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 ( BacteroidesFusobacteriumPorphyromonas).
  • 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

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

Recommended antimicrobials

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


Spectrum of bacteria involved

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:

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. colistaphylococciProteusKlebsiella.

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.


Spectrum of bacteria involved

Recommended antimicrobials

  • To eliminate leptospiremia:
  • 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.
  •  Staphylococcistreptococci.
  •  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. coliProteusBacillus  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.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Litster A, Moss S M, Honnery M et al (2007) Prevalence of bacterial species in cats with clinical signs of lower urinary tract disease: Recognition of Staphylococcus felis as a possible feline urinary tract pathogen. Vet Microbiol 121 (1-2), 182-188 PubMed.
  • Wagner K A, Hartmann F A, Trepanier L A (2007) Bacterial culture results from liver, gall bladder, or bile in 248 dogs and cats evaluated for hepatobiliary disease: 1998-2003​. J Vet Intern Med 21 (3), 417-424 PubMed.
  • Sykes J E, Kittleson M D, Pesavento P A et al (2006) Evaluation of the relationship between causative organisms and clinical characteristics of infective endocarditis in dogs: 71 cases (1992-2005). J Am Vet Med Assoc 228 (11), 1723-1734 PubMed.
  • Barrs V R, Allan G S, Martin P et al (2005) Feline pyothorax: a retrospective study of 27 cases in Australia. J Feline Med Surg (4), 211-222 PubMed.
  • Burkert B A, Kerwin S C, Hosgood G L et al (2005) Signalment and clinical features of diskospondylitis in dogs: 513 cases (1980-2001). J Am Vet Med Assoc 227 (2), 268-275 PubMed.
  • Elliott D R, Wilson M, Buckley C M et al (2005) Cultivable oral microbiota of domestic dogs. J Clin Microbiol 43 (11), 5470-5476 PubMed.
  • Ganiere J P, Medaille C, Mangion C (2005) Antimicrobial drug susceptibility of Staphylococcus intermedius clinical isolates from canine pyoderma. J Vet Med B Infect Dis Vet Public Health 52 (1), 25-31 PubMed.
  • Hagman R, Greko C (2005) Antimicrobial resistance in Escherichia coli isolated from bitches with pyometra and from urine samples from other dogs. Vet Rec 157 (7), 193-196 PubMed.
  • White S D, Brown A E, Chapman P L et al (2005) Evaluation of aerobic bacteriologic culture of epidermal collarette specimens in dogs with superficial pyoderma. J Am Vet Med Assoc 226 (6), 904-908 PubMed.
  • Breitschwerdt E B, Blann K R, Stebbins M E et al (2004) Clinicopathological Abnormalities and Treatment Response in 24 Dogs Seroreactive to Bartonella vinsonii (berkhoffii) Antigens. J Am Anim Hosp Assoc 40 (2), 92-101 PubMed.
  • Foster S F, Martin P, Braddock J A et al (2004) A retrospective analysis of feline bronchoalveolar lavage cytology and microbiology (1995-2000). J Feline Med Surg (3), 189-198 PubMed.
  • MacDonald K A, Chomel B B, Kittleson M D et al (2004) A prospective study of canine infective endocarditis in northern California (1999-2001): emergence of Bartonella as a prevalent etiologic agent. J Vet Intern Med 18 (1), 56-64 PubMed.
  • Waddell L S, Brady C A, Drobatz K J (2002) Risk factors, prognostic indicators, and outcome of pyothorax in cats: 80 cases (1986-1999). J Am Vet Med Assoc 221 (6), 819-824 PubMed.
  • Ling G V, Norris C R, Franti C E et al (2001) Interrelations of organism prevalence, specimen collection method, and host age, sex, and breed among 8,354 canine urinary tract infections (1969-1995). J Vet Intern Med 15 (4), 341-347 PubMed.
  • Speakman A J, Dawson S, Corkill J E et al (2000) Antibiotic susceptibility of canine Bordetella bronchiseptica isolates. Vet Microbiol 71 (3-4), 193-200 PubMed.
  • Walker A L, Jang S S, Hirsh D C (2000) Bacteria associated with pyothorax of dogs and cats: 98 cases (1989-1998). J Am Vet Med Assoc 216 (3), 359-363 PubMed.
  • Dhaliwal G K, Wray C, Noakes D E (1998) Uterine bacterial flora and uterine lesions in bitches with cystic endometrial hyperplasia (pyometra). Vet Rec 143 (24), 659-661 PubMed.
  • Harvey C E, Thornsberry C, Miller B R (1995) Subgingival bacteria--comparison of culture results in dogs and cats with gingivitis. J Vet Dent 12 (4), 147-150 PubMed.
  • Harvey C E, Thornsberry C, Miller B R et al (1995) Antimicrobial susceptibility of subgingival bacterial flora in dogs with gingivitis. J Vet Dent 12 (4), 151-155 PubMed.
  • Harvey C E, Thornsberry C, Miller B R et al (1995) Antimicrobial susceptibility of subgingival bacterial flora in cats with gingivitis. J Vet Dent 12 (4), 157-160 PubMed.
  • Jameson P H, King L A, Lappin M R et al (1995) Comparison of clinical signs, diagnostic findings, organisms isolated, and clinical outcome in dogs with bacterial pneumonia: 93 cases (1986-1991). J Am Vet Med Assoc 206 (2), 206-209 PubMed.
  • Randolph J F, Moise N S, Scarlett J M et al (1993) Prevalence of mycoplasmal and ureaplasmal recovery from tracheobronchial lavages and of mycoplasmal recovery from pharyngeal swab specimens in cats with or without pulmonary disease. Am J Vet Res 54 (6), 897-900 PubMed.
  • Kerwin S C, Lewis D D, Hribernik T N et al (1992) Diskospondylitis associated with Brucella canis infection in dogs: 14 cases (1980-1991). J Am Vet Med Assoc 201 (8), 1253-1257 PubMed.
  • Isogai E, Isogai H, Miura H et al (1989) Oral flora of mongrel and beagle dogs with periodontal disease. Nippon Juigaku Zasshi 51 (1), 110-118 PubMed.

Other sources of information

  • American College of Veterinary Dentistry website:
  • American Veterinary Medical Association (2006) Basic Guidelines of Judicious Therapeutic Use of Antimicrobials.
  • Chew D J, DiBartola S (2006) Tips for managing lower urinary tract disorders: bacterial UTI. Proceedings of the 24th Annual Forum of the American College of Veterinary Internal Medicine 2006.
  • Chew D J (2003) Bacteriuria in dysuric cats: fact or fiction? Proceedings of the Western Veterinary Conference 2003.
  • Miller C, McKiernan B, Hauser C, Fettman M (2003) Gentamicin aerosolization for the treatment of infectious tracheobronchitis. Proceedings of the 21st Annual Forum of the American College of Veterinary Internal Medicine 2003.
  • Grauer G (2002) Appropriate use of antimicrobials in urinary tract infections. Proceedings of the 20th Annual Forum of the American College of Veterinary Internal Medicine 2002.
  • Sherding R (2001) Diagnosis and management of bacterial pneumonia. World Small Animal Veterinary Association World Congress 2001.
  • Wallace M (2001) Diagnosis and medical managment of canine prostatic disease. Atlantic Coast Veterinary Conference 2001.
  • AliAbadi F S, Lees P (2000) Antibiotic treatment for animals: effect on bacterial population and dosage regime optimisation. Int J Antimicrob Agents 14, 307-313.
  • Trepanier L, Elliott J (1998) Good prescribing practice. In: Gorman N T, editor. Canine Medicine and Therapeutics. 4th ed. London: Blackwell. pp 3-4.
  • Watson A D J, Elliott J, Maddison J E (1998) Rational use of antibacterial drugs. In: Gorman N T, editor. Canine Medicine and Therapeutics. 4th edn. London: Blackwell. pp 53-72.

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