Immuno 4, Clinical Microbiology for Dx and Management of Bacterial Infections Flashcards
Why do we need to worry about Abx use?
- prolonged exposure –> Abx resistance
- subtherapeutic conc more likely to generate resistance
- orally administered Abx –> major problem for resistance
- 40-50% of all Abx rx’s are clinically inappropriately (no infection, wrong Abx, duration too long, dose too low, wrong route, etc)
What about MRSA and MRSI infections?
- methicillin-resistant Staph aureus, S. intermedius, and S. pseudointermedius –> in all vet hospitals
- MRSA/MRSI implies resistance to nearly all classes of penicillins and many cephalosporins
- MRSA strains may be more pathogenic in some cases; not clear for MRSI
- Staph able to colonize mucous membranes (esp nose) for wks to months
What are the key decision points in deciding to use Abx?
- is bacterial infection present?
- what types of bacteria are present?
- will the drug kill the bug?
- how long should I treat?
- what route should I use?
Why is infection site cytology so helpful in Abx therapy?
- tells us whether infection is present or not
- allows me to tentatively ID types of bacti present
- serves as a check on the accuracy of culture results
- often eliminates the need for culture altogether
- simple to perform, rapid results, information available when initially selecting Abx
How do we perform gram stain?
- use commercial kits
- 10 secs/side, slide done in 1 min
- practice with samples from abscess to check technique
- neuts should have orange nuclei
- should see both Gram + and - on same slide
What is the cytology-based infection checklist (CBIC)?
- is neut inflammation present?
- are more than one type of bacti present?
- are bacti present within WBC
What are some key steps to follow to increase your chances of getting + bacterial cultures without getting contamination?
- avoid routine use of swabbed samples; use aspirates or biopsies instead
- collect samples away from wound edges with needle, never swab skin surface
- all samples should be stored at room temp (don’t refrigerate!)
- samples should be shipped to lab quickly (don’t store until the next day)
- use transport medium for certain cultures (feces, jt and CSF fluid, anaerobes)
How do I know if I should culture for anaerobic bacti?
- site of infection: abscesses; closed space infections; infections near mouth or anus
- cytology reveals multiple different forms of bacti
- presence of putrid odor
- presence of devitalized tissue (sequestrum, gangrene)
What are the best specimens to collect for anaerobic bacti culture?
- aspirates of wound fluid or blood
- tissue biopsies
- do not even bother to culture swabbed samples (swabs kill anaerobes)
What samples should rarely be cultured for anaerobes?
- urine
- nasal or oral swabs or feces
- skin pustules
- transtracheal lavage or BAL samples
What are the best samples to collect for cutaneous wound infections?
- skin biopsies
- skin aspirates
How should we collect blood cultures?
- should always collect at least 2, preferably 3 cultures
- culture at least 10 ml blood per sample
- severely ill: 3 cultures, 10 min apart
- less ill: 3 cultures over 2-3 hours
- collect blood into pre-warmed blood culture medium, don’t refrigerate!
How should we culture deep tissue and bone infection?
- tissue biopsies best
- aspirate of any fluid
- don’t bother with swabbed samples
- don’t refrigerate
Do we need anything special for UTIs?
- cysto only sample that can be interpreted in SA
- sample can be stored at room temp or refrigerated
When do we need to submit fecal cultures?
- fecal culture is indicated when fecal leukocytes are seen on rectal cytology
- samples should be transported in fecal transport medium
- 2-3 cultures to be sure
- don’t refrigerate
