Bacterial infections and Abx Flashcards
Describe the layers of gram positive and gram negative bacterias’ cell wall
gram positive:
* thick outer peptidoglycan wall and one inner phospholipid membrane
gram negative
* thin peptidoglycan wall surrounded by an inner and an outer phospholipid membrane
* lipopolysacchardie layer on the outside
What are the most common Staph bacteria isolated from dogs and cats?
dogs: Staphylococcus pseudointermedius, S. schleiferi
cats: S. pseudointermedius
Which Staph species indicates transfer from people?
Staphylococcus aureus
What are the most common bacteria to cause postsurgical infections?
Staphylococcus
Name 2 bacteria producing urease enzymes, leading to struvite infections
S pseudointermedius
Proteus mirabilis
Which S species are coagulase positive versus negative? What does this indicate?
S pseudointermedius - coagulase positive
S schleiferi - depending on subsp can be either
S aureus - most coagulase positive
virulence factor - low virulence if negative
coagulase induces blood clotting and fibrin clots covering bacteria can help avoid phagocytosis
How do Staph appear microscopically?
perfectly round and clustered
How do Streptococcus bacteria appear on cytology?
round and in chains
What does usually determine the virulence of Streptococci?
differentiate between
* alpha (partial) hemolytic
* beta (complete) hemolytic
* gamma (non) hemolytic
beta hemolytic bacteria most virulent
What is the most common Streptococcus species isolated in dogs and cats?
- Streptococcus canis
beta-hemolytic
part of the normal canine flora
can cause pneumonia, UTIs, wound infections
associated with toxic shock syndrome and necrotizing fasciitis
Why are Fluoroquinolones use contraindicated in Streptococcus canis infections?
can induce bacteriophage and increase the risk of toxic shock syndrome and necrotizing fasciitis
What bacteria has been associated with outbreaks of hemorrhagic pneumonia in dogs in shelter setting?
Streptococcus equi subsp zooepidemicus
What are the most common Enterococcus isolates in dogs and cats, where are they normal inhabitants?
E faecalis
E faceium
gastrointestinal tract
What are infections caused by Enteroccous and how are they treated?
UTIs, cholangiohepatitis, wound infections
E. faecalis - less resistant, tx of choice penicillin
E. faecium - more resistant
What classes of abx are enteroccus species generally resistant to?
- cephalosporins
- fluoroquinolones
- low dose aminoglycosides
- sulfonamides
- macrolides
What are 3 members of the Actinomycetales order?
- Actinomyces
- Nocardia
- Mycobacterium
Actinomyces - normal oral flora
Nocardia and Mycobacterium - environemnt
Actinomyces/Nocardia common pyothorax isolates
Mycobacterium infections rare
What is the treatment of choice for Actinomyces, Nocardia, or Mycobacterium?
Actinomyces - Penicillin, high dose and frequency
Nocardia - TMS
Mycobacterium - macrolide (clarithromycin)
What predisposes to Clostridium difficile diarrhea?
previous abx tx
What is caused by adherent-invasive E.coli? How is the condition treated?
Granulomatous colitis
enrofloxacin at 10-20 mg/kg q24h for 8 weeks
What is Pseudomonas aeruginosa resistant to and how are infections treated?
Resistant to:
* aminopenicillins
* most cephalopsorins
* TMS
* chloramphenicol
* tetracyclines
* often acquired resistance to aminoglycosides and fluoroquinolones
treatment with anti-pseudomonal beta-lactams i.e., ceftazidime, pipercaillin => reserve for life-threatening systemic infections
What Pasteurella spp. are isolated in dogs and cats and what kind of infections do they usually cause?
P. multicide, P. canis => normal flora of oral cavity and upper respiratory tract
can cause bite wound infections and pneumonia
best tretment: penicillins or aminopenicillins
What is the most sensitive diagnostic for Bartonellosis?
PCR followng enrichment culture
What is increaesed time to antibiotic therapy in sepsis associated with?
- increased mortality
- increased rate of AKI
- increased rate of organ dysfunction
- increased length of hospitalization
Explain how to use the MIC information for dosing regiments of time-dependent or concentration dependent antibiotics
Minimum inhibitory concentration - i.e., the lower the MIC the more susceptible
time-dependent abx - reversibly act on abx - i.e., want to minimize the time the plasma cc is less than MIC
* fT > MIC is the percent of time the plasma drug concentration is above the MIC
* ideally 100% for critically ill patients
* non critically ill: 50-60% penicillins, 60-70% cephalosporins, 30-40% carbapenems
concentration-dependent abx - irreversibly bind to abx
* want Cmax to be over MIC
* post-antibiotic effect
* Cmax:MIC should be 8 in critically ill patients
Explain how fluid overload may alter the PK of antibiotics and how to address this
increases the Vd - especially for hydrophilic antibiotics (e.g., beta lactams)
=> lower plasma cc => lower target tissue cc
- increase dose and frequency for time-dependent abx
- increase dose for concentration-dependent abx
Explain how hypoalbuminemia may affect the PK of abx
- increases the volume of distribution for hydrophilic abx
- increases renal clearance for abx that are usually mostly protein-bound
- increases fraction of free/active compound
net effect of hypoalbuminemia
* time-dependent => decreased efficacy because of fast elimination
* concentration-dependent => increased efficancy due to increased Cmax
- time-dependent antibiotics => increase dose or frequency
- concentration-dependent => no change needed
- not highly protein-bound => no change needed
In what ways can kidney disease affect antimicrobial PK?
AKI
* decreased renal clearance
* incresed fT>MIC
* higher risk of toxicity
* if high therapeutic index => likely safe, if narrow therapeutic index => frequency reduction or avoid drug overdose
Augmented renal clearance (ARC)
* may need to increase dose and frequency
* difficult to identify - need to measure renal creatinine clearance (>120-150 mL/minute people)
How does hepatic disease affect antimicrobial PK?
hepatic dysfunction would need reduction of at least 90% of metabolic capacity to substantially alter antimicrobial clearance
unlikely to play a role in most patients
Which group of beta lactams is MRSA resistant to?
all, except 5th gen cephalosporin (ceftaroline)
Name 4 classes of beta lactams
- penicillins
- cephalosporins
- monobactams
- carbapenems
Are beta lactams bacteriostatic or bactericidal?
bactericidal
Describe how beta lactams excert antibiotic properties
beta-lactam rings binds to penicillin-binding protein (PBP) –> inactivates transpeptidase enzymes –> bacteria can not build peptidoglycan layer –> defects –> permeability –> lysis
Name 4 ways of beta lactam resistance by bacteria
- antimicrobial efflux pump
- changes to porins in cell walls
- PBP mutation
- beta-lactamases
Name 4 systems of beta-lactamases
- penicillinases
- AmpC-type cephalosporinases
- extended spectrum beta-lactamases
- carbapenemases
How does MRSA exert its resistance
PBP2a mutation - beta-lactam ring cannot bind
MacA gene
Explain how beta lactams distribute in tissues. Which tissues do not typically achieve high concentration?
hydrophilic weak acid => cannot cross cell membranes, stays in EC space but with high Vd - interstitial cc will reach same as serum levels
tissue exceptions: ocular, reproductive, CNS
How are beta lactams excreted?
urine - high cc in urine!
Name 2 beta-lactams with a higher half-life
cefpodoxime
cefovecin
high protein-binding
Compare the spectrum of:
* penicillin
* aminopenicillins
* 1st through 5th gen Cephalosporins
- Penicillin - gram positive and anaerobic but minimal gram negative
- aminopenicillins - same gram positive and anerobic but better gram negative than penicillin
- 1st gen ceph: good gram positive, gram neg similar to aminopenicillins
- 2nd gen ceph: moderate gram pos and neg coverage, increased anerobe spectrum compared to 1st gen ceph
- 3rd gen ceph: broad spectrum, resistant against many beta-lactamases, ceftazidime covers P. aeroginosa and can reach CSF
- 4th gen ceph: good against enteric organism
- 5th gen ceph: covers MRSA
List examples for the 5 generations of cephalosporins
- 1st gen: cefazolin, cephalexin
- 2nd gen: cefoxitan
- 3rd gen: cefpodoxime, cefovecin, ceftiofur, ceftazidime
- 4th gen: cefquinome
- 5th gen: ceftaroline
What is the coverage of monobactams?
gram negative
poor gram pos or anaerobe coverage
List 2 examples of carbapenems and compare their risks of adverse effects
imipenem
maropenem
imipenem nephrotoxic and can cause seizures