Path (Micro) - Exam 2 Flashcards
Which bacteria won’t be seen on a gram stain?
- Myobacteria
Why does myobacteria not show up on gram stains?
Although there is peptidoglycan in the cell wall, this is joined to a layer of mycolic acid and beyond this a layer of outer lipids. Waxy, hydrophobic components of their cell wall make it difficult for aqueous stains to penetrate.
How would you stain mycobacteria?
The Ziehl - Neelsen stain (ZN stain)
What is The Ziehl - Neelsen stain (ZN stain)?
This staining technique utilises strong carbol fuchsin at a concentration greater than that used in the Gram stain, to visualise mycobacteria.
After they are stained, they appear red as Bacteria containing mycolic acid resist decolorisation with an acid-alcohol mix and remain red
What are the important cellular properties of myobacteria?
Rod shaped bacteria with peptidoglycan wall.
Layer of myopic acid around cell wall
Slow growth
What is ABF and what is its relevance?
Acid-fast bacilli = myobacteria.
They are called AFBs as they resist the avid decolorisation step of the ZN stain.
How are myobacteria classified? (nomenclature)
1. Mycobacterium tuberculosis (the cause of tuberculosis or TB)
2. Mycobacterium leprae (the cause of leprosy)
3. “Atypical mycobacteria”, also referred to by the following acronyms:
NTM - non tuberculous mycobacteria
MOTB - mycobacteria other than TB
MOTT - mycobacteria other than tuberculosis
What bacteria are part of the Mycobacterium tuberculosis complex?
M. tuberculosis M. bovis M. bovis BCG M. africanum others
What are the names given to drug-resistant TB?
MDR-TB - multi drug resistant TB
XDR-TB - extensively drug resistant TB
How is TB acquired?
AIRBORNE. Inhalation from another person with active pulmonary TB.
- The transmitter sheds tubercle bacilli from the lung in large amounts when coughing, sneezing, shouting or singing.
- Particles are of a size defined as “aerosol particles” – 0.5 to 5.0 μm
What are the potential disease manifestations following M. tuberculosis infection?
- 90% - asymptomatic
- 5% - develop symptoms in 2 years (primary)
- 5% - >2 years (secondary)
Gradual, nonspecific onset: fever night sweats tiredness weight loss persistent cough ± blood stained sputum
Slowly progressive involvement of the lungs may occur, resulting in cavity formation and scarring. The process usually involves the upper lobes.
What is the Mantoux test?
Tuberculin skin test.
This involves the intradermal injection of a bleb purified preparation of M. tuberculosis antigen (PPD – purified protein derivative). People who have been infected with MTB will develop a local skin reaction which is measured after 48 hours. A positive test does not differentiate between latent infection and active infection.
What drugs are used to treat TB?
The first line drugs used to treat susceptible TB are:
isoniazid
rifampicin
pyrazinamide
ethambutol
The standard course of treatment is 6 months.
How much of the worlds population is infected with M. tuberculosis?
1/3
What effects does HIV have on TB?
- higher progression rate
- risk factor
What is the main tissue infected by M leprae?
Nervous - schwann cells
What is the gram stain appearance of Neisseria meningitides?
gram negative cocci, but sometimes coccobacilli (in-between rod and cocci)
What is one of the important virulence factors of Neisseria meningitides and why?
Polysaccharide capsule.
What are the usual manifestations of Neisseria meningitides?
MENINGOCOCCOL DISEASE:
• meningitis characterised by fever, meningism (headache, neck stiffness, photophobia), and pus in the CSF
• bacteraemia characterised by fever and rash (petechiae evolving into purpura and ecchymoses)
• meninigitis and bacteraemia together
Where is Neisseria meningitides usually found?
nasopharynx of 5-15% of the healthy population
- bacteria can cross the mucosal barrier and cause bacteraemia
What do you do with people who have been exposed to Neisseria meningitides (household contacts - ‘kissing cousins’)
Ciprofloxacin/rifampicin prophylaxis
What are common morphologies of gram negative rods?
- Capsule shaped (i.e. Enterobacteriaceae)
- Curved,(comma9shaped(rods,(eg.( genus(Vibrio&
- Helical(rods,(eg:( genus&Campylobacter& genus&Helicobacter&
What are beta-lactamases?
Enzymes that some bacteria (i.e. gram negative rods) produce which destroy beta-lactam antibiotics (penicillins, cephalosporins, carbapenems).
What are beta-lactam antibiotics?
penicillins, cephalosporins, carbapenems
What are the 3 broad groups of beta-lactamases of most concern in Gram negative rods
- ESBLs - Extended Spectrum Beta-Lactamases
- AmpC beta lactamases
- Carbapenemases
What are the broad groups of gram negative rods?
- Enterobacteriaceae
- non-fermantative gram negative rods
- oxidase positive fermenters
- Miscellaneous, fastidious gram negative rods
- Campylobacteria
- Helicobacter
- Legionella
- Haemophilus
What are the Enterobacteriaceae?
- Escherichia
- Enterobacter
- Klebsiella
- Proteus
- Serratia
- Salmonella
- Shigella
- Yersinia
What are the non-fermantative gram negative rods?
- Pseudomonas
- Acinetobacter
- Stenotrophomonas
- Burkholderia
Its members don’t utilise glucose by fermentative biochemical pathways
What are the oxidase positive fermenters?
- Vibrio
- Aeromonas
What are the Miscellaneous, fastidious gram negative rods?
- HACEK group
- Pasteurella
- Bordetella
- Brucella
- Bartonella
What test/result can distinguish Enterobacteriaceae from other gram negative rods?
Oxidase Test
It is negative
What common diseases can Escherichia coli cause?
- particular strains cause most UTI’s
- These strains are called uropathogenic because they possess virulence factors which enable them to colonise the urethra and survive in the urinary tract.
- nosocomial infections
- diarrhoeal illness (diarrhoeagenic strains)