Class of Path Bac

Question 1

Staphylococci aureus

Answer 1

• 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

Question 2

Coagulase-negative staphylococci

Answer 2

• 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

Question 3

Streptococci α-haemolytic

Answer 3

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

Question 4

Streptococci β-haemolytic

Answer 4

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

Question 5

Group A Streptococci β-haemolytic

Answer 5

• Streptococcus pyogenes

- Major pathogen: sore throats, cellulitis, necrotising fasciitis

Question 6

Group B Streptococci β-haemolytic

Answer 6

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

Question 7

Group D Streptococci β-haemolytic

Answer 7

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

Question 8

Clostridium difficile

Answer 8

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

Question 9

Clostridium perfringens

Answer 9

• 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

Question 10

Clostridium tetani

Answer 10

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

Question 11

Neisseria meningitides

Answer 11

• Gram negative cocci

- Causes meningitis, inflammation of meninges and septicaemia

Question 12

Neisseria gonorhoeae

Answer 12

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

Question 13

Moraxella catarrhalis

Answer 13

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

Question 14

Preliminary test in identifying Gram negative bacilli

Answer 14

Lactose fermentation

Question 15

Coliforms

Answer 15

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

Question 16

Escherichia coli

Answer 16

• 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

Question 17

Salmonella spp

Answer 17

• Coliform
• Gram negative bacilli
• Does not ferment lactose

Question 18

Salmonella enterica

Answer 18

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

Question 19

Salmonella typhi

Answer 19

• 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

Question 20

Shigella spp.

Answer 20

• Coliform
• Gram negative bacilli
• Diarrhoea and dysentery

Question 21

Klebsiella spp.

Answer 21

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

Question 22

Proteus spp

Answer 22

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

Question 23

Campylobacter spp

Answer 23

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

Question 24

Helicobacter pylori

Answer 24

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

Question 25

Haemophilus influenza

Answer 25

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

Question 26

Pseudomononas spp

Answer 26

• 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

Question 27

Bacteriodes spp

Answer 27

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

Question 28

Oral anaerobes

Answer 28

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

Question 29

Miscellaneous bacteria

Answer 29

• Not all bacteria can be stained with Gram stains

- Not all can be cultured using standard methods

Question 30

Mycobacterium species

Answer 30

• 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

Question 31

Mycobacteria leprae

Answer 31

• Miscellaneous
• Cannot be cultured
• Attacks PNS

Question 32

Spirochaetes

Answer 32

• 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
• BLT

Question 33

BLT

Answer 33

• Borrelia burgdorferi
• Leptospira interrogans
• Treponema pallidum

Question 34

Borrelia burgdorferi

Answer 34

• 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

Question 35

Leptospira interrogans

Answer 35

• 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

Question 36

Treponema pallidum

Answer 36

• 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

Question 37

Chlamydia

Answer 37

• 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.

Question 38

Chlamydia trachomatis

Answer 38

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