''Mannheimia haemolytica'' is a species of

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

bacteria belonging to the family

Pasteurellaceae The Pasteurellaceae comprise a large family of Gram-negative bacteria. Most members live as commensals on mucosal surfaces of birds and mammals, especially in the upper respiratory tract. Pasteurellaceae are typically rod-shaped, and are a notabl ...

. It is a facultatively anaerobic, non-spore-forming, and non-motile

coccobacillus Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archae ...

. ''M. haemolytica'' is a primary bacterial pathogen implicated in the bovine respiratory disease complex (BRDC), also commonly known as "shipping fever," particularly affecting cattle, sheep, and goats.

History

''Mannheimia haemolytica'' was originally described as ''Pasteurella haemolytica'' by Newsom and Cross in 1932, based on bipolar organisms isolated from cases of pneumonia in sheep and cattle. For decades, it was classified within the genus ''Pasteurella''. However, advances in molecular taxonomy led to a reassessment of the '' asteurellahaemolytica'' complex. In 1999, Angen and colleagues conducted a comprehensive study using DNA–DNA hybridization and 16S rRNA gene sequencing, which demonstrated sufficient genetic divergence to warrant creation of a new genus, ''Mannheimia''.

Pathogenesis

''Mannheimia haemolytica'' primarily colonizes the upper respiratory tract of cattle and other ruminants but can become pathogenic under stress conditions such as transport, crowding, or viral infections. This bacterium secretes leukotoxins, endotoxins, and other virulence factors that damage respiratory tissues and impair host immunity, resulting in severe fibrinous pneumonia.

Clinical signs

Affected cattle commonly exhibit symptoms such as fever, depression, reduced appetite, nasal discharge, coughing, and difficulty breathing. In severe cases, animals can rapidly progress to acute respiratory distress and death if untreated.

Diagnosis

Diagnosis of ''Mannheimia haemolytica'' infection typically involves bacterial culture from nasal swabs, lung tissue, or

bronchoalveolar lavage Bronchoalveolar lavage (BAL), also known as bronchoalveolar washing, is a diagnostic method of the lower respiratory system in which a bronchoscope is passed through the mouth or nose into an appropriate airway in the lungs, with a measured amou ...

samples. Samples are commonly cultured on blood

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from " ogonori" and " tengusa". As found in nature, agar is a mixture of two components, t ...

, where ''M. haemolytica'' forms characteristic β-hemolytic colonies. Confirmation is supported by biochemical tests and species-specific

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...

(PCR) assays. In research and advanced diagnostic contexts,

whole genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing or just genome sequencing, is the process of determining the entirety of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's ...

(WGS) is increasingly used to characterize isolates, monitor strain diversity, and investigate

antimicrobial resistance Antimicrobial resistance (AMR or AR) occurs when microbes evolve mechanisms that protect them from antimicrobials, which are drugs used to treat infections. This resistance affects all classes of microbes, including bacteria (antibiotic resista ...

Treatment and prevention

Effective management of ''Mannheimia haemolytica'' infections involves prompt administration of appropriate

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

, such as

macrolides Macrolides are a class of mostly natural products with a large macrocycle, macrocyclic lactone ring to which one or more deoxy sugars, usually cladinose and desosamine, may be attached. Macrolides belong to the polyketide class of natural prod ...

(e.g., tulathromycin, gamithromycin),

tetracyclines Tetracyclines are a group of broad-spectrum antibiotic compounds that have a common basic structure and are either isolated directly from several species of ''Streptomyces'' bacteria or produced semi-synthetically from those isolated compounds. ...

, or

fluoroquinolones Quinolone antibiotics constitute a large group of broad-spectrum antibiotic, broad-spectrum bacteriocidals that share a bicyclic molecule, bicyclic core structure related to the substance 4-Quinolone, 4-quinolone. They are used in human and ve ...

. However, the emergence of

, including multidrug-resistant strains, underscores the importance of prudent antibiotic use and the need for alternative control strategies. Preventative measures include

vaccination Vaccination is the administration of a vaccine to help the immune system develop immunity from a disease. Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism. In stimulating ...

programs targeting prevalent

serotypes A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their shared reactivity between their su ...

. Studies have shown that vaccines incorporating multiple serotypes, such as A1 and A6, or recombinant proteins like leukotoxin, can enhance protective efficacy. In addition, good husbandry practices such as reducing stress, ensuring adequate ventilation, and avoiding overcrowding can reduce the risk of disease.

References

External links

Overview of ''Mannheimia haemolytica'' infection
– Merck Veterinary Manual {{Taxonbar, from=Q21325785 Pasteurellales Bacteria described in 1932 Animal bacterial diseases