First identification of Bordetella bronchiseptica subclinical mastitis in a lactating dairy cow in New Zealand.

Abstract

Case history: A gland of a cow with a high somatic cell count (385,000 cells/mL at 116 days in milk) was enrolled in a therapeutic subclinical mastitis study following a positive pre-enrolment culture. One week later, the quarter was treated with 1 g of procaine penicillin on three occasions, 12 hours apart (Day 0 and 1). A further milk sample was obtained from the quarter on Days 6, 14, and 21 after initiation of treatment.

Clinical findings: Milk samples were submitted for routine bacteriological culture and matrix-assisted laser desorption/ionised time-of-flight mass spectrometry (MALDI-TOF) analysis. A Gram-negative motile rod was isolated from all samples which could not be speciated using the laboratory's standard panel of biochemical tests. The isolates were identified by MALDI-TOF as Bordetella bronchiseptica. Whole genome sequencing and comparison with publicly available genomic sequences showed that the bovine isolate did not cluster with any previously published B. bronchiseptica sequences.

Diagnosis: Subclinical mastitis caused by infection with Bordetella bronchiseptica.

Clinical relevance: Only one other case report could be found of this organism being identified in milk samples. Greater use of advanced identification systems will likely increase the number of organisms identified from mastitic milk samples. Appropriate identification is important to aid decision-making as, given the response to therapy and laboratory findings, there is a poor likelihood of bacteriological cure with beta-lactam therapy for this organism.