Characterization of resistance profile of Leptospira interrogans serovar Pomona isolated from swine in Brazil

The objective of this study is the characterization of antimicrobial sensitivity of 9 Leptospira interrogans serovar Pomona isolates. Leptospira not only represents a risk to human health, but the study of its susceptibility also lies on the development of its treatment and control in farms to reduce economic losses (e.g. piglets' abortion). Existing studies have used L. interrogans human isolates serogroup Icterohaemorrhagiae serovar Icterohaemorrhagiae/Copenhageni to determine strain susceptibility to existing treatments. This study introduces the susceptibility profile of L. interrogans serovar Pomona from swine, an important host species.

9 Leptospira interrogans Sorovar Pomona were isolated from diseased and apparently healthy swine. For isolation, kidney and abortion samples were collected. For the inoculum, cultures were grown at 30°C for 7 days and then diluted. Broth microdilution was performed and adapted for use with the Sensititre® Standard Susceptibility MIC Plate BOPO6F following Murray and Hospenthal protocol (2004). 50µL of inoculum were added in each Sensititre® MIC Plate well. After 3 days of incubation, 5 μL of 10X alamarBlue® were added to each well. MICs were assessed visually as the lowest antibiotic concentration in the wells without alamarBlue® color change at the 5th incubation day.

Every isolate had high MIC values to tiamulin, gentamicin, chlortetracyclin, oxytetraciclin, neomycin, tilmicosin, trimethoprim/sulfamethoxazole, spectinomycin, sulfadimethoxine. High fluoroquinolone MIC values were also observed. Every isolate appeared to be sensitive to penicillin, ampicillin, ceftiofur, tylosin tartrate and tulathromycin. MIC variability was observed for florfenicol. One isolate presented a slightly different profile with low MIC values for gentamicin, florfenicol, chlortetracyclin and oxytetracycline, while apparently resistant to clindamycin. Clinically, the most important findings are the sensitive strains to β-lactams, the most common treatment for leptospirosis; and MIC values increase for aminoglycosides, tetracyclines and macrolides, widely used in animal production. Our results corroborate previous studies presenting high MIC values for tetracycline, trimethoprim/sulfamethoxazole, sulfadimethoxine, and chloramphenicol/florfenicol. However, higher MIC values for tiamulin, gentamicin, neomycin and spectomycin were unexpected and their veterinary use requires attention.

Pomona strains of this study showed different antimicrobial susceptibility profiles compared to profiles previously described for other strains of L. interrogans. More research is needed to define serovar susceptibility profiles.

Disclosure of Interest: None Declared.