Tracing Mastitis Pathogens-Epidemiological Investigations of a Pseudomonas aeruginosa Mastitis Outbreak in an Austrian Dairy Herd

Abstract

The present study describes an outbreak of Pseudomonas (P.) aeruginosa mastitis in a 20-cow dairy herd where throughout genotyping of isolates reusable udder towels were identified as the source of infection. Sampling of cows during three herd surveys and bacteriological culturing showed that P. aeruginosa was isolated from nine cows with a total of 13 infected quarters. Mastitis occurred as mild clinical or subclinical infection. P. aeruginosa was additionally isolated from a teat disinfectant solution, containing N-(3-aminopropyl)-N-dodécylpropane-1,3-diamine 1 as active component, and microfiber towels used for pre-milking teat preparation. Disc diffusion antimicrobial resistance testing revealed that all isolates were susceptible to piperacillin, piperacillin-tazobactam, ceftazidime, cefepime, aztreonam, imipenem, meropenem, tobramycin, amikacin, and ciprofloxacin. Thirty-two isolates of milk samples and 22 randomly selected isolates of one udder towel and of the teat disinfectant solution were confirmed as P. aeruginosa with matrix-assisted laser desorption, ionization time-of-flight mass spectrometry (MALDI Tof MS). Isolates were further characterized with rep-PCR and randomly amplified polymorphic DNA (RAPD) as well as with multiple locus variable-number tandem repeat analysis (MLVA). Results obtained in this study suggested that one single strain was responsible for the whole outbreak. The transmission occurred throughout a contaminated teat cleaning solution as a source of infection. The farmer was advised to change udder-preparing routine and to cull infected cows.

Keywords: MLVA; Pseudomonas aeruginosa; mastitis; transmission route; udder cleaning microfiber towels.

Figure 1

Increase of MSCC from July until September 2018 (data from individual monthly test day SCC).

Figure 2

Colony morphology (pigmentation) of five P. aeruginosa strains belonging to the same MLVA type. All 54 isolates (32 from milk, 11 from the teat cleaning solution and eleven from the udder wipes) were identified as P. aeruginosa by MALDI-TOF MS. All score levels ranged between 2.11 and 2.45, indicating a reliable species identification. The species-specific PCR yielded an amplicon of the expected size (391 bp). With the various applied methods (ERIC-, REP-, BOX and RAPD-PCR, MLVA) all 54 isolates were indistinguishable.