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2. Foundations of Medicine PoD > Classification of Pathogenic Bacteria > Flashcards

Classification of Pathogenic Bacteria Flashcards

1
Q

What type of bacteria has a more complex cell wall

how so?

A

Gram negative: periplasmic space + outer membrane (lipoprotein/Lipopolysaccaride (LPS))

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2
Q

How is Gram staining useful/important

general knowledge/understanding - probs not in course

A
  • Quick and simple way to classify organisms
  • Provides early indication og genus of infectious bacteria
  • Allows for targeted treatment (Gram +ve/-ve)
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3
Q

How can we braodly classify Gram +ve bacteria

first 2 “classification”

A
  1. Aerobic or anaerobic
  2. Cocci Bacilli
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4
Q

Aerobic and anaerobic

A
  • Aerobic: grow in presence of O2
  • Anaerobic: grow in abscence of O2
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5
Q

Give exmples of Aerobic Gram Positive bacteria

A
  • Staphylococci (clusters)
  • Streptococci (chains)
  • Enterococci (chains)
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6
Q

How can we further differenctiate between staphylococci

aerobi gram positive bacteria

A

Colagulase test: colagulase positive (s.aureus –> MSSA/MRSA) or colagulase negative

collagulase = enzyme

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7
Q

Explain the collagulase positive staphylococci

name, location, diseases

A
  • staphylococcus aureus
  • Commensal organism carried in nose/axilla/perineum
  • Causes boils/abscesses and soft tissue infections to septicaemia and osteomyelitis
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8
Q

S.aureus: property in terms of antibiotics

A
  • Often penicillin resistant due to production of penicillnase (destroys B-lactate righ around panicillin
  • By different mechanism, some strains are methicillin resistant
  • methicillin resistant staph aureus (MRSA) post major problem for infection prevention and control in hospitals
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9
Q

Colagulase negative staphylococci

Key ones

A

S.lungundsis - mainly skin commensals. Form biofilsm and maybe significant pin the presence of foreign bodies/prostheses

S.epidemidis, S.haemolyticus, S.sarophyticus

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10
Q

G+ve, cocci, chains name

+ how can it subdivide

A

Streptococci:
* a-haemolytic
* B-haemolytic
* Non-haemolytic

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11
Q

Explain the subdivisions of streptococci

A
  • a-haemolytic: (partial haemolysis) -> turns blood agar green
  • B-haemolytic: (complete haemolysis) -> turns blood agar clear
  • Non-haemolytic: -> no difference
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12
Q

Give an example of a a-haemolytic streptococci (G+ve ) and explain what it causes

+ explain the rest of this type of bacteria

A

Streptococcus pneumoniae (pneumococcus) –> pneumonia, mengingitis, septicaemia - has blood capsure which protects it

Viridans streptococci:
* many different species
* normal oral flora (oral cavities)
* cause infective endocarditis (infection of heart valves)

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13
Q

Explain B-haemolytic streptococci

A
  • Further identified by carbohydrate surface antigens (Lancefield Group)
  • Groups A-G
  • A,B,F and D clinically most important
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14
Q

Group A streptococci

A

streptococcus pyogenes
Major pathogen - pharyngitis, cellulitis, necrotising fasciitis (flesh eating)

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15
Q

Group B streptococci

A
  • Streptococcus agalactiae
  • Neonatal sepsis: meningitis, bacteraemia
  • Also invasive infection in venerable adults –> sepsis
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16
Q

Group D streptococci

A
  • Reclasses as enterococcus meaning it is often non-haemolytic
  • Found in gut as normal commensal
  • Cause urinary tract infection and infective endocarditis
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17
Q

Clostridiodes difficile

A
  • Clinically important but hard to culture
  • asymptomatic gut carriage in healthy people
  • Cause of diarrhoea, associated with toxin production and potentially fatal
  • Inc risk with antibiotic use.anything to disrupt gut flora
  • Pseudomembranous colitis
  • Transmitted via spores
  • Detect antigen and toxin in stool sample by ELISA
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18
Q

Clostridium perfringens

A
  • Found in soil and normal commensal in human and animal gut/faeces
  • Spores
  • Can contaminate food and cause gastroenteritis (enterotoxin-producing strains)
  • Infects wounds, can cause “gas gangree”
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19
Q

What does clostridium tetani produce and what does it do

A

toxin production causes tetanus - uncontrolled muscle spasm due to loss of inhibition at NMJ
Is vaccine preventable

20
Q

4 common, clinically important G+ve bacteria

A
  • Staphylococcus aureus
  • Streptococcus pyogenes
  • Streptococcus pneumoniae
  • Clostridium difficile
21
Q

Define:
* colonisation
* Infection

A
  • Colonisation: presence of a microorganism on/in a host, with growth and multiplication of the organism, but without interaction between host and organism
  • Infection: when bacteria enter the body, increase in number, and cause a reaction in the body
22
Q

How are G-ve bacteria “worse”

A

75% of terrible twelve are G-ve

23
Q

2 major genuses of G-ve cocci

A
  • Neisseria spp (n.meningitidis, n.gonorrhoeae)
  • Moracella catarrhalis

First more important for now

24
Q

Explain neisseria meningitidis (meningococcus)

A
  • Meningitis - inflammation of the meninges and associated septicaemia
  • Important when isolated from sterile site (e.g. blood cultures/CSF)
  • PCR available on EDTA blood for N.menigitidis
  • Often life threatining
25
Q

Neisseria gonorrhoeae (G-ve cocci)

A
  • Causes urethritis in men and pelvic inflammatory disease in women
  • Spread by sexual contact
26
Q

moracella catarrhalis (G-ve cocci)

not so important

A
  • Causative agent of respiratory tract infections (e.g. pneumonia)
  • Especially in those with underlying lung pathology
27
Q

what is a coliform

A
  • A Gram (-) rod that ferments lactose to acid and gas.
  • Mainly commensals of the human large intestine
  • Lactose fermentation is a useful preliminary test in classifying Gram negative bacilli.
28
Q

What family are coliforms in (G-ve)

A

Enterobacteriaceae

29
Q

Escherichia coli

A
  • Several virulence mechanisms: pili, capsule, endotoxin and exotoxins
  • Ferments lactose
  • Strains vary considerably in disease potential
  • Important cause of urinary tract infection (UTI)
    • sepsisemia/pnuemonia
30
Q

2 types of diarrhoea causing E.coli

A
  • Enterotoxogenic E.coli (“traveller’s diarrhoea”)
  • Enterohaemorrhagic E.coli (bloody diarrhoea, HUS)
31
Q

Curved G-ve bacilli

A
  • Campylobacter spp
  • Microaerophilic - likes low O2 content
  • Source is domestic animals and chickens, spread via faecal-oral route
  • Foul smelling -> bloody diarrhoea (incubation period 2-5 days)
  • Commonest cause of bacterial diarrhoea in UK
32
Q

Helicobacter pylori

G-ve

A
  • Curved rods
  • Natural habitiat is human stomach
  • Damages mucosa and causes ulcers
  • Strong risk factor for gastric adenocarcinoma
33
Q

Haemophilus influenzae

A
  • cocco-bacilli (mixed appearance)
  • Causes respiratory tract infections
  • Capsulate form (type B) was formarly an important cause of meningitis in children
34
Q

Pseudomonas spp

G-ve bacillus

A
  • Water and soil coloniser - drains, sinks, mops
  • May contaminate medical equipment
  • Hospital acquired cause of sepsis: e.g. UTI, bacteraemia, pneumonia (rare)
  • Feared respiratory pathogen in cystic fibrosis
  • Multi-drug resistance mechanisms and limited treatment options
35
Q

G-ve anaerobes

explain and give examples

A

Often part of polymicrobial infection with increasing importance and recognition
* Bacteriodes spp
* Prevotella
* Porphyromonas

36
Q

Bacteroides fragilis

A
  • Part of normal colonic flora
  • Causes intra-abdominal abscess
  • May spread to other sites (bloodstream)
37
Q

List the common G-ve bacteria

7 genuses/individual bacteria

A
  • E.coli
  • Salmonella spp
  • Campylobacter spp
  • Pseudomanas spp
  • Helicobacter pylori
  • Haemophilus influenzae
  • Bacteroides and other anaerobes
38
Q

micellaneous bacteria

A
  • not all bacteria can be stained with Gram’s method
  • Not all bacteria can be cultured by standard methods
  • For ex:
  • Mycobacterium spp
  • Spirochaetes
  • Chlamydia / Chlamydophila
39
Q

Acid And Alcohol Fast Bacilli (AAFB)

A

*Resistant to decolourisation by acid or alcohol after staining with carbol fuchsin.
*Mycobacterium species are visualised with special stains e.g Ziehl-Neelsen (ZN) or Auramine

40
Q

Tuberculosis: bacteria to cause it, link with what?

A

*Caused by Mycobacterium tuberculosis.
*Link with HIV

41
Q

What causes leprosy

A

Mycobacterium leprae - cannot be cultured
Attacks peripheral nerves

42
Q

Spirochaetes

A
  • Long, spiral-shaped bacteria
  • Not easily visualised by light microscopy
  • Very difficult to culture (never Treponema pallidum)
  • Dark ground microscopy or immunofluorescence
  • Often diagnosed by serology
43
Q

common spirochaete diseases

A
  • Treponema pallidum= causes syphilis
  • Borrelia burgdorferi= causes lyme disease
  • Leptospira interrogans= leptospirosis
44
Q

syphilis

A

*Primary syphilis: non-painful skin lesion (chancre) at the site of infection (skin or mucous membranes)
*Secondary syphilis (6-8 weeks after primary symptoms): generalised systemic illness and rash
*Latent phase: symptomatic episodes may occur
*Tertiary syphilis (years after primary symptoms): central nervous system
*Congenital syphilis: stillbirth, neonatal death or disease
*Part of antenatal screening
*Management - antibiotics, contact tracing and screening.

45
Q

SHape of:
* Cocci
* Bacilli

A
  • Cocci - round
  • Bacilli - rod-shaped

2. Foundations of Medicine PoD (28 decks)

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