A mouse mastitis model to study the effects of the intramammary infusion of a food-grade Lactococcus lactis strain

Abstract

Lactococcus lactis is one of the most important microorganisms in the dairy industry and has “generally recognized as safe” (GRAS) status. L. lactis belongs to the group of lactic acid bacteria (LAB) and is encountered in a wide range of environments. Recently, the use of the intramammary infusion of a live culture of LAB has been investigated as a new antibiotic alternative for treating mastitis in dairy ruminants. Controversial results are described in literature regarding its efficacy and safety. In this study we conducted in-depth investigation of the mammary gland immune response induced by intramammary inoculum of a live culture of L. lactis LMG 7930 using the mouse mastitis model. Overnight cultures either of L. lactis (≈ 107 CFU) or of the mastitis pathogens Staphylococcus chromogenes (≈ 105 CFU) or S. aureus (≈ 102 CFU/ml) were injected into the mouse inguinal glands. A double injection, consisting of S. chromogenes first and then L. lactis, was also investigated. Bacterial recovery from the gland and inflammatory cell infiltration were assessed. L. lactis-treated and control glands were analysed for proinflammatory cytokine production. Microbiological results showed that L. lactis was able to survive in the mammary gland 24 h post infection, as were the mastitis pathogens S. chromogenes and S. aureus. L. lactis reduced S. chromogenes survival in the glands and increased its own survival ability by coexisting with the pathogen. Histology showed that L. lactis-treated glands presented variable histological features, ranging from undamaged tissue with no inflammatory cell infiltrate to severe PMN infiltrate with focal areas of tissue damage. S. aureus-treated glands showed the most severe histological grade of inflammation despite the fact that the inoculum size was the smallest. In contrast, most S. chromogenes-treated glands showed normal structures with no infiltration or lesions. Significant increases in IL-1β and TNF-α levels were also found in L. lactis-inoculated glands. The above findings seem to suggest that food-grade L. lactis at a high-inoculum dose such as an overnight culture may elicit a suppurative inflammatory response in the mammary gland, thus becoming a potential mastitis-causing pathogen. Because of the unpredictable potential of L. lactis in acting as a potential mastitis pathogen, this organism cannot be considered a safe treatment for bovine mastitis.

Impact of intramammary inoculation of inactivated Lactobacillus rhamnosus and antibiotics on the milk microbiota of water buffalo with subclinical mastitis

“…The scientific background behind the experimental design was that Lactobacillus rhamnosus , in combination with other Lactic acid bacteria, was able to modulate the pathogenic environment in the vaginal tract by regulating Escherichia coli infection and inflammation of the bovine endometrium [29]. At least so far, live cultures of probiotic were not found to improve mouse [46], cow [18,22,47] or ewe [24] mastitis. On the contrary, most of the Lactobacilli and Lactococci strains used so far for in vivo studies have been demonstrated to exert a pro-inflammatory activity: Lactococcus lactis , for example, is regarded as a pathogen causing mastitis [48,49].…”

A Critical Appraisal of Probiotics for Mastitis Control

“…It is worth noticing that the characteristics that distinguish L. lactis mastitis isolates from dairy starter strains (higher tolerance to body temperature, lysozyme and bile, wider carbohydrate fermentation capacity and better adhesion to MECs) are considered desirable probiotic attributes ( 113 ). According to their pathogenic potential, in most studies, LABs elicited an immune response that was potentially harmful and detrimental to the secretion of milk when infused into the MG. A mouse mastitis model was used to conduct in depth investigations of the immune response induced by the intramammary infusion of a food-grade L. lactis strain ( 100 ). The authors concluded that the strain used could not be considered safe for the MG. Other studies showed that the infusion of L. lactis into the bovine MG induced an intense recruitment of neutrophils, increased concentrations of acute phase proteins in milk, and overexpression of genes encoding the chemokine IL-8 and the pro-inflammatory cytokine IL-1 β ( 102 , 103 ).…”

Adipose stem cells in reparative goat mastitis mammary gland

“…For analysis of the infiltrate of inflammatory cells we used methodology of Camperio et al [26], 0- absence of lesions, absence of interstitial and/or alveolar inflammatory cell infiltrate and undamaged tissue, 1- focal to multifocal, slight interstitial and/or alveolar inflammatory cell infiltrate and undamaged tissue, 2- moderate interstitial and/or multifocal alveolar of inflammatory cells infiltrate and undamaged tissue 3- interstitial and/or diffuse alveolar infiltrate of inflammatory cells and focal areas of tissue injury, 4- interstitial and/or diffuse alveolar infiltrate, severe inflammatory cells and extensive necrotic areas.…”