1.1 Reasons to submit clinical specimens for bacterial isolation and identification

Bacterial isolation and identification through culture is valuable for disease diagnosis in the following situations:

  • If it is more cost-effective or easier to use than non-culture-based diagnostic methods.
  • If the pathogen cannot be accurately predicted clinically and its identification is likely to influence treatment/disease management decisions.
  • As part of complex disease investigations or multifactorial/polymicrobial infections.
  • If a farm antibiogram is needed (hence the need to obtain an isolate).
  • If bacterial subtyping is required, for example, for surveillance purposes (hence the need to obtain an isolate).
  • When a definitive aetiological diagnosis is necessary by law (e.g. notifiable diseases).

However, bacterial isolation is not commonly used for the routine diagnosis of some important bacterial diseases of farm animals, and alternative diagnostic methods are used for various reasons.

Activity 2: Endemic bacterial diseases of animals where the diagnosis is usually made without bacterial isolation

Timing: Allow about 10 minutes

Use the text box to list important animal bacterial diseases that are common in your area where the diagnosis is usually made without bacterial isolation and the reasons why.

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Answer

Some examples are below; you may have others.

  • Bovine tuberculosis is generally diagnosed via tuberculin skin testing as infections are subclinical and Mycobacterium bovis is a slow grower (long turnaround time of culture).
  • Glasser disease of pigs is often diagnosed by polymerase chain reaction (PCR) due to the fragility of Hemophilus parasuis which often dies in the specimens during transport.
  • Mycoplasma gallisepticum/synoviae infections in poultry are often diagnosed by means of PCR or serology due to the slow growth rate of these pathogens.

1 Specimens

1.2 Types of specimens submitted for bacterial isolation