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Equine Health Resource

Blood Culture

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Bacteria in the bloodstream is a very uncommon finding in adult horses, but quite common in foals.

Blood culture is sampling of the blood, placement of it in bacterial media that favors ongoing bacterial survival and growth and then culture in a lab.

A positive blood culture indicates that bacteria are in fact within the blood (or the sample has been contaminated). A negative culture is not a guarantee that the blood is free of bacteria. In neonatal intensive care facilities up to 20% of foals admitted have a positive blood culture. Once growth of bacteria is confirmed, antibiotic sensitivity is determined, which can guide therapy.

Benefits

The only way of positively determining the presence of bacteria in blood, determining the species of bacteria, and determining what antibiotics will kill it.

Limitations

Growth of bacteria and determination of sensitivity can take up to 48 hours. Treatment must be started before results are returned. If the patient is treated with antibiotics prior to blood sampling, there is a greatly reduced likelihood of growth of bacteria in the sample. Even when conditions are good, bacteria sometimes do not grow. Some species of bacteria are fastidious and hard to grow. In other cases, bacteria are only present in the blood intermittently. Timing of sampling may not be right.

QUESTIONS TO ASK MY VET

  • What is the likelihood that this bacterial isolate is real, versus a contaminant?
  • Author: Doug Thal DVM Dipl. ABVP

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