Gram-Positive and Gram-Negative Bacteria: Introduction, Differences, and Related Footage

Introduction of Gram-Positive and Gram-Negative Bacteria

Table of Contents

Differences between Gram Positive and Gram Negative Bacteria: Introduction, and Related Footages
Fig. Gram-Positive Bacteria (Left) and Gram-Negative Bacteria (right)

Gram-Positive Bacilli (GPB)‘ is also called Gram-Positive Rods (GPR) bacteria which retain crystal violet dye and stain blue or purple on Gram’s staining. The most common medically important bacteria of GPR are Mycobacterium tuberculosis, Mycobacterium leprae, Listeria monocytogenes, Nocardia asteroides, Actinomyces israelii, Bacillus anthracis, Bacillus cereus, Bifidobacterium species, Corynebacterium diphtheriae, and Clostridium species.

Gram-Positive Cocci (GPC)‘ bacteria retain crystal violet dye and stain blue or purple on Gram’s staining. The most common medically important bacteria of GPC are Staphylococcus aureusStreptococcus pneumoniaeEnterococcus species, Streptococcus pyogenes, Streptococcus agalactiae, and Staphylococcus saprophyticus.

Gram-Positive Negative (GNB)‘ is also called Gram-Negative Rods (GNR) bacteria which take safranin after decolorization and stain pink or red on Gram’s staining. Most GNR bacteria are medically important and among them, a few are Escherichia coli, Klebsiella pneumoniae,  Salmonella enterica serotype Typhi,  Shigella species, Proteus species, Citrobacter, Pseudomonas aeruginosa, and Acinetobacter species.

Medically relevant gram-negative cocci bacteria are Neisseria gonorrhoeae (causative agent of sexually transmitted disease), Neisseria meningitidis (causes meningitis), Moraxella catarrhalis (responsible for respiratory symptoms), and Veillonella parvula (anaerobic gram-negative coccus cause osteomyelitis).

Differences between Gram-Positive and Gram-Negative Bacteria

The differences between Gram-Positive and Gram-Negative Bacteria are summarized as follows-

S. No.PropertyGram-Positive BacteriaGram-Negative Bacteria
1Gram ReactionTake crystal violet (primary stain) and stain violet or purple on stainingRetain safranin (counterstain) after decolorization and stain pink or red on staining
2Cell wall thickness20-80 nm8-10 nm
3Peptidoglycan LayerMultilayered (Thick)single-layered (Thin)
4Rigidity and ElasticityRigid and less elasticLess rigid and more elastic
5Outer MembraneAbsentPresent
6Variety of amino acid in cell wallFewSeveral
7Aromatic and Sulfur-containing amino acid in cell wallAbsentPresent
8Periplasmic SpaceAbsentPresent
9Teichoic AcidsMostly presentAbsent
10PorinsAbsentPresent
11Lipopolysaccharide (LPS) ContentAlmost NoneHigh
12Lipid and Lipoprotein ContentLow (acid-fast bacteria have lipids linked to peptidoglycan)High (due to presence of outer membrane)
13The ratio of RNA and DNA
8:1
Nearly 1
14MesosomesFully ProminentLess Prominent
15Flagellar Structure2 rings in basal body4 rings in basal body
16MagnetosomesUsually absentSometimes present
17MorphologyNormally cocci or spore-forming rods (except- Lactobacillus and Corynebacterium)Usually non-spore-forming rods (Except-Neisseria)
18Endospore formationSome produce endospores during unfavorable conditions like Bacillus, Clostridium, Sacchropolyspora, Micromonospora, and Streptomyces.Normally not producing endospores
19Toxin ProducedExotoxinEndotoxin or Exotoxin
20PathogensOnly a few are pathogens.Most of them are pathogens.
21Nutritional RequirementsRelatively ComplexRelatively Simple
22Resistance to Physical DisruptionHighLow
23Cell Wall Disruption by LysozymeHighLow ( since it requires pretreatment to destabilize outer membrane)
24Susceptibility to Penicillin and Sulfonamide Sulfonamide
High
Low
25
Susceptibility to Streptomycin, Chloramphenicol, and Tetracycline
Low
High
26Inhibition by Basic Dyes
High

Low
27Susceptibility to Anionic DetergentsHigh
Low
28Resistance to Sodium Azide
High
Low
29Resistance to DryingHigh
Low
30RenderingThey can render Gram-negative by increasing acidityThey can render Gram-positive by increasing alkalinity
31Common ExamplesStaphylococcus aureus
Streptococcus pnrumoniae
Streptococcus pyogenes
Streptococcus agalactiae
Enterococcus
species
Bacillus
Clostridium
Listeria
monocytogenes
Corynebacterium diphtheriae
Escherichia coli
Salmonella Typhi
S. Paratyphi,
Klebsiella pnumoniae,
Proteus vulgaris,
Helicobacter pylori
Pseudomonas aeruginosa,
Acinetobacter
spp.
32Common InfectionsPneumococcal infections
Staphylococcal aureus infections
Streptococcal infections
Toxic shock syndrome
Anthrax
Diphtheria
Enterococcal infections
Erysipelothricosis
Listeriosis
E. coli infections,
Klebsiella infections,
Haemophilus influenzae infections,
Cholera,
Plague,
Typhoid fever,
Shigellosis,
Brucellosis,
Pseudomonas infections,
Campylobacter infections
Table: Gram-positive versus Gram-negative bacteria

Gram-Positive and Gram-Negative Bacteria Footages

Bacillus species growth on Muller-Hinton Agar

Bacillus species growth on Muller-Hinton Agar
Fig. Bacillus species growth on Muller-Hinton Agar

Bacillus species in Gram staining of culture

Bacillus species in Gram staining of culture
Fig. Bacillus species in Gram staining of culture

Mycobacterium tuberculosis in Ziehl-Neelsen staining of Sputum at a high magnification

Mycobacterium tuberculosis in Ziehl-Neelsen staining  of Sputum at a high magnification
Fig. Mycobacterium tuberculosis in Ziehl-Neelsen staining of Sputum at a high magnification

Mycobacterium leprae in Ziehl-Neelsen staining of Sputum at a high magnification

Mycobacterium leprae  in Ziehl-Neelsen staining  of Sputum at a high magnification
Fig. Mycobacterium leprae in Ziehl-Neelsen staining of Sputum at a high magnification

Clostridium growth on blood agar

Clostridium growth on blood agar
Fig. Clostridium growth on blood agar

Clostridium in Gram staining

Clostridium in Gram staining
Fig. Clostridium in Gram staining

Listeria monocytogenes colony morphology on blood agar

 Listeria monocytogenes colony morphology on blood agar
 Fig. Listeria monocytogenes colony morphology on blood agar

 Listeria monocytogenes in Gram staining of culture

 Listeria monocytogenes in Gram staining of culture
 Fig. Listeria monocytogenes in Gram staining of culture

Nocardia in modified Ziehl-Neelsen Staining

Nocardia in modified Ziehl-Neelsen Staining
Fig. Nocardia in modified Ziehl-Neelsen Staining

Staphylococcus aureus in Gram staining pus

Staphylococcus aureus in Gram staining pus
Fig. Staphylococcus aureus in Gram staining of pus

Staphylococcus aureus colony morphology on blood agar

Staphylococcus aureus colony morphology on blood agar
Fig. Staphylococcus aureus colony morphology on blood agar

Beta-hemolytic colony of Staphylococcus aureus on blood agar

Beta-hemolytic colony of Staphylococcus aureus on blood agar
Fig. Beta-hemolytic colony of Staphylococcus aureus on blood agar

Gram positive cocci in singles, pairs and clusters of Staphylococcus aureus in Gram staining of culture

Gram positive cocci in singles, pairs and clusters of Staphylococcus aureus in Gram staining of culture
Fig. Gram-positive cocci in singles, pairs, and clusters of Staphylococcus aureus in Gram staining of culture

Micrococcus luteus growth on blood agar

Micrococcus luteus growth on blood agar
Fig. Micrococcus luteus growth on blood agar

Gram positive cocci in tetrads of Micrococcus

Gram positive cocci in tetrads of Micrococcus
Fig. Gram positive cocci in tetrads of Micrococcus

Micrococcus roseus growth on MHA

Micrococcus roseus growth on MHA
Fig. Micrococcus roseus growth on MHA

Micrococcus roseus growth on blood agar

Micrococcus roseus growth on blood agar
Fig. Micrococcus roseus growth on blood agar

Enterococcus in Gram staining of sputum

Enterococcus in Gram staining of sputum
Fig. Enterococcus in Gram staining of sputum

Enterococcus growth on blood agar

Enterococcus growth on blood agar
Fig. Enterococcus growth on blood agar

Enterococcus faecalis in Gram staining of culture microscopy at a high magnification

Enterococcus faecalis in Gram staining  of culture microscopy at a high magnification
Fig. Enterococcus faecalis in Gram staining of culture microscopy at a high magnification

Enterococcus faecalis colony characteristics on MacConkey agar without bile salt and crystal violet

Enterococcus faecalis colony characteristics on MacConkey agar without bile salt and crystal violet
Fig. Enterococcus faecalis colony characteristics on MacConkey agar without bile salt and crystal violet

Enterococcus faecalis colony characteristics on blood agar

Enterococcus faecalis colony characteristics on blood agar
Fig. Enterococcus faecalis colony characteristics on blood agar

Streptococcus pneumoniae colony morphology on blood agar

Streptococcus pneumoniae colony morphology on blood agar
Fig. Streptococcus pneumoniae colony morphology on blood agar

Beta-hemolytic streptococci (Streptococcus pyogenes or Streptococcus agalactiae) colony morphology on blood agar

Beta-hemolytic streptococci (Streptococcus pyogenes or Streptococcus agalactiae) colony morphology on blood agar
Fig. Beta-hemolytic streptococci (Streptococcus pyogenes or Streptococcus agalactiae) colony morphology on blood agar

E. coli colony morphology on MacConkey agar

E. coli colony morphology on MacConkey agar
Fig. E. coli colony morphology on MacConkey agar

Escherichia coli in Gram staining of culture

Escherichia coli in Gram staining of culture
Fig. Escherichia coli in Gram staining of culture

Klebsiella pneumoniae mucoid lactose fermenter colony on MacConkey agar

Klebsiella pneumoniae mucoid lactose fermenter colony on MacConkey agar
Fig. Klebsiella pneumoniae mucoid lactose fermenter colony on MacConkey agar

Klebsiella pneumoniae in Gram staining

Klebsiella pneumoniae in Gram staining
Fig. Klebsiella pneumoniae in Gram staining

Proteus non-lactose fermenter colony on MacConkey medium

Proteus non-lactose fermenter colony on MacConkey medium
Fig. Proteus non-lactose fermenter colony on MacConkey medium

Proteus mirabilis in Gram staining of culture

Proteus mirabilis in Gram staining of culture
Fig. Proteus mirabilis in Gram staining of culture

Salmonella Typhi in Gram staining

Salmonella Typhi in Gram staining
Fig. Salmonella Typhi in Gram staining

Pyocyanin and pyoverdin pigments of Pseudomonas aeruginosa

Pyocyanin and pyoverdin pigments of Pseudomonas aeruginosa
Fig. Pyocyanin and pyoverdin pigments of Pseudomonas aeruginosa

Pseudomonas aeruginosa in Gram staining

Pseudomonas aeruginosa in Gram staining
Fig. Pseudomonas aeruginosa in Gram staining

Acinetobacter colony morphology on MacConkey agar

Acinetobacter colony morphology on MacConkey agar
Fig. Acinetobacter colony morphology on MacConkey agar

Acinetobacter in Gram staining of culture

Acinetobacter in Gram staining of culture
Fig. Acinetobacter in Gram staining of culture

Neisseria gonorrhoeae in Gram staining of urethral discharge showing Gram negative diplococci

Neisseria gonorrhoeae in Gram staining of urethral discharge showing Gram negative diplococci
Fig. Neisseria gonorrhoeae in Gram staining of urethral discharge showing Gram-negative diplococci

Neisseria gonorrhoeae on blood agar of urethral discharge culture

Neisseria gonorrhoeae on blood agar of urethral discharge culture
Fig. Neisseria gonorrhoeae on blood agar of urethral discharge culture

Pure well isolated colony of Neisseria gonorrhoeae on chocolate agar

Pure well isolated colony of Neisseria gonorrhoeae on chocolate agar
Fig. Pure well-isolated colony of Neisseria gonorrhoeae on chocolate agar

Neisseria meningitidis growth on blood agar with Micrococcus

Neisseria meningitidis growth on blood agar with Micrococcus
Fig. Neisseria meningitidis growth on blood agar with Micrococcus

Neisseria meningitidis in Gram staining of culture

Neisseria meningitidis in Gram staining of culture
Fig. Neisseria meningitidis in Gram staining of culture

Further Readings

  • https://universe84a.com/gram-stain/
  • Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut
  • https://connects.catalyst.harvard.edu/Profiles/display/Concept/Gram-Positive%20Endospore-Forming%20Bacteria
  • Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
  • https://www.msdmanuals.com/home/infections/bacterial-infections-gram-negative-bacteria/overview-of-gram-negative-bacteria
  • Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
  • Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
  • Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
  • Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
  • Clinical Microbiology Procedure Hand book Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC180726/
  • https://www.asmscience.org/content/education/protocol/protocol.2886
  • https://www.sigmaaldrich.com/catalog/product/sigma/ht90a?lang=en

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