Microbiology- Species of bacteria

Question 2

S.pneumoniae

Answer 2

Normal commensal in oro-pharynx ~ 30% of population
Causes - pneumonia, otitis media, sinusitis, meningitis
Predisposing factors- impaired mucus trapping (e.g. viral infection)
-hypogammaglobulinaemia
-asplenia

Question 3

S.pneumoniae virulence factors

Answer 3

Capsule: -polysaccharide (84 types), antiphagocytic
-polyvalent vaccine
Inflammatory wall constituents: -teichoic acid (choline)
-peptidoglycan
Cytotoxin: -pneumolysin

Question 4

Viridans group streptococci

Answer 4

Alpha- haemolytic (or non-haemolytic)
Some cause dental caries & abscesses
Important in infective endocarditits- S. sanguinis, S. oralis
Cause deep organ abscesses (e.g. brain, liver)
Most virulent are the “milleri group”- S.intermedius, S.anginosus, S.constellatus

Question 5

Diagnostic characteristics of pathogenic Enterobacteria

Answer 5

Enterobacteriaceae consists of multiple Gram negative rod-shaped bacterial species
Metabolic processes of bacteria can help diagnosis
Lactose fermentation produces acids
Distinguishes Escherichia coli and Klebsiella sp.

Question 6

Escherichia coli- Commensals and pathogenic

Answer 6

Commensals- Most abundant facultative anaerobe (107-108/g faeces)
Principal infections caused by pathogenic E. coli
-Wound infections (surgical)
-UTIs
-Cystitis-75-80% of female UTIs –faecal source or sexual activity
-Catheterisation – most common type of nosocomial infection
-Gastroenteritis
-Travellers’ diarrhoea
-Bacteraemia (potentially sepsis syndrome)
-Meningitis (infants) – rare in UK

Question 7

Shigella

Answer 7

Very closely related to Escherichia
-“E. coli + virulence plasmid”
Shigellosis: severe bloody diarrhoea (bacillary dysentery)
S. dysenteriae causes most severe form
S. sonnei most prevalent in developed world
Endemic in developing countries where sanitation is poor
Mainly children

Question 8

Why does Escherichia coli become pathogenic?

Answer 8

Several biotypes (pathovars)
-Members of a species with distinct pathogenic strategies
Members of the same species possess a common ‘core genome’.
Acquisition of pathogenicity genes ‘en bloc’ by ‘lateral gene transfer’
New E. coli pathovars continue to appear due to genetic exchange

Question 9

Four species of shigella

Answer 9

Four species S. boydii
S. sonnei
S. dysenteriae
S. flexneri

Question 10

Symptoms and pathology of shigella

Answer 10

Frequent passage of stools (>30/day)
Small volume, pus and blood, prostrating cramps, pain in straining, fever
Self-limiting (in adults)
Pathology like EIEC but with the addition of Shiga toxin

Question 11

Salmonella

Answer 11

S. enterica - responsible for salmonellosis
>2,500 serovars
Many of the serovars were originally thought to be distinct species, such as ‘Salmonella typhi’ but they are now recognised as serovars of S. enterica
i.e. Salmonella typhi is now Salmonella enterica serovar Typhi.
S. bongori - rare (contact with reptiles)

Question 12

Three forms of salmonellosis caused by S. enterica

Answer 12

1. Gastroenteritis/enterocolitis (serovars Enteritidis and Typhimurium)
2. Enteric fever - typhoid/paratyphoid fever (serovars Typhi and Paratyphi)
3. Bacteraemia (serovars Cholerasuis and Dublin)
   -Uncommon

Question 13

Gastroenteritis/enterocolitis (serovars Enteritidis and Typhimurium)

Answer 13

-Frequent cause of food poisoning (milk, poultry meat & eggs)
-Second highest no. of food-related hospitalisations/deaths (UK)
-6-36 hr incubation period, resolves (~7 days)
Localised infection, only occasionally systemic

Question 14

Enteric fever - typhoid/paratyphoid fever (serovars Typhi and Paratyphi)

Answer 14

-Poor quality drinking water/poor sanitation
-Systemic disease
- ~20 million cases, ~200,000 deaths/year (globally)

Question 15

Pseudomonas aeruginosa

Answer 15

Ubiquitous, free-living
Motile (single polar flagellum)
Rod-shaped
Opportunistic (serious cause of nosocomial infections)
Resistant to multiple antibiotics (& disinfectants) - very difficult to treat

Question 16

Pseudomonas aeruginosa: Acute and Chronic infections

Answer 16

Acute infections (due to multiple toxins):
-Localised -Burn/surgical wounds
Systemic (bacteraemic > sepsis)
-neutropenic patients (leukaemia, chemotherapy, AIDS)
ICU patients (ventilator acquired pneumonia)
-leading cause of nosocomial pneumonia
Chronic infections:
Cystic fibrosis (CF) patients
Common denominator to all infections - compromised host defences

Question 17

P. aeruginosa and cystic fibrosis

Answer 17

CF, most common inherited lethal disorder among Caucasians.
defective CFTR >thick mucus produced in lungs.
Lungs prone to microbial infection.
P. aeruginosa most problematic.
Chronic inflammation leading to progressive lung damage and deterioration of lung function
-Occurs following infection of the CF lung by P. aeruginosa
-Mainly due to host immune system trying to clear the infection

Question 18

Vibrio cholerae

Answer 18

Facultative anaerobe
Saline environments: commensal to planktonic crustaceans such as copepods
-Ingestion by shellfish
-Contamination of drinking water due to flooding of coastal areas or poor sanitation (faecal contamination

Question 19

Campylobacter

Answer 19

Spiral rods
Unipolar (monotrichous) or bipolar (amphitrichous) flagella
Most common cause of food poisoning in UK & US
-Undercooked poultry
-Cattle (unpasteurised milk)

Question 20

Helicobacter pylori

Answer 20

Spiral shaped- Tuft of polar flagella
Major role in gastritis and peptic ulcer disease (80-90% of ulcers)

Question 21

Haemophilus influenzae

Answer 21

Exclusively human reservoir
Opportunistic infections seen mainly in young children and adult smokers
Fastidious
Non-motile

Question 22

Virulence determinants of H. influenzae

Answer 22

Capsule - invasive strains are capsulate (‘encapsulated’)
-Can penetrate nasopharyngeal epithelium
-Resistance to phagocytosis and complement system
-Commensals and upper respiratory tract pathogens are non-capsulate (‘unencapsulated’) referred to as ‘non-typeable’ H. influenzae (NTHi)
LPS (‘endotoxin’)
-Inflammation
-Complement resistance

Question 23

Bordetella pertussis

Answer 23

Short (sometimes oval) rods (‘coccobacilli’)
Fastidious
Humans - only known reservoir (obligate human pathogen)
Pertussis (whooping cough)

Question 24

Legionella pneumophila

Answer 24

Legionnaires’ disease - severe inflammatory pneumonia (1-3% of all pneumonias)
Immunocompromised (elderly, alcoholics, smokers)
Severe (15-20% mortality)
Infection from man-made aquatic environments

Question 25

Neisseria

Answer 25

Aerobic gram negative cocci
Non-flagellated diplococci
Fastidious
Two species of medical importance: N. meningitidis, N. gonorrhoeae

Question 26

Borrelia burgdorferi

Answer 26

Lyme disease, transmitted to humans by tick nymphs, Dissemination via lymphatics/blood to other organs

Question 27

Leptospira interrogans

Answer 27

Leptospirosis (zoonosis)
Common infection of rats
Flu-like symptoms
Severe form (Weil’s disease*) in 10-15% infected individuals
2-4 week incubation period, clinical multi-organ infection occurs

Question 28

Treponema pallidum

Answer 28

Causes Syphilis (STD)

Question 29

Syphilis (STD)- Primary stage

Answer 29

Localised genital infection (ulcer (“chancre”))
Days-weeks post-infection
-Highly transmissible phase

Question 30

Syphilis- secondary stage

Answer 30

Systemic
Skin (rash), swollen lymph nodes, joint pains, muscle aches, headache, fever
1-3 months post-infection
-Still highly transmissible

Question 31

Syphilis-Tertiary stage

Answer 31

‘Gummas’ (granulomas) in bone and soft tissue
Cardiovascular syphilis (aorta)
Neurosyphilis (brain and spinal cord)
Occurs several years post-infection
Non-infectious form