Gram-negative bacteria are detected in a process called Gram staining. Colour, role in the organism, representative species…Explanations with Gaël Saintenoy, biologist.
Definition: what is a gram negative?
We call Gram negative the bacteria that appear colored pink when using the technique of Gram stain. Gram staining can be done on all types of samples: blood, urinary, vaginal, digestive, articular… Thanks to the differentiation that takes place between Gram-negative bacteria and those with Gram positive, we can classify the different bacteria. The Gram-negative bacteria have a double membrane and contain many protein. Between the two membranes there are large quantities of enzymes and nutrients involved in particular in protein synthesis and metabolism.
What is the difference between a gram positive and a gram negative?
“Gram staining is a bacteriological technique that allows bacteria to be visibly and quickly differentiated from each other.“, explains Gaël Saintenoy, biologist. Gram positive bacteria keep blue color after the coloring process, while the Gram-negative bacteria stain pink. “The difference between Gram positive and Gram negative bacteria lies in the composition of the membrane and the wall if there is one. The Gram positive bacteria have a thicker wall because they contain a lot of peptidoglycan, sugary proteins, which is not the case with Gram-negative bacteria whose membrane and walls are much thinner, which explains why discoloration recoloration works on Gram-negative bacteria that take a pinkish-red color but not on the Gram Positives which remain blue. Gram Positives and Gram Negatives are not responsible for the same types of infections“, he continues. In terms of appearance, there are three forms of bacteria: bacilli which correspond to elongated bacteria, coccus which are spherical bacteria collected like bunches of grapes, and cocobacilli.
What is the color of gram negative staining?
Gram-negative bacteria appear a rose.
What is the role of gram negatives in the body?
Whether Gram-positive or Gram-negative, bacteria are able to multiply in our body. Some we protect against infection and participate in the rregulation of our immune system while others cause infections.
What species are representative of gram negatives?
The main representative species of Gram negatives are the enterobacteriaceae : Escherichia, Salmonella, Shigella, Klebsiella, Enterobacter, Serratia, Proteus, Morganella and Yersinia. We also mention the legionella pneumophila, responsible for legionellosis, Pseudomonas aeruginosa, Brucella, Campylobacter, Haemophilus influenzae.
Which gram-negative bacteria are responsible for infections?
All Gram-negative bacteria can be responsible for infections such as pneumoniaperitonitis, meningitis, blood infections, salmonellosis, lung infections or even typhoid fever. Gaël Saintenoy explains that the two most common types of infection due to Gram-negative bacilli are:
► The urinary tract infections which range fromurinary tract infection up to pyelonephritis, or even more if there is blood passage with positive blood cultures. The bacteria most frequently found in women are Escherichia coli and Klebsiella pneumoniae
► The infectious diarrhea with another group of bacteria, salmonella and shigella, which can lead to digestive tract infections.
Are they resistant to antibiotics?
Gram-negative bacteria are increasingly resistant to antibioticseither naturally or acquired. “Escherichia coli is sensitive to all antibiotics, although acquired resistance mechanisms may appear. The other major species is Klebsiella pneumoniaea bacterium that has a natural resistance to certain beta-lactams because it contains an enzyme called penicillinase which is able to destroy certain types of antibiotics. We also mention the enzymes acquired like cephalosporinases, an enzyme responsible for resistance to cephalosporins, extended-spectrum beta-lactamases (ESBL) are also capable of destroying many of the antibiotics used. In recent years, we have also isolated carbapenemases which are capable of altering the last generation of ATB”. says the specialist.
What treatment against gram negative?
Many antibiotics can be used against Gram negatives. Several criteria will make it possible to determine the appropriate treatment: the gender, location of infection and intensity. “For example, we will not use the same antibiotic for a mild urinary tract infection in women as for prostatitis in men. There is also the intensity of the infection which will be taken into account. In the same way, between a urinary tract infection and pyelonephritis, we will not use the same antibiotics. We can use beta-lactams (the large family of penicillins, cephalosporins, fluoroquinolones, bactrim, furans)“, informs our interlocutor. In general, the therapeutic strategy is as follows: an antibiotic is placed in probabilistic, that is to say that we assume, in view of the infection and the signs of infection, that we are dealing with an enterobacteria for example. Antibiotic treatment is then initiated, the validity of which will be confirmed or not by the examination that will be carried out, such as a ECBU for a urinary tract infection. During a cytobacterioligical urine exam, the species responsible for the infection will be isolated and controlled. A antibiogram is then carried out to determine the sensitivity of different antibiotics to this bacterium and depending on the result, the doctor can decide to readjust the treatment or maintain the initial treatment.
Thanks to Gaël Saintenoy, biologist.