2. The Microbial World Flashcards
List some microbial and non-microbial agents that can cause infections/infestations of man.
Distinguish between prokaryotes and eukaryotes.
Describe viruses.
Microbes: bacteria, viruses, fungi, protozoans. Non-microbes: worms, insects, arachnids.
Pro: DNA and RNA, no nuclear membrane, e.g. bacteria. Euk: DNA and RNA, DNA enclosed in nuclear membrane e.g. fungi, protozoa
Posess DNA OR RNA but not both. Totally dependant on living cell. Obligate intracellular parasites. Small. May have receptor binding protein for attaching to cells.
Describe bacteria.
What defines gram +ve and gram -ve?
What are the different bacterial shapes?
Single circular chromosome, free in cytoplasm. Sometimes contain plasmids (smaller circular DNA molecules). 70s ribosomes (80s in euk), no mitochondria, no membrane-based vacuolar organelles, posess only mesosome (involved in cell division).
Most have cell wall containing peptidoglycan - if thick with no outer membrane = gram +ve, if thin with outer membrane = gram -ve.
Rigid cell wall imposes shape: spherical (cocci e.g. staphylococci, streptococci, pneumococi), cylindrical (bacilli), helilcal (spirochaetes).
Label the cell envelope of a gram +ve bacterium.
A) capsule (hyaluronic acid)
B) call wall (M-, T-, R-antigens)
C) group carbohydrate (N-acetyl-glucosamine, rhamnose)
D) Mucopeptide (N-acetyl-glucosamine, N-acetylmuramic acid, alanine, glutamic acid, lysine, glycine)
E) cytoplasmic membrane (like that of gram -ve bacteria)
Describe the structure of a gram negative cell wall.
List some other features of bacteria.
What are the 3 ways genetic material may be transferred between bacteria?
Define parasite.
Flagella (motility), pili/fimbriae (adherance), capsule outside cell wall (evade immune response), spores (resistant to physical/chemical agents).
1) conjugation (transfer of DNA via cojugation tube)
2) transduction (bacteriophage viruses)
3) transformation (pick up exogenous bacterial DNA)
Any living form which is dependant on other living forms for survival, and causing some damage to host. (E.g. protozoa and helminths)
Describe 3 ways bacteria can be identified.
What are gram positive cocci divided in to (and further divided in to)?
1) Microscopy: shape and staining characteristics. Most bacteria gram +ve cocci/bacilli, or gram -ve cocci/bacilli
2) Growth characteristics: e.g. haemolysis, lactose fermentation, aerobic/anaerobic growth
3) PCR: huge libraries of info that speimen can be matched to
Catalase test divides gram +ve cocci into streptococci (catalase negative) and staphylococci (catalase positive). Strep divided into alpha and beta-haemolytic and non-haemolytic. Staph divided into coagulase +ve (S. aureus - usually produces yellow colonies) and coagulase -ve by the coagulase test - usually produces white colonies.
Give some examples of:
a) gram +ve cocci - staphylococci
b) gram +ve cocci - streptococci
c) gram -ve cocci - Neisseriae spp.
What are the 2 causes of staphylococcal disease?
a) S. aureus, S. epidermidis
b) S. pneumoniae, E. faecalis, beta haemolytic A,B,C,D,G
c) N. meningitidis, N. gonorrhoeae
1) invasiveness of the agent: localised (abcess, osteomyelitis, wound infections, pneumonia etc.), generalised (sepsis, bacteraemia, endocarditis)
2) enterotoxins: acute staphylococcal enterocolitis, staphylococcal “scalded skin” syndrome
What is this condition?
Impetigo - caused by staphylococci or streptococci
What is this condition?
Cellulitis - spreading soft tissue infection. Commonly caused by streptococcus pyogenes.
Distinguish between obligate and facultative pathogens.
What are spirochaetes?
Describe the main features of mycobacteria spp.
Obligate: parasitic organism that cannot complete its life-cycle without exploiting a suitable host e.g. Salmonella spp. Facultative: may resort to parasitic activity, but does not absolutely rely on any host for completion of its life cycle e.g. E. coli
Spiral shaped, thin, cell wall similar to gram -ve, but usually too thin to see with gram stain (need special stains)
Thick cell wall, long HC chains and some peptidoglycan. Don’t take up gram stain/counter stain. Detected by Ziehl-Neelsen or auramine stain.
What are the growth requirements for most bacteria?
What 6 tests could be done for further bacterial identification?
What are protozoa?
370C in air, some need CO2, some only grow under anaerobic conditions
biochemical tests, antigen detection, toxin demonstration, molecular probes, PCR, serology
Unicellular eukaryotic organisms e.g. amoebae, flagellates, plasmodium spp.
Describe fungi.
Describe helminths.
Describe arthropods.
Organisms with characteristics of plant life but unable to photosynthesise. May grow as filaments (hyphae) which form a mesh (mycelium). May grow as single cells (yeasts) which divide by budding.
Multicellular euk organisms lacking backbones, notochords or exoskeletons. “Worms”. Divided into trematodes (flukes), cestodes (tapeworms), nematodes (round worms and filaria)
Important as vectors, occasionally cause disease e.g. scabies, poisonous venoms. Insects (flea, mosquito, louse) and arachnids (spiders, mites, ticks) are important members.
What are scrapie-like agents?
What sort of information is required on each pathogen?
Cause spongiform encephalopathies. Abnormal forms of self proteins which can induce normal proteins to become abnormal. Don’t contain nucleic acids. Prion hypothesis.
Ecology, epidemiology, structure and function, virulence mechanisms, effects on man, diagnosis, therapy and prevention.
