Susceptibility evaluation of Anaplasma marginale to antimicrobials used in controlling Bovine Anaplasmosis

• Grant number: 17/23199-8
• Support type: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): December 01, 2017
• Effective date (End): December 31, 2020
• Field of knowledge: Biological Sciences - Parasitology - Entomology and Malacology of Parasites and Vectors
• Principal researcher: Sirlei Daffre
• Grantee: Beatriz Iglesias Alonso
• Home Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 13/26450-2 - Molecular characterization of the interactions among ticks, rickettsiae and vertebrate hosts, AP.TEM

Abstract

Bovine anaplasmosis, caused by the Gram-negative bacteria Anaplasma marginale, is a world-wide rickettsial disease, being of great economic importance for Brazil. The infection by this bacterium can cause anemia, abortion and presents high mortality rates in some localities. In Brazil, the ticks R. microplus and R. annulatus are the most common biological vectors. A. marginale is an obligate intracellular a-proteobacterium, proliferating in bovine erythrocytes. In the tick-vector, the bacterium initially infects the gut epithelial cells and then reaches another tissues such as the salivary glands. The control of bovine anaplasmosis is carried out mainly by the use of acaricides (combating the biological vector) and antibiotics. The chemoprophylaxis and treatment of clinical disease with antibiotics are the most commonly used prevention methods in rural properties. Among the available drugs, oxytetracycline, imidocarb dipropionate and enroflaxin are the most widely used. The continuous use of antibiotics, often in sub-therapeutic doses, may select resistant strains of A. marginale. The main goal of this research project is to develop an in vitro test to assess sensitivity to antimicrobials, including resistant strains. During the first year of the project, the conditions of infection of erythrocytes by the Jaboticabal strain of A. marginale were standardized. However, a very slow growth of A. marginale was observed over 8 days, which is inappropriate to assess antimicrobial susceptibility. Therefore, we started the use of tick cells Ixodes scapularis (ISE6) as host cells. Infection of A. marginale in ISE6 proved to be effective, with bacterial growth of one order of magnitude on the fifth day after infection. Thus, ISE6 cells will be used to establish an in vitro test for sensitivity to antimicrobials. (AU)