What is the Difference Between Lactose Fermenting and Non-lactose Fermenting Bacteria

The key difference between lactose fermenting and non-lactose fermenting bacteria is that lactose fermenting bacteria are able to convert glucose into cellular energy and lactic acid, while non-lactose fermenting bacteria are unable to convert glucose into cellular energy and lactic acid.

Lactic acid fermentation is a metabolic process that converts glucose or other six-carbon sugars into cellular energy and lactic acid (metabolite lactate). This is an anaerobic fermentation reaction. Lactic acid fermentation takes place in some bacteria and animal cells (muscle cells). Lactose fermenting bacteria are able to carry out lactose fermentation reactions, while lactose non-fermenting bacteria are unable to carry out lactose fermentation reactions.

CONTENTS

1. Overview and Key Difference
2. What is Lactose Fermenting Bacteria
3. What is Non-lactose Fermenting Bacteria
4. Similarities – Lactose Fermenting vs Non-lactose Fermenting Bacteria
5. Lactose Fermenting vs Non-lactose Fermenting Bacteria in Tabular Form
6. Summary – Lactose Fermenting vs Non-lactose Fermenting Bacteria

What are Lactose Fermenting Bacteria?

Lactose fermenting bacteria are the bacteria that have the ability to convert glucose into cellular energy and lactic acid. In these bacteria, the conversion process can take place by using three different pathways: homofermentative pathway, heterofermentative pathway, and bifidum pathway. The bacteria that use the homofermentative pathway convert glucose into two molecules of lactate and use this reaction to carry out substrate-level phosphorylation in order to make two molecules of ATP. Examples of homofermentative bacteria include Streptococcus, Lactococcus, Enterococcus, Pediococcus, and Lactobacillus. Bacteria that follow the heterofermentative pathway produce less lactate and less ATP (one ATP) but produce other end products such as ethanol and CO₂. Examples of these bacteria include Leuconostoc mesenteroides, Lactobacillus bifermentous, and Leuconostoc lactis. Moreover, bifidum pathway produces more ATP (5 ATP) than either homolactic or heterolactic fermentation pathways. Examples of bacteria that use the bifidum pathway are Bifidobacterium bifidum.

Bacterial strains in Escherichia, Citrobacter, Enterobacter, and Klebsiella are able to produce lactic acid for glucose. All these genera belong to the family Enterobacteriaceae. Bacterial strains in these genera can only be separated through biochemical testing, biological tests, whole genome sequencing, and common tests such as H₂S production, motility, use of citrate, indole, methyl red, and Voges-Proskauer tests.

What are Non-lactose Fermenting Bacteria?

Non-lactose fermenting bacteria are unable to convert glucose into cellular energy and lactic acid. These bacteria are also known as non-fermenters. They are taxonomically classified under the phylum Pseudomonadota. Non-lactose fermenting bacteria are unable to catabolize glucose and thus are unable to ferment. However, this does not necessarily exclude these bacteria from catabolizing other sugars. Non-lactose fermenting bacteria are coccoid or bacillary and can be found in the soil or wet areas. Moreover, they are also non-sporulating and Gram-negative. Some species are highly pathogenic. Therefore, their detection is highly important.

Furthermore, examples of non-lactose fermenting bacteria include Acinetobacter, Alcaligenes, Bordetella, Burkholderia, Legionella, Moraxella, Pseudomonas, Shewanella, and Stenotrophomonas.

What are the Similarities Between Lactose Fermenting and Non-lactose Fermenting Bacteria?

• Lactose fermenting and non-lactose fermenting bacteria are prokaryotic organisms.
• Both bacteria types can be coccoid or bacillary in shape.
• They can be Gram-negative.
• Both bacteria types may be pathogenic.
• Bacteria like the coli can be lactose fermenting or non-lactose fermenting.

What is the Difference Between Lactose Fermenting and Non-lactose Fermenting Bacteria?

Lactose fermenting bacteria are able to convert glucose into cellular energy and lactic acid, while non-lactose fermenting bacteria are unable to convert glucose into cellular energy and lactic acid. Thus, this is the key difference between lactose fermenting and non-lactose fermenting bacteria. Furthermore, lactose-fermenting bacteria can be Gram-positive or negative, while non-lactose-fermenting bacteria are predominantly Gram-negative.

The below infographic presents the differences between lactose fermenting and non-lactose fermenting bacteria in tabular form for side-by-side comparison.

Summary – Lactose Fermenting vs Non-lactose Fermenting Bacteria

Lactic acid fermentation is a metabolic process that involves the conversion of glucose into metabolite lactate. Lactose fermenting and non-lactose fermenting bacteria are two types of prokaryotic organisms that are classified based on lactose fermentation. Lactose fermenting bacteria are able to convert glucose into cellular energy and lactic acid. In contrast, non-lactose fermenting bacteria are unable to convert glucose into cellular energy and lactic acid. So, this is the key difference between lactose fermenting and non-lactose fermenting bacteria.

Reference:

1. Gibbons, Norman E., and NORMAN E. GIBBONSView all articles by this author. “Lactose-Fermenting Bacteria from the Intestinal Contents of Marine Fish.” Contributions to Canadian Biology and Fisheries, 1 Jan. 1933.
2. “Non-Fermenting Bacterium.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “E. coli Bacteria (16578744517)” By NIAID – E. coli Bacteria (CC BY 2.0) via Commons Wikimedia
2. “Acinetobacter growth on MacConkey agar” By Ajay Kumar Chaurasiya – Own work (CC BY-SA 4.0) via Commons Wikimedia