Minimum bactericidal concentration tests

The evaluation of patients treated for IE includes assessment of signs and symptoms, blood cultures, microbiologic tests (e.g., MIC, minimum bactericidal concentration [MBC], or serum bactericidal titers), serum drug concentrations, and other tests to evaluate organ function. 

Structure—Activity Relationships. Biological evaluation of penicillins yields information such as in vitro and in vivo antibacterial activities, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), protective effectiveness in laboratory animals (PD50), and pharmacokinetic characteristics including efficiency of absorption, serum levels, tissue distribution, urinary excretion, recycling, etc. Penicillins are also tested for ability to resist inactivation by (S-lactamase produced by both gram-positive and gram-negative bacteria,... 

Minimum bactericidal concentration (MBC) testing is required for the evaluation of novel antimicrobials. The MBC is the lowest concentration (in mg/L) of antimicrobial that results in >99.9% killing of the bacterium under test. The 99.9% cutoff is an arbitrary in vitro value with 95% confidence limits that has uncertain clinical relevance. 

The broth dilution method is a simple procedure for testing a small number of isolates, even a single isolate. It has the added advantage that the same tubes can also be used for minimum bactericidal concentration(s) (MBC) tests. 

Antibacterial activity testing. Determined using the broth microdilution method. Incubations were performed for 18 h using an Ominolog automated incubator (Biolog Inc. 21,124 Cabot Boulevard, Hayward, CA 94545, USA). After this period MIC were checked by eye-ball observation and all weUs plated to determine the minimum bactericidal concentration (MBC). 

To compare the bactericidal efficacy of silver nanoparticles and silver ions, the minimum inhibitory concentration (MIC) assays were conducted for gram-negative bacterium E. coli, gram-positive bacteria S. aureus and B. subtilis and fungus P. phoeniceum. The data on MICs are summarized in Table 18.1. The results demonstrated that the antimicrobial activity of silver ions was superior to that of silver nanoparticles against all microbes tested. 

Isoniazid is the hydrazide of isonicotinic acid. It is a first-line drug for therapy and prophylaxis of tuberculosis. It is bactericidal for rapidly dividing mycobacteria, but bacteriostatic for resting bacilli . Among non-tuberculous mycobacteria, only a few strains, such as Mycobacterium kansasii, are susceptible. As a rule, sensitivity should always be tested in vitro, since the minimum inhibitory concentration varies greatly. 

Tests considered to date have, without exception, measured unequivocally the bactericidal effect. In some instances it is useful to know the minimum concentration which inhibits growth (reproduction) rather than those concentrations which achieve a rapid kill. The implications ofthe terms bactericide and bacteriostat were discussed earlier (see section 1.1, Fig. 11.1). 

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