Comparative Efficacy of Horse and Chicken Serum for the In Vitro Cultivation of Mycoplasma hyorhinis Clinical Isolates

Abstract

Mycoplasma hyorhinis is an important respiratory pathogen in swine, yet optimal culture conditions for high-yield propagation remain undefined. This study compared horse serum (HS) and chicken serum (CS) at graded concentrations (10%, 20%, 30%) for their ability to support in vitro growth of four clinical M. hyorhinis isolates (strains A, B, C, and D). Cultures were prepared in modified Friis medium, and growth performance was assessed by final titer (color changing unit, CCU/mL) and time-to-detection at 10² and 10⁴ CCU/mL. All media supported growth, but HS consistently outperformed CS in both yield and growth kinetics. The highest titers (10⁹ CCU/mL) and shortest detection times (3.6-6 days) were observed in 20% HS for most strains. Increasing HS concentration to 30% reduced yield for several strains, suggesting a concentration-dependent inhibitory effect. CS demonstrated limited but strain-dependent growth support, with comparable performance to HS for strain B at lower thresholds. These findings identify 20% HS as an optimal supplement for efficient M. hyorhinis cultivation, while highlighting the potential of CS as a cost-effective alternative under certain conditions, with implications for diagnostic reagent production and vaccine development.

Keywords: CCU (color changing unit); Mycoplasma hyorhinis; chicken serum; culture medium optimization; horse serum.

Figure 1

Final growth yield of four M. hyorhinis isolates in media supplemented with different sera. The final titer of four clinical isolates was determined after 30 days of incubation in modified Friis medium supplemented with 10%, 20%, or 30% of either horse serum (HS) or chicken serum (CS). The four panels show the results for Strains A, B, C, and D. Bars indicate the mean final titer (Log₁₀ CCU/mL) of three independent biological replicates (n = 3), with error bars representing the standard deviation (SD). Different lowercase letters (a, b, c) above the bars indicate a statistically significant difference between groups (p < 0.05); groups not sharing a common letter are significantly different.

Figure 2

Time-to-detection (10² CCU/mL) for four Mycoplasma strains (Strains A–D) cultured in different serum-based media. Each panel illustrates the result for an individual strain: Strains A, B, C and D. The Y-axis represents the time-to-detection in days required to reach a titer of 10² CCU/mL. The X-axis displays the six different medium groups supplemented with various concentrations of HS or CS. Bars indicate the mean values, and error bars represent the standard deviation. Different lowercase letters (a, b, c) above the bars denote a statistically significant difference in the time-to-detection between groups (p < 0.05); groups that do not share a common letter are significantly different.

Figure 3

Time-to-detection (10⁴ CCU/mL) for four Mycoplasma strains (Strains A–D) cultured in different serum-based media. Each panel illustrates the result for an individual strain: Strains A, B, C and D. The Y-axis represents the time-to-detection in days required to reach the target titer 10⁴ CCU/mL. The X-axis displays the six different medium groups supplemented with various concentrations of HS or CS. Bars indicate the mean values, and error bars represent the standard deviation (n = 3). Bars without error bars for Strain D represent the mean of two replicates (n = 2) due to one replicate failing to reach the target. The absence of a bar for a specific group indicates that the strain failed to reach the target titer of 10⁴ CCU/mL in that medium within the observation period. Different lowercase letters (a, b, c, d) above the bars denote a statistically significant difference between groups (p < 0.05); groups that do not share a common letter are significantly different.