Use of a proposed antimicrobial susceptibility testing method for Haemophilus parasuis

Abstract

The aim of this study was to examine the antimicrobial susceptibility of 97 Haemophilus parasuis cultured from Australian pigs. As there is no existing standard antimicrobial susceptibility technique available for H. parasuis, methods utilising the supplemented media, BA/SN for disc diffusion and test medium broth (TMB) for a microdilution technique, were initially evaluated with the reference strains recommended by the Clinical and Laboratory Standards Institute. The results of the media evaluation suggested that BA/SN and TMB can be used as suitable media for susceptibility testing of H. parasuis. The proposed microdilution technique was then used with 97 H. parasuis isolates and nine antimicrobial agents. The study found that Australian isolates showed elevated minimum inhibitory concentrations (MICs) for ampicillin (1%), penicillin (2%), erythromycin (7%), tulathromycin (9%), tilmicosin (22%), tetracycline (31%) and trimethoprim-sulfamethoxazole (40%). This study has described potential antimicrobial susceptibility methods for H. parasuis and has detected a low percentage of Australian H. parasuis isolates with elevated antimicrobial MICs.

The determination of minimum inhibitory concentrations of selected antimicrobials for porcine Haemophilus parasuis isolates from the Czech Republic

“…High level of resistance to tetracycline is in agreement with findings in previous studies and our previously published results (Wissing et al 2001;Pejsak et al 2005;Dayao et al 2014). In contrast, low level of resistance to tetracycline has been reported from China (3.6%) but a different breakpoint ≤ 8 μg/ml was used in the study (Zhou et al 2010).…”

“…Based on this proposed criteria, 12 (40%) isolates from our study would belong to a resistance pattern. Tulathromycin resistance has recently been identified in H. parasuis isolates from Australia (Dayao et al 2014). An experimental challenge study demonstrated a failure in protection and development of polyserositis with a high isolation rate of H. parasuis with the metaphylactic use of tulathromycin (Palzer at al.…”

Towards a Standardized Method for Broth Microdilution Susceptibility Testing of Haemophilus parasuis

“…H. parasuis is a fastidious organism which requires specific ingredients or supplements to achieve visible growth in broth, and hence, media which are used to test rapidly growing bacteria are not adequate (6,7). As a consequence, no validated and standardized method is available (7,8), and many diagnostic laboratories are currently unable to offer susceptibility testing of this very important pathogen in pig production.…”

“…H. parasuis is a fastidious organism which requires specific ingredients or supplements to achieve visible growth in broth, and hence, media which are used to test rapidly growing bacteria are not adequate (6,7). As a consequence, no validated and standardized method is available (7,8), and many diagnostic laboratories are currently unable to offer susceptibility testing of this very important pathogen in pig production. However, a few studies investigated the susceptibility status of H. parasuis isolates quantitatively by using media such as veterinary fastidious medium (VFM) or Haemophilus test medium (HTM) for broth microdilution susceptibility testing (7,(9)(10)(11)(12)(13)(14)(15)(16).…”

“…As a consequence, no validated and standardized method is available (7,8), and many diagnostic laboratories are currently unable to offer susceptibility testing of this very important pathogen in pig production. However, a few studies investigated the susceptibility status of H. parasuis isolates quantitatively by using media such as veterinary fastidious medium (VFM) or Haemophilus test medium (HTM) for broth microdilution susceptibility testing (7,(9)(10)(11)(12)(13)(14)(15)(16). VFM is recommended in CLSI standard VET01-A4 for susceptibility testing of Actinobacillus pleuropneumoniae and Histophilus somni (17), while HTM and cation-adjusted Mueller-Hinton broth (CAMHB) supplemented with 2.5% to 5% lysed horse blood (LHB) are CLSI-approved broth media for the testing of fastidious organisms, with HTM being recommended for Haemophilus influenzae and Haemophilus parainfluenzae (18).…”