Finding the right treatment to combat bacterial infection L10 Flashcards
What are the 3 factors taken into account to combat bacterial infection
- diagnosis
- correct treatment
- finding the source
how are the correct tests to diagnose infection determined
Case history and details
define serology
relies on diagnostic identification of antibodies in the serum eg. latex agglutination tests (only the relevant antigens will be bound by the specific antibody)
define Serotyping
determines the subtype of organism
- Salmonella has >2,500 serotypes (but less than 5% infect humans).
- Knowing which serotype is present allows effective treatment.
- Serotypes often correlate with antibiotic resistance patterns.
what are 3 different diagnosis methods
- CFU’s
- latex agglutination
- biochemical assays
- molecular diagnosis
describe CFU’s
culture forming units
- take sample e.g urine
- carry out serial dilution and grow selective medium that only allows certain bacteria to grow
- quantify and qualify
what are advantages and disadvantages of CFUS
AD:
- in a mixed culture, you can extract infectious pathogen
- machines can quantify quickly
- taken straight from sample such urine
DIS:
- overgrowth of flora may make plate difficult to see
describe latex agglutination
latex beads have antibodies on them
- mix sample with the beads
- if you have antigens comp to the antibodies on the beads, agglutination will occur
- clump together to give positive result
what are disadvantages and advantages of latex agglutination
AD:
- rapid
DIS:
- only use liquid samples (serum, urine, blood)
- faeces wont work this
describe biochemical assays
sample put in different wells with different environments to test its metabolic activity and nutritional requirements
- enzymes
- sugars
exploits the needs of bacteria to identify them
- rapid and accurate
- top wells are control, bottom are
what are the standard enzymes used in biochemical assays
Oxidases - Pseudomonas spp.: +, E. coli: -
Catalase - Gram +ve bacteria e.g. Listeria spp.
Urease - Helicobacter pylori
what types of molecular diagnosis are there
- detection of DNA sequences
Gene / sequence specific = detection + ID
- use PCR to detect specific sequence in bacteria and use gel electrolysis to identify it
- Add fluorescent DNA intercalating agent to the finished reaction or gel OR other fluorescent DNA binding dyes
Can add dyes to a PCR reaction without inhibiting it: detect PCR product in ‘REAL-TIME
describe real time PCR
as PCR reaction happens, incorporate florescent dye
- the more positive DNA sequence we have, more fluorescence detected
- reduces time to 1 hour
give 2 successes of real time PCR
- Neisseria meningitidis - Meningitis
- normally used CFU method
- RT-PCR gave 56% positive diagnosis successful
- Very important for rapid, correct treatment - Bordetella pertussis - Whooping Cough
- Very slow culture growth: 3 - 12 days incubation
- RT-PCR diagnoses within hours
- Important for correct treatment and prophylaxis of contacts
what are advantages and negatives of molecular diagonsis methods
AD:
- Bacterial genomes are unique
- Genetic material can be extracted from infected specimens
- DNA is easy to detect and even quantify
- Extremely sensitive 1-10 CFU / reaction
DIS:
- Technology is still being developed
- Some tests require the bacteria to be isolated first
- Some tests are TOO sensitive
- Standardisation from lab to lab can be problematic
what are and where do antibiotics come from
Natural or synthetic compounds that prevent microbial growth
bacteria naturally produce it to compete with other bacteria
- First discovered by finding that one of the plates got contaminated with mould- zone of clearance as mould was producing penicillin killing off the bacteria we was trying to grow
what is the danger with using antibiotics
over use can cause them to evolve and gain antibiotic resistance
why has antibiotic discovery slowed
- new bacteria found are producing antibiotics that have already been found
- lack of investment by pharmocital companies as it is expensive to do and gross a small yield
what does one health try to achieve
to manage use of antibiotics better
- look at its use holistically
we give animals antibiotics to prevent infection but this overuse has lead to antibiotic resistant strains that eventually get into us
we should only use antibiotics when we really need to
- ABR will kill 10 million by 2050
define bacteriostatic
Bacteria static stop bacterial growth while they are present, if they are removed, bacteria will start to grow again
Reduce number then allow our immune system to deal with the rest
- chloramphenicol
bacteria can hide in niches or own body cells- drugs may not find them so you need drug and immune system to get all
define bactericidal
kills bacteria completely
- penicillin
what are the targets on bacteria antibiotics use
structures that are in bacteria but not humans
- cell wall
- DNA/RNA synthesis
- folate synthesis
- cell membrane (may be toxic to human cells also)
- protein synthesis
what mechanisms do bacteria have to resist antibiotics
- pumps: pump out antibiotics
- immunity proteins and bypass the antibiotics
- modify antibiotic targets
- mechanisms that inactivate enzymes
give 3 examples of antibiotics that target protein synthesis and how they work
- chloramphenicol, macrolides, glycosamides
- bind 50s ribosome subunit
- prevent peptide formation - aminoglycosides
- bind 30s ribosomal subunit
- impair proof reading= faulty proteins - tetracyclines
- bind 30S subunit
- block binding of tRNAs
what is Minimum Inhibitory Concentration and how is it determined
The minimum concentration of antibiotic needed to inhibit growth
- using wells:
concentration of antibiotics decreases in wells
MIC is the value where well above does not grow bacteria and the well below (less concentrated) does
- using strip
strip that has increasing amount of antibiotic drop it on plate full of bacteria, creates clearing zone
concentration where clearing zone stops is MIC
give examples of modifications to infection treatments
- Limiting antibiotic use (antimicrobial stewardship and One Health approach)
2.Last resort antibiotics (e.g. polymyxin) - Combination therapy- combine 2 different classes of antibiotics- may be targeting different parts of bacteria
- Phage therapy- viruses that target bacteria, very specific- one phage kills one bacteria so give person phage that will kill the pathogen
- Faecal transplant (e.g. for treatment of C. difficle)- over compete pathogen with healthy bacteria in gut
what is needed to know by UK Health Protection Teams within PHE centres when outbreak happens
Reported by whom and where
Type of suspected outbreak
Who is affected
Population at risk
why is global knowledge of outbreak/ infections important
Global knowledge such as WHO reporting allows us to spot trends and intervene quicker
Newzeland during covid slayed
why do we need global monitoring
- Health education and protection can limit spread.
- Monitoring outbreaks can prevent an epidemic
- In the field diagnostics now available
- Transient population and air travel mean no infection ‘barriers’
what is the Notification sheet
used by UK Health Security Agency
Notifiable disease, quite rare but has very negative effects
Doctors have to report notifiable diseases off the sheet
what are Endemic
communicable disease such as influenza, diarrhoea and vomiting, measles, mumps, pneumonia which is characteristic of a particular place, or among a particular group, or area of interest or activity
what are Epidemics
the disease is found to infect a significantly larger number of people at the same time than is common at that time, and among that population, may spread through one or several communities (can affect a region in a country or a group of countries)
what are pandemics
describe global disease outbreaks, when epidemics spread worldwide
how can DNA help understanding infections
Understanding the serotype of the organism allows us to tailor the treatment
Genome sequencing is rapid and RT-PCR is very fast
Monitoring the MIC tells us if we are winning
Sharing data tells us about patterns of spread
