Diagnosis of bacterial infections Flashcards
clinical signs of a bacterial disease
Inflammation
* purrulent discharge
* fever
* swelling/heat
* pain
* loss of function
clinicopathologic changes from bacterial disease
- increased leukocytes (neutrophilia)
- left shift
- hyperfribrinogenemia
- hyperglobulinemia
presumptive diagnosis
Diagnosis based on history and findings of physical examination (clinical signs)
Ok to do when:
* identifying bacteria would not change treatment
* pathognogmonic signs
empirical therapy
Administration of therapy based on previous experience
Either yours or someone else’s
indicated when:
* spectrum of care (cannot afford tests)
* high level of efficacy for recommended treatments
* waiting for results of testing
based on:
* Likely bacteria to cause this disease
* Likely antimicrobial sensitivity pattern of these bacteria
* Other factors (site of infection, cost of antibiotic, ease of administration etc)
definitive/artiological diagnosis
identifies the specific cause of disease; in our case also the specific bacteria
do this when:
* very young, old or seriously ill animal
* infection in a difficult to treat place (bone, joint, brain)
* suspected pathogens dont have a predictable bacterial pattern
* no responding to earlier therapy
* zoonootic/reportable disease
* outbreak in heard
ways to identify specific bacteria
- collect sample and culture
- PCR (DNA)
- antibodies/antigens (serology)
When is the best time to collect a sample?
- NOT while giving antimicrobials
- in acute stage of infection
- within 4 hours of death
is the draining tract the site of infection?
NO do not sample draining tract
collection from sterile site
collect sterily, easy to interpret (any bacteria is bad)
collect from site with normal flora
collect cleanly
interpret:
* pathogens that are not part of normal flora
* increased numbers of normal flora can cause disease
when would you use a swab to collect a sample?
- mucus membranes
- ears
- uterine
- conjuctiva
- ears
Issues with swabs to collect sample?
- mostly dont get enough bacteria
- bacteria can adhere to them
- dry out - therefore bacteria die
- exposed to air (not good for anaerobes)
- people stick them where they shouldn’t!!! e.g., open wounds or draining tracts
When to use FNA (fine needle aspirate)?
- joint fluid
- thoracic/abd fluid
- blood
- csf
- pustule/abscess
- tracheal absess
Issues/pros with FNA?
Not many, better than swabs
* Cheap and easy to use
* Preferred technique for sample collection if possible
* Easier for collecting sample using a sterile technique
* the better you do this the easier it is to interpret results
* Easier to get more material
* But bacteria don’t live in them forever; particularly anaerobes
when to use biopsy?
- surgery (tissue)
- sequestrum (dead bone)
- deep skin infections (Punch biopsy)
issues/pros to using biopsy?
may be needed to by-pass normal flora e.g. draining tract
bacteria can survive “longer” in tissues
tissue may represent entire pathological process
but invasive and expensive!
sampling surface of skin
not sterile
sticky tape test
sampling superficial pyoderma (pustules)
sterile site= sterile technique
* Pick intact pustule
* Clean skin surface over pustule with alcohol and allow to dry
* Open pustule with fine needle
* Use swab to collect pus
* Place in transport media and send to diagnostic laboratory
sample collection for deep pyoderma
Sterile site: so FNA or biopsy is preferred when when have deep pyoderma or open wounds
Sampling the ear
swabs
try to collect from horisontal canal
how do we sample the udder?
milk samples
* clean and dry teat
* clean with alcohol
* collect milk
How to sample lungs?
horse: transtracheal aspirate
* make small hole in trachea or use endoscope with guarded catheter
* add fluid and aspirate
* NOT bronchoalveolar lavage
dog/cat: bronchoalveolar lavage or transtracheal aspirate
how to sample urinary tract?
- cystocentesis (sterile)
- free catch (not sterile)
- catheterization (not sterile but less contamination)
How to sample uterus?
Mares: guarded swab
bitch: FNA surgical sample, swab anterior uterus
microscopic examination of sample
check for:
presense of inflammation
* inflammatory cells, or indirectly
presense of pathogen
* may be diagnostic based on distinctive morphology
look for mixed infection or not
contamination
transporting the sample to a lab
Goals of Transportation of Sample
* get the sample to the lab in the “same state” as when it was collected
* same numbers of bacteria and same types of bacteria
Principles of Transportation
* use transportation media that supports survival but not growth of bacteria
* use appropriate media depending on suspected pathogen (e.g., anaerobes, Salmonella)
* transport as quickly as possible
* transport cool (refrigerator temp)
4 point rule for sterile sites
- the sample must be collected from an appropriate fashion from the actual site
- evidence of inflammation
- good evidence of bacteria in sample
- bacteria that is isolated must have the opportunity to and be capable of causing this disease
