Animal, Mycoplasma strains and Bacteria
120 commercial Leghorn chickens were obtained from Chia Chau Chicken Farm (Harbin, Heilongjiang, China), which did not undergo vaccination and raised to day 7. The MG strain Rlow was obtained from Harbin Institute of Veterinary Medicine, Chinese Academy of Agricultural Science. The mycoplasmas were cultured at 37 ℃ as described previously [13]. MG was used to challenge chickens at the density of 1 × 109 CCU/ml (color change unit per milliliter) in the culture medium. E.coli O78, was isolated from chickens infected with colibacillosis in our laboratory and cultured in Mueller-Hinton Broth (Beijing Aoboxing BIO-TECH CO., LTD). The concentration of E.coli was adjusted to 109 CFU/ml before infection.
Chicken Infection And Groupings
A total of 120 White Leghorn chickens were purchased from Chia Chau Chicken Farm (Harbin, Heilongjiang, China). The infectious dose was diluted into 0.2 ml MG medium in left caudal thoracic air sac at the 7th day, and injected intraperitoneally with 0.1 ml of E.coli at day 10 in chickens. From the 13th day, 120 chickens were randomly divided into 10 groups, of which 10 groups were treated with different CMC (Group A-J). The chickens of treatment groups were given as the dose of 450 mg/kg continuously by intragastric administration for a week [14].
UD design
The six Chinese herbs were purchased from Runhe Chinese medicine processing plant Ltd. (Harbin, China) and were selected as the six factors and each factor set 10 levels for UD. The minimum dose range for each TCM is 0 and the highest value refers to the use and dosage as mentioned in Chinese Pharmacopoeia by State Pharmacopoeia Committee (Edition, 2015). As shown in Table.1, the experiment was arranged following the uniform table U*10(106). The method of water extraction is described previously [15].
Standardization Of Evaluation Index And Calculating Comprehensive Index
The min-max normalization method was adopted to eliminate the effects of different dimension [16]. Four indices were used to calculate the total score, including the MIC of MG and E.coli in vitro, air sac and tracheal lesion scores in vivo, and these four were standardized using the formula (1). The composite score was calculated following formula (2). (see Formula 1 in the Supplementary Files)
i represents sample serial number; Ri is non-dimensionalized value after conversion by min-max normalization method; xi is the ith measured value, xmax is the maximum of all measured values, xmin is the minimum of all measured values. (see Formula 2 in the Supplementary Files)
D represents the comprehensive evaluation index; Ri is nondimensionalized value after conversion by min-max normalization method.
Evaluation rules for respiratory diseases assessment
The severity of the gross air sac lesions was scored on a scale of 0 - 3 as described previously [17]. The tracheal lesion score was determined from the same three discontinuities of the trachea. The tracheal infection score was also calculated on the basis of 0 to 3 scoring system [18]. The MIC of MG and E.coli in vitro were divided into 10 serial dilutions ranged from 640 μg/mL to 1.25 μg/mL. We define the results based on the number of plates that detect MIC and calculate them in formula (1).
Mic Determination
MIC was determined using a microdilution technique with MG titers of 2 × 105 CCU/mL. A 0.1 mL aliquot of that media was added to a 96-well plate and another 0.1 mL CMC (1280 µg/mL) was added to the first plate. A series of concentrations of CMC were diluted by doubling (Range from 640 µg/mL to 1.25 µg/mL) and the last 0.1 ml discarded. Another 0.1 mL aliquot of prepared MG was supplemented to each well, achieving the final titers of 1 × 105 CCU/mL. The above method is the same to the test of E.coli. Tests were conducted in triplicate and the method of determination was used as described previously [12, 19].
Statistical analysis
Data are presented as mean results ± standard deviation (SD). Multi-nonlinear regression equation was made by the method of secondary polynomial gradual regression in DPS software [20].