Group of bacteria that do not retain the Gram stain used in bacterial differentiation

Gram-negative bacteria

Gram-negative bacteria

Gram-negative bacteria are <a href="/en/Bacteria" title="Bacteria" class="wl">bacteria</a> that do not retain the <a href="/en/Crystal_violet" title="Crystal violet" class="wl">crystal violet stain</a> used in the <a href="/en/Gram_stain" title="Gram stain" class="wl">Gram staining</a> method of bacterial differentiation.<a href="#cite_note-Baron-1" style="counter-reset: mw-Ref 1;">[1]</a> They are characterized by their <a href="/en/Cell_envelope" title="Cell envelope" class="wl">cell envelopes</a>, which are composed of a thin <a href="/en/Peptidoglycan" title="Peptidoglycan" class="wl">peptidoglycan</a> <a href="/en/Cell_wall" title="Cell wall" class="wl">cell wall</a> sandwiched between an inner <a href="/en/Cytoplasm" title="Cytoplasm" class="wl">cytoplasmic</a> <a href="/en/Cell_membrane" title="Cell membrane" class="wl">cell membrane</a> and a <a href="/en/Bacterial_outer_membrane" title="Bacterial outer membrane" class="wl">bacterial outer membrane</a>.

<div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none" about="#mwt1">Group of bacteria that do not retain the Gram stain used in bacterial differentiation</div>
<figure class="mw-default-size wiki-thumb"><a href="/en/File:Pseudomonas_aeruginosa_Gram.jpg" class="mw-file-description image media-thumb" data-hash="File:Pseudomonas_aeruginosa_Gram.jpg"><img loading="lazy" src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Pseudomonas_aeruginosa_Gram.jpg/220px-Pseudomonas_aeruginosa_Gram.jpg" decoding="async" data-file-width="500" data-file-height="375" data-file-type="bitmap" height="165" width="220" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Pseudomonas_aeruginosa_Gram.jpg/330px-Pseudomonas_aeruginosa_Gram.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Pseudomonas_aeruginosa_Gram.jpg/440px-Pseudomonas_aeruginosa_Gram.jpg 2x" alt="Pseudomonas_aeruginosa_Gram.jpg"></a><figcaption>Microscopic image of gram-negative <a href="/en/Pseudomonas_aeruginosa" title="Pseudomonas aeruginosa" class="wl">Pseudomonas aeruginosa</a> bacteria (pink-red rods)</figcaption></figure>

Gram-negative bacteria are found in virtually all environments on <a href="/en/Earth" title="Earth" class="wl">Earth</a> that support life. The gram-negative bacteria include the <a href="/en/Model_organism" title="Model organism" class="wl">model organism</a> <a href="/en/Escherichia_coli" title="Escherichia coli" class="wl">Escherichia coli</a>, as well as many <a href="/en/Pathogenic_bacteria" title="Pathogenic bacteria" class="wl">pathogenic bacteria</a>, such as <a href="/en/Pseudomonas_aeruginosa" title="Pseudomonas aeruginosa" class="wl">Pseudomonas aeruginosa</a>, <a href="/en/Chlamydia_trachomatis" title="Chlamydia trachomatis" class="wl">Chlamydia trachomatis</a>, and <a href="/en/Yersinia_pestis" title="Yersinia pestis" class="wl">Yersinia pestis</a>. They are a significant medical challenge as their <a href="/en/Bacterial_outer_membrane" title="Bacterial outer membrane" class="wl">outer membrane</a> protects them from many <a href="/en/Antibiotic" title="Antibiotic" class="wl">antibiotics</a> (including <a href="/en/Penicillin" title="Penicillin" class="wl">penicillin</a>), <a href="/en/Detergent" title="Detergent" class="wl">detergents</a> that would normally damage the inner cell membrane, and <a href="/en/Lysozyme" title="Lysozyme" class="wl">lysozyme</a>, an <a href="/en/Antimicrobial" title="Antimicrobial" class="wl">antimicrobial</a> enzyme produced by animals that forms part of the <a href="/en/Innate_immune_system" title="Innate immune system" class="wl">innate immune system</a>. Additionally, the outer leaflet of this membrane comprises a complex <a href="/en/Lipopolysaccharide" title="Lipopolysaccharide" class="wl">lipopolysaccharide</a> (LPS) whose <a href="/en/Lipid_A" title="Lipid A" class="wl">lipid A</a> component can cause a toxic reaction when bacteria are <a href="/en/Lysis" title="Lysis" class="wl">lysed</a> by immune cells. This toxic reaction may lead to <a href="/en/Hypotension" title="Hypotension" class="wl">low blood pressure</a>, <a href="/en/Respiratory_failure" title="Respiratory failure" class="wl">respiratory failure</a>, <a href="/en/Hypoxia_(medical)" title="Hypoxia (medical)" class="wl">reduced oxygen delivery</a>, and <a href="/en/Lactic_acidosis" title="Lactic acidosis" class="wl">lactic acidosis</a> – manifestations of <a href="/en/Septic_shock" title="Septic shock" class="wl">septic shock</a>.<a href="#cite_note-ww.ncbi.nlm.nih.gov-2" style="counter-reset: mw-Ref 2;">[2]</a>

Several <a href="/en/Antibiotics#Classes" title="Antibiotics" class="mw-redirect wl">classes of antibiotics</a> have been designed to target gram-negative bacteria, including <a href="/en/Aminopenicillin" title="Aminopenicillin" class="wl">aminopenicillins</a>, <a href="/en/Ureidopenicillin" title="Ureidopenicillin" class="wl">ureidopenicillins</a>, <a href="/en/Cephalosporin" title="Cephalosporin" class="wl">cephalosporins</a>, <a href="/en/Beta-lactam" title="Beta-lactam" class="wl">beta-lactam</a>-<a href="/en/Β-Lactamase_inhibitor" title="Β-Lactamase inhibitor" class="wl">betalactamase inhibitor</a> combinations (e.g. <a href="/en/Piperacillin/tazobactam" title="Piperacillin/tazobactam" class="wl">piperacillin-tazobactam</a>), <a href="/en/Antifolate" title="Antifolate" class="wl">Folate antagonists</a>, <a href="/en/Quinolone" title="Quinolone" class="wl">quinolones</a>, and <a href="/en/Carbapenem" title="Carbapenem" class="wl">carbapenems</a>. Many of these antibiotics also cover <a href="/en/Gram-positive_bacteria" title="Gram-positive bacteria" class="wl">gram-positive</a> organisms. The drugs that specifically target gram-negative organisms include <a href="/en/Aminoglycoside" title="Aminoglycoside" class="wl">aminoglycosides</a>, <a href="/en/Monobactam" title="Monobactam" class="wl">monobactams</a> (<a href="/en/Aztreonam" title="Aztreonam" class="wl">aztreonam</a>) and <a href="/en/Ciprofloxacin" title="Ciprofloxacin" class="wl">ciprofloxacin</a>.

Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane. Gram-negative bacteria are found in virtually all environments on Earth that support life. The gram-negative bacteria include the model organism Escherichia coli, as well as many pathogenic bacteria, such as Pseudomonas aeruginosa, Chlamydia trachomatis, and Yersinia pestis. They are a significant medical challenge as their outer membrane protects them from many antibiotics , detergents that would normally damage the inner cell membrane, and lysozyme, an antimicrobial enzyme produced by animals that forms part of the innate immune system. Additionally, the outer leaflet of this membrane comprises a complex lipopolysaccharide whose lipid A component can cause a toxic reaction when bacteria are lysed by immune cells. This toxic reaction may lead to low blood pressure, respiratory failure, reduced oxygen delivery, and lactic acidosis – manifestations of septic shock. Several classes of antibiotics have been designed to target gram-negative bacteria, including aminopenicillins, ureidopenicillins, cephalosporins, beta-lactam-betalactamase inhibitor combinations , Folate antagonists, quinolones, and carbapenems. Many of these antibiotics also cover gram-positive organisms. The drugs that specifically target gram-negative organisms include aminoglycosides, monobactams and ciprofloxacin. 