Gram negative: definition, color, representative species

Gram negative: definition, color, representative species


Gram-negative bacteria are detected during a process called Gram staining. Color, role in the body, representative species … Explanations with Gaël Saintenoy, biologist.

Definition: What is a negative gram?

Gram-negative bacteria that appear colored pink when using the technique of Gram staining. Gram staining can be done on all types of samples: blood, urinary, vaginal, digestive, articular … Thanks to the differentiation between Gram – negative and Gram – negative bacteria Gram positive, the different bacteria can be classified. Les Gram-negative bacteria have a double membrane and contain many protein. Between the two membranes are large amounts of enzymes and nutrients that are involved in protein synthesis and metabolism.

What is the difference between a positive gram and a negative gram?

Gram staining is a bacteriological technique that allows bacteria to be visibly and rapidly differentiated from each other.“says Gaël Saintenoy, a biologist Gram-positive bacteria retain the blue color after the staining process, while the Gram-negative bacteria turn pink. “The difference between Gram – positive and Gram – negative bacteria lies in the membrane and wall composition if there is one. Les Gram-positive bacteria have a thicker wall because they contain a lot of peptidoglycan, sweet proteins, which is not the case with Gram-negative bacteria whose membrane and walls are much less thick, which explains why discoloration recoloration works on Gram-negative ones that take a pink-red color but not on the Gram Positive which remain blue. Gram Positive and Gram Negative are not responsible for the same types of infections“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 color is the gram negative for staining?

Gram-negative bacteria appear in pink.

What is the role of gram negative in the body?

Whether Gram-positive or Gram-negative, bacteria can multiply in our body. Some of us protect against infections and participate in the rregulation of our immune system while others cause infections.

What are the representative species of negative grams?

The main representative species of Gram negatives are enterobacteria : Escherichia, Salmonella, Shigella, Klebsiella, Enterobacter, Serratia, Proteus, Morganella and Yersinia. Let’s 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 typhoid fever. Gaël Saintenoy explains that the two most common types of Gram-negative bacillus infections are:
► The urinary tract infections that go from theurinary tract infection to pyelonephritis, or even more so if there is a blood passage with positive blood cultures. The most common bacteria found in women are Escherichia coli and Klebsiella pneumoniae.
► The infectious diarrhea with another group of bacteria that are salmonella and shigella, which can lead to digestive tract infections.

Are they resistant to antibiotics?

Gram-negative bacteria are increasingly resistant to antibiotics, either naturally or acquired. “Escherichia coli is susceptible to all antibiotics, although mechanisms of acquired resistance may occur. The other large species is Klebsiella pneumoniaea bacterium that has a natural resistance to certain beta-lactams because it contains an enzyme called penicillinase which is capable of destroying certain types of antibiotics. Let’s also mention the enzymes Acquired as cephalosporinases, an enzyme responsible for cephalosporin resistance, broad spectrum beta-lactamases (BLSEs) are also capable of destroying many used antibiotics. In recent years, carbapenems have also been isolated that are capable of altering the latest generation of ATBs. “ says the specialist.

What gram-negative treatment?

Many antibiotics can be used against Gram negative. Several criteria will determine the appropriate treatment: the sex, the location of the infection and its intensity. “For example, the same antibiotic will not be used for mild urinary tract infection in women as in prostatitis in men. There is also the intensity of the infection that will come into play. Similarly, between a urinary tract infection and a pyelonephritis, the same antibiotics will not be used. We can use beta-lactams (large family of penicillins, cephalosporins, fluoroquinolones, bactrim, furans)“In general, the therapeutic strategy is as follows: an antibiotic is put on probation, that is, it is assumed, in view of the infection and the signs of infection, that one is dealing with an enterobacterium for example. Antibiotic treatment is then instituted, the validity of which will be confirmed or not by the examination to be performed, as a ECBU for a urinary tract infection. During a cytobacteriological examination of urine, the species responsible for the infection will be isolated and controlled. One antibiograms is then performed to determine the susceptibility of the various antibiotics to this bacterium and depending on the result, the doctor may decide to readjust the treatment or maintain the initial treatment.

Thanks to Gaël Saintenoy, biologist.

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