Infectious diseases and the diversity of bacterial pathogens L8

Question 1

how do pathogenic microbes cause disease

Answer 1

Pathogenic microbes cause infection by gaining a foothold in a particular niche

Question 2

define
1. colonisation
2. pathogenicity
3. virulence

Answer 2

1. growth of a microbe after gaining access to host tissue
2. ability of a pathogen to inflict host damage
3. the degree of pathogenicity of an infecting pathogen

Question 3

what are the mechanisms of microbial pathogenesis

Answer 3

person is EXPOSED, and microbe ADHERSE and INVADES. microbe then COLONISES and GROWS (producing virulence factors)
results in TOXCITY or further INVASIVNESS resulting in TISSUE DAMAGE and DISEASE

Question 4

what are 3 features of infections

Answer 4

1. Infections can be invasive but this is not exclusive (e.g. Salmonella and E. coli gut infection)
2. Infections can be symptomatic or asymptomatic
3. Infections can be highly acute or chronic causing long term complications

Question 5

give 4 types of infections

Answer 5

1. respiratory
2. gastroenteritis (gut)
3. UTI and bloodstream infections
4. skin infections

Question 6

describe microbiome of respiratory tract
and give two pathogens that can result in infection

Answer 6

Upper respiratory tract has an abundant microbiome (often asymptomatic carriage due to colonisation resistance)
Lower respiratory tract typically devoid of microbes
1. Mycobacterium tuberculosis
2. Legionella pneumophila

Question 7

describe mycobacterium tuberculosis

Answer 7

Transmission risk due to respiratory expulsion (>40,000 aerosol droplets per sneeze; low infectious dose)
Survives within immune cells- microbacteria can survive in macrophages by stopping acidficiation, kill macrophage and use cell to replicate
Drug resistance rising,
Multiple mechanisms such as cell wall structure and efflux (getting something from inside cell to outside) - resistance

Question 8

describe Legionella pneumophila

Answer 8

Grows in stagnant water
Can cause pneumonia, leading to high mortality (elderly and immunocompromised)
Survives inside immune cells by generating a protective vacuole
Amino acid auxotroph - promotes proteasomal degradation to gain nutrients
Use macrophage to produce amino acids

Question 9

what are the causes of gut infections and give the two types the infection can be

Answer 9

Bacterial: usually ingestion, faecal-oral, contamination
Viral: winter vomiting bugs
Parasitic: less frequent, water-borne

Acute – rapid content ejection, typically self limiting after 48 hours
Chronic – long lasting illness

Question 10

give 4 common pathogens of the gut

Answer 10

1. E.coli
2. intestinal pathogenic E.coli
3. Vibrio cholerae
4. Helicobacter pylori

Question 11

describe E.coli

Answer 11

• gram negative
• rod bacterium
• 2 pathotypes
  Intestinal pathogenic E. coli (InPEC)

Extraintestinal pathogenic E. coli (ExPEC)

Question 12

give examples of InPEC

Answer 12

Enterohaemorrhagic E. coli (EHEC)*
Enteropathogenic E. coli (EPEC)
Enteroaggregative E. coli (EAEC)
Enteroinvasive E. coli (EIEC)
Enterotoxigenic E. coli (ETEC)
Diffusely adherant E. coli (DAEC)

Question 13

give examples of ExPEC

Answer 13

Uropathogenic E. coli (UPEC)
Neonatal meningitis E. coli (NMEC)

Question 14

describe Enterohaemorrhagic E. coli
InPEC

Answer 14

O157:H7 is the most common serotype EHEC
replicates in beef or leafy green reservoir
Encodes a Shiga Toxin – causes HUS, massive health and economical burden
constantly evolving to form different strains
- O104:H4 outbreak

Question 15

describe Vibrio cholerae

Answer 15

• gram negative motile
• associated with aquatic reservoirs
• causes constant activation of adenylate cyclase by B subunit resulting in Loss of ions into ECF causing large fluid loss

Question 16

describe Helicobacter pylori

Answer 16

• gram negative
• mainly asymptomatic but can cause stomach pain
• causes gastric and peptic ulcers in stomach

Question 17

what are UTIs caused by

Answer 17

wide range of pathogens from the gut- asymptomatic in the gut
they may get out of gut and into bladder
causes inflam response and neutrophil infiltration
form reservoirs, biofilms or subcellular communities
UTIs can be recurrent and commonly drug resistant
can enter blood stream causing sepsis

Question 18

describe skin infections

Answer 18

normally caused by opportunistic pathogens
- An organism that causes disease in the absence of normal host resistance
- Can cause skin lesions and inflammation but also disseminate to infection of throat, middle ear, blood, lungs
- Often caused by Gram positive cocci such as Staphylococcus and Streptococcus sp.

Question 19

what are the two types of immunity

Answer 19

innate and adaptive

Question 20

what is inflamation

Answer 20

A nonspecific reaction driven by neutrophil accumulation

Question 21

give signs of acute infection

Answer 21

1. rubor: redness
2. calor: heat
3. tumor/ swelling
4. dalor: pain
5. change in function: reduced motility

Question 22

give methods of adaptive immunity

Answer 22

1.specifc and memory
2. humoral
3. cellular
4. ADCC: Antibody dependent Cell mediated cytotoxicity

Question 23

describe immune response to S. enterica

Answer 23

0: Ingest contaminated food
15 min: Invasion of epithelial cells
1 h: Neutrophils appear, increased vascular permeability
3 h: Neutrophil induced tissue damage and inflammatory induced fluid accumulation
8 h: Massive effusion of Neutrophils and fluid in intestinal lumen
24 - 48 h: Evident tissue damage, diarrhoea, more fluid accumulation

Question 24

define
1.Bacteraemia
2. sepsis
3. systematic shock

Answer 24

1. the presence of bacteria in the bloodstream
   - Leads to mass organ dissemination
2. extreme, system-wide inflammatory response to blood poisoning
3. systemic drop in blood pressure leading to mass organ failure

Question 25

give 3 examples of pathogenic reservoirs

Answer 25

Environmental = V. cholerae Zoonotic = EHEC Human = UPEC

Question 26

describe the human reservoir

Answer 26

UPEC reside harmlessly in the gut They can get in bladder and evolve to be pathogenic in bladder cause UTI

Question 27

Why do we need to identify the cause of an infection in the clinic

Answer 27

To provide accurate information about the presence or absence of microorganisms (bacteria) in a specimen that may be involved in a patient’s disease process

Question 28

What is the pathway to diagnosis

Answer 28

1. doctors- treatments 2. disease surveillance centres- outbreak monitoring, evaluate disease control, data processing 3. lab- further investigation

Question 29

describe patient to diagnosis pathway

Answer 29

specimen taken - antibody or other essays rapid testing on sample or it is cultured and identified using sterology

Question 30

give 4 types of diagnostic media

Answer 30

1. general purpose - non-selective established growth 2. enrichment - select for certain species 3. selective - grows only certain bacteria 4. differential - selects between two bacteria species

Question 31

describe general purpose media

Answer 31

uses LB agar generally (Luria-Bertani) contains Yeast extract, salts, water and agar Grows both fastidious (fussy/ with needs) and non-fastidious bacteria (and yeast/fungi) Often a starting point to look for unexpected organisms

Question 32

describe enrichment media

Answer 32

Dependent on the symptoms and sample site For fastidious bacteria, often supplement media with sheep’s blood (blood agar) In a mixed sample this allows the causative organism to grow faster

Question 33

describe selective media

Answer 33

Mixed bacterial population sample taken - put on blood based agar containing antimicrobials Incubated at 42°C in microaerobic (low O2) conditions - Inhibits growth of most enteric bacteria and Allows growth of Campylobacter Uses not only media but growth conditions as selection -Once isolated can use other serological tests or May use antibiotic selection

Question 34

describe differential media

Answer 34

General purpose media with chromogenic substrate additives Tests for the presence/absence of enzymes = diagnosis E.coli has B galactosidase- goes pink if present on agar E.facalis has B glucosidase which goes blue on agar p. mirabillis has niether so stays colourless on agar