Felis ISSN 2398-2950

Therapeutics: bacterial infection

Principles of antimicrobial therapy

• Before commencing antimicrobial therapy a few important questions should be answered:
• Is an antimicrobial agent really required?
  • Antimicrobial therapy should not be used indiscriminantly.
• Which microorganisms are likely involved?
  • Appropriate sample.
  • Gram stain to guide therapy while awaiting culture results.
  • Culture: specify type of culture (aerobic, anaerobic, mycobacteria) at time of sample submission.
  • Susceptibility testing: essential for unpredictable bacteria such as Gram negative bacteria ( Proteus  species   Proteus spp  , Escherichia coli   Escherichia coli and especially Pseudomonas species   Pseudomonas spp  )
• Which antimicrobial agent is suitable?
  • Spectrum of activity (as narrow as possible preferable to broad).
  • Infection site environment (pH, barriers to therapy, eg specific cellular transport mechanism, cellular debris, abscess walls).
  • Route of administration.
  • Duration of treatment.
  • Safety.
  • Legal considerations: whenever possible, a product approved for the indication in that species should be prescribed.
• Other considerations:
  • Compliance.
  • Cost.
  • Host defences (bactericidal better than bacteriostatic if immune compromise present).
  • Mixed infections.
  • Single or combination therapy synergism, eg a penicillin   Therapeutics: antimicrobial drug   with clavulanic acid   Clavulanate  , trimethoprim   Trimethoprim  with a sulphonamide); antagonism, eg penicillin   Benzylpenicillin   (bactericidal) with tetracycline   Tetracycline   (bacteriostatic).

Oral and dental infections

Spectrum of bacteria involved

• Gram negative anaerobes ( Bacteroides, Fusobacterium, Porphyromonas).
• Gram positive aerobes (staphylococci   Staphylococcus spp  , streptococci   Streptococcus spp  ).
•  Actinomyces  Actinomyces pyogenes    Actinomyces viscosus  .
  The American Veterinary Dental College only endorses the use of systemic antibiotics prior to oral surgery and dental procedures in "animals that are immune compromised, have underlying systemic disease (such as clinically-evident cardiac, hepatic, and renal diseases) and/or when severe oral infection is present."

Recommended antimicrobials

• Clindamycin   Clindamycin  .
• Amoxicillin-clavulanic acid   Amoxicillin      Clavulanate  .
• Metronidazole   Metronidazole  .

Bacterial rhinitis  Rhinitis 

• Rarely a primary entity.
• Nasal swab cultures are low yield - often reflect normal commensal flora.
• Avoid repeated rounds of different antibiotics.
• Look for underling cause and address that (foreign body, Aspergillosis in dogs, Cryptococcus spp   Cryptococcus neoformans  in cats, prior viral damage to nasal epithelium, neoplasia, allergic rhinitis).

Bordetella bronchiseptica infection   Bordetella bronchiseptica infection  

Spectrum of bacteria involved

•  Bordetella bronchiseptica  Bordetella bronchiseptica  .

Recommended antimicrobials

• Tetracycline   Tetracycline   (if mature dentition).
• Doxycycline   Doxycycline   (risk of dental enamel discoloration unclear, but appears to be low)
• Amoxicillin-clavulanate.

Bronchopneumonia

Spectrum of bacteria involved

• Wide range of bacteria isolated.
•  Staph   Staphylococcus spp , Strep   Streptococcus spp , Klebsiella   Klebsiella pneumoniae , E. coli   Escherichia coli  .
•  Mycoplasma    Mycoplasma and Ureaplasma  .

Recommended antimicrobials

• Amoxicillin-clavulanate.
• Cephalexin   Cefalexin  .
• Potentiated sulfonamide.
• Culture by tracheal wash if no response to single empirical trial.

Endocarditis  Endocarditis 

Spectrum of bacteria involved

•  Streptococcus, other gram positive cocci (about half of cases with known cause).
• Gram negatives (22% of cases with known cause).
•  Bartonella  Bartonella  (20-28% of cases with known cause; aortic valve especially).

Commonly effective antimicrobials

• Blood culture and sensitivity strongly recommended due to severe nature of disease, long course of treatment required, and negative consequences of choosing wrong antimicrobial.
• Recommended antimicrobials while awaiting cultures and Bartonella titers:
  • Cephalexin.
  • Amoxicillin-clavulanate.
• For Bartonella vinsonii:
  • Azithromycin   Azithromycin  , doxycycline, or a fluoroquinolone   Ciprofloxacin    Difloxacin    Enrofloxacin    Ibafloxacin    Marbofloxacin    Ofloxacin  .

Pyothorax  Pyothorax 

Spectrum of bacteria involved

• Mixed anaerobic infections most common.
• May also include E. coli(especially in dogs), and Actinomyces or Pasteurella(especially in cats).
• Culture and sensitivity recommended in all cases.
• Recommended antimicrobials while awaiting aerobic and anaerobic culture.
• Metronidazole + ampicillin   Ampicillin   + fluoroquinolone.

Bacterial cholecystitis

Spectrum of bacteria involved

•  E.coli.
•  Enterococcus.
• Anaerobes.

Recommend culture of bile whenever possible (ultrasound guided or at laparotomy)

• Consider combination therapy with:
  • Amoxicillin-clavulanic acid + fluoroquinolone.
  • Clindamycin + fluoroquinolone.
  • Metronidazole + fluoroquinolone.

Cystitis  Cystitis: bacterial 

Spectrum of bacteria involved

•  E. coli, staphylococci, Proteus, Klebsiella.

Recommended antimicrobials

• Tailor therapy based on gram stain of urine:
  • Gram positive:
    • Amoxicillin, amoxicillin-clavulanic acid, cefadroxil   Cefadroxil   or cephalexin.
  • Gram negative:
    • Potentiated sulfonamide or fluoroquinolone.
  • Culture and sensitivity   Urinalysis: culture and sensitivity  essential if no response to single empirical trial.

Leptospirosis

Spectrum of bacteria involved

•  Leptospira  Leptospira spp  .

Recommended antimicrobials

• To eliminate leptospiremia:
  • Sodium penicillin G   Benzylpenicillin  .
  • Ampicillin.
  • Doxycycline.
• To eliminate the renal carrier state of leptospirosis:
  • Doxycycline.
• Renal and/or hepatic failure should be treated with fluid therapy and other supportive measures to maintain normal fluid, electrolyte, and acid-base balance.

Prostatitis  Prostate gland: disease 

Spectrum of bacteria involved

•  E. coli, Klebsiella, Proteus, Pseudomonas.
•  Staphylococci, streptococci.
•  Mycoplasma, Ureaplasma  Mycoplasma and Ureaplasma  (opportunistic).

Recommended antimicrobials

• Fluoroquinolone.
• Potentiated sulfonamide.
• Doxycline (for Brucella).
• Chloramphenicol   Chloramphenicol  .
• Culture and sensitivity essential if no response to single empirical trial.

Pyometra  Pyometra 

• Secondary bacterial infection may be present.

Spectrum of bacteria involved

•  E. coli predominates.
• Ovariohysterectomy   Ovariohysterectomy  is treatment of choice, following appropriate fluid therapy.

Recommended antimicrobials

• Ampicillin.
• Potentiated sulfonamide.
• Fluoroquinolone.

Pyoderma  Bacterial skin disease: overview 

Spectrum of bacteria involved

•  Staphylococcus intermedius  Staphylococcus intermedius   predominates.
• Gram negatives (eg E. coli, Proteus, Bacillus  Bacillus anthracis  , Pseudomonas) may play a secondary role.
• Often secondary to underlying disease.

Recommended antimicrobials

• Cephalexin or cefadroxil.
• Amoxicillin-clavulanate.
• Potentiated sulfonamide.
• Recommend culture and sensitivity for cases that do not respond as expected, require multiple courses of treatment and/or have cytological or other evidence that non-staphylococcal bacteria are involved.

Diskospondylitis  Diskospondylitis 

Spectrum of bacteria involved

•  Staphylococci, Streptococcus.
•  Brucella.
•  E.coli.
• Recommended antimicrobials while awaiting blood and  Brucellatiter:
  • Cephalexin, cefadroxil.
• Doxycycline (if Brucella suspected).
• When no response to antibiotic therapy is seen, or when recurrence is a problem, surgical biopsy, bacterial culture, and antibiotic sensitivity testing are needed.