Bacteriology - Diagnosis Flashcards
Step one of determining if you need to specifically diagnose a disease is to determine if the bacteria is in fact an infection. What are the clinical signs that can alert you on if it is a bacterial disease
purulent disease
fever
swelling
heat
pain
discharge
Define pathognomic. Is inflammation often seen bacterial infections pathognomic?
Pathognomic means that a symptom is directly related to the disease it is causing. Inflammation is a common sign of bacterial infection but also many other diseases therefore it is NOT pathognomic
What are clinicopathological changes that could alert you to a bacterial disease?
Neutrophilia
Leukocytosis
+/- left shift
+/- toxic change
hyperfibrogenemia
+/- hyperglobinemia
What is disease in most bacterial infections caused by?
Inflammation
To help you identify what the bacteria are most likely to be involved in and if you need to identify them, what should you always start your evaluation of a clinical case with?
Problem list and location of high yield problems
Differential diagnosis of most important problems starting with most likely
list the specific bacteria that could cause the problem
What question should you ask if deciding if you want to make a presumptive or definitive diagnosis?
Will it change the outcome of the case?
i .e. will it change how i will treat or control this infection or the prognosis I will give the client
What is a presumptive or clinical diagnosis?
diagnosis based on history and findings of physical examination
When is it appropriate to use a presumptive diagnosis?
- pathognomic signs and accepted therapy
- empirical therapy
Define empirical therapy
administration of therapy based on previous experience either yours or someone else
When is empirical therapy appropriate?
high level of efficacy for recommended therapy
waiting for results of c/s
client cant afford c/s
If you do treat empirically, what should you base it on?
The likely bacteria to cause the dx
The likely antimicrobial sensitivity pattern of the disease
Other factors such as site of infection, cost of antibiotic, ease of administration
What is a definitive or aetiological diagnosis? When do you want to use this over a presumptive or clinical diagnosis?
in very old, young, or sick animals
suspected infection is in a difficult site or serious consequences
Not responding to earlier treatment
not predictable susceptibility pattern
notifiable dx such as in an outbreak
herd situation
What are 4 ways in which we can make a specific diagnosis of bacterial infections?
- culture/sensitivity
- specific antibody (serology)
- specific antigen
- detection of DNA
What are common issues/problems associated with sample collection in practice?
sample is taken from incorrect site or contaminate sample
sample is not collected in correct way - unsure of bacteria and how it grows
RUBBISH IN = RUBBISH OUT
What do you need to consider before collecting a sample?
Determine the best time to collect a sample
When are the 3 best times to collect a sample?
- already started empirical therapy
- acute stages of infection
- within 4 hrs of death
If empirical therapy has already been started, how long should you wait before collecting a sample?
until trough concentration (when next dose is due)
until after a wash out period - (2-5 days after last dose)
Why is it important to collect a sample on a deceased patient within a 4 hour window?
Within this window you will only be collecting bacteria in the tissue - if wait too long, bacteria colonizing other areas such as the gut will have free reign due to no mechanisms in place to stop them so will lead to inaccurate results
Why is it important to specifically localize the site of infection and directly collect the sample directly from that site?
CONTAMINATION
What should you NEVER collect a sample from?
Draining tract
Why is it important to determine whether the site you are sampling consists of normal flora or is sterile?
Determines how sample is collected - do not want to introduce bacteria into sterile site.
IF bacteria is found in a sterile site….bingo was his name-o
Determining whether a strict anaerobes are involved in an infection will affect what 3 things?
how you collect the sample
how you transport it to a lab
how they culture the sample
What are 4 different methods that can be used to collect a sample?
swabs
FNA
Biopsy
Free catch
In what instances would you use swabs toto collect a sample?
mm, ears, uterine, conjunctiva, cornea
What are 4 types of swabs
dry
with transport media
guarded
anaerobic
What are some issues associated with swabbing a sample?
dont get enough material
bacteria can adhere to swab
swab dries out and bacteria dies
exposure to air can kill anaerobes
people stick where they shouldnt
When would you use a fine needle aspirate (FNA) to collect a sample?
joint fluid
thoracic fluid
blood
CSF
pustule
tracheal
abdominal fluid
abscess
Why is fine needle aspirate the preferred technique for sample collection if possible?
cheap and easy for sterile technique and to get more materia
What is an issue associated with fine needle aspirate sample collection?
bacteria dont live in them forever especially anaerobes
When would a tissue biopsy sample collection be appropriate?
sx
sequestrum (dead bone)
deep skin infections
When should a sterile vial be used with tissue biopsy?
milk
feces
urine (midstream voided)
What are issues related to tissue biopsy?
invasive and expensive
What is an issue associated with sterile vials?
difficult to collect a sample without contaminated it so often inappropriate for sterile sites
What are some advantages of using tissue biopsy?
bacteria can survive longer in tissue
can represent entire pathological process
Where are normal flora located on the skin? What type of bacteria does this consist of?
all over the skin especially in moist areas or ones that are in contact with more environmental contamination
Gram + and yeast
Explain the normal skin structure and where there is normal flora vs where is sterile
surface - normal flora present
superficial epidermis -sterile
deep epidermis - sterile
If collecting a sample for surface pyoderma, what technique would you use? What would you look for?
Not a sterile site - can use a sticky tape test
Would be looking an increase in # of normal flora or looking for gram negative bacteria which wouldnt typically be seen on the skin
What type of bacteria inhabits the skin as normal flora?
gram positive cocci and yeast
If collecting a sample for superficial pyoderma, what technique would you use?
sterile site so use a sterile technique to sample a pustule
1. pick intact pustule
2. clean skin surface over pustule with alcohol and allow to dry
3. open pustule with fine needle
4. use swab to collect pus
5. place in transport media and send to lab
If collecting a sample for deep pyoderma, what technique would you use?
sterile site so FNA or biopsy
Where is normal flora on the ear? Where are sterile sites?
Norrmal flora is on the ear flap (pinna), the vertical canal (fewer), horizontal canal (fewer)
sterile is after the tympanic membrane (ear drum)
What type of bacteria predominately inhabit the ear?
gram postive and yeast
When collecting a sample from the ear where do you want to collect from?
Horizontal canal
Where are normal flora on the udder? How would you collect a sample?
skin outside of udder and the streak canal has normal flora but sterile are in the udder tissue and on teat cistern
What type of bacteria is predominately on the udder?
gram positive
How would you collect a sample from a cow with suspected mastitis
- label tubes
- clean and dry teats
- clean teat end and everted streak canal with alcohol
- Strip out couple of streams
- collect sample carefully by holding horizontally
- use teat dip
- store and transport appropriately
Where are the normal flora in the respiratory tract? Where is it sterile?
normal flora cranial to the larynx in the URT
sterile in the LRT
What type of bacteria is predominately in the respiratory tract?
Gram + and -
How would you sample the LRT of a horse vs dogs and cats
in horses would do a tracheal aspirate but not bronchiolar lavage (BAL)
in dogs/cats would do blind technique for BAL or tracheal aspirate
Where is normal flora in the urinary tract and where are sterile sites?
nf in distal urethra but sterile in proximal urethra and bladder
What type of bacteria is predominately in the urinary tract?
Gram + and -
What are 3 ways to collect a sample for lower urinary tract infections in a dog?
cytocentesis - sterile
free catch - not sterile
catheterization - not sterile
Why are females more prone to UTIs?
urethra is shorter so less area for bacteria
When interpreting colony counts what will influence whether or not you determine the bacteria to be significant or not?
sample collection and technique
the more sterile, a smaller amount of bacteria will be more significant
Where in the genital tract is normal flora? Where are sterile sites?
nf = vagina posterior to cervix
sterile in uterus anterior to cervix
What type of bacteria is present in the genital tract?
gram + and -
How would you collect a sample in mares vs in bitches?
in mares would use guarded swab up vagina
in bitches FNA of surgical sample with pyometra or swab anterior vagina
Microscopic examination is a simple and cost effective way to determine what?
- presence of inflammation
- presence of pathogens
- predominant pathogen if there is mixed infection
- suitability of specimen for culture
What are your goals of transporting a sample?
get the sample to the lab in the same state as when it was collected
What are important principles to follow for transportation?
use transportation media that supports survival but not growth of bacteria
use appropriate media depending on suspected pathogen
transport as quickly as possible
transport cool
Name a few of the ways of cultivation and identification of bacteria
performing gram stains
primary culture on blood agar
using differential media to help identify bacteria
oxidase test
indole test
catalase test
Explain the 4 point rule for sterile sites
- sample must be collected appropriately from actual site of infection
- must be evidence of inflammation in the sample
- good (but not essential) if also evidence of bacteria in sample
- bacteria isolated must have opportunity to and be capable of causing disease
