Original Article J Vet Sci 2019, 20(1), 58-62ㆍhttps://doi.org/10.4142/jvs.2019.20.1.58 J VS Received 20 Aug. 2018, Revised 10 Nov. 2018, Accepted 30 Nov. 2018 *Corresponding author: Tel: +39-0881786330; Fax: +39-0881786205; E-mail: viviana.manzulli@izspb.it This study was presented in part at the 16th Medical Biodefense Conference; October 28–31, 2018; Munich, Germany. Journal of Veterinary Scienceㆍⓒ 2019 The Korean Society of Veterinary Science. All Rights Reserved. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN 1229-845X eISSN 1976-555X Evaluation of in vitro antimicrobial susceptibility of Bacillus anthracis strains isolated during anthrax outbreaks in Italy from 1984 to 2017 Viviana Manzulli 1, * , Antonio Fasanella 1 , Antonio Parisi 1 , Luigina Serrecchia 1 , Adelia Donatiello 1 , Valeria Rondinone 1 , Marta Caruso 1 , Sabine Zange 2 , Alina Tscherne 2 , Nicola Decaro 3 , Carmine Pedarra 1 , Domenico Galante 1 1 Anthrax Reference Institute of Italy, Experimental Zooprophylactic Institute of Puglia and Basilicata Regions, Foggia 71121, Italy 2 Bundeswehr Institute of Microbiology, Munich 80937, Germany 3 Department of Veterinary Medicine, University of Bari, Valenzano 70010, Italy Anthrax, caused by Bacillus anthracis, is a non-contagious infectious disease that affects a wide range of animal species (primarily ruminants) including humans. Due to the often-fatal outcome in humans, quick administration of definitely effective antimicrobials is crucial either as prophylaxis or as a clinical case therapy. In this study, 110 B. anthracis strains, temporally, geographically, and genetically different, isolated during anthrax outbreaks in Italy from 1984 to 2017, were screened using a broth microdilution method to determine their susceptibility to 16 clinically relevant antimicrobial agents. The strains were isolated from various matrices (human, animal, and environmental samples) and were representative of thirty distinct genotypes previously identified by 15-loci multiple-locus variable-number of tandem repeats analysis. The antimicrobials tested were gentamicin, ceftriaxone, streptomycin, penicillin G, clindamycin, chloramphenicol, vancomycin, linezolid, cefotaxime, tetracycline, erythromycin, rifampin, amoxicillin, ciprofloxacin, doxycycline, and trimethoprim. All isolates were susceptible to most of the tested antimicrobials, with the exception of trimethoprim for which all of them showed high minimal inhibitory concentration values. An intermediate level of susceptibility was recorded for ceftriaxone and cefotaxime. Although the Centers for Disease Control and Prevention recommend the use of doxycycline, ciprofloxacin, penicillin G, and amoxicillin for treatment of human cases and for post-exposure prophylaxis to anthrax spores, this study shows a high degree of in vitro susceptibility of B. anthracis to many other antimicrobials, suggesting the possibility of an alternative choice for prophylaxis and therapy. Keywords: Bacillus anthracis; Antimicrobial susceptibility testing; Anthrax treatment; Minimum inhibitory concentration Introduction Anthrax is a serious infectious disease, that mainly affects ruminants (farmed and wild animals) and can be transmitted to humans exposed to infected animals or infected products of animal origin (farmers, vets, butchers, carders, workers in the textile industry, etc.) [7]. The etiological agent of anthrax is Bacillus anthracis, a Gram-positive rod-shaped bacterium able to produce extremely resistant spores that, under unfavorable environmental conditions, can survive in the environment for several decades. In particularly receptive animals (cattle, buffalo, sheep, goats, deer, and other wild ungulates), anthrax develops without apparent symptoms but has a fatal outcome characterized by sudden death due to acute or hyperacute septicemia and leakage of uncoagulated blood from natural openings. In humans, anthrax can occur in three different forms with clinical signs dependent on the penetration route of the pathogen: cutaneous (generally non-fatal), pulmonary, and gastrointestinal [7]. Moreover, another fatal form has been described in drug users occurring after the intravenous injection of drugs contaminated with anthrax spores [2]. B. anthracis lives most of its existence in the form of a spore in soil, until ideal conditions develop allowing it to enter the reproductive cycle, which is presented mainly in domestic and wild ruminants. In animals, B. anthracis expresses its