# The Phenotypic Divergence and Potential Microevolution of a Dominant Mycoplasmopsis bovis ST-52 Clone Within a Closed Dairy Herd in China

## TL;DR

A study in China found that a single Mycoplasmopsis bovis clone can evolve phenotypically within a closed dairy herd, affecting biofilm formation, antibiotic resistance, and cell invasion.

## Contribution

The study provides evidence of microevolution in a dominant M. bovis clone within a closed herd, highlighting adaptive phenotypic changes.

## Key findings

- A single ST-52 clone of M. bovis was found to exhibit significant phenotypic diversity in biofilm formation and antibiotic resistance.
- Isolates showed varying abilities to invade different bovine-derived cell types.
- Genetic identity was maintained despite phenotypic divergence, suggesting microevolution.

## Abstract

Mycoplasmopsis bovis is a significant pathogen causing substantial economic losses in cattle, yet its within-herd microevolution remains poorly understood. This study aimed to characterize phenotypic and genomic variations within a dominant ST-52 clone circulating in a closed dairy herd. We isolated M. bovis from respiratory (n = 11) and milk (n = 5) samples. Phenotypic characterization included biofilm formation, antimicrobial susceptibility testing, and cellular invasion assays. Whole-genome sequencing was performed on four representative isolates to identify genetic variations. All isolates were genetically identical according to MLST (ST-52). However, significant phenotypic diversity was observed. Biofilm formation capacity varied significantly (OD595 from 0.25 to 1.10), and resistance to doxycycline was higher in nose swabs (100%) than milk isolates (20%). Cellular invasion assays demonstrated that all isolates could invade bovine-derived cells (MDBK, MAC-T, EBL, and PBMC), but the invasion efficiency differed by strain and cell type. These findings confirm the circulation of a single genetic lineage within a closed herd while highlighting significant phenotypic diversification in biofilm formation, antibiotic resistance, and cellular invasiveness. The results provide evidence consistent with microevolution and underscore the adaptive potential of M. bovis. This study underscores the adaptive potential of M. bovis during within-host colonization and cross-tissue transmission, providing critical insights for optimizing herd management and treatment strategies.