The racehorse bacterium (Lactobacillus equicursoris)-Erakina

Lactobacillus equicursoris is a novel bacterial species isolated along with four other bacterial strains from the faeces of thoroughbred racehorses.

Genus Lactobacillus: An overview

Bacteria belonging to this genus are ubiquitously present in both humans and animals. They form a significant part of the microbiota of all animals and are usually commensals in nature. They form symbiotic relationships with their hosts and provide the following benefits to the host in exchange for nutrition and shelter[Lactobacillus equicursoris]-

  • They help in the reduction of complex molecules into simple molecules.
  • They improve digestion and maintain gut health.
  • They maintain the pH levels of both the gastrointestinal tract and the urogenital tract in humans.
  • They boost immunity and mitigate the effects of infections of the digestive and reproductive tract.[Lactobacillus equicursoris]

Physiology and morphology

Bacteria belonging to this genus have certain physiological and morphological features which make them distinct from other bacterial species. [Lactobacillus equicursoris]These physiological and morphological characteristics are as follows-

  • They are rod-shaped.
  • They do not form spores.
  • They are facultative anaerobes; metabolism can take place even in the absence of oxygen.
  • They are Gram-positive; they do not possess an outer lipid membrane but do possess a thick peptidoglycan outer layer as part of their cell walls.
  • They are catalase-negative; they do not use oxygen molecules as the terminal electron acceptor during the process of respiration.
  • When observed in colonies, they appear singly or in pairs. 
  • They produce lactic acid as a by-product of carbohydrate fermentation.[Lactobacillus equicursoris]
Lactobacillus equicursoris paracasei
SEM image of a species of Lactobacillus.

Colony characteristics

All Lactobacillus species exhibit common morphological features when observed in the form of colonies. Some of these shared features are as follows-

  • The colour of the colony ranges from white to brown.
  • The size of the colonies produced is usually between 2 and 5 mm in diameter.
  • Colonies are usually round in shape with irregular edges.
  • The edges are umbonate; the presence of a protrusion along the edges.
  • The colonies produced are usually opaque in appearance.
  • The texture of the colonies is usually rough. 
  • The profile of the colonies produced is raised in the shape of a convex.

Lactobacillus equicursoris: An introduction

Lactobacillus colonies
Growth of a Lactobacillus species on an agar plate

This novel species of Lactobacillus was first isolated from the faeces of a thoroughbred racehorse indicating that this bacterium is part of the microflora of horses. Upon analysis, it was found that this species resembled the Lactobacillus species, Lactobacillus delbrueckii, by almost 97%.

After isolating the bacterium, it was grown on an appropriate nutrient medium and analysed using 16s RNA sequence analysis leading to the construction of phylogenetic trees that confirmed its place in the genus Lactobacillus.

Physiology and morphology 

Some of the distinct physiological and morphological features of the novel isolated bacterial strain are as follows-

  • Cells are in the shape of curved rods.
  • They appear singly when grown as colonies. 
  • They are non-spore-forming. 
  • They are Gram-positive and are also catalase-negative.
  • They are homofermentative organisms and produce D-Lactic acid as a product of D-glucose fermentation.
  • They are obligate anaerobes meaning they can only grow in the absence of oxygen.

Optimal growth conditions

This novel bacterial species requires certain growth conditions to grow optimally. These conditions are as follows-

  • They grow well at room temperature. 
  • They need to be incubated in oxygen-free conditions. 
  • They are acid-resistant and grow well in low pH conditions. 
  • These bacteria were grown on MRS nutrient agar plates.


Racehorse breeds
A thoroughbred horse

Lactobacillus equicursoris was isolated from the rectum and stomach of equines belonging to the breed, Thoroughbred. This breed is specifically used for horse racing. Some of the prominent features of this horse breed are as follows-

  • The height of these horses lies in the range of 157-173 cm.[Lactobacillus equicursoris]
  • These horses have a well-chiselled head, a chest that is prominent and deep along with a long neck and lean body.
  • The commonly observed colours of this breed of horses are- bay, brown, black and chestnut.
  • The presence of only a single colour is a sign of good quality breeding among horse breeders and racers.[Lactobacillus equicursoris]


The novel bacterial species Lactobacillus equicursoris was isolated from the faeces of a thoroughbred racehorse (male) along with four other bacterial species. The species was identified as part of the genus Lactobacillus after due analysis via 16s RNA sequencing analysis and phylogenetic studies. This species is symbiotic and forms a part of the microflora of the gastrointestinal tract of horses (equines).[Lactobacillus equicursoris]

Internal links:

The starter bacterium (Lactobacillus delbrueckii)-Erakina

A novel pathogenic bacterium (Lactobacillus psittaci)-Erakina

An Introduction to Bacterial Cell- Erakina

External links:

Read more about Lactobacillus optimal growth condition

By -Deepika Thilakan

Date: 27/06/2022

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