Lyme Disease Gram Stain
Lyme disease bacteria are usually considered Gram-negative and a Lyme disease Gram stain is used in identification of Borrelia. ¬†Gram-negative bacteria are called this simply because they do not retain the crystal violet colored dye in their cell wall during a Gram stain test. ¬†Once a counter-stain chemical is used however, the Gram-negative bacteria cell wall holds the pinkish dye and this is a characteristic feature of bacteria with a cell wall constituting a thin layer of peptidoglycan. ¬†Borrelia spirochaetes are not straight-forwardly Gram-negative however, as their double-membrane envelopes have a number of significant differences in structure and composition to other Gram-negative bacteria so defined by their double-membrane structure. ¬†
Basic Bacterial Biology
To explain this further an understanding of some cell biology and genetics is necessary. ¬†Firstly, a diderm is a double-membrane envelope which is found in Gram-negative bacteria and which consists of an outer membrane and an inner cytoplasmic membrane. ¬†Lipopolysaccharides are molecules formed using a covalent bond between a lipid and a polysaccharide. These molecules may also be referred to as lipoglycans and they are usually found in the outer membrane of Gram-negative bacteria. ¬†Other important definitions include the term ‚Äėperiplasmic‚Äô. ¬†The periplasmic space (periplasm) is the space in Gram-negative bacteria found between the inner and outer membranes and may account for some 40% of the total cell volume in such bacteria. ¬†It is much smaller in Gram-positive bacteria and is essentially the space outside the inner membrane in such bacteria.
Borrelia bacteria, whilst classified as gram-negative, have major surface lipoproteins at the host-pathogen interface during infection transmission, and the periplasmic flagella play a peculiar role in defining both cell motility and cell shape. ¬†Lyme disease bacteria are also lacking lipopolysaccharides (LPS) in their diderm, and some cell biologists consider these bacteria as neither Gram-positive nor Gram-negative but their own special bacterial cell type. ¬†Despite their double-membrane structure, the genetic make-up of Borrelia identifies them, along with other spirochaetes, as a separate eubacterial phylum. ¬†
‘Herxing’ and Endotoxins in Lyme Disease
LPS act as endotoxins and are responsible for triggering a strong immune system response in animals infected with such Gram-negative bacteria. ¬†The lack of LPS in the outer membrane of Borrelia burgdorferi has implications for the presumed Jarisch-Herxheimer reaction (‚Äėherxing‚Äô) attributed to endotoxin-release during antibiotic treatment of Lyme disease but which may instead be a reaction to the die-off induced by the immune system. ¬†A Lyme disease Gram-stain is far from straightforward therefore, and an improved understanding of the Borrelia bacterial structure is essential for proper disease management to occur.