Effect of bismuth subnitrate on in vitro growth of major mastitis pathogens

Abstract

The mode of action of bismuth subnitrate in teat sealant formulations as a preventative for intramammary infections during the dry period is unknown. Although previous studies proposed an action mechanism-creating a physical barrier in the teat canal to prevent bacterial invasion-it has not been proven experimentally. We hypothesized that bismuth subnitrate has an inhibitory effect on bacterial growth, in addition to its barrier effect. The objective of this study was to assess the effect of bismuth subnitrate on bacterial growth of major mastitis-causing agents. A strain of Streptococcus uberis (SR115), 2 strains of Staphylococcus aureus (SA3971/59 and SA1), and a strain of Escherichia coli (P17.14291) were tested in vitro for their ability to grow in the presence or absence of bismuth subnitrate. Disk diffusion testing, impedance measurement, and evaluation of bacterial growth in shaking conditions were the methods used to test this hypothesis. A reduction of growth in the presence of bismuth subnitrate occurred for all the strains tested. However, we observed strain and species variations in the extent of growth inhibition. These results suggest that an inhibitory effect on bacterial growth by bismuth subnitrate could partially explain the efficacy of bismuth-based formulations for preventing intramammary infections over the dry period. Further research is required to test the effect of teat sealant formulations on bacterial growth.

Colonization and local host response following intramammary Staphylococcus chromogenes challenge in dry cows

“…We hypothesize this might be due either to the fact that no samples could be taken in the dry period, or because the internal teat sealant might have a negative influence on the survival of S. chromogenes IM in the dry period. Indeed, a negative effect of bismuth subnitrate on the in vitro growth of major mastitis pathogens was already described by others [54]. Therefore, our study data suggest that a quarter is more likely to be colonized with S. chromogenes IM during the entire dry period if a dose of 10 000 000 CFU is used in a quarter that is not sealed.…”

A Randomized Controlled Trial of Teat-Sealant and Antibiotic Dry-Cow Treatments for Mastitis Prevention Shows Similar Effect on the Healthy Milk Microbiome

“…Bonsaglia et al ( 25 ) also found lower Chao1 and Shannon indices at DIM 7 with teat sealant compared to the combination of antibiotic plus teat sealant, though not significant. Bismuth subnitrate products not only act as a physical barrier, but also show inhibitory effect on bacterial growth ( 16 ): this can partially explain the efficacy of bismuth-based formulations in the prevention of intramammary infections over the dry period. Other products have been tested as teat sealants for their physical-barrier action, like wax plugs or intramammary polystyrene devices, but were unsuccessful in the long-term protection of cows against IMI and mastitis ( 52 – 54 ).…”

“…Internal teat sealants (ITS) are a class of non-antimicrobial products that has proven to be just as efficacious as dry-cow therapy (DCT) in the prevention of IMI during the dry period. ITS may provide just a physical barrier or also inhibit bacterial growth ( 16 ). The use of an ITS in a SDCT program ensures that all healthy quarters have some form of protection against dry-period IMI.…”

Administration of internal teat sealant in primigravid dairy heifers at different times of gestation to prevent intramammary infections at calving

“…Though ITS is generally considered to be a preventative tool rather than a treatment for IMI, the substantial proportion of quarters that cured their IMI after administration warrants such consideration. Bismuth subnitrate was recently reported to inhibit the growth of some mastitis-causing pathogens in vitro (Notcovich et al, 2020). This curing effect may be due to the inhibitory effects of ITS on the growth of microorganisms (Notcovich et al, 2020), but also by physical irritation of the epithelium in the teat cistern.…”

“…Bismuth subnitrate was recently reported to inhibit the growth of some mastitis-causing pathogens in vitro (Notcovich et al, 2020). This curing effect may be due to the inhibitory effects of ITS on the growth of microorganisms (Notcovich et al, 2020), but also by physical irritation of the epithelium in the teat cistern. As shown in Figure 5, the bismuth subnitrate component of Lockout has a monoclinic crystalline structure similar to that described for Orbeseal (Zoetis) by Kimbrell et al (2017).…”