Role of Microbiology Lab Flashcards
role of microbiology lab
diagnosis of infections performed by the laboratory has two important functions:
- clinical
- epidemiological
Clinical and epidemiological role of the microbiology laboratory are very much connected: knowledge of an infective microbe in a patient helps find its source and route of transmission and prevent the spread to other patients.
clinical role of microbiology lab
- Diagnosis of infection in an individual patient for everyday management of infections
epidemiological role of microbiology lab
- Support for infection prevention and control in searching for source and route of transmission of HAI
- Bigger picture – drives infection control and prevention measures
6 minimal requirements for microbiology services
- set up insider the facility
- available every day, including sundays and holidays
- able to examine different clinical specimens
- identify common bacteria and fungi to species level
- perform susceptibility testing using disc-diffusion methodology/broth microdilution
- perform basic phenotyping
- serotyping
- biotyping
Every microbiology laboratory has to have quality assurance procedures and a microbiologist with good communication skills.
if not possible to have microbiology service set up within facility
negotiate a contract for diagnostic microbiology with the nearest laboratory
operating times of microbiology lab
24 hours, every day
every microbiology lab MUST
have quality assurance procedures and a microbiologist with good communication skills.
e.g. clinical samples variety which lab needs to be able to examine
blood, cerebrospinal fluid, urine, stool, wound exudate or swab, respiratory secretions, and perform basic serological tests (HIV, HBV, HCV)
e.g. organisms ID by serotyping phenotyping
- Salmonellae, Shigellae, P. aeruginosa, N. meningitidis
e.g. organism ID by biotyping phenotyping
S.typhi
3 things microbiology lab should be able to determine
- what the species is
- what it is senstive to
- any differences between the species
how to send sample and grow it
- appropriate device (sheath) to microbiology lab*
- Most organisms from clinical samples grow well on blood agar (non-selective)*
- place in incubator (generally 37o), looking for single colonies – take colony and spread over agar dish with antibiotic disc to see if a zone of inhibition forms*
- Obligate anaerobes – grow without oxygen – need to get to lab quickly or they will die*
issue with obligate anaerobes
grow without oxygen
need to get to lab quickly or they will die
what clinical sample would be taken for an abscess
pus
- Insert needle into abscess and withdrawing the pus*
- Tends to be anaerobic organisms in pus – need to get specimen to lab quickly as organism may die*
diagnosis should be
rapid and accurate to the species level wherever possible
4 methods of diagnosis
classical bacteriological methods
sensitivity testing
antibody detection
molecular methods
3 classical bacteriological methods of diagnosis
- Direct smear – pseudomembranous candidiasis
- Culture
- Antigen detection
sensitivity testing for diganosis helps determine
if pt non compliance or organism resistant
antibody detection useful
in later stages of infection
not very useful in early stages of infection as none developed
e.g. viruses – COVID, hepatitis – indicator of active infection
molecular methods use
Rarely used in routine work for the diagnosis of bacterial HAI – expense
- Limitation is that culture is important – to enable sensitivity tests for HAIs
why do we need to know the aetiology of infection ASAP in HAIs
we can give to the patient targeted antimicrobial therapy – in that case patient’s causative agent will be eradicated earlier
so he/she will stop to be a source for other patients earlier than if the therapy would be unsuccessful
when is antibody detection useful
only in some viral diseases when we can detect IgM
who can give advice to ward staff about collection and transport of specimens
labratory staff
6 stages in simplified scheme for bacterial identification
- specimen
- direct examination
- culture
- pure culture and identification of species
- species name established
- typing or fingerprinting for taxonomic or epidemiological purposes
specimen collection involves
stating site of origin
collection correctly
transport correctly to labratory
direct examination involves
microscopy
- wet film and gram stain
- smell
- gross appearance
- types of bacteria and other cells
culture involves
plate culture
- non selective or selective mediu
- gaseous enviroment - aerobic, anaerobic, microaerophillic, CO2
- quantitive or non-quantitive
- enrichment broth culture
pure culture and identification to species involves
colonal morphology
- microscopy
- wet film for observation of motility and spores and gram stain for gram reaction and cell morphology
- biochemical (metabolic) tests
- traditional or commercial ‘kit’
a.k.a APIs
typing or fingerprinting for taxonomic or epidemiologycal purposes involves
serological, phenotypic and genotypic methods
2 shapes of bacteria
cocci
rods (bacilli)
cocci
round, grape like