Classification of Pathogenic Bacteria Flashcards
What type of bacteria has a more complex cell wall
how so?
Gram negative: periplasmic space + outer membrane (lipoprotein/Lipopolysaccaride (LPS))
How is Gram staining useful/important
general knowledge/understanding - probs not in course
- Quick and simple way to classify organisms
- Provides early indication og genus of infectious bacteria
- Allows for targeted treatment (Gram +ve/-ve)
How can we braodly classify Gram +ve bacteria
first 2 “classification”
- Aerobic or anaerobic
- Cocci Bacilli
Aerobic and anaerobic
- Aerobic: grow in presence of O2
- Anaerobic: grow in abscence of O2
Give exmples of Aerobic Gram Positive bacteria
- Staphylococci (clusters)
- Streptococci (chains)
- Enterococci (chains)
How can we further differenctiate between staphylococci
aerobi gram positive bacteria
Colagulase test: colagulase positive (s.aureus –> MSSA/MRSA) or colagulase negative
collagulase = enzyme
Explain the collagulase positive staphylococci
name, location, diseases
- staphylococcus aureus
- Commensal organism carried in nose/axilla/perineum
- Causes boils/abscesses and soft tissue infections to septicaemia and osteomyelitis
S.aureus: property in terms of antibiotics
- 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
Colagulase negative staphylococci
Key ones
S.lungundsis - mainly skin commensals. Form biofilsm and maybe significant pin the presence of foreign bodies/prostheses
S.epidemidis, S.haemolyticus, S.sarophyticus
G+ve, cocci, chains name
+ how can it subdivide
Streptococci:
* a-haemolytic
* B-haemolytic
* Non-haemolytic
Explain the subdivisions of streptococci
- a-haemolytic: (partial haemolysis) -> turns blood agar green
- B-haemolytic: (complete haemolysis) -> turns blood agar clear
- Non-haemolytic: -> no difference
Give an example of a a-haemolytic streptococci (G+ve ) and explain what it causes
+ explain the rest of this type of bacteria
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)
Explain B-haemolytic streptococci
- Further identified by carbohydrate surface antigens (Lancefield Group)
- Groups A-G
- A,B,F and D clinically most important
Group A streptococci
streptococcus pyogenes
Major pathogen - pharyngitis, cellulitis, necrotising fasciitis (flesh eating)
Group B streptococci
- Streptococcus agalactiae
- Neonatal sepsis: meningitis, bacteraemia
- Also invasive infection in venerable adults –> sepsis
Group D streptococci
- Reclasses as enterococcus meaning it is often non-haemolytic
- Found in gut as normal commensal
- Cause urinary tract infection and infective endocarditis
Clostridiodes difficile
- 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
Clostridium perfringens
- 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”
What does clostridium tetani produce and what does it do
toxin production causes tetanus - uncontrolled muscle spasm due to loss of inhibition at NMJ
Is vaccine preventable
4 common, clinically important G+ve bacteria
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Clostridium difficile
Define:
* colonisation
* Infection
- 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
How are G-ve bacteria “worse”
75% of terrible twelve are G-ve
2 major genuses of G-ve cocci
- Neisseria spp (n.meningitidis, n.gonorrhoeae)
- Moracella catarrhalis
First more important for now
Explain neisseria meningitidis (meningococcus)
- 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
Neisseria gonorrhoeae (G-ve cocci)
- Causes urethritis in men and pelvic inflammatory disease in women
- Spread by sexual contact
moracella catarrhalis (G-ve cocci)
not so important
- Causative agent of respiratory tract infections (e.g. pneumonia)
- Especially in those with underlying lung pathology
what is a coliform
- 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.
What family are coliforms in (G-ve)
Enterobacteriaceae
Escherichia coli
- 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
2 types of diarrhoea causing E.coli
- Enterotoxogenic E.coli (“traveller’s diarrhoea”)
- Enterohaemorrhagic E.coli (bloody diarrhoea, HUS)
Curved G-ve bacilli
- 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
Helicobacter pylori
G-ve
- Curved rods
- Natural habitiat is human stomach
- Damages mucosa and causes ulcers
- Strong risk factor for gastric adenocarcinoma
Haemophilus influenzae
- cocco-bacilli (mixed appearance)
- Causes respiratory tract infections
- Capsulate form (type B) was formarly an important cause of meningitis in children
Pseudomonas spp
G-ve bacillus
- 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
G-ve anaerobes
explain and give examples
Often part of polymicrobial infection with increasing importance and recognition
* Bacteriodes spp
* Prevotella
* Porphyromonas
Bacteroides fragilis
- Part of normal colonic flora
- Causes intra-abdominal abscess
- May spread to other sites (bloodstream)
List the common G-ve bacteria
7 genuses/individual bacteria
- E.coli
- Salmonella spp
- Campylobacter spp
- Pseudomanas spp
- Helicobacter pylori
- Haemophilus influenzae
- Bacteroides and other anaerobes
micellaneous bacteria
- 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
Acid And Alcohol Fast Bacilli (AAFB)
*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
Tuberculosis: bacteria to cause it, link with what?
*Caused by Mycobacterium tuberculosis.
*Link with HIV
What causes leprosy
Mycobacterium leprae - cannot be cultured
Attacks peripheral nerves
Spirochaetes
- 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
common spirochaete diseases
- Treponema pallidum= causes syphilis
- Borrelia burgdorferi= causes lyme disease
- Leptospira interrogans= leptospirosis
syphilis
*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.
SHape of:
* Cocci
* Bacilli
- Cocci - round
- Bacilli - rod-shaped
