Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Infectious Diseases > Classification of Microbes > Flashcards

Classification of Microbes Flashcards

1
Q

What is the definition of:

  • Prions
  • Viruses
  • Bacteria
  • Fungi
  • Parasites?
A
  • Prions: infectious particles composed entirely of proteins e.g. Transmissible Spongiform Encephalopathies (TSEs)
  • Viruses: acellular agents, can only replicate inside living cells e.g. respiratory, hepatitis viruses, HIV
  • Bacteria: living agents with a cell wall, mycobacteria
  • Fungi: single or multicellular e.g. candida and aspergillus
  • Parasites: protozoa (single cells e.g. malaria, giardia) and helminths (parasitic worms)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are gram negative bacteria?

A

Thin peptidoglycan layer that is sandwiched between inner cell membrane and a bacterial outer membrane, stains pink/red

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are examples of bacilli gram negative bacteria?

A

Bacilli (rod-shaped)

  • Coliforms
  • E. coli
  • Salmonella sp.
  • Klebsiella sp.
  • Proteus sp.
  • Pseudomonas sp.
  • Campylobacter sp.
  • Legionella sp.
  • Bacteroides sp. (anaerobe)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are examples of cocci gram negative bacteria?

A

Cocci - spherically shaped

  • Neisseria meningitides
  • N. gonorrhoeae
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are gram positive bacterias?

A

Thick peptidoglycan layers that stain purple/blue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are examples of bacilli gram positive bacteria?

A
  • Listeria sp.

- Clostridium sp. (anaerobe)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are examples of cocci gram positive bacteria?

A 
Staphylococci:
- S. aureus
- Coagulase negative
- Staphylococcus
Streptococci:
- S. pneumoniae (most common cause of CAP)
- S. pyogenes
- 'Group B Strep'
- Enterococci
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are mycobacteria?

A

Acid-fast bacilli (AFB)

  • M. tuberculosis
  • Non-tuberculosis
  • Mycobacteria
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are atypical bacterias?

A

Non-culturable

  • Mycoplasma sp.
  • Chlamydia sp.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do you stain bacteria?

A

Crystal violet dye is added to microorganisms on culture plate - the thicker the peptidoglycan layer, the more crystal violet is held. Iodine is added to make the peptidoglycan layer react with the crystal violet dye. The dye is then washed away using acetone.

  • Gram positive have a thicker peptidoglycan layer so stays blue
  • Gram negative decolourises so needs to be stained a second time using carbol fuchsin > turns pink/red
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the types of fungi?

A
  • Yeasts: single cells but many form biofilms, reproduce by budding, some can form elongated filament - like buds (psuedohyphae) e.g. candida, cryptococcus
  • Moulds: grow as filaments (hyphae), produce spores e.g. aspergillus, dermatophytes
  • Dimorphic fungi: can grow as yeasts and moulds depending on temperature e.g. histoplasmosis - not found on UK soil (traveller)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is fungi classified according to the site/mode of infection?

A
  • Cutaneous (caused by dermatophytes)
  • Subcutaneous e.g. following inoculation injury
  • Systemic/deep: opportunistic (mainly affect immunocompromised hosts) e.g. candida, aspergillus, crytococcus; primary pathogens (can cause disease in immunocompetent hosts) e.g. dimorhpic fungi
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How are viruses classified?

A
  • Acute vs chronic vs latent
  • DNA vs RNA
  • Route of spread: blood borne vs non-blood borne viruses
  • Predominant manifestation: resp, liver, gastroenteritis, rash/blisters, returning traveller with fever
  • Can present atypically in immunocompromised patients
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are ectoparasites?

A

Live on the skin and hair (outside the body) e.g. scabies, head/body/pubic lice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are endoparasites?

A

Live on mucosal surfaces or in tissues (within the body). Divided into:

  • Protozoa (single cells) e.g. malaria, giardia, toxoplasma, trichomonas
  • Helminths (parasitic worms) e.g. enterobills (pin worm), schistoma, strongyloides, tape worm (taenia)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are coliforms (enterobacteriaceae)?

A
  • E.coli, Klebsiella pneumoniae, proteus mirabilis, enterobacter cloacae
  • Gram negative aerobic rods
  • Commensal flora of the GI tract and transient flora in oropharynx
  • From these ‘homes’ they can move to other body sites and cause infection (endogenous infection)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What infections can be caused from coliforms?

A
  • GI tract > urethra > UTIs (can lead to ascending infection and BSI)
  • Chemotherapy > GI tract mucositis > translocation to bloodstream > BSI (bloodstream infections)
  • Oropharynx > LRT > pneumonia
  • Biliary tract obstruction > stasis > translocation to bloodstream > BSI
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are common causes of UTI?

A
  • Clinical syndrome: cystitis, pyelonephritis
  • Bacteria: enterobacteriaceae (mostly E. coli), pseudomonas aeruginosa, staphylococcus saprophyticus
  • Virus: immunocompromised > BK virus, adenovirus
  • Fungi: candida spp
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are non-fermenters?

A
  • Strict aerobes
  • Environmental bacteria (P. aeruginosa can permanently colonise gut)
  • Opportunistic pathogens (exogenous)
  • Pseudomonas aerugionsa, acinetobacter baumannii, stenotrophomonas maltrophilia, Burkholderia cepalia
  • Otitis externa - typically caused by pseudomonas aeruginosa, resistant to penicillin, amoxicillin and ceftriaxone/cefotaxime
  • Form biofilms rapidly and are difficult to treat
20
Q

How are streptococci classified according to pattern of haemolysis?

A
  • Beta-haemolytic (complete): S. pyogenes (Group A, GAS) (can produce lots of toxins > necrotising fasciitis), also Lancefield Groups B, C, D, G, F
  • Alpha-haemolytic (incomplete): streptococcus pneumoniae (diplococci), viridans streptococci (live in mouth)
  • Gamma-haemolytic (non-haemolytic) - enterococcus faecalis + E. faecium (live in bowels)
21
Q

What are the common colonisers of the upper airways, skin and urinary tract?

A
  • Pharyngitis: Group A Strep
  • Pneumonia: S. pneumoniae
  • Skin and soft tissue infections: Beta-haemolytic streptococci (especially GAS)
  • UTIs: Group B Strep, enterococci
22
Q

Describe staphylococci

A
  • Gram positive cocci in clusters
  • Coagulase positive: staphylococcus aureus
  • Coagulase negative (CoNS): e.g. staphylococcus epidermis - usually colonisers or contaminants, EXCEPT if: central line, prosthetic joints or devices, staphylococcus saprophyticus causes UTI in young women
  • All staphylococci form biofilms on prosthetic materials (lines, devices)
23
Q

What infections are caused by staphylococci aureus?

A
  • Carriage is common: 30% colonised in nose
  • Skin and soft tissue infections, also deeper infections e.g. osteomyelitis
  • Recommended ECHO - association with IE
  • Causes pneumonia, particularly infection following influenza
  • Virulent organism e.g. toxins > SSSS, toxic shock syndrome
24
Q

How is MRSA treated?

A
  • 1/30 people have MRSA living on their nose, armpits, groin or buttocks. These are ‘colonisation/carrying’ MRSA - not usually skin.
  • If MRSA is found on the skin, it may be treated (decolonisation): antibacterial cream inside nose 3x/day for 5 days, washing with antibacterial shampoo every day for 5 days
  • Changing towel, clothes and bedding every day during treatment - laundry should be washed separately from other people’s and at high temperature
  • Put a dressing over any breaks in skin, like sores or cuts to stop MRSA getting into the body
25
Q

What are the most important invasive fungal infections?

A
  • Candidaemia
  • Invasive aspergillosis
  • Pneumocystis jiroveci pneumonia
  • Cryptococcal meningitis
26
Q

Where do fungal microbes colonise?

A
  • Candida is part of commensal flora in GI tract and genital area - can cause invasive fungal infections
  • Aspergillus, pneumocystis and cryptococcus are environmental and colonise the airways, mostly only transiently
27
Q

When would you suspect fungal infections?

A
  • Deep and systemic fungal infections are more commonly seen in immunocompromised hosts and on ICU
  • Think fungi if a septic patient is not responding to broad spectrum abx
  • Systemic infection in immunocompetent patient usually occurs due to: exposure to high fungal load (post GI surgery, high inhalation exposure), primary fungal pathogens (dimorphic fungi)
28
Q

What is herpesviridae?

A
  • Pharyngitis, lymphadenopathy and fatigue > think of EBV and cytomegalovirus (CMV)
  • Other human herpes viruses: HSV1+2, VZV, HHV8
  • DNA viruses
  • Typically acquired during childhood and adolescence (EBV > kissing disease)
  • Can establish latent infection within specific tissues
  • Reactivation is triggered by stress or immunosuppression
  • Treatment only indicated in: severe infection, pregnant women, immunocompromised patients
29
Q

What are common respiratory viruses?

A
  • Influenza A+B
  • Respiratory syncytial virus (RSV) - babies
  • Human Metapneumovirus (HMPV)
  • Rhinovirus - common cold
  • Severe pneumonia in immunocompromised and ICU patients due to: parainfluenza type 3, herpes simplex, cytomegalovirus, adenovirus
30
Q

What are the features of influenza presentation and management?

A
  • Mild illness in most people
  • Treat with oseltamivir/zanamivir in severe infections and vulnerable patients
  • Vaccine updated yearly
  • Secondary bacterial pneumonia may occur - S.aureus
31
Q

What is norovirus?

A
  • D+v

- Return to work 24 hours after being symptom free

32
Q

How many blood cultures need to be taken?

A
  • In suspected bacteraemia it is generally recommended 2 sets (of 2 bottles) are taken at separate times from separate sites. The total volume of blood > 10-20ml.
  • Take 3 separate sets in suspected endocarditis and PUO
  • Final report available after 2-3 days, slow growing may take up to 7-8 days (anaerobes) or up to 6 weeks (mycobacteria)
33
Q

What investigations are done for lung infections?

A
  • TB - culture then PCR
  • CMV - blood and sputum for CMV PCR
  • Urinary pneumococcal antigen test (~15 mins) - high specificity moderate sensitivity
  • Nucleic Acid Amplification Tests (NAATs): sputum/BAL PCR for respiratory viruses - rapid, highly specific, sensitivity depends on virus concentration in sample
34
Q

What is Beta-D-glucan?

A

Released into blood in invasive fungal infection (except: mucorales, crytococcus). Cross reactivity with other beta glucans, false positive with cellulose filters, surgery gauzes, some beta-lactams, severe mucositis etc

35
Q

What causes hospital acquired infections?

A
  • C. difficile
  • MRSA
  • E.coli
  • Norovirus
36
Q

What infections cause lymphadenopathy?

A
  • Streptococcal tonsilitis
  • Toxoplasma
  • TB
  • HIV
  • EBV
37
Q

What can be caused by injecting illegal drugs?

A
  • Hep C
  • IE
  • Candida endopthalmitis
38
Q

What infections are spread by the faeco-oral route:

A
  • Norovirus
  • Hep A
  • C. diff
  • Campylobacter jejuni
39
Q

What are the growth requirements for different classes of bacteria?

A
  • Obligate aerobes: these will only grow in the presence of oxygen
  • Obligate anaerobes: these will only grown in the absence of oxygen
  • Facultative anaerobes and facultative aerobes: grow cell in presence and absence of O2. Most human pathogens come under this, referred to as aerobe as they can be grown aerobically - includes E.coli, Klebsiella sp, proteus sp etc
  • Microaerophilic bacteria: prefer lower concentrations of O2
40
Q

How is mycobacteria stained?

A

e.g. mycobacterium tuberculosis, mycobacterium leprae

Ziehl-Neelson staining - the bacteria hold onto the stain after being washed with acid called ‘acid-fast bacilli (ARB)’.

41
Q

What is the morphology of bacteria?

A
  • Cocci: round, appear as chains, pairs or in clusters
  • Rods: appear elongated
  • Coccobacilli: intermediate between cocci and rods
  • Spiral: examples include Treponema pallidium (cause of syphilis) + Borrelia burgdorferi (cause of Lyme disease)
42
Q

What are the shapes of the gram positive cocci?

A
  • Staphylococci: appear in clusters

- Streptococci: appear in chains

43
Q

What is the interaction between beta lactam abx and bacteria?

A

Beta lactam abx e.g. penicillin, work by inhibiting peptidoglycan synthesis in bacterial cell walls. Some bacteria can neutralise this effect by using beta-lactamase enzymes to break down the beta-lactam ring. We combine some penicillins with beta-lactamase inhibitors to overcome this effect. Piperacillin/tazobactam is one such combination. It has a broad spectrum which includes many gram negative and gram positive bacteria. It also covers pseudomonas aeruginosa, a gram negative bacteria responsible for many HAIs.

44
Q

Describe the action of meropenum

A

Class of abx known as carbapenems, very broad spectrum and are last resort against resistant gram negative bacteria.

45
Q

What does Klebsiella pneumoniae cause?

A

Normally lives in the bowel

  • UTI
  • Biliary sepsis - jaundice, RUQ pain, fever
  • Prostatitis/bowel perforation/intra-abdominal abscess/liver abscess
  • Pneumonia (typically VAP)
  • Post-operative wound infections
  • Meningitis

Infectious Diseases (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions