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Folia microbiologica2026; doi: 10.1007/s12223-026-01578-z

Identification and phylogenetic analysis of Mannheimia haemolytica isolated from nasal samples of horses.

Abstract: The Mannheimia genus, which is part of the upper respiratory tract microbiota, harbours species that have the potential to cause progressive infections, such as haemorrhagic septicaemia and enzootic pneumonia, when the host immune system is suppressed. Among these species, Mannheimia haemolytica is considered the most pathogenic, and horses can be a host for this agent. This study aimed to investigate the occurrence of Mannheimia haemolytica in horses with and without respiratory clinical signs and to assess the potential pathogenic significance of isolates recovered from animals through serotyping, detection of virulence-associated genes, and phylogenetic analysis. In this study, a total of 134 nasal swab samples were collected from horses reared in 15 farms in five provinces of Türkiye. Of these animals, 20 exhibited clinical signs of respiratory disease, while 114 were clinically healthy. All samples were analysed using cultural, phenotypic, and molecular methods for the detection of M. haemolytica. Ten (7.46%) isolates were identified as M. haemolytica by culture and subsequently confirmed by 16 S rDNA-PCR analysis. All M. haemolytica isolates were obtained exclusively from horses with clinical signs such as high fever, lethargy, loss of appetite, rhinorrhea, and coughing. Serotyping revealed that nine isolates belonged to Serotype 2 and one to Serotype 1. The leukotoxin (lkt) gene was detected in only one (11.11%) Serotype 2 isolate. Similarly, the Ssa-1 protein gene was detected in one Serotype 1 strain. One Serotype 2 isolate carrying the lktCABD operon clustered closely with leukotoxin-associated sequences of both M. haemolytica and M. glucosida, while remaining consistent with its independently established species identity. These findings indicate that M. haemolytica, including strains carrying virulence-associated markers, can be recovered from the upper respiratory tract of horses exhibiting respiratory disease. The exclusive recovery of M. haemolytica from clinically affected horses suggests a potential association with equine respiratory disease, although its causal role requires further investigation.
© 2026. Institute of Microbiology, Academy of Sciences of the Czech Republic, v.v.i.
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Publication Date: 2026-09-03 PubMed ID: 42690607PubMed Central: 10357255DOI: 10.1007/s12223-026-01578-zGoogle Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Research Overview

  • This study investigated the presence and genetic characteristics of Mannheimia haemolytica bacteria in horses with and without respiratory symptoms in Türkiye.
  • The research aimed to determine whether these bacteria, known to cause respiratory infections in animals, are associated with respiratory disease in horses.

Introduction and Background

  • Mannheimia genus: Part of the normal microbiota in the upper respiratory tract of animals, containing species that can cause infections when the host’s immune system is compromised.
  • Mannheimia haemolytica (M. haemolytica): The most pathogenic species, known to cause diseases like haemorrhagic septicaemia and enzootic pneumonia in other animals.
  • Host relevance: Horses can act as hosts for M. haemolytica, but its role in equine respiratory disease requires clarification.

Objectives

  • To detect the occurrence of M. haemolytica in nasal samples from horses both with and without respiratory clinical signs.
  • To analyze the potential pathogenicity of the isolated strains using serotyping, detection of virulence genes, and phylogenetic analysis.

Methods

  • Sample collection: 134 nasal swabs were taken from horses housed in 15 farms across five provinces in Türkiye.
  • Clinical status: 20 horses showed clinical respiratory signs; 114 appeared clinically healthy.
  • Detection techniques:
    • Cultural and phenotypic methods for initial identification.
    • 16S rDNA-PCR for molecular confirmation of M. haemolytica isolates.
  • Serotyping: To classify isolates into known serotypes (types of strains based on their surface structures).
  • Virulence gene detection: Focused on leukotoxin (lkt) gene and Ssa-1 protein gene, both associated with pathogenicity.
  • Phylogenetic analysis: Used to understand genetic relationships of isolated strains with known M. haemolytica and related species.

Key Findings

  • Isolation rate: 10 (7.46%) of the 134 samples were positive for M. haemolytica.
  • Clinical association: All positive isolates were from horses exhibiting clinical signs (fever, lethargy, loss of appetite, rhinorrhea, coughing), none from healthy horses.
  • Serotyping results:
    • 9 isolates belonged to Serotype 2.
    • 1 isolate belonged to Serotype 1.
  • Virulence gene distribution:
    • The leukotoxin (lkt) gene was found in only one Serotype 2 isolate (11.11% of that serotype group).
    • The Ssa-1 protein gene was detected in the single Serotype 1 isolate.
  • Phylogenetic relationships: The Serotype 2 isolate with the lktCABD operon grouped closely with leukotoxin gene sequences of both M. haemolytica and M. glucosida, supporting its species identity.

Interpretation and Implications

  • The exclusive detection of M. haemolytica in symptomatic horses suggests a possible link between the bacteria and equine respiratory disease.
  • Presence of virulence-associated genes in some isolates indicates potential for these strains to contribute to disease severity.
  • Phylogenetic analysis confirms the identity of isolates and their genetic relatedness to known pathogenic strains.
  • Despite the association, direct causality between M. haemolytica and respiratory disease in horses is not yet established and requires further research.

Conclusions

  • M. haemolytica can be recovered from the upper respiratory tract of horses showing respiratory illness but not from healthy ones.
  • Some strains carry genes linked to virulence, suggesting these bacteria might play a role in equine respiratory infections.
  • Further studies are necessary to confirm whether M. haemolytica is a direct cause of respiratory disease in horses or an opportunistic pathogen.

Cite This Article

APA
Yeni DK, Paksoy Y, Balevi A, Büyük F, Ashraf A, Padron B, Toslak EE. (2026). Identification and phylogenetic analysis of Mannheimia haemolytica isolated from nasal samples of horses. Folia Microbiol (Praha). https://doi.org/10.1007/s12223-026-01578-z

Publication

Folia microbiologica
ISSN: 1874-9356
NlmUniqueID: 0376757
Country: United States
Language: English

Researcher Affiliations

Yeni, Derya Karataş
  • Faculty of Veterinary Medicine, Department of Microbiology, Necmettin Erbakan University, Konya, 42310, Türkiye. derya.karatasyeni@erbakan.edu.tr.
Paksoy, Yavuzkan
  • Ceyhan Faculty of Veterinary Medicine, Department of Animal Science and Animal Nutrition, Division of Animal Husbandry, Çukurova University, Adana, 01250, Türkiye.
Balevi, Aslı
  • Faculty of Veterinary Medicine, Department of Microbiology, Selçuk University, Konya, 42250, Türkiye.
Büyük, Fatih
  • Faculty of Veterinary Medicine, Department of Microbiology, Kafkas University, Kars, 36300, Türkiye.
Ashraf, Asma
  • Department of Zoology, Government College University, Faisalabad, 38000, Pakistan.
Padron, Beatriz
  • Faculty of Veterinary Medicine, Department of Microbiology, Selçuk University, Konya, 42250, Türkiye.
Toslak, Emine Eda
  • Faculty of Veterinary Medicine, Department of Microbiology, Selçuk University, Konya, 42250, Türkiye.

Conflict of Interest Statement

Declarations. Authorship: The manuscript has been read, approved, and accepted for submission to the journal by all authors. Use of generative AI and AI-assisted technologies statements: No AI or AI-assisted technologies were used in the preparation of this manuscript. Competing interests: The authors declare no competing interests.

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