ISSN 2398-2993      

Mastitis: Streptococcus uberis



  • Cause: Streptococcus uberis (S. uberis) is the most prevalent cause of mastitis in the United Kingdom (UK).
  • UK prevalence is reported to be 23.5% for clinical mastitis cases and 13.8% for subclinical mastitis cases.
  • Although S. uberis is traditionally referred to as an environmental pathogen, research has shown that S. uberis can act as both an environmental and a contagious pathogen.
  • Signs:
    • Alterations to the milk:
      • Elevated Somatic Cell Count (SCC), as demonstrated by a positive California Milk Test (CMT) .
      • Presence of clots and sometimes discoloration of the milk .
    • Swelling, edema, pain and heat may be identified in the affected udder.
    • Other signs such as pyrexia, decreased rumination and decreased appetite may be identified in approximately 10-20% of cases.
  • Diagnosis: S. uberis may be identified by culture, polymerase chain reaction (PCR) or Matrix-assisted laser desorption/ionization (MALDI-TOF) in commercial laboratories.
  • Treatment and prevention:
    • Various antibiotic regimes are effective against S. uberis clinical mastitis.
    • Antibiotics known to be effective against S. uberis include: penicillin penicillin, tetracyclines tetracyclines, chloramphenicol and rifampicin.
    • Vaccines are under development, but their efficacy has not been proven at the time of writing (Jan 2022).
  • Prognosis:
    • A successful outcome is influenced by various factors including:
      • Rapid identification and treatment of clinical cases.
      • Host immune function.
      • The use of adjunctive therapy such as non-steroidal anti-inflammatory drugs (NSAIDs) Anti-inflammatory drugs: overview.
  • Treatment of chronic cases during the lactation period can be unrewarding.
  • The dry period offers the best chance for a cure and effective Dry cow therapy (DCT) Dry cow therapy: overview should be utilized.



Predisposing factors

General risk factors for mastitis

  • Increasing parity.
  • Early stage of lactation.
  • Very dirty udders.
  • Quarters with very severe Hyperkeratosis Teat scoring and hyperkeratosis (score 4 out of 4).

Specific risk factors for S. uberis

  • Cow and quarter level risk factors:
    • Older cows are more likely to become infected compared to first and second parity cows.
    • Cows in early lactation (0 to 120 days in milk) are more likely to become infected than cows in later lactation (>121 days in milk).
    • Quarters that have previously been infected by S. uberis are at a higher risk of recurrent infections, as well as quarters having previously had an elevated SCC.
    • Severe Hyperkeratosis Teat scoring and hyperkeratosis of the teat end.
  • Risk factors which have been shown to not significantly increase the risk of S. uberis mastits include:


  • It has been shown that after experimental infection of the lactating mammary gland, S.uberis was predominately found in the luminal areas of the secretory alveoli and ductular tissues.
  • The appearance of clinical signs coincides with an increase in the SCC of the gland to >5,000 CFU/ml, alongside an increase in bacterial count of >5,000 CFU/ml.
  • The host response begins with a large influx of neutrophils, which has been shown to be ineffective in reducing the number of bacteria in experimental infections.
  • S.uberis has been found to have been internalized by macrophages in one study, suggesting that the macrophages may be effective in clearing the bacteria. However, as macrophages allow the bacteria to replicate inside them, their effectiveness may be limited.


  • Incubation: the appearance of clinical signs of mastitis were delayed with experimental infections of S. uberis (72 to 108 hours), when compared to E.coli E coli mastitis  (8 to 16 hours), suggesting the possibility of a lag phase in the growth of S. uberis within the mammary gland.
  • Duration: this will vary on different factors including previous udder damage, time lag between initiation of infection and treatment and efficacy of the host’s immune response.


  • S. uberis tends to be an opportunistic infection and in the majority of cases will occur as a result of environmental contamination of the teat.
  • S. uberis has been discovered in many different places within the dairy environment, as well as on cow sites. For S. uberis to be present within the environment, there must have been cows present within the last 2-3 weeks.
  • S. uberis intramammary infections are found in both grazing and housed herds.
  • The prevalence of S. uberis infections tends to be highest around calving.
  • The vast majority of S. uberis intramammary infections lead to subclinical infections.


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Kromker V et al (2014) Bovine Streptococcus uberis intramammary infections and mastitis. Case Report Clinical Microbiology 3 (157).
  • Breen J E, Green M J & Bradley A J (2009) Quarter and cow risk factors associated with the occurrence of clinical mastitis in dairy cows in the United Kingdom. J Dairy Sci 92 (6), 2551–2561 PubMed.
  • Ericsson et al (2009) Microbial aetiology of acute clinical mastitis and agent-specific risk factors. Vet Microbio 137 p90-97
  • Sherwin & Breen (2022) Streptococcus uberis-associated mastitis in dairy herds : dealing with outbreak and improving control. In Practice 44 (1) p32 – 45.
  • Pitkala A, Koort J & Bjorkroth J (2008) Identification and antimicrobial resistance of Streptococcus uberis and Streptococcus parauberis isolated from bovine milk samples. J Dairy Sci 91 (10), 4075–4081 PubMed.
  • Denis M et al (2006) Bactericidal activity of macrophages against Streptococcus uberis is different in mammary gland secretions of lactating and drying off cows. Vet Immunol Immunopathol 114 (1/2), 111–120 PubMed.
  • Rambeaud M, Almeida R A & Oliver S P (2004) Growth of Streptococcus uberis in skim milk obtained from Holstein and Jersey dairy cows during different stages of lactation. J Vet Med 51 (3), 143–145 PubMed.
  • Sherwin VE, Egan SA, Green MJ, Leigh JA. 2021 Survival of Streptococcus uberis on bedding substrates. Vet J. Oct;276:105731. doi: 10.1016/j.tvjl.2021.105731. Epub 2021 Aug 12. PMID: 34391916.
  • Zadoks R N et al (2001) Cow- and Quarter- Level Risk Factors for Streptococcus uberis and Staphylococcus aureus Mastitis. J Dairy Sci 84 (12), 2649–2663 PubMed.

Other sources of information

  • Bradley A J et al (2012) Control of Mastitis and Enhancement of Milk Quality. Dairy Herd Health, CAB International, UK. pp 115-168.
  • Petersson-Wolfe & Currin (2012) Streptococcus Uberis: A Practical Summary for Controlling Mastitis. Available at:
  • Leigh J (2010) Streptococcus Uberis – Are We Nearer an Effective Treatment? British Mastitis Conference Proceedings. pp 23-39. 
  • Leigh J A (2010) Streptococcus Uberis - Are We Nearer an Effective Control? Ed: Pocknee B. British Mastitis Conference 2010. Sixways, UK. pp 23–29.


  • University of Nottingham 

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