Difference Between Bactericidal and Bacteriostatic

Bactericidal vs Bacteriostatic

Depending upon the killing or inhibiting ability of drugs, they can be classified into two categories; bactericidal and bacteriostatic. Physicians use either one of these agents or sometimes a combination of these two when treating an infection and it all depends on the type of infection, growth conditions of microorganisms, bacterial density, test duration, and reduction rate of Bactria. Well known bactericidal and bacteriostatic agents are the antibiotics. Antibiotics can also be classified into bactericidal and bacteriostatic antibiotics based on their mechanism of action. However, in some cases, one antibiotic can be bactericidal for one strain of bacteria and may only inhibit the growth of a different strain. Therefore, all the aspects mentioned above should be clearly known before choosing an antibiotic.


Bactericidal agents are used to kill microorganisms by inhibiting the synthesis of cell wall. Usually, endocarditis and meningitis are treated by bactericidal drugs. Examples for bactericidal antibiotics include; penicillin derivatives, cephalosporins, monobactams, and vancomycin. In addition, aminoglycosidic antibiotics are also considered as bactericidal, but they may also be bacteriostatic for some infections. The minimum concentration of a drug that is needed to kill a certain strain of bacteria is called the ‘minimum bactericidal concentration’ or MBC.


Bacteriostatic agents are used to limit the growth and reproduction of microorganisms by interfering with their protein production, DNA replication, or other aspects of bacterial cellular metabolism. Unlike the bactericidal agents, the bacteriostatic agents must works 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, whereas low concentration of bactericidal agents may act as bacteriostatic. In most urinary tract infections, it is recommended to use bacteriostatic antibiotics. The antibiotics include tetracycline, sulfonamides, spectinomycin, trimethoprim, chloramphenicol, macrolides and lincosamides are some examples for bacteriostatic agents. Minimum concentration of a drug that is needed to inhibit the growth of a certain strain of bacteria is known as ‘minimum inhibitory concentration’ or MIC.

Bactericidal vs Bacteriostatic

• Bactericidal activities kill microbial cells, whereas bacteriostatic activities prevent the growth of microbial cells.

• Number of microorganisms decreases in the presence of bactericidal agents, whereas the number of microorganisms remains the same in the presence of bacteriostatic agents.

• Unlike the bactericidal agents, when bacteriostatic agents are used, microorganisms remain viable.

• Unlike the bactericidal agents, bacteriostatic agents allow the immune system to deal with infections.

• If the doses of bacteriostatic agents are high, those may act as bactericidal agents.

• If the doses of bactericidal agents are low, those may act as bacteriostatic agents.

• MIC (minimum inhibitory concentration) is the minimum concentration of drug need to inhibit bacterial growth by bacteriostatic agents. In contrast, MBC (minimum bactericidal concentration) is the minimum concentration of bactericidal drug needed to kill bacteria.