Difference Between Bactericidal and Bacteriostatic

The key difference between bactericidal and bacteriostatic is that the bactericidal is a drug that kills the bacteria while the bacteriostatic is a drug that inhibits the growth of bacteria.

Bacteria are susceptible to antibacterial agents. Therefore, depending upon the killing or inhibiting ability of the antibacterial agents, they can be classified into two categories as bactericidal and bacteriostatic. Usually, physicians use either one of these agents or sometimes a combination of these two when treating a bacterial infection, and it all depends on the type of infection, growth conditions of microorganisms, bacterial density, test duration, and reduction rate of bacteria, etc. Furthermore, some well known bactericidal and bacteriostatic agents are the antibiotics. Hence, antibiotics can also be classified into bactericidal and bacteriostatic based on their mechanism of action. However, in some cases, one antibiotic can be bactericidal for one bacterial strain and may only inhibit the growth of a different strain. Therefore, all the aspects mentioned above should be clearly known before choosing an antibiotic.

CONTENTS

1. Overview and Key Difference
2. What is Bactericidal
3. What is Bacteriostatic
4. Similarities Between Bactericidal and Bacteriostatic
5. Side by Side Comparison – Bactericidal vs Bacteriostatic in Tabular Form
6. Summary

What is Bactericidal?

Bactericidal is a drug or an agent that kills bacteria. These drugs employ different mechanisms to destroy bacteria such as the breakdown of the cell wall by protein degradation, etc. Endocarditis and meningitis are two common diseases that are treated by bactericidal drugs. Examples of bactericidal antibiotics include; penicillin derivatives, cephalosporins, monobactams, and vancomycin. In addition, aminoglycosidic antibiotics are also bactericidal agents, but they may also become bacteriostatic for some infections as well.

Besides, the minimum concentration of a drug that requires killing a certain strain of bacteria is the ‘minimum bactericidal concentration’ or MBC. This concentration varies strain wise. Some bacterial strains are more virulent while some are easily destroyable.

What is Bacteriostatic?

Bacteriostatic is a substance that inhibits the growth of bacteria. It is a type of antibacterial agent. However, its action is reversible. Once the bacteriostatic removes from the system, bacteria can grow again. In clinical applications, bacteriostatic are able to limit the growth and reproduction of microorganisms by interfering with their protein production, DNA replication, or other aspects of bacterial cellular metabolism. Here, the minimum concentration of a drug that is required to inhibit the growth of a certain strain of bacteria is the ‘minimum inhibitory concentration’ or MIC.

Furthermore, unlike the bactericidal agents, the bacteriostatic agents must work together with the immune system to inhibit the microorganisms’ activities. According to drug concentration, the activity may vary. For examples, if we use high concentrations of bacteriostatic agents, they may act as bactericidal.

Considering the usage, bacteriostatic antibiotics have a significant value in treating most urinary tract infections. Antibiotics such as tetracycline, sulfonamides, spectinomycin, trimethoprim, chloramphenicol, macrolides, and lincosamides are some examples for bacteriostatic agents.

What are the Similarities Between Bactericidal and Bacteriostatic?

• Bactericidal and Bacteriostatic are antibacterial substances.
• They are drugs used to treat bacterial infections.
• Both work against bacteria.
• Also, both are important agents in antibacterial thrapy.
• However, both may be influenced by growth conditions, bacterial density, test duration, and the extent of reduction in bacterial numbers.
• Besides, bacteria can develop resistance against both types of drugs.
• Therefore, low doses of both drugs may not be effective against bacteria.

What is the Difference Between Bactericidal and Bacteriostatic?

Bactericidal and bacteriostatic are two types of antibacterial substances. However, bactericidal kills bacteria while bacteriostatic inhibits or retards the growth of bacteria. Therefore, this is the key difference between bactericidal and bacteriostatic. Another important difference between bactericidal and bacteriostatic is that the action of bactericidal is irreversible while the action of bacteriostatic is reversible. Once the bacteriostatic agent removes from the system, bacteria start to grow again. Hence, bacteriostatic agents temporally inhibit the growth of bacteria. On the other hand, bacteria will die when applying a bactericidal.

The below infographic presents more details on the difference between bactericidal and bacteriostatic in tabular form.

Summary – Bactericidal vs Bacteriostatic

Antibacterial substances can be bactericidal or bacteriostatic. In summary, bactericidal is a substance that is capable of killing bacteria. On the other hand, bacteriostatic is a substance that is capable of inhibiting the growth of bacteria. The bactericidal action is irreversible once applies. On the contrary, bacteriostatic action is reversible. Therefore, this is one major difference between bactericidal and bacteriostatic. Another difference between bactericidal and bacteriostatic is that when applying a bactericidal, bacteria will not remain alive while when applying a bacteriostatic, bacteria remain alive though they are not active.

Reference:

1.“Bactericide.” NeuroImage, Academic Press. Available here  
2.Pankey, et al. “Clinical Relevance of Bacteriostatic versus Bactericidal Mechanisms of Action in the Treatment of Gram-Positive Bacterial Infections | Clinical Infectious Diseases | Oxford Academic.”OUP Academic, Oxford University Press, 15 Mar. 2004. Available here  

Image Courtesy:

1.”Cephalosporin core structure”By Fvasconcellos (Public Domain) via Commons Wikimedia  
2.”Chloramphenicol”By Calvero. – Own work (Public Domain) via Commons Wikimedia