Diagnosing Intramammary Infection: Meta-Analysis and Mapping Review on Frequency and Udder Health Relevance of Microorganism Species Isolated from Bovine Milk Samples

Daryna Kurban, Jean Philippe Roy, Fidèle Kabera, Annie Fréchette, Maryse Michèle Um, Ahmad Albaaj, Sam Rowe, Sandra Godden, Pamela R.F. Adkins, John R. Middleton, Marie Lou Gauthier, Greg P. Keefe, Trevor J. DeVries, David F. Kelton, Paolo Moroni, Marcos Veiga dos Santos, Herman W. Barkema, Simon Dufour

Research output: Contribution to journalReview articlepeer-review

11 Scopus citations


Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry provides accurate species-level identification of many, microorganisms retrieved from bovine milk samples. However, not all those microorganisms are pathogenic. Our study aimed to: (1) determine the species-specific prevalence of microorganisms identified in bovine milk of apparently healthy lactating quarters vs. quarters with clinical mastitis (CM); and (2) map current information and knowledge gaps on udder health relevance of microorganisms retrieved from bovine milk samples. A mixed study design (meta-analysis and mapping review) was chosen. We gathered several large Canadian, US and Brazilian data sets of MALDI-TOF results for organisms cultured from quarter milk samples. For meta-analysis, two datasets (apparently healthy quarters vs. CM samples) were organized. A series of meta-analyses was conducted to determine microorganisms’ prevalence. Then, each species reported was searched through PubMed to investigate whether inflammation (increased somatic cell count (SCC) or signs of CM) was associated with microorganism’s recovery from milk. A total of 294 different species of microorganisms recovered from milk samples were identified. Among 50,429 quarter-milk samples from apparently healthy quarters, the 5 most frequent species were Staphylococcus chromogenes (6.7%, 95% CI 4.5–9.2%), Aerococcus viridans (1.6%, 95% CI 0.4–3.5%), Staphylococcus aureus (1.5%, 95% CI 0.5–2.8%), Staphylococcus haemolyticus (0.9%, 95% CI 0.4–1.5%), and Staphylococcus epidermidis (0.7%, 95% CI 0.2–1.6%). Among the 43,924 quarter-milk CM samples, the 5 most frequent species were Escherichia coli (11%, 95% CI 8.1–14.3%), Streptococcus uberis (8.5%, 95% CI 5.3–12.2%), Streptococcus dysgalactiae (7.8%, 95% CI 4.9–11.5%), Staphylococcus aureus (7.8%, 95% CI 4.4–11.9%), and Klebsiella pneumoniae (5.6%, 95% CI 3.4–8.2%). When conducting the PubMed literature search, there were 206 species identified by MALDI-TOF for which we were not able to find any information regarding their association with CM or SCC. Some of them, however, were frequently isolated in our multi-country dataset from the milk of quarters with CM (e.g., Citrobacter koseri, Enterococcus saccharolyticus, Streptococcus gallolyticus). Our study provides guidance to veterinarians for interpretation of milk bacteriology results obtained using MALDI-TOF and identifies knowledge gaps for future research.

Original languageEnglish (US)
Article number3288
Issue number23
StatePublished - Dec 2022

Bibliographical note

Funding Information:
This research is supported by a contribution from the Dairy Research Cluster 3 (Dairy Farmers of Canada (Ottawa, ON, Canada) and Agriculture and Agri-Food Canada (Ottawa, ON, Canada)) under the Canadian Agricultural Partnership AgriScience Program, and through the Mastitis Network (Saint-Hyacinthe, QC, Canada. The first author (DK) was also supported by the NSERC CREATE in Milk Quality Program. The senior author (SD) was supported by a Discovery grant from the Natural Sciences and Engineering Research Council of Canada (RGPIN-2020-05237; Ottawa, ON, Canada).

Publisher Copyright:
© 2022 by the authors.


  • cattle
  • mastitis
  • milk microbiology
  • species-specific prevalence

PubMed: MeSH publication types

  • Journal Article
  • Review


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