Levofloxacin

Peptides were purchased from GL Biochemistry Inc. (Shanghai, China). The purity of peptides was ≥5%. Amino acid sequences and physical characteristics for peptides are shown in Supplementary Table S1. TRIzol reagent and Super Script^TM III kits were purchased from TaKaRa Inc. (Dalian, China). Ceftazidime, piperacillin and levofloxacin were purchased from Solarbio Inc. (Beijing, China). C4-HSL standards is purchased from Sigma (Sigma, China). All other reagents were of analytical grade. The MDR P. aeruginosa (MRPA) strain 0108 (MRPA0108) was obtained from the Clinical Laboratory Department, the First Affiliated Hospital of Dalian Medical University. MRPA0108 exhibits resistance to gentamicin, kanamycin, ampicillin, cefepime, streptomycin, tetracycline, amoxicillin, and ciprofloxacin. Identification and antimicrobial susceptibility testing (AST) of MRPA0108 were performed by an automated MicroScan WalkAway 96 Plus system (Siemens Ltd., Germany) at the First Affiliated Hospital of Dalian Medical University.

Standard S. aureus strain ATCC 29213 was provided by the China Medical Culture Collection Center (Beijing, China). Ten clinical strains of S. aureus (MRSA 4642 and 4670; MSSA 4611 and 4672; S. aureus 4563, S. aureus 4612, S. aureus 4623, S. aureus 4643, S. aureus 4644 and S. aureus 4474) were isolated from the China-Japan Friendship Hospital. Five MRSA strains, MRSA 3183, MRSA 2961, MRSA 2047, MRSA 41122 and MRSA 3335, were isolated from the First Hospital of Jilin University, Changchun, China. This study was conducted in accordance with the declaration of Helsinki. This study was conducted with approval from the Ethics Committee of Xinxiang Medical University. Carnosol was purchased from Sigma-Aldrich, and a stock solution was dissolved in dimethyl sulfoxide (Sigma-Aldrich). Seven antibiotic drugs (penicillin G, vancomycin, oxacillin, ciprofloxacin, levofloxacin, tetracyclines and gentamicin) were purchased from Beijing Solarbio Science & Technology Co., Ltd., Beijing, China. All strains were grown in tryptic soy broth medium (TSB, Qingdao Hope Bio-Technology Co., Ltd., Qingdao, Shandong, China) at 37°C.

The standard disk diffusion assay was used to determine the sensitivity or resistance of LAB to conventional antibiotics. Paper disks containing ampicillin (10 μg), penicillin (10 μg), amoxycillin (10 μg), norfloxacin (10 μg), levofloxacin (5 μg), gentamicin (120 μg), streptomycin (10 μg), amikacin (30 μg), and erythromycin (15 μg), which were purchased from Solarbio Technology Co., Ltd. (Beijing, China), were employed for the antibiotic resistance tests (Lee et al., 2014 (link)). From the MRS broth culture of each one of the test strains, 100 μL was mixed with 8 mL of liquid MRS agar, over-layered on a pre-solidified agar plate and allowed to solidify, and then disks were aseptically placed onto the center of plates using sterile forceps. The plates were incubated for 48 h at 30°C in an anaerobic chamber. The results were recorded according to the interpretive category defined by the Clinical and Laboratory Standards Institute (CLSI) (Sharma et al., 2017 (link)). The tests were carried out in triplicate.