Microbial World I: Bacteria

Question 1

what do we mean by commensals

Answer 1

Commensals are those types of microbes that reside on either surface of the body or at mucosa without harming human health.

Question 2

define opportunistic pathogen

Answer 2

oppurtunistic pathogens are organisms that can become pathogenic following a perturbation to their host (e.g., disease, wound, medication, prior infection, immunodeficiency, and ageing).

Question 3

what does ‘carriage’ mean in microbiology

Answer 3

‘carriage’ is the occupation of microbial species in the respiratory tract.

Question 4

define virulence

Answer 4

virulence is the ability of a microorganism to cause damage to its host.

Question 5

Bacteria have 70S ribosomes ,eukaryotic organisms have _____

Bacteria have no mitochondria and no membrane-based organelles present in eukaryotic cells

Answer 5

Bacteria have 70S ribosomes ,eukaryotic organisms have 80S

Bacteria have no mitochondria and no membrane-based organelles present in eukaryotic cells

Question 6

structure of cell wall determines staining characteristics:
→ thick peptidoglycan w NO outer membrane = Gram ____ =(purple)
Thinner peptidoglycan W outer membrane= Gram _____ =(pink)

Answer 6

structure of cell wall determines staining characteristics:
→ thick peptidoglycan w NO outer membrane = Gram +ve =(purple)
Thinner peptidoglycan W outer membrane= Gram -ve =(pink)

technique used is called gram staining use gram stain

Question 7

what are bacterial cell walls made up of?

Answer 7

Bacteria cell walls contain PEPTIDOGLYCAN : cross-linked complex of polysaccharides (sugars) and peptides (proteins)

Question 8

Special stains for other organisms;
* Ziehl-Nielsen stain for ________
* Cotton blue stain for _______
* Darkfield microscopy for _____

Answer 8

Special stains for other organisms
* Ziehl-Nielsen stain for Mycobacteria
* Cotton blue stain for fungi
* Darkfield microscopy for spirochaetes

Question 9

is staphylococcus aureus gram +ve or -ve, what diseases does it cause?

Answer 9

staphylococcus aureus is gram +ve

Staphylococcal diseases
= caused by ENTEROTOXINS
* causes cellulitis
* Acute staphylococcal enterocolitis: enterotoxins (A – E)
Staphylococcal “scalded skin” syndrome**:
Ritter’s disease, “bullous impetigo” (Caused by exfoliative exotoxin, causing upper skin layers lesions, high fever, septicaemia possible
**Toxic Shock Syndrome: superantigens (high fever, rash, low blood pressure, malaise-confusion, can progress to coma+ multiple organ failure)

Question 10

what can cause ‘strawberry tongue’?

Answer 10

• Low levels of vitamin B-12
• low levels of folate
• scarlet fever (streptococcus pyogenes)

=can cause a strawberry tongue!

Question 11

what are some examples of gram +ve bacilli which cause primarily toxin-mediated diseases

Answer 11

• clostridium (C.tetanni, C.difficile, )
• Bacillus (B.athracus, B.cereus)
  *Corynebacterium (C.diptheriae)
  *Listeria (L.monocytogenes)

= all above gram +ve, the toxins these produce are highly toxic/deadly

Question 12

what disease does C.perfringens cause

Answer 12

Gas gangrene is a highly lethal infection of soft tissue, caused by Clostridium species, with Clostridium perfringens being the most common.

Clostridium perfringens is an anaerobic Gram-positive spore-forming bacillus associated with acute gastrointestinal infections ranging in severity from diarrhea to necrotizing enterocolitis and myonecrosis(rapidly progressive gangrene of the injured tissue along with the production of foul-smelling gas) in humans.

Question 13

which clostridium pathogen causes antibiotic associated diarrhoeae

Answer 13

Clostridium difficile (aka C.difficile) causes antibiotic associated diarrhoeae

Question 14

what pathogen causes tetanus

Answer 14

Clostridium tetani

Question 15

what gram -ve cocci causes

*meningitis
*gonorrhea

Answer 15

meningitis= neisseria meningitidis

gonorrhea= neisseria gonorrhoea

Question 16

what causes the following diseases (these are increasing in severity as they go down)
*Asymptomatic colonisation
*wound infection/diabetic foot
*Lower UTI
*Upper UTI
* nosocomial pneumonia/VAP
* intra-abdominal/ pelvic infection
* bacteraemia/septicaemia
* neurosurgical meningitis

Answer 16

gram -ve rods= enterobacterales

e.g. E.coli, Klebsiella, Enterobacter, Serratia, Citrobacter, Morganella

Question 17

define obligate pathogen

Answer 17

Obligate pathogens require a host to fulfil their life cycle. All viruses are obligate pathogens as they are dependent on the cellular machinery of their host for their reproduction

Question 18

what is the dye called that we use for bacteria with an oxidative metabolism
e.g. Oxidase Positive=
Pseudomonas, Neisseria, Campylobacter
e.g. Oxidase Negative= Enterobacterales, Most Gram Positives, Anaerobes

Answer 18

Cytochrome Oxidase
* Bacteria with an oxidative metabolism possess cytochrome oxidase which activates cytochrome c in the electron transport chain
* Found in bacteria using O2 as a terminal electron acceptor, reduces the O2 to H2O
* if it’s an oxidative organism it will turn the cytochrome oxidase purple

e.g. Oxidase Positive=
Pseudomonas, Neisseria, Campylobacter
e.g. Oxidase Negative= Enterobacterales, Most Gram Positives, Anaerobes

Question 19

to identify mycobacteria do we use gram stain? List some characteristics of mycobacteria

Answer 19

WE DO NOT USE GRAM STAIN FOR MYCOBACTERIA e.g. tuberculosis because their cell wall is not made up of peptidoglycan, instead mycobacteria cell wall is made of lipid(mycolic acid)= the cell wall is v virulent its hard to kill, it survives in macrophages its why ppl can die from TB

Mycobacteria Thick wax-like cell wall containing mycolic acids, fatty acids and lipids; detected by Ziehl- Neelsen (Zn) stain (bacteria stained bright red)
* Aerobic
* Non-motile
* Straight or slightly curved rods
* Distinctive cell wall
* Fatty acids

Characteristics of mycobacteria:
- ‘waxy’ cell wall (lipid-rich)
- Resistance to drying + hydrophobic
- Resistance to antibiotics + disinfectants
- Resistance to acids + alkalis
- ‘acid and alcohol fast’{}
- Impermeable to standard stains
Survives in macrophages

Question 20

How does a standard PCR test work?

Answer 20

• we amplify DNA using primers
• we then raise temp to denature it (denaturation) to separate the DNA strands
• the temp is then decreased (annealing) to allow primers to complementary base pair DNA template
• polymerase extends primer (extension) to form new DNA strand
• then process repeated, its DNA amplified and PCR machine decodes it and tells u wtf it is