Antibiotic susceptibilities of livestock isolates of leptospira

Abstract

Leptospirosis is the most common zoonotic disease and is endemic worldwide. The antibiotic susceptibilities of Leptospira strains isolated from both humans and animals are poorly documented. This issue is particularly important for isolates from food-producing animals which are regularly exposed to antibiotic treatments. This study assessed the susceptibility of 35 leptospira strains isolated from food-producing animals of diverse geographical origins between 1936 and 2016 to the antimicrobial agents used most commonly in animals. A broth microdilution method was used to determine the susceptibilities of Leptospira strains isolated from livestock to 11 antibiotics. All isolates were susceptible to penicillin, amoxicillin, clavulanate, cephalexin, ceftriaxone, doxycycline, tetracycline, streptomycin, enrofloxacin and spectinomycin, but not polymyxin [minimum inhibitory concentration (MIC) ≥ 4 μg/L]. For tetracycline and doxycycline, the MIC was significantly higher for the recent isolates from Sardinia, Italy than for the other isolates. Antimicrobial susceptibilities were also determined with 10- and 100-fold higher inocula. High inocula significantly diminished the antibacterial effect by at least 10-fold for enrofloxacin (MIC ≥256 μg/L), streptomycin (MIC ≥16 μg/L) and tetracycline (MIC ≥32 μg/L), suggesting selection of resistant strains for high inocula. These findings contribute to the assessment of whether certain antibiotics are potentially useful for the treatment of leptospirosis, and point out the risk of failure for some antibiotics during infection with a high inoculum in both animals and humans. This study strengthens the need to detect and prevent the emergence of antimicrobial resistance of this major emerging zoonotic pathogen.

Bacteriostatic and Bactericidal Effect of Tigecycline on Leptospira spp.

“…The obtained results were consistent with other data available in literature, according to which tetracycline MIC values for Leptospira reference strains or isolates are, on average, between 0.25 and 6.25 µg/mL [ 29 , 30 , 31 , 32 , 33 , 34 ]. Considering that the results obtained for tetracycline were very similar to those reported in literature, it is correct to suppose that the results for MIC and MBC for tigecycline were also similar, not under- or overestimated.…”

“…The knowledge of antibiotic treatments against leptospirosis is strictly connected to in vivo clinical evaluation, usually in patients with severe and acute Leptospira infections [ 1 , 4 , 23 ]. Very few studies explored the efficacy and mechanisms of the action of new chemotherapeutic molecules [ 29 , 30 , 31 ]. This is the first investigation showing the in vitro effect of tigecycline against Leptospira spp.…”

“…Studies on the antimicrobial effects on Leptospira isolates or reference cultures are scarce, probably due to problems in the determination of antibiotic susceptibility [ 1 , 23 ]. A standardized microdilution method has been developed to accurately investigate the Leptospira antibiotic susceptibility, resolving the difficulties related to preventing the contamination of the medium, evaluating the bacterial growth, and reproducibility of the assay [ 29 , 30 , 31 ].…”

Determination of minimum inhibitory and minimum bactericidal concentrations of Brazilian strains of Leptospira spp. for streptomycin sulphate

“…These results showed a wide variation in the susceptibility of the strains against streptomycin, not only regarding MIC, but also MBC. The obtained outcomes are consistent with the values observed in other studies such as Correia et al [1] and Liegeon et al [2], and could define all studied strains as sensitive to streptomycin. These findings validate the usage of streptomycin in field conditions, a fact that can be considered positive, since this is the most common antibiotic used for the treatment of leptospirosis in livestock, particularly ruminants.…”

Preliminary Evaluation of In Vitro Bacteriostatic and Bactericidal Effect of Salt on Leptospira spp.

“…Sterile NaCl was added to EMJH medium in order to reach a stock solution with 21.05% of salt; this allowed to start to test a concentration of 20% of NaCl, considering the inoculum addition, as reported below. The minimum inhibitory concentration (MIC) determination was performed by the broth microdilution method, as previously reported [37,38]. Leptospira cultures were quantified with spectrophotometry using optical density at 420 nm (Multiskan™ FC Microplate Photometer; Thermo Fisher Scientific, Haverhill, MA, USA) to reach a concentration which corresponds approximately to 1.5 × 10 8 cfu/mL: considering that an OD ranging between 0.052 to 0.1 corresponds to approximately 2-3 × 10 8 leptospires per mL, cultures were diluted in EMJH to reach this OD, using EMJH as blank; after, standardized culture was diluted 1:2 in EMJH to reach the desired inoculum concentration [39,40].…”