Classification of pathogenic bacteria Flashcards
What are the 4 types of pathogens we are concerned about?
Bacteria
Viruses
Parasites
Fungi
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?
Murein
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?
Lipopolysaccharides
Outer membrane proteins
Porins
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?
Commensal organism
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?
S. epidermis
S. haemolyticus
S. saprophyticus
S. lugdunensis
Coagulase negative staphylococci bacterium tend to be commensals where?
On the skin
How are Streptococci bacteria further classified?
A-haemolytic
B-heamolytic
Non-haemolytic
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?
Groups A-G
Grouped according to their carbohydrate surface antigen
What are the main features of Group A Strep Bacteria?
Group A = Streptococcus pyogenes
“Flesh eating bacteria”
Causes:
- Pharyngitis
- Cellulitis
- Necrotising fasciitis
What are the main features of group B Strep bacteria
Group B = Streptococcus agalactiae
Causes:
- 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
Often non-haemolytic
Found as commensal in gut
Cause:
- UTI
- Infective endocarditis
Describe the main features of Clostridium difficile
Anaerobic Gram positive
Bacilli shaped
Causes:
- Pseudomembranous colitis
- Leading to diarrhoea (after antibiotic usage)
Often carried asymptomatically
How would you test someone for infection by Clostridium difficile?
ELISA test
Detect antigen & toxin in stool sample
What health conditions can be caused by Clostridium perfringens?
Gastroenteritis
Gangrene
What condition is caused by the toxin, released by Clostridium tetani?
Tetanus
What are the two main species of Gram negative Cocco bacteria?
Neisseria spp
Moraxella spp
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?
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
Colliform, aerobic
Gram negative
Lactose fermenting
Causes (pathogenic serotypes):
- UTI
- Diarrhoea
- Haemolytic uraemic syndrome (HUS)
Many serotypes exist - some are commensal, some are pathogenic
What are the main features of Salmonella enterica
Colliform, aerobic
Gram negative
Does not ferment lactose
Causes:
- Diarrhoea
- Enterocolitis (inflam of SI & colon)
Many serotypes - all pathogenic
What is the most important pathogenic serotype of E.coli?
Serotype O157
Associated with haemolytic uraemic syndrome (HUS)
What are the main features of Salmonella typhi?
Colliform, aerobic
Gram negative
Does not ferment lactose
Causes:
- Typhoid fever
- Constipation & fever (early stages)
Can be isolated from blood cultures & faeces for identification
Vaccine avalaible
What health conditions are caused by the coliform, Shigella spp?
Diarrhoea
Dysentery
What health conditions are associated with the colliform, Klebsiella spp?
UTI
Hospital acquired pneumonia
What health conditions are associated with the colliform, Proteus spp?
UTI
Stones
What shape does ___bacter imply?
Curved bacilli
What are the main features of curved bacilli bacteria?
Microaerophilic
Gram negative
Two groups based on shape:
- Spiral
- Small
What are the main features of Campylobacter spp?
Gram negative
Microaerophilic
Small curved bacilli
Causes:
- (Bloody) diarrhoea - commonest cause in the UK
Faecal-oral route
Domestic animals & chickens
What are the main features of Helicobacter pylori?
Gram negative
Microaerophilic
Spiral curved bacilli
Causes:
- Stomach ulcers
- Damges mucosa
- Strong risk factor for gastric adenocarcinoma
What are the main features of Haemophilus influenzae?
Cocci-bacilli mixed appearance
Gram negative
Aerobic
Small bacilli
Causes:
- Respiratory tract infection
What are the main features of Pseudomonas spp, and why are they a problem in hospitals?
Gram negative
Aerobic
Bacilli shaped
Hospital acquired source of sepsis: UTI, bacteraemia, pneumonia
Resistant to antibiotics
Can contaminate equipment
What are the main types of anaerobic Gram negative bacteria?
Bacteroides spp
Prevotella
Porphyromonas
What health condition may be caused by Bacteroides?
Abdominal abscesses
What are the main features of Oral anaerobes?
Prevotella
Porphyromonas
Causes/associations:
- 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
– Spirochaetes.
– 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?
HIV
What are the main features of spirochaetes?
Gram negative
Long, spiral shaped bacteria
Identified using serology
What diseases are caused by spirochaetes?
Syphilis
Lyme disease
Leptospirosis
What are the main features of Chlamydia bacteria
Obligate intracellular bacteria
Gram negative
Can not be cultured
Diagnosed by serology
Causes: - Respiratory tract infections - Ophthalmic & genital tract infections - Trachoma (eye infections) - Genital & neonatal infections -
How would you diagnose someone with Chlamydia trachomatis
nucleic acid amplification tests (NAAT) on first void urine or vulval/vaginal swabs
