Microbiota of semen from stallions in Sweden identified by MALDI-TOF

Ziyad Al-Kass,Erik Eriksson,Elisabeth Bagge,Margareta Wallgren,Jane M Morrell

doi:10.1016/j.vas.2020.100143

Abstract

Stallion semen is known to contain environmental bacteria and normal commensals, and in some cases may contain opportunistic pathogens. These bacteria may negatively influence sperm quality during storage before artificial insemination. The bacteria isolated depend on the culture conditions and method of identification; therefore, the aim of this study was to identify as many of the bacteria present in stallion semen as possible by culturing aliquots of semen under a variety of conditions. Eleven semen samples were available: five extended semen samples from one stud together with a sample of the extender, and six raw semen samples from another stud. Aliquots of semen samples were cultured on different agars and under specialized conditions; individual bacterial colonies were identified using Matrix-assisted laser desorption ionization time of flight mass spectrometry. Approximately 55% of the bacteria could be identified, with 20 bacterial taxa being isolated from semen samples from the five stallions on the first stud and 11 taxa from the semen samples from six stallions on the second stud. Staphylococcus spp. were present in all samples, and Micrococcus spp. were present in all of the extended semen samples although they were also isolated from the extender. The number of bacteria in colony forming units per mL varied considerably among samples. Only one microbe known to be associated with equine infertility, Pseudomonas spp., was isolated from three samples, albeit in low numbers. In conclusion, bacterial culture followed by MALDI-TOF does not identify all bacteria present in stallion semen samples. In-depth knowledge of which microbes are likely to be present is useful in determining their effects on sperm quality and, where appropriate, developing protocols for effectively controlling microbial growth.

Highlights

Bacteria are normally found on the genital organs and skin of the abdomen in stallions, where they form part of the normal flora
The bacteria isolated depend on the culture conditions and method of identification; the aim of this study was to identify as many of the bacteria present in stallion semen as possible by culturing aliquots of semen under a variety of conditions
The remaining taxa were Staphylococcus and Streptococcus, which are commensals on skin, mucus membranes and the respiratory tract; Kytococcus and Propionobacterium, which are commensals on skin Al‐Kass et al (2018); Neisseria which is a commensal of mucosa; Mycoplasma which is present in the oral cavity and urogenital tract; Oligella which is a commensal of the urogenital tract and may cause opportunistic infections (Roussau et al, 1987); Kocuria which are isolated from the human oropharynx (Al‐Kass et al, 2018); and Psychrobacter, which is found in water but has been isolated occasionally from human beings

Summary

Introduction

Bacteria are normally found on the genital organs and skin of the abdomen in stallions, where they form part of the normal flora. Semen becomes contaminated with bacteria as it passes out of the male reproductive tract. The reproductive tract of the mare has a well-defined response to deal with bacteria deposited during mating (Parlevliet & Samper, 2000; Samper & Tibary, 2006), Mycoplasma equigenitalium, M. subdolum and Acholeplasma spp. are responsible for cases of infertility, endometritis and abortions in mares The semen extender used to maintain sperm viability serves as a nutrient broth to support bacterial multiplication, and these bacteria are transferred to the mare during insemination. They may affect sperm quality, during storage. Antibiotics are routinely added to commercial semen doses to prevent multiplication of the contaminating bacteria (Morrell & Wallgren, 2014)

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