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Biological and molecular characterization of a sheep pathogen isolate of Mannheimia haemolytica and leukotoxin
Dounia Bkiri1,2, Noha Semmate1, Zineb Boumart1
1Department of Research and Development, Multi-chemical Industry, Mohammedia, Morocco.
Background And Aim:
Mannheimia haemolytica (Mha) is a common agent of pneumonia in ruminants globally, causing economic losses by morbidity, mortality, and treatment costs. Infection by Mha is often associated with or promoted by respiratory viral pathogens and environmental conditions. Infections due to Mha have rarely been described in small ruminants. This study reports the biological and molecular characteristics of a new Moroccan Mha isolate from small ruminants presenting typical respiratory symptoms. We also studied the cultural parameters, growth kinetics, and Lkt excretion of the isolate and its pathogenicity on laboratory animals and small ruminants.
Materials And Methods:
Suspected pasteurellosis cases in sheep and goat flocks in Morocco were investigated. A local strain of Mha was isolated and identified using biochemical and molecular methods. Polymerase chain reaction-targeting specific genes were used for serotyping and phylogenetic analyses; further, leukotoxin production, cytotoxicity, and pathogenicity of the isolate in mice, goats, and sheep were investigated.
Results:
Phylogeny analysis revealed 98.76% sequence identity with the USA isolate of 2013; the strain growth with a cycle of 9-10 h with leukotoxin secretion was detected by NETosis and quantified by cytotoxicity and mortality of mice. Goat and sheep infections cause hyperthermia, with characteristic postmortem lesions in the trachea and lung.
Conclusion:
A local isolate of Mha from sheep that died of pneumonia was characterized for the 1st time in North Africa using biological and molecular methods. Although growth on appropriate culture media is accompanied by intense leukotoxin secretion, experimental infections of sheep and goats cause hyperthermia and typical lesions of pneumonia.
Insights
A new Moroccan isolate of Mannheimia haemolytica (Mha) was characterized. This bacterium causes pneumonia in small ruminants, exhibiting leukotoxin secretion and pathogenicity in experimental infections.
Area of Science:
- Veterinary Microbiology
- Ruminant Pathology
Background:
- Mannheimia haemolytica (Mha) is a significant global cause of ruminant pneumonia, leading to substantial economic losses.
- Mha infections are less frequently documented in small ruminants and often linked to viral co-infections and environmental stressors.
- This study focuses on a novel Mha isolate from Moroccan small ruminants with respiratory symptoms.
Purpose of the Study:
- To characterize the biological and molecular features of a newly identified Moroccan Mha isolate from small ruminants.
- To investigate the isolate's growth kinetics, leukotoxin excretion, and pathogenicity in laboratory animals and small ruminants.
Main Methods:
- Isolation and identification of Mha using biochemical and molecular techniques from suspected cases in Morocco.
- Serotyping and phylogenetic analysis via polymerase chain reaction (PCR).
- Assessment of leukotoxin production, cytotoxicity, and pathogenicity in mice, goats, and sheep.
Main Results:
- Phylogenetic analysis showed high sequence identity (98.76%) with a 2013 USA isolate.
- The Mha strain exhibited a growth cycle of 9-10 hours with significant leukotoxin secretion, confirmed by NETosis and quantified via cytotoxicity and mouse mortality.
- Experimental infections in goats and sheep resulted in hyperthermia and characteristic postmortem lesions in the trachea and lungs.
Conclusions:
- This marks the first biological and molecular characterization of a local Mha isolate from sheep pneumonia cases in North Africa.
- Despite intense leukotoxin secretion during in vitro growth, experimental infections induced typical pneumonia symptoms and lesions in sheep and goats.
