Diagnosis of Bacterial Infections

Question 1

True or False: fever, pain, heat, swelling, loss of function, and discharge are all pathgonomic clinical signs for a bacterial infection.

Answer 1

False

Non-infectious agents are capable of producing inflammation.
Not all pathogenic bacteria cause disease through induction of inflammation.

Question 2

True or False: increased (or decreased with toxic changes) total WBC count w/ neutrophilia, increased fibrinogen, and hyperglobulinemia are pathognomic clinicopathological signs for a bacterial infection.

Fibrinogen = a protein produced by the liver. This protein helps stop bleeding by helping blood clots to form

Answer 2

False

Non-infectious conditions can result in these findings.

Question 3

What is a presumptive diagnosis?

Answer 3

A diagnosis based on a patient’s history, signalement and clinical signs.

Question 4

What is a definitive diagnosis?

etiological diagnosis

Answer 4

A diagnosis that is required in order to identify the causative agent of the infection or disease and potentially perform antibiotic susceptibility testing.

Susceptibility testing is used to determine which antimicrobials will inhibit the growth of the bacteria causing a specific infection

Question 5

What are 2 situations during which you can make a presumptive diagnosis?

Answer 5

1. Px is showing pathognomic clinical signs for an infection whose tx is standard
2. When a client cannot afford further diagnostic testing

Question 6

Uncomplicated bacterial cystitis in dogs, cat bite abscesses, and surface & superficial pyoderma in dogs are all infections that can be treated with what?

Answer 6

Empirical therapy

When the presumptively diagnosed infection typically responds well to a specific antibiotic/treatment

Question 7

My patient’s infection is not responding to my original treatment plan. What should I do?

Answer 7

Pursue further diagnostics (culture sampling, swabbing, biopsy, etc.) in order to make a definitive diagnosis and target the exact cause of the infection.

Question 8

My patient has a suspected infection in a diffult-to-treat site (brain, bone, joint). Why must I make a definitive diagnosis?

Answer 8

Because if I do not treat the specific cause of this infection, I risk inducing secondary infections and complications, which can lead to serious consequences.

E.g., neurons are uncapable of regenerating

Question 9

What type of diagnostic test is appropriate for identifying the bacteria in a deep pyoderma?

Pyoderma: bacterial skin infection

Answer 9

Culture

Question 10

What type of diagnostic test is appropriate for diagnosing Leptospirosis?

Answer 10

Serology

Question 11

How does a smear allow for identifying bacteria?

Answer 11

Direct visualization of the organisms

Question 12

What is a very common site that is often incorrectly sampled from?

Answer 12

Draining tracts

Draining tracts or fistulous tracts are tract lesions that connect with a central area or focus of inflammation to the skin’s surface

Question 13

Why is it imperative to collect samples at the earliest course of disease process as possible, in both acute and chronic cases?

Answer 13

As an infection/disease progresses, tissue begins to necrose. This causes some of the bacteria to die, or be overgrown by saphrocytes.

Question 14

If you are unable to collect a sample before the start of antimicrobial therapy, when can proceed you collect a sample?

Answer 14

At trough concentration of the drug (~2-5 days after the last administration)

Question 15

What is the rule of thumb for collecting samples from deceased animals?

Answer 15

Within 4 hours of death

Question 16

What is the best way to maximize the accuracy of how likely the sampled bacteria are the causative agents?

Answer 16

By sampling directly from the site of infection

Question 17

True or False: microorganisms isolated from an infected site are often very similar to those found in the normal flora.

Answer 17

True

Emphasizes the importance of collecting directly from site of infection

Question 18

I have determined that the site of infection is a sterile site. How must I go about collecting my sample?

Answer 18

In a way that avoids both contamination with nearby flora and contamination with external bacteria (e.g., table, hands, floor, etc.)

Question 19

Why is it imperative to determine if strict anaerobes may be causing the infection?

Determined by site of infection (GIT lumen, mm of gums, etc.)

Answer 19

Because it affects how the sample is collected, transported to a lab, and cultered by the lab tech.

Question 20

What is a common error when collecting a sample?

Answer 20

Not getting a sufficient enough volume of sample//getting a sufficient volume without contamination

Question 21

Why is a swab collection the least preferred method for sampling?

Answer 21

Swabs collect inadequate amounts of sample; bacteria can absorb into the swab fibers –> decreased effective sample volume; samples are prone to desiccation

Question 22

Identify the different types of swabs:

Answer 22

1. Guarded (cultures in deep body cavities; e.g., uterus)
2. Transport media (avoid desiccation)
3. Transport media (avoid desiccation)
4. Dry
5. Anaerobic

Question 23

What are the best collection methods for bacterial isolation?

Answer 23

FNA, catheterization, biopsy; ALL must be aseptically prepped

Question 24

I need a sample from the cerebral spinal fluid. How should I collect it?

Answer 24

FNA

Question 25

What are the main cons to tissue biopsy samples?

Answer 25

invasive and expensive

Question 26

Why must different parts of the skin be sampled differently?

Answer 26

The surface = non-sterile, while the superficial and deep parts are sterile

Question 27

What type of bacteria primarily make up the microbiome of the surface of skin and of the pinna and externical canals of the ears?

Answer 27

Gram (+) cocci, and yeast

Question 28

What is a tracheal wash used for?

Answer 28

To collect bacteria from the lower respiratory tract (sterile) to evaluate for infection (pneumonia)

Question 29

A mare has endometritis. What is the required sample?

Answer 29

Guarded uterine swab, or culture from endometrial biopsy.

Question 30

Why must you evaluate a sample for suitabiltity via microscope examination prior to laboratory submission?

Answer 30

To identify…
1. the presence of host inflammatory response (essential) (neutrophilic inflammation)
2. the presence of a pathogen(s)
3. the predominant pathogen, if it is a mixed infection
4. any evidence of contamination (and therefore unsuitable for culture)

Question 31

Why might you be able to make a definitive diagnosis when micrscopically examining your collected sample?

Answer 31

Simple staining methods alow for direct visualization of bacterial morphology and arrangement, heloing narrow down list of possible etiologies (i.e.,antimicrobial therapy targeted at spore-forming rods vs staphylococcus spp.)

Question 32

What are the principles of transportation in order to maintain the integrity of your sample when sending off to a lab?

Answer 32

1. Get the sample to the lab in the same state it was in when you collected it (same # and type) (prevent contamination)
2. Use the approproate transport media that support survival, not growth
3. Transport ASAP (the bacteria are not viable forever in these media)
4. Transport in cool temperature (prevent growth; exceptions = suspected salmonella spp. or anaerobic spp.)

Question 33

What is differential media like blood agar used for?

Answer 33

To grow a wide range of pathogens, and to grow fastidious bacteria

Fastidious bacteria: require specific nutrional requirements, and have slower growth

Question 34

What is selective media like mannitol salt used for?

Answer 34

To inhibit the growth of some microorganisms, but allow others to grow; specifically, to allow staphylococci (gram +) to grow.

Question 35

What is differential media like MacConkey agar used for?

Answer 35

To grow gram (-) bacteria, and differentiate between lactose-fermenting vs non-lactose-fermenting bacteria

E.g., E. coli

Question 36

What is the 4-Point Rule for sterile sites?

Answer 36

Must always be applied when interpreting results of samples obtained from sample sites.

1. Sample must be collected in an appropriate fashion, directly from the site of infection
2. There must be evidence of inflammation in the sample
3. Attempt to identify evidence of bacteria in the sample
4. The bacteria isolated must have to opportunity to, and be capable of, causing the disease process from which the sample was collected.

Question 37

True or False: If the 4-Point Rule system is upheld, then the bacteria you have isolated are likely to be clincally significant.

Answer 37

True

and should be addressed in your therapeutic plan(s)!