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Flashcards in Class of Path Bac Deck (38):

Staphylococci aureus

- Gram positive
- Coagulase positive
- Commensal organism, carried in nose, groin, hairline: sweaty, salt rich environments
- Wide range of diseases from boils and soft tissue infections to septicaemia and food poisoning
- Commonly penicillin resistant due to β-lactamase
- By a different mechanism, some are methicillin resistant - MRSA


Coagulase-negative staphylococci

- Gram positive
- Many different species
- Skin commensals
- Pathogenic in presence of foreign bodies/prostheses e.g. prosthetic heart valves, hips, pacemaker wires
- Also pathogenic for immunocompromised e.g. neonates and BMT


Streptococci α-haemolytic

- Gram positive
- Partial haemolysis
- Blood agar turns green
- Streptococcus pneumoniae: pneumonia, meningitis, septicaemia
- Viridans streptococci: normal oral flora, cause infective endocarditis


Streptococci β-haemolytic

- Complete haemolysis
- Blood agar turns clear
- Identified based on surface antigens
- Groups A-G, A, B and D most important


Group A Streptococci β-haemolytic

- Streptococcus pyogenes
- Major pathogen: sore throats, cellulitis, necrotising fasciitis


Group B Streptococci β-haemolytic

- Streptococcus agalatiae
- Neonatal sepsis: meningitis, bacteraemia
- Genital tract carriage common (25% women)


Group D Streptococci β-haemolytic

- Enterococcus spp
- Often non-haemolytic
- Cause of UTI
- Found in gut as normal commensal, if you have GI surgery, this is a risk


Clostridium difficile

- Gram positive bacilli
- Anaerobic
- In gut of healthy people, 3% adults
- Important cause of diarrhoea, associated with toxin production
- Pseudomembranous colitis, breakdown of gut


Clostridium perfringens

- Gram positive bacilli
- Anaerobic
-Found in soil and normal commensal in gut/faeces
- Can contaminate food, food poisoning with enterotoxin-producing strains
- Infects serious wounds, can lead to gas gangrene also seen in farmers that stand on nails


Clostridium tetani

- Gram positive bacilli
- Anaerobic
- Toxins cause tetanus by loss of inhibition at NMJ
- Antigenically modified toxin used for imms


Neisseria meningitides

- Gram negative cocci
- Causes meningitis, inflammation of meninges and septicaemia


Neisseria gonorhoeae

- Gram negative cocci
- Causes urerthritis in men, pelvic inflammatory disease in female
- Spread by sexual contact


Moraxella catarrhalis

- Gram negative cocci
- Aerobic
- Diplococcus
- Causative agent of respiratory tract infections
- Especially if underlying pathology e.g. COPD


Preliminary test in identifying Gram negative bacilli

Lactose fermentation



- Gram negative bacilli
- Organisms which are in the family of Enterobacteriaceae
- Mostly in gut


Escherichia coli

- Coliform
- Gram negative bacilli
- Human and animal reservoirs
- Several virulence mechanisms: pili, capsule, endotoxin, exotoxins produced
- Ferments lactose
- Strains vary considerably: UTIs, most common traveller's diarrhoea, blood diarrhoea, haemolytic uraemic syndrome


Salmonella spp

- Coliform
- Gram negative bacilli
- Does not ferment lactose


Salmonella enterica

- Self limiting enterocolitis with or without bloody diarrhoea
- Can be invasive


Salmonella typhi

- Cause of typhoid fever
- Passed from human to human
- Fever, constipation in early stages
- Can do blood test as well as faecal culture
- Vaccine available


Shigella spp.

- Coliform
- Gram negative bacilli
- Diarrhoea and dysentery


Klebsiella spp.

- Coliform
- Gram negative bacilli
- Occasional cause of UTI and pneumonia


Proteus spp

- Coliform
- Gram negative bacilli
- Causes UTI often associated with stones


Campylobacter spp

- Curved Gram -ve bacilli
- Non-coliform
- Microaerophilic, likes low O2
- Faecal-oral route
- Foul smelling and then bloody diarrhoea


Helicobacter pylori

- Curved Gram -ve bacilli
- Non-coliform
- Natural habitat is human stomach
- Damages mucosa and causes ulcers


Haemophilus influenza

- Curved Gram -ve bacilli
- Non-coliform
- Cocco-bacilli (mixed appearance)
- Causes RTI
- Capsulate form before HiB conjugate vaccine was important cause of meningitis


Pseudomononas spp

- Curved Gram -ve bacilli
- Not coliforms
- Can stay in sinks, drains, mops
- Can contaminate medical equipment, why you wash your hands in special hand washing sinks
- HAI: sepsis, pneumonia, UTI
- Respiratory infection in cystic fibrosis
- Sensitive to limited antibiotics


Bacteriodes spp

- Anaerobic Gram negative bacteria
- Part of normal colonic flora
- Causes intra-abdominal abscess
- May spread to other sites


Oral anaerobes

- Prevotella, Porphyromonas, Pasteurella spp, Capnocytyophyga spp
- Anaerobic Gram negative bacteria
- Cause of dental abscess
- Aspiration pneumonia
- Human and animal bite infections


Miscellaneous bacteria

- Not all bacteria can be stained with Gram stains
- Not all can be cultured using standard methods


Mycobacterium species

- Seen using the Ziehl-Neelsen (ZN) stain
- They are Acid and Alcohol Fast Bacilli (AAFB): Resistant to decolourisation by acid or alcohol following staining with carbol fuchsin
- These don't identify species and culture required for full I.D
- TB caused Mycobacterium tuberculosis and linked with HIV
- Non-TB Mycobacteria: wide range of environmental and atypical mycobacteria


Mycobacteria leprae

- Miscellaneous
- Cannot be cultured
- Attacks PNS



- Miscellanoeous bacteria
- Long spiral shaped bacteria
- Not easily cultured or visualised by light microscopy
-Dark microscopy or immunofluorescence can be used
- Often diagnosed by serology



- Borrelia burgdorferi
- Leptospira interrogans
- Treponema pallidum


Borrelia burgdorferi

- Lyme disease - ticks
1. Skin rash
2. Systemic illness: cardiac or neurological and musculoskeletal symptoms
3. Chronic disease: chronic skin, nervous system or joint abnormalities


Leptospira interrogans

- Leptospirosis
- Infects animals and concentrates largely in kidneys
- Spreads via infected urine and other body fluids and tissues
- Risk groups: sewerage workers, water sports
- Presentations: Weil's disease, febrile illness with systematic upset, liver and renal failure, aseptic meningitis


Treponema pallidum

- Syphilis
- Primary infection: non-painful skin lesion at site of infection, skin or mucous membranes
- Secondary infection: generalised systemic illness and rash
- Tertiary infection: CNS
- Congenital syphilis: stillbirth, neonatal death or disease
- Management: antibiotics, contact tracing and screening, antenatal screening



- Miscellaneous
- Obligate intracellular bacteria
- Don't grow in agar, only in cell lines
- Diagnosis with serology
- Respiratory infection: Chlamydophila pneumoniae, Chlamydophila psittaci (birds)
- Ophthalmic and genital tract infections: Chlamydia trachomatis.


Chlamydia trachomatis

- Trachoma, tropical eye infection
- Genital and neonatal infection
- Diagnosed by nucleic acid amplification tests (NAAT) on first void urine, vulval/vaginal swabs