Introduction Flashcards
What is the purpose of peptidoglycan?
Gives rigid support and protects against osmotic pressure
What is the purpose of the capsule?
To protect against phagocytosis and T cell mediated immune responses
What is the structure of glycocalyx?
Polysaccharide
What is the function of glycocalyx?
Mediates adherence to surfaces (especially foreign surfaces)
What kind of bacteria contain an outer membrane?
Gram negative
What are spores made out of?
Keratin-like coat, dipicolinic acid
Describe the role of the outer membrane (present in gram negatives)
- It is made out of lipopolysaccharide which is a major surface antigen
- Lipid A induces TNF and IL-1
Wat type of bacteria contain lipoteichoic acid?
Gram positives
What kind of bacteria contain thinner peptidoglycan cell walls?
Gram negatives
What kind of bacteria contain a larger periplasmic space?
Gram negatives
What does the periplasmic space contain?
Contains enzymes necessary for bacterial virulence such as lipases, Beta lactamases, phosphatases and proteases (can inhibit penicillin)
What structure can cause the release of TNF-alpha from macrophages? (causing toxic shock)
Lipopolysaccharide endotoxins on outer membranes of gram negatives
What bacteria does not contain a cell wall? What do they contian instead?
Mycoplasma (gram positive organism)
- instead contain sterols
What is unique about the cell wall of mycobacteria?
- Contains mycolic acid and has a high lipid content
What is a gram stain made from?
- Crystal Violet and iodine cause a dark purple/blue colour in gram positives
- Safranin acts as a counter stain (causes gram negatives to stain pink)
What organisms cannot be identified via gram staining?
- Treponema
- Rickettsia
- Mycobacteria
- Mycoplasma
- Legionella pneumophila
- Chlamydia
These Rascals May Microscopically Lack Colour
Why can mycoplasma not be gram stained?
No cell wall
Why can mycobacteria not be gram stained?
The cell wall has a high lipid content (requires acid-fast stain)
What are mycobacteria visulaized with?
Acid-fast staining
Why can Treponema not be gram stained?
Too thin
Why can Rickettsia, Legionella pneumophila and Chlamydia not be visualised with gram staining?
They are all intracellular organisms (Chlamydia also lacks muramic acid in its cell wall)
How are treponemes visualised?
Darkfield microscopy and fluorescent antibody staining
What is legionella visualised with?
Silver stain (or immunofluorescent staining)
What organisms can be visualised with immunofluorescent staining?
Intracellular parasites (Rickettsia, legionella pneumophila and chlamydia)
What can a Giemsa stain be used to visualise?
- Borrelia
- Plasmodium
- Trypansomes
- Chlamydia
What can PAS (periodic acid Schiff) be used to identify?
And what does it stain specifically?
- Tropheryma whippelii (cause of Whipple’s disease)
- Stains glycogen, mucopolysaccharides
What does the Ziehl-Neelsen visualise?
Acid-fast organisms (such as mycobacteria e.g TB)
What can the India ink stain be used to visualise?
Cryptococcus neoformans (mucicarmine can also be used to stain the thick polysaccharide capsule red)
What can the silver stain be used to visualise?
- Fungi
- Legionella
What media is used to grow haemophilus influenzae?
Chocolate agar with factors V (NAD+) and X (hematin)
What media is used to grow Neisseria gonorrhoeae?
- Thayer-Martin media
- aka VPN media (Vancomycin, Polymyxin and Nystatin)
What type of organisms turn pink on MacConkey’s agar?
Lactose-fermenting enterics (e.g E. coli)
What other than MacConkey’s agar can E. coli be grown on?
Eosin-methylene blue (EMB) agar (grows as blue/black colonies with metallic sheen)
What media is legionella grown on?
Charcoal yeast extract agar buffered with cysteine and iron
What medium are fungi grown on?
Subouraund’s agar
What are examples of obligate aerobes? (organisms which require O2 to generate ATP)
- Nocardia
- Pseudomonas aeruginosa
- Mycobacterium tuberculosis
- Bacillus
Nagging Pests Must Breathe
Where can psedomonas aeruginosa be found?
- Burn wounds
- Nosocomial pneumonia
- Pneumonias in cystic fibrosis patients
Where can M. tuberculosis commonly reactivate? (e.g after immune compromise or TNF-alpha inhibitor use)
The apices
What are examples of obligate anaerobes?
- Clostridium
- Bacteroides
- Actinomyces
Can’t Breathe Air
What enzyme do obligate anaerobes lack?
Catalase and/or superoxide dismutase
- Makes them susceptible to oxidative damage
Where can anaerobes be found as normal flora?
GI tract (foul-smelling)
Why are aminoglycosides ineffective against anaerobes?
They require O2 to enter into the bacterial cell
What are examples of obligate intracellular organisms?
- Rickettsia
- Chlamydia
Stay inside cells when its Really Cold
What are examples of facultative intracellular organisms?
- Salmonella
- Neisseria
- Bruccella
- Mycobacterium
- Listeria
- Francisella
- Legionella
- Yersinia pestis
Some Nasty Bugs May Live FaculativeLY
What are examples of encapsulated bacteria?
- Streptococcus pneumoniae
- H. influenza type B
- Neisseria Meningitidis
- Salmonella
- Klebsiella pneumoniae
- Group B strep
SHiN SKis
What is a positive quellung reaction?
If encapsulated bug is present the capsule swells when specific anticapsular antisera are added
What does catalase degrade?
H2O2 (hydrogen peroxide)
What organisms are catalase positive?
- Staph aureus
- Serratia
- Pseudomonas
- Actinomyces
- Candida
- E. coli
you need SSPACE for your cats
What kind of miccrobes are patients with chronic granulomatous disease vulnerabe to?
Catalase positive organisms as they reley on H2O2 to fight infection (they have a NADPH oxidase deficiency)
What disease does Borrelia cause?
Lyme’s disease
