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

Abstract

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.

Association between Mastitis Occurrence in Dairy Cows and Bedding Characteristics of Compost-Bedded Pack Barns

“…In our study, Escherichia coli (12.5% of the total samples) and environmental streptococci (>15.0%) were the most frequent pathogens isolated from CM cases, which agrees with previous reports (11.0% and >15.0%; 6.0% and >10.0%; 22.6% and 12.7% [14,31,32], respectively). Coliforms and environmental streptococci are described in many cow habitats, including bedding materials [11,33].…”

“…Coliforms (including Escherichia spp., Klebsiella spp., and other Gramnegative bacteria) and environmental streptococci (e.g., Streptococcus uberis and Streptococcus dysgalactiae) are the most prevalent pathogens causing clinical mastitis (CM) on many modern dairy farms that have successfully controlled contagious mastitis [11][12][13]. Additionally, non-aureus staphylococci and environmental streptococci are described as one of the pathogens groups most isolated from subclinical mastitis (SCM) cases worldwide [14,15]. Bedding was described as an important source of udder exposure to environmental mastitis pathogens [16].…”

Immune profiling of experimental murine mastitis reveals conserved response to mammary pathogenic Escherichia coli, Mycoplasma bovis, and Streptococcus uberis

“…Mastitis, inflammation of the mammary gland, is an important disease in dairy animals and breast-feeding women. The disease is caused by ascending infection through the teat canal of pathogenic bacteria such as Escherichia coli, Streptococcus uberis, Staphylococcus aureus, and Mycoplasma bovis (Shpigel et al, 1998;Dyson et al, 2022;Gelgie et al, 2022;Kurban et al, 2022). Mastitis is a good example of an infectious disease caused by a dominant pathogen and heeding the concept of Koch's postulates.…”

Milk as diagnostic fluid for udder health management

“…According to a recent mapping review, close to 300 different organisms have been isolated from quarter milk samples of dairy cows but literature on their relevance to udder health was available for fewer than 90 species. 41 Based on observational, experimental and molecular studies, species of micro-organisms differ in their ability to survive in the environment and within the mammary gland, and in their response to various types of treatment. 42,43 Consequently, identification of the predominant pathogens causing IMI is widely considered to be an essential step in investigating milk quality or udder health issues.…”