A novel pathogenic bacterium (Lactobacillus psittaci)-Erakina

Lactobacillus psittaci is a novel bacterial species that was recently isolated from the hyacinth macaw.

Genus Lactobacillus: An overview

This is the largest genus belonging to the Lactic Acid Bacteria family. Bacterial species that belong to this genus are present ubiquitously in the bodies of both humans and animals. They are usually present in the gastrointestinal tract of humans and ruminant animals and they play a primary role in maintaining the health, pH and balance of the gut. Since Lactobacillus bacteria are a major component of the gut microflora, it has been concluded that most Lactobacillus species are non-pathogenic. Lactobacillus species are commonly known for their probiotic properties and health benefits.

Probiotics refer to microorganisms that provide a multitude of health benefits to humans such as-

  • Boosting immunity
  • Improving digestion
  • Maintaining the balance and pH of the gastrointestinal tract.

Morphology and physiology

Lactobacillus species are morphologically and physiologically distinct from other LAB bacteria. The following characteristics distinguish them from other ubiquitously present bacterial species-

  • They are rod-shaped.
  • Lactobacilli are Gram-positive i.e., they have a peptidoglycan outer covering and no outer lipid membrane.
  • They are non-motile.
  • All Lactobacillus species are non-spore-forming.
  • They are catalase-negative i.e., they do not respire using oxygen as the terminal electron acceptor.
  • They produce lactic acid as a by-product of glycolysis or glucose fermentation. This feature of Lactobacillus bacteria has been exploited in the industrial sector for brewing, baking and enzyme synthesis.
  • These bacterial species are also resistant to low pH environments. Some species also exhibit a high degree of resistance to heat.
Lactobacillus rhamnosus
SEM image of Lactobacillus rhamnosus cells.

Colony characteristics

Lactobacillus bacterial strains form very distinct colonies which when observed exhibit the following features-

  • Colours vary between white, light brown and even orange.
  • Colonies are round in shape with a raised profile.
  • Edges are irregular and umbonate; there is the presence of a protrusion along the edges of the colony.
  • The profile of the colony is convex in shape.
  • Sizes range from 0.5-to 1.2 micrometres in width. 
  • The texture of the colonies is usually rough.
  • Bacterial cells occur singly or sometimes in pairs.
Lactobacillus brevis
Colonies of Lactobacillus brevis

An introduction to Lactobacillus psicatti

This novel bacterial strain was isolated from a male hyacinth macaw during a post-mortem examination of the dead bird. The bird had died at a zoological enclosure. The isolated bacteria were directly transferred to a nutrient medium to obtain a pure culture of the microbes. The strain was isolated specifically from the pulmonary air sacs of the bird. These air sacs were found to be inflamed and infected. However, excipient studies produced no results of fungal or mycoplasma growth in the air sacs.

Optimal growth conditions 

The isolated bacterial strain was grown under the following culture conditions-

  • The culture was grown on a nutrient medium containing Columbia blood agar which was supplemented by 5% horse blood.
  • The colony was incubated at room temperature in the presence of 5% carbon dioxide for two days.

Further investigation

Since these bacterial species were phenotypically similar to Lactobacillus bacteria, their whole-cell profiles were analysed using SDS-PAGE (an electrophoretic technique) and compared to the profiles of Lactobacillus species.

The genome of the isolated strain was amplified using the Polymerase Chain Reaction (PCR) which was followed by the 16s RNA analysis. This is an analytical technique commonly used for the identification and classification of microbial organisms. The phylogeny of the novel bacterial species was established using the neighbor-joining method which is a derivative method for the formation of phylogenetic trees. Phylogenetic trees exhibit evolutionary relationships between organisms and also establish the similarity or dissimilarity of any two organisms. 

Physiology and morphology of the novel strain

Even though the novel isolated bacterial strain was phenotypically similar to Lactobacillus species, it also exhibited certain dissimilarities in shape and size. Some of the distinct physiological and morphological characteristics of Lactobacillus psittaci are as follows-

  • These bacteria are round in shape with some cells being rod-shaped.
  • They are Gram-positive.
  • They are non-motile.
  • They are non-spore-forming.
  • They are catalase-negative.
  • These bacteria are facultatively anaerobic.

Is this species pathogenic?

Most Lactobacillus bacteria are commensals or form mutually beneficial relationships with their host organism. These bacteria are generally non-pathogenic. Some species of Lactobacillus species cause dental caries, but none of the bacterial species that belong to this genus cause any issues that are detrimental to the overall health and well-being of the host.

The isolation of this novel bacterial species, however, has created some doubt in regards to the non-pathogenicity of Lactobacillus bacteria. Since this bacterium was isolated from the infected air sacs of a hyacinth macaw, it has been hypothesised that this bacterium is an opportunistic pathogen. Opportunistic pathogens refer to those microorganisms that do not infect healthy hosts but instead infect immunologically defective hosts. 

The hyacinth macaw

Anodorhynchus hyacinthinus, also known as the hyacinth macaw, is a parrot species native to the central and eastern regions of South America. It is the largest known flying parrot species and also the largest macaw in the world. Its diet mainly consists of nuts and seeds. These birds are currently endangered due to habitat loss and deforestation and hence, they are currently being kept in special enclosures to prevent them from going extinct. 

The eggs of these birds are often preyed on by toco toucans and corvids. These birds are the longest psittacines (hence, the name Lactobacillus psittaci was proposed for the bacterial species isolated from this bird). They are known for their calm dispositions and are also referred to as “gentle giants”.

Hyacinth macaws
A hyacinth macaw or “blue parrot”.


Lactobacillus psittaci is a novel bacterial species that were isolated from the inflamed air sacs of a dead male hyacinth macaw. This discovery has led to the hypothesis that some species of the genus Lactobacillus might even be opportunistic pathogens. This bacterium exhibits phenotypic characteristics that are very similar to other Lactobacillus species. Phylogenetic studies have established the placement of this species in the genus Lactobacillus.

Tags: Life Sciences

One Comment

  1. Humera

    Lactobacillus psittaci (psit. ta‘ci. L. gen. masc. n. psittaci of the parrot, from which the organism was first isolated).

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