells or surfaces Adhesins at the tip for host interaction - e.g. EPEC bfp Can also be used for twitching motility
Pili and fimbriae example
Pseudomonas spp.
Pathogens with 2 examples
Disease causing bacteria
e. g. Vibrio cholera - Cholera
e. g. Yersinia pestis - Plague
Opportunistic pathogens with 3 examples
Commensals that sometimes cause disease
e.g. MRSA, C. difficile, Major hospital infections
N.meningitidis- isolated epidemics in UK
Commensals
The unseen hordes
Mainly harmless
Colonise surfaces and mucosa
Commensals examples
Staphylococcus epidermidis: harmless commensal gram positive cocci
Propionibacterium acne: gram positive bacilli- can cause acne
Staphylococcus aureus: carriage in anterior nares and skin
-gram positive cocci - MRSA
Digestive tract in terms of bacteria
Main reservoir of bacteria within the body 1,000,000,000 per gram
Around 1kg mass in bacteria
Examples of bacteria in the digestive tract
E. Coli: -gram negative rod -essential commensal -some strains are Pathogenic Bacteroides species: -gram-negative anaerobic bacilli -most numerous in the body Clostridia species: -gram positive anaerobic spore forming bacilli -includes C. difficile an increasingly drug resistant -related to tetanus and botulism causing bacteria
Mycobacterium spp. (unusual example 1)
Gram positive rods, unusual cell wall- mycolic acid (lipolitic sugars)
Impervious to gram-staining
Need Ziehl-Neelsen acid-fast staining procedure: mycobacteria in red
Mycobacterium spp. examples
M. tuberculosis
M. leprae
-first bacteria to be clinically associated with a disease (leprosy)
-Leprosy-Hansens disease
Leper colonies
Leper colonies persisted until relatively recently in poorer countries, only 1 remaining in Europe (Romania - people stay there now by choice)
Treatable with antibiotics- Dapsone and rifampicin
NOT thalidomide
Chlamydia (unusual example 2)
C. trachomatis Extremely unusual life cycle: -elementary body facilitates spread -reticulate body- intracellular replication Small- 0.4 microns STI -urethral and vaginal infection -conjunctivitis - trachoma -infertility (ectopic pregnancy) -asymptomatic carriage important in spread
Flagellum
Spins around moving electrons across the membranes so can move around
Electric motor built from scratch in membranes
The carrier state + 2 examples
Asymptomatic carriage of pathogenic bacteria
Examples: gonnorhoea, chlamydia
Why is the carrier state a problem?
Important in disease transmission esp for gon, HIV, and typhoid- gall bladder- famous example
Case of Thypoid Mary - Salmonella typhi - thyphoid fever
-small % remain in gall bladder –> faeces
-so can transmit with poor hygiene (working with food also dangerous)
Viruses
Obligate intracellular parasites
Cause of major world epidemics:
e.g. H1N1: 1918 Flu 20 million deaths, HIV
Unable to reproduce without host factors
Viral genome uses host to encode viral proteins
Basic viral structure
Nucleic acid encapsulated by proteinaceous capsid
Varying shape and symmetry
Some further coated with lipid coat - enveloped
e.g. HIV
Lytic life cycle
Attach, invade, replicate, break out
Viral latency
Infection does not necessarily result in lytic cycle
- Incorporation into genome – retrovirus
- Latent infection of host cell away from site of infection e.g. Herpes, Varicella zoster
Retroviral replication + example
mRNA –reverse transcription–> DNA –> into nucleus, integration into host genome –transcription–> mRNA –> viral proteins and RNA genome
e.g. HIV sits in CD4 cells
Latent infection vs re-activcation
Latent e.g. Herpes simplex virus in response to mild pharygitis fever, varicella (chickenpox)
Leads to recurrence
Cold sore due to fever, sunlight, menstruation and zoster (shingles) due to age, immunocompromise and local injury
Thalidomide
Removes symptoms but not disease
Can lead to people being born with malformed limbs
Bacteriophage
Bacteria eaters
Capsid head, tail and fibres
Most numerous organisms on earth !!!- viruses
Attack and kill bacteria- like cold virus attacks you
They live in your mouths - isolated recently
Prions
Heat resistant, filterable, stick to instruments
Can be detected in tonsils… but not outside lymphatics so far in humans- but in animals…
Scrapie, BSE, CJD (familial, variant and sporadic)
Normal PrPC converted into ‘Rogue’ PrPSC
Aggregate into long fibers and amyloid plaques
Prion example
KURU - Papua New Guinea
kuru : “trembling with fear” in Fore language
Fatal brain disorder
First symptoms are unsteady gait, tremors, and slurred speech
Epidemic during the 1950s-60s among the Fore people
Prions likely transmission
via Brain tissue
KURU - how and why?
Ritualistic cannibalism
Funeral rituals:
-Fore cooked and ate their dead relatives.
‘the mortuary practice of consumption of the dead and incorporation of the body of the dead person into the bodies of living relatives, thus helping to free the spirit of the dead’
Brains eaten mostly by the Fore women and children.
Men rarely affected (up to 40-50yrs incubation…)
