Is Galleria mellonella model a good alternative to study virulence in Staphylococcus aureus from bovine mastitis?

Staphylococcus aureus is one of the agents of bovine mastitis of hardest control due to a complex pathogenesis comprising a variety of virulence factors, which ensures its persistence in the mammary gland, causing significant health and economic losses. Therefore, understanding the pathogenesis of this agent is imperative. Galleria mellonella has stood out as an invertebrate animal model for the study of infectious diseases that affect several hosts. This work aimed to evaluate G. mellonella larvae as an experimental model for the study of virulence phenotypes in an S. aureus population isolated from bovine mastitis. Thirty genetically divergent S. aureus strains were chosen based on PFGE analysis. After experimental infection, larvae survival rates, bacterial growth in hemolymph, melanization intensity of the dorsal vessel, and histological characteristics of the infected tissues were evaluated. The G. mellonella model showed a clear diversity in the S. aureus pathogenicity pattern, allowing the differentiation of strains with virulence phenotypes ranging from high to low degrees. Histological analysis confirmed that the strains tested were capable of inducing the formation of nodules and melanization spots in the dorsal vessels of the larvae in different magnitudes. The strains 16S-717, 19C-828, and 31S-1443 presented the highest virulence intensity among the bacteria tested and will be used further for the generation of S. aureus mutant populations to prospect genetic targets aimed to develop control strategies of bovine mastitis. Altogether, our results suggest that G. mellonella is an attractive and low-cost animal model for characterizing virulence phenotypes of large S. aureus populations.

Nutritive value of elephant grass hay ammoniated by urea / Valor nutritivo do feno de capim elefante amonizado por uréia

The aim of this study was to evaluate the effect of ammoniation by urea on the nutritional value of elephant grass hay harvested after flowering. A completely randomized design, in double factorial designs with an additional treatment: 4 urea doses (2, 4, 6 and 8%) x 2 treatment periods (30 and 45 days) + 1 (Control) with four replicates each, was employed. Dry matter, ash, ether extract, neutral detergent fiber, acid detergent fiber, cellulose, lignin, neutral detergent fiber corrected for the ash and the protein, total nitrogen, acid detergent insoluble nitrogen, neutral detergent insoluble nitrogen, non-protein nitrogen, in vitro gas production and carbohydrates fractionation were analyzed. The treatments influenced the contents of DM, EE, NDF, ADF, lignin, cellulose, NDFap, fraction A + B1, fraction B2, fraction C, TN, NPN, ADIN, NDIN, L and Vf2. There was a positive linear effect of urea dose for NDF, ADIN, NDIN and L, positive linear effect on fraction A + B1, NT and NPN, and positive quadratic effect for Vf2, with absolute maximum point of 4.5%. Elephant grass hay harvested after flowering has its nutritional value improved, with a minimum dose of 4.5% urea on a dry matter basis.(AU)

Objetivou-se avaliar o efeito da amonização com ureia sobre o valor nutritivo do feno de capim elefante colheitado após florescimento. O estudo foi delineado, em esquema fatorial duplo com um tratamento adicional: 4 doses de ureia (2, 4, 6 e 8%) x 2 período de tratamento (30 e 45 dias) + 1 tratamento controle, com 4 repetições cada. As variáveis analisadas foram: matéria seca (MS), cinzas, extrato etéreo (EE), fibra em detergente neutro (FDN) e ácido (FDA), FDN corrigida para cinzas e proteínas (FDNcp), celulose, lignina, nitrogênio total (NT), nitrogênio insolúvel em detergente ácido (NIDA) e neutro (NIDN), nitrogênio não proteico (NNP). Produção de gases in vitro proveniente dos carboidratos não fibrosos (Vf1) e fibrosos (Vf2), taxa de fermentação dos carboidratos não fibrosos (k1) e fibrosos (k2) e tempo de colonização bacteriana do substrato (L), além do fracionamento de carboidratos. Os tratamentos influenciaram os teores de MS, EE, FDN, FDA, lignina, celulose, FDNcp, fração A + B1, fração B2, fração C dos carboidratos, NT, NNP, NIDA, NIDN, L e Vf2. Houve efeito linear decrescente de dose de ureia para FDNcp, NIDA, NIDN e L, crescente para fração A+B1, NT e NNP, e, quadrático crescente de dose de ureia para Vf2, com ponto máximo absoluto de 4,5% de ureia obtido após derivar a equação de regressão aos 45 dias de tratamento do feno. Concluindo que feno de capim elefante colheitado após florescimento tem seu valor nutricional melhorado, com dose mínima de 4,5% de ureia em base da matéria seca.(AU)