Leuconostoc mesenteroides-Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Introduction

Leuconostoc mesenteroides is a species of lactic acid bacteria that plays a significant role in food fermentation and preservation. It is characterized by its ability to convert sugars into lactic acid, a process that enhances the shelf life and safety of many foods. This bacterium is commonly found in various natural environments, including plant material and fermented foods such as sauerkraut and kimchi. L. mesenteroides is distinguished by its spherical to ovoid cells, which form chains and are Gram-positive. It is facultatively anaerobic, thriving in both the presence and absence of oxygen. Beyond its applications in the food industry, this bacterium has also been explored for its potential in biotechnological applications, including the production of dextran, a polysaccharide used in pharmaceuticals. However, it is important to handle it with care in industrial settings due to its ability to cause spoilage in certain food products.


Morphology

Leuconostoc mesenteroides exhibits a distinctive morphology, primarily characterized by its spherical to ovoid-shaped cells that often appear in pairs or short chains. These cells are Gram-positive, indicating that they retain the crystal violet stain used in the Gram staining method, due to the thick peptidoglycan layer in their cell walls. They typically range from 0.5 to 0.7 micrometers in diameter, with a smooth surface texture. Unlike some other bacteria, it lacks flagella and is non-motile, relying on the movement of the medium for dispersion.

Leuconostoc mesenteroides ssp. cremoris growth on CLED agar of urine culture
Fig. Leuconostoc mesenteroides ssp. cremoris growth on CLED agar of urine culture

Pathogenicity

Leuconostoc mesenteroides, primarily known for its crucial role in food fermentation, exhibits low virulence. It occasionally causes opportunistic infections, such as bacteremia and endocarditis, in people with weakened immune systems, though these cases are rare. The bacterium’s capacity to form biofilms may enhance its persistence and resistance in clinical environments, contributing to its pathogenic potential. Despite these risks, it is more celebrated for its positive impact on the food industry and its probiotic qualities. The majority of encounters with this bacterium, through the consumption of fermented foods, are not only safe but also beneficial. Therefore, the pathogenicity of L. mesenteroides does not pose a significant threat to healthy individuals. Its contributions to health and industry greatly surpass the infrequent and isolated instances of infection, highlighting its overall benefit to human health and food technology.

Lab Diagnosis

Diagnosing L. mesenteroides in laboratories involves culturing suspected samples on MRS agar, a selective medium that promotes lactic acid bacteria growth while suppressing others. This bacterium’s ability to grow at 10°C aids in distinguishing it from other lactic acid bacteria.

Leuconostoc mesenteroides ssp. cremoris Gram positive cocci in Gram staining of culture microscopy at a magnification of 4000x
Fig. Leuconostoc mesenteroides ssp. cremoris Gram positive cocci in Gram staining of culture microscopy at a magnification of 4000x

Gram staining reveals its characteristic Gram-positive cocci, which may form chains. Biochemical tests further identify L. mesenteroides by its sugar fermentation profile, including specific tests for gas production from glucose and dextran production from sucrose.

Leuconostoc mesenteroides in wet mount of culture microscopy at a magnification of 1600X
Fig. Leuconostoc mesenteroides in wet mount of culture microscopy at a magnification of 1600X

Molecular techniques like PCR and 16S rRNA gene sequencing provide definitive identification by comparing the genetic material of the isolate with known sequences of L. mesenteroides. MALDI-TOF MS offers rapid, accurate species-level identification through the bacterium’s unique protein fingerprint. These combined diagnostic methods ensure precise detection and identification of L. mesenteroides in clinical and food industry settings, leveraging its unique characteristics for accurate differentiation from other bacteria.

Treatment

Treatment of infections caused by L. mesenteroides is relatively rare due to its low virulence and infrequent occurrence as a pathogen in humans. When infections do occur, they are typically treated with antibiotics, although the bacterium shows variable susceptibility to different antibiotic classes.

Leuconostoc mesenteroides Antibiogram Report
Fig. Leuconostoc antimicrobial susceptibility testing (AST) Result

Vancomycin is often considered an effective antibiotic against L. mesenteroides, whereas the organism may exhibit resistance to certain other antibiotics, such as penicillin, due to the inherent characteristics of its cell wall.

Leuconostoc mesenteroides Antibiogram Report
Fig. Leuconostoc mesenteroides Antibiogram Report

It is crucial to perform susceptibility testing on the isolated strain to guide the selection of the most effective antibiotic treatment. In cases of serious infection, such as endocarditis, combination antibiotic therapy and supportive care may be necessary to ensure the best outcome.

Prevention

Preventing Leuconostoc mesenteroides infections requires strict hygiene, sterilization, and continuous monitoring in healthcare and food industries. Healthcare settings must enforce rigorous infection control practices, like maintaining hand hygiene and sterilizing equipment, to protect immunocompromised patients from opportunistic infections. Food producers must adhere to sanitation protocols, controlling the temperature and pH of products to prevent L. mesenteroides growth. Regular testing during fermentation spots contamination early, while using starter cultures can block harmful microbes, including L. mesenteroides. Educating those in food handling and healthcare on prevention strategies is crucial. Implementing rapid detection methods enables quick identification and response to this bacterium. Applying good agricultural practices reduces the microbial load on raw materials, lowering contamination risks. This comprehensive approach effectively manages L. mesenteroides-related health risks in sensitive environments.


Keynotes

Keynotes concerning Leuconostoc mesenteroides highlight its significance in both industrial applications and rare instances of pathogenicity:

  • Beneficial Role in Fermentation: L. mesenteroides plays a crucial role in the fermentation of foods, contributing to flavor development, texture improvement, and preservation. It is integral to the production of traditional fermented foods such as sauerkraut, kimchi, and certain dairy products.
  • Production of Dextran: This bacterium is known for its ability to produce dextran, a polysaccharide used in the food industry as a thickener and stabilizer, and in medicine as a blood plasma extender and in drug delivery systems.
  • Gram-Positive Cocci: Morphologically, L. mesenteroides presents as Gram-positive cocci that can form chains, facilitating its identification in laboratory settings.
  • Facultative Anaerobe: It thrives in both the presence and absence of oxygen, which allows it to occupy a variety of niches in food fermentation processes.
  • Low Virulence Pathogen: While generally considered safe and beneficial in food applications, it can act as an opportunistic pathogen in immunocompromised individuals, leading to rare infections such as bacteremia or endocarditis.
  • Antibiotic Resistance and Sensitivity: It exhibits variable susceptibility to antibiotics, being resistant to some like penicillin but sensitive to others such as vancomycin, highlighting the need for susceptibility testing in cases of infection.
  • Prevention and Control: In both healthcare and food production, adherence to strict hygiene and sanitation practices is essential to prevent the growth and spread of it, particularly focusing on temperature and pH control to inhibit its activity.

Further Readings

  • https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-018-3452-7
  • https://www.sciencedirect.com/topics/immunology-and-microbiology/leuconostoc-mesenteroides
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2600284/
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5364644/
  • https://www.mdpi.com/2076-2607/9/8/1612
  • https://annalsmicrobiology.biomedcentral.com/articles/10.1007/s13213-014-0933-9
  • https://www.culturecollections.org.uk/nop/product/leuconostoc-mesenteroides-2

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