Part 2 ch2 Flashcards
1
Q
What are the characteristics of bacteria?
A
- no true nucleus (prokaryotes)
- may have plasmids that provide extra functions (eg. antibiotics resistance)
- most with a single chromosome
- have cell wall (except mycoplasma)
- with different shapes
=> sphere: coccus
=> rod-shaped: bacillus
=> spiral: spirochete or spirillum
2
Q
What are the forms of cocci bacteria?
A
- diplococcus (in pairs)
- tetracoccus (in groups of 4)
- streptococcus (in chains)
- staphylococcus (in grape-like clusters)
3
Q
What are the structures of a bacterial cell?
A
- pili –> enable bacteria to adhere to surfaces
- flagella –> enable motility
- capsule –> inhibit phagocytosis
- cell wall –> provides rigidity, strength and protection
- plasma membrane
- ribosome –> site of protein synthesis
- nucleoid region (DNA)
4
Q
What are the functions of bacterial cell wall? What is the rigid part of the cell wall made of? What is the use of Gram staining?
A
- to provide rigidity and protect cell shape & against osmotic damage
- made up of peptidoglycan
- to distinguish bacteria with different cell wall composition –> Gram +ve (purple); Gram -ve (pink)
5
Q
What is the difference between Gram +ve and -ve bacteria?
A
- Gram +ve
=> thick peptidoglycan cell wall –> retain crystal violet after washing by alcohol –> purple - Gram -ve
=> thin peptidoglycan cell wall (lipoprotein and protein in outer membrane) –> crystal violet easily washed away by alcohol –> counterstained by safranin –> pink
6
Q
How to perform Gram staining?
A
- first stage: smear preparation
=> smear bacterial sample on the slide and left to air dry
=> heat fixing the smear briefly by passing the slide through the Bunsen burning - second stage: staining
=> staining with crystal violet
=> add iodine to stabilise crystal violet staining
=> decolourization by alcohol –> gram -ve bacteria becomes colourless
=> counterstaining with safranin. Gram +ve will remain purple and Gram -ve are stained pink
7
Q
What are the three external structures in bacteria and their respective functions?
A
- capsule
=> layers of anti-phagocytic polysaccharides or protein that surround the cell wall - flagella
=> long, rope-like structures for movement - pili
=> short, hair-like appendages anchored in plasma membrane
=> somatic pili –> for attachment to host cells
=> sex pili –> for transfer of plasmid DNA from bacterium to another
8
Q
What are the characteristics of endospores? How are they formed and worked? What special thing about endospores? How are the spored killed? How do sterilisation procedures relate to endospores?
A
- resistant to heat, desiccation, ultraviolet light and chemicals
- formed inside the original cell –> remain dormant for years –> form new cells when conditions are favourable
- most notorious bacteria are spore-formers
- killed by autoclaving (>120 degree Celsius at elevated pressure)
- sterilisation procedures are assessed by their ability to inactivate endospores
9
Q
What are the steps of bacterial reproduction? How do they reproduce? What is the doubling time? What is the example?
A
- cell elongation –> DNA replication –> cross wall completed –> daughter cells separate
- reproduce by binary fission
- 15-30 minutes
- a single E. coli cell in a nutritionally complete medium –> >10 million in just 8 hours
10
Q
What are the stages of the bacterial growth curve?
A
- lag phase: growth and reproduction just begin
- log phase: exponential growth phase
- stationary phase: cell growth=cell growth due to limited environmental factors (eg. nutrients)
- death phase: cell death > cell growth (eg. toxic wastes accumulate)
11
Q
What are the types of bacteria with different oxygen requirement?
A
- obligate aerobes: grow only with the presence of oxygen
- anaerobes: able to grow in the absence of oxygen
=> obligate: killed by O2 (eg. bacteria in gut)
=> aerotolerant: unaffected by O2
=> facultative: grow in both anaerobic and aerobic conditions but grow best with O2
=> microaerophiles: grow at low [O2] but killed by high [O2]
12
Q
What are the characteristics of pathogenic bacteria? What are the types of toxins?
A
- flagella: escape from phagocytes
- capsule: anti-phagocytic
- pili: for attachment to host surfaces
- toxins
=> endotoxins: released by dead Gram -ve bacteria (cell wall) –> fever and septic shock
=> exotoxins: toxic protein released by living bacteria (usually Gram +ve)
=> neurotoxins: cause damage to the brain
=> enterotoxins: cause intestinal diseases
13
Q
What are the general features of Staphylococcus aureus?
A
- Gram +ve cocci (round; grape-like clusters)
- facultative anaerobes
- catalase and coagulase +ve
- non-motile
- normal flora of skin but may cause opportunistic infections which are difficult to treat
- transmitted by person-to-person contact, blood and ingestion of enterotoxins
14
Q
What are the diseases caused by Staphylococcus aureus?
A
- major cause of nosocomial infections
- most disease are caused by the presence of toxins in:
=> blood: toxic shock syndrome (TSS) toxins –> TSS –> fever, chill, diarrhoea and vomiting –> shock –> coma
=> intestine: heat-resistant enterotoxins –> food poisoning –> diarrhoea and vomiting
=> skin –> inflammation and skin lesions
15
Q
What is the treatment of S. aureus? What may be the risk result?
A
- requires aggressive treatment by antibiotics (methicillin)
- excessive use of methicillin –> methicillin-resistant S. aureus (MRSA) –> serious nosocomial infections (surgical wounds) –> bacteremia –> high mortality
16
Q
How to prevent S. aureus? What is the reason for the present treatment? What is the alternative treatment for MRSA?
A
- wash hands before and after contact with food or infected individuals
- use of methicillin –> resistant to penicillin because they produce an enzyme (beta-lactamase) that digest penicillin
- treated with alternative antibiotics (vancomycin)
17
Q
What are the general features of Streptococcus pneumoniae?
A
- Gram +ve cocci (round, in chains or pairs)
- facultative anaerobes
- catalase -ve
- non-motile
- normally present in the throat and nasopharynx
18
Q
What diseases can be caused by Streptococcus pneumoniae?
A
- pneumonia
=> inflammation of the lungs –> fever, shortness of breath, chill and cough –> death in old adults, especially cancer patients with weak immunity - meningitis
=> inflammation of the protective membrane covering the brain and the spinal cord –> high mortality
19
Q
How is S. pneumoniae spread? What is the treatment and prevention?
A
- spread through droplets (coughing and sneezing)
- treated by antibiotics (eg. penicillin for pneumonia and vancomycin for resistant strains)
- prevented by good hygiene
=> wash hands
=> cover mouth and nose when coughing/ sneezing
=> vaccination
20
Q
What are the general features of Escherichia coli?
A
- Gram -ve bacilli (rod-shaped)
- facultative anaerobes
- catalase +ve but oxidase -ve
- motile (presence of antigen H)
- have 3 types of antigens (O,K,H)
- normal flora of colon but can cause disease when they get genes from other organisms –> pathogenic E. coli –> invasion and production of toxins
- can be found in decal-contaminated food or water
21
Q
What are the diseases caused by E. coli?
A
- diarrhoea (gastroenteritis)
=> due to heat-labile enterotoxin produced by enterotoxigenic E. coli –> hypersecretion of Cl- and inhibition of Na+ reabsorption in gut –> watery faces - urinary tract infections (UTI)
=> common cause of bladder and kidney infections - bloody diarrhoea and hemolytic-uremic syndrome (HUS)
=> caused by enterohemorrhagic E. coli (O157:H7) –> destruction of villi and RBCS –> blood diarrhoea and renal failure
22
Q
What are the source and symptoms of Enterohemorrhagic E. coli?
A
- cattle/ cow that are infected –> uncooked meat or unsterilised milk
- fruit or vegetables contaminated by the faces of infected animals
- fever, diarrhoea, vomiting, stomach muscle spasm
23
Q
What are the preventions and treatment of E. coli infection?
A
- good hygiene and clean food
- thoroughly cook ground beef and pasteurise milk
- carefully wash and thoroughly cook vegetables before consumption
- diarrhoea can be treated by intake of fluid and electrolytes; extraintestinal diseases need antibiotics
