Flashcards in Classification of pathogenic bacteria Deck (56):
What are the 4 types of pathogens we are concerned about?
Describe the difference in the peptidoglycan layer in a Gram positive, and gram negative bacterial cell.
Positive - thick peptidoglycan layer
Negative - thin
What is another name for peptidoglycan?
What enzyme is present in the cytoplasmic membrane of all bacterial cells?
Cell wall synthesising enzymes
(penicillin binding proteins)
What 2 molecules are projected from the surface of gram positive bacteria?
Cell wall - teichoic acid
Membrane - lipoteichoic acid
Aside from the two teichoic acid types, what is found on the surface of gram negative bacteria?
Cell surface proteins
What is present on the surface of gram negative bacteria, that is not found on the surface of gram positive?
Outer membrane proteins
Where is the 'O-antigen- found on a gram negative bacterium?
On the lipopolysaccharide
What are the main types of Gram positive aerobic cocci?
Staphylococci - Clusters
Streptococci + enterococci - Chains
Staphylococcus aureus is a major pathological bacterium.
What are it's key features?
Carried in nose, axilla & perineum
Diseases from boils/abscesses, soft tissue infection to septicaemia & osteomyelitis
What is a major problem regarding antibiotic resistance by Staph. aureus?
Commonly penicillin resistant due to production of penicillinase
Other strains are methicillin resistant - MRSA major infection problem in hospitals
What does 'staphylo___' indicate about a bacteria?
Forms in clusters
What are the main coagulase negative staphylococci bacteria?
Coagulase negative staphylococci bacterium tend to be commensals where?
On the skin
How are Streptococci bacteria further classified?
Describe the test used to differentiate between alpha, beta and non-haemolytic streptococci bacteria
Blood agar test
- Alpha - partial haemolysis - agar turns green
- Beta - complete haemolysis - agar turns clear
- Non-H - no haemolysis - no change to the agar
What are the 2 main types of alpha haemolytic streptococci bacteria?
Strep. pneumoniae - pneumonia + meningitis
Strep. "Viridans" - endocarditis
What are the groups of beta haemolytic streptococci bacteria?
How are these groups differentiated?
Grouped according to their carbohydrate surface antigen
What are the main features of Group A Strep Bacteria?
Group A = Streptococcus pyogenes
"Flesh eating bacteria"
- Necrotising fasciitis
What are the main features of group B Strep bacteria
Group B = Streptococcus agalactiae
- Neonatal sepsis - meningitis, bacteraemia
- Invasive infections in adults
Commonly carried in genital tract of woman (25%)
What are the main features of group D Strep bacteria
Now reclassified as Enterococcus bacteria
Found as commensal in gut
- Infective endocarditis
Describe the main features of Clostridium difficile
Anaerobic Gram positive
- Pseudomembranous colitis
- Leading to diarrhoea (after antibiotic usage)
Often carried asymptomatically
How would you test someone for infection by Clostridium difficile?
Detect antigen & toxin in stool sample
What health conditions can be caused by Clostridium perfringens?
What condition is caused by the toxin, released by Clostridium tetani?
What are the two main species of Gram negative Cocco bacteria?
What health conditions are associated with Neisseria meningitidis?
Meningitis - inflammation of the meninges
Septicaemia - basically blood poisoning
What is the coagulase test?
Test for Staphylococcus aureus bacteria
Positive = aureus
What are the health conditions associated with Neisseria gonorrhoeae?
Urethritis in men
Pelvic inflammatory disease in women
Moraxella catarrhalis is a causative agent of what?
Respiratory tract infections
Especially in those with previous lung pathologies
What is a useful preliminary test to identify the type of a gram negative bacteria?
Lactose fermentation test
Culture using MacConkey agar (MAC)
Useful for identifying enterobacteria - these ferment lactose
Describe the main features of MacConkey agar, and how it is used
Contains bile salts + crystal violet to inhibit growth of Gram positive bacteria
Neutral red indicator - If bacteria ferments lactose, then it will turn pink
Describe the main features of Escherichia coli
Causes (pathogenic serotypes):
- Haemolytic uraemic syndrome (HUS)
Many serotypes exist - some are commensal, some are pathogenic
What are the main features of Salmonella enterica
Does not ferment lactose
- Enterocolitis (inflam of SI & colon)
Many serotypes - all pathogenic
What is the most important pathogenic serotype of E.coli?
Associated with haemolytic uraemic syndrome (HUS)
What are the main features of Salmonella typhi?
Does not ferment lactose
- Typhoid fever
- Constipation & fever (early stages)
Can be isolated from blood cultures & faeces for identification
What health conditions are caused by the coliform, Shigella spp?
What health conditions are associated with the colliform, Klebsiella spp?
Hospital acquired pneumonia
What health conditions are associated with the colliform, Proteus spp?
What shape does ___bacter imply?
What are the main features of curved bacilli bacteria?
Two groups based on shape:
What are the main features of Campylobacter spp?
Small curved bacilli
- (Bloody) diarrhoea - commonest cause in the UK
Domestic animals & chickens
What are the main features of Helicobacter pylori?
Spiral curved bacilli
- Stomach ulcers
- Damges mucosa
- Strong risk factor for gastric adenocarcinoma
What are the main features of Haemophilus influenzae?
Cocci-bacilli mixed appearance
- Respiratory tract infection
What are the main features of Pseudomonas spp, and why are they a problem in hospitals?
Hospital acquired source of sepsis: UTI, bacteraemia, pneumonia
Resistant to antibiotics
Can contaminate equipment
What are the main types of anaerobic Gram negative bacteria?
What health condition may be caused by Bacteroides?
What are the main features of Oral anaerobes?
- Periodontal disease
- Polymicrobial dental abscess (part of)
- Role in aspiration pneumonia
- Human & animal bite infections
Not all bacteria can be classified according to Gram staining, and are miscellaneous.
What important bacteria types are miscellaneous?
– Mycobacterium spp
– Chlamydia / Chlamydophila.
What would you use to stain Mycobacterium ?
Ziehl-Neelsen (ZN) or Auramine
What are the main types of Mycobacterium and their associated health conditions
Myco. tuberculosis - tuberculosis
Myco. leprae - leprosy
What other health condition is linked to Tuberculosis?
What are the main features of spirochaetes?
Long, spiral shaped bacteria
Identified using serology
What diseases are caused by spirochaetes?
What are the main features of Chlamydia bacteria
Obligate intracellular bacteria
Can not be cultured
Diagnosed by serology
- Respiratory tract infections
- Ophthalmic & genital tract infections
- Trachoma (eye infections)
- Genital & neonatal infections