The Different Susceptibilities of Gram Positive and Gram Negative Bacteria to Antimicrobial Agents

1. Introduction

Infectious diseases caused by bacteria are one of the leading causes of morbidity and mortality worldwide. The choice of antimicrobial agents is crucial in the treatment of these infections. The main difference between gram positive and gram negative bacteria is the structure of the cell wall. Gram positive bacteria have a thick peptidoglycan layer with many cross-linkages while gram negative bacteria have a thin peptidoglycan layer with few cross-linkages. This difference in cell wall structure affects the susceptibility of these bacteria to different antimicrobial agents.

2. What are Bacteria?

Bacteria are single-celled microorganisms that can be found in all environments on Earth. They are generally classified as gram positive or gram negative bacteria based on how they respond to use of dyes (Gram Stain) used in staining in the process of identifying them.

2. 1. Gram Positive Bacteria

Gram positive bacteria have a thick peptidoglycan layer with many cross-linkages. This thick peptidoglycan layer provides structural support to the cell and also acts as a barrier to prevent entry of harmful substances into the cell. The cross-linkages make it difficult for enzymes to break down the peptidoglycan layer and also make it resistant to osmotic pressure. Gram positive bacteria are susceptible to beta lactam antibiotics (such as penicillin) which inhibit the enzyme that synthesizes the peptidoglycan layer. They are also susceptible to cephalosporins (antibiotics that are structurally similar to penicillin) and polymyxins (antibiotics that act by destabilizing the bacterial cell membrane).

2. 2. Gram Negative Bacteria

Gram negative bacteria have a thin peptidoglycan layer with few cross-linkages. This thin peptidoglycan layer provides little structural support to the cell and does not act as an effective barrier against entry of harmful substances into the cell. The lack of cross-linkages makes it easy for enzymes to break down the peptidoglycan layer and also makes it susceptible to osmotic pressure. Gram negative bacteria are resistant to beta lactam antibiotics but are susceptible to cephalosporins and polymyxins (antibiotics that act by destabilizing the bacterial cell membrane).

3. Antimicrobial Agents

The choice of antimicrobial agents is crucial in the treatment of infectious diseases caused by bacteria. The most common types of antimicrobial agents are penicillins, cephalosporins, and polymyxins.

3. 1 Penicillin

Penicillin is a beta lactam antibiotic that inhibits the enzyme that synthesizes the peptidoglycan layer in gram positive bacteria. It has a wide range of activity against gram positive bacteria but is relatively inactive against gram negative bacteria. Penicillin is used to treat infections caused by Streptococcus pneumoniae, Staphylococcus aureus, and other gram positive bacteria. It is also used to treat syphilis, which is caused by a gram positive bacterium called Treponema pallidum. Penicillin is usually given orally or intramuscularly but can also be given intravenously in cases of severe infection. The most common side effects of penicillin are nausea, vomiting, and diarrhea.

3. 2 Cephalosporins

Cephalosporins are beta lactam antibiotics that are structurally similar to penicillin. They have a wide range of activity against both gram positive and gram negative bacteria. Cephalosporins are used to treat infections caused by Escherichia coli, Klebsiella pneumoniae, and other gram negative bacteria. They are also used to treat meningitis, which is an infection of the membranes that surround the brain and spinal cord. Cephalosporins are usually given intravenously but can also be given orally in some cases. The most common side effects of cephalosporins are nausea, vomiting, and diarrhea.

3. 3 Polymyxins

Polymyxins are antibiotics that act by destabilizing the bacterial cell membrane. They have a wide range of activity against both gram positive and gram negative bacteria. Polymyxins are used to treat infections caused by Pseudomonas aeruginosa and other gram negative bacteria. Polymyxins are usually given intravenously but can also be given intramuscularly or topically in some cases. The most common side effects of polymyxins are nephrotoxicity (kidney damage) and neurotoxicity (nerve damage).

4. Conclusion

In conclusion, the choice of antimicrobial agents is crucial in the treatment of infectious diseases caused by bacteria. The main difference between gram positive and gram negative bacteria is the structure of the cell wall which affects the susceptibility of these bacteria to different antimicrobial agents. Penicillin is a beta lactam antibiotic that inhibits the enzyme that synthesizes the peptidoglycan layer in gram positive bacteria. Cephalosporins are beta lactam antibiotics that are structurally similar to penicillin and have a wide range of activity against both gram positive and gram negative bacteria. Polymyxins are antibiotics that act by destabilizing the bacterial cell membrane and have a wide range of activity against both gram positive and gram negative bacteria.

FAQ

The different types of bacterial cells are cocci, bacilli, and spirilla.

Antimicrobial agents work to kill bacteria by inhibiting the growth of bacteria or by killing the bacteria outright.

The factors that influence the choice of antimicrobial agent for a particular infection include the type of bacteria causing the infection, the severity of the infection, and the patient's individual medical history.

There are potential side effects associated with using antimicrobial agents, including allergic reactions and resistance to the medication.