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

Introduction of Gram-Positive and Gram-Negative Bacteria

‘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 aureus, Streptococcus pneumoniae, Enterococcus 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.	Property	Gram-Positive Bacteria	Gram-Negative Bacteria
1	Gram Reaction	Take crystal violet (primary stain) and stain violet or purple on staining	Retain safranin (counterstain) after decolorization and stain pink or red on staining
2	Cell wall thickness	20-80 nm	8-10 nm
3	Peptidoglycan Layer	Multilayered (Thick)	single-layered (Thin)
4	Rigidity and Elasticity	Rigid and less elastic	Less rigid and more elastic
5	Outer Membrane	Absent	Present
6	Variety of amino acid in cell wall	Few	Several
7	Aromatic and Sulfur-containing amino acid in cell wall	Absent	Present
8	Periplasmic Space	Absent	Present
9	Teichoic Acids	Mostly present	Absent
10	Porins	Absent	Present
11	Lipopolysaccharide (LPS) Content	Almost None	High
12	Lipid and Lipoprotein Content	Low (acid-fast bacteria have lipids linked to peptidoglycan)	High (due to presence of outer membrane)
13	The ratio of RNA and DNA	8:1	Nearly 1
14	Mesosomes	Fully Prominent	Less Prominent
15	Flagellar Structure	2 rings in basal body	4 rings in basal body
16	Magnetosomes	Usually absent	Sometimes present
17	Morphology	Normally cocci or spore-forming rods (except- Lactobacillus and Corynebacterium)	Usually non-spore-forming rods (Except-Neisseria)
18	Endospore formation	Some produce endospores during unfavorable conditions like Bacillus, Clostridium, Sacchropolyspora, Micromonospora, and Streptomyces.	Normally not producing endospores
19	Toxin Produced	Exotoxin	Endotoxin or Exotoxin
20	Pathogens	Only a few are pathogens.	Most of them are pathogens.
21	Nutritional Requirements	Relatively Complex	Relatively Simple
22	Resistance to Physical Disruption	High	Low
23	Cell Wall Disruption by Lysozyme	High	Low ( since it requires pretreatment to destabilize outer membrane)
24	Susceptibility to Penicillin and Sulfonamide	Sulfonamide High	Low
25	Susceptibility to Streptomycin, Chloramphenicol, and Tetracycline	Low	High
26	Inhibition by Basic Dyes	High	Low
27	Susceptibility to Anionic Detergents	High	Low
28	Resistance to Sodium Azide	High	Low
29	Resistance to Drying	High	Low
30	Rendering	They can render Gram-negative by increasing acidity	They can render Gram-positive by increasing alkalinity
31	Common Examples	Staphylococcus 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.
32	Common Infections	Pneumococcal 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

Gram-Positive and Gram-Negative Bacteria Footages

Bacillus species growth on Muller-Hinton Agar

Bacillus species in Gram staining of culture

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

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

Clostridium growth on blood agar

Clostridium in Gram staining

Listeria monocytogenes colony morphology on blood agar

 Listeria monocytogenes in Gram staining of culture

Nocardia in modified Ziehl-Neelsen Staining

Staphylococcus aureus in Gram staining pus

Staphylococcus aureus colony morphology on blood agar

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

Micrococcus luteus growth on blood agar

Gram positive cocci in tetrads of Micrococcus

Micrococcus roseus growth on MHA

Micrococcus roseus growth on blood agar

Enterococcus in Gram staining of sputum

Enterococcus growth on blood agar

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 blood agar

Streptococcus pneumoniae colony morphology on blood agar

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

E. coli colony morphology on MacConkey agar

Escherichia coli in Gram staining of culture

Klebsiella pneumoniae mucoid lactose fermenter colony on MacConkey agar

Klebsiella pneumoniae in Gram staining

Proteus non-lactose fermenter colony on MacConkey medium

Proteus mirabilis in Gram staining of culture

Salmonella Typhi in Gram staining

Pyocyanin and pyoverdin pigments of Pseudomonas aeruginosa

Pseudomonas aeruginosa in Gram staining

Acinetobacter colony morphology on MacConkey agar

Acinetobacter in Gram staining of culture

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

Neisseria gonorrhoeae on blood agar of urethral discharge culture

Pure well isolated colony of Neisseria gonorrhoeae on chocolate agar

Neisseria meningitidis growth on blood agar with Micrococcus

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