Minimum inhibitory concentration antibiotic resistance

The plasmid expressing Tet repressor (pcDNA6/TR) has a blas-ticidin-resistance cassette, while the plasmid used for the shRNA conditional expression (pSuperior) confers resistance to puromycin. Therefore, before starting the procedures, these two antibiotics need to be titrated on the selected cell line to find out the minimum inhibitory concentration necessary to kill completely untransfected cells. 

Resistance to tetracyclines. The tetracyclines Figure 7.3) are a family of closely related antibiotics now numbering at least seven, which are inhibitors of protein synthesis [150]. The tetracyclines are broad spectrum antibiotics, oxytetracycline being the most active against strains of Ps. aeruginosa. In sensitive strains, the range of minimum inhibitory concentrations (MIC values) is 10-30 /xg/ml. However, strains with MIC values of greater than lOp-g/ml are considered clinically resistant. 

Although a potential advantage of inhaled antibiotic therapy is the achievement of high concentrations in the sputum, there is substantial variability reported, which may reflect differences in collection and bioassay techniques. There is no clear relationship between systemic and inhaled doses of individual agents. Currently, the decisions about inhaled doses should be made on data specific for an individual agent. In trials with the commercially available inhaled tobramycin product, sputum concentrations of 1200 pg per mL were measured 10 minutes after the dose. Measured concentrations exceeded 25 times the minimum inhibitory concentration (MIC) for the most resistant isolate in 95% of subjects evaluated [7]. 

Further complicating antibiotic selection is the increasing resistance of the common bacterial pathogens to first-line agents. As many as 30% to 40% of H. influenzae and 95% of M. catarrhalis produce 8-lactamase. Moreover, up to 30% of S. pneumoniae isolates demonstrate resistance to penicillin (minimum inhibitory concentration [MIC] = 0.1-2 mg/L), with approximately 14% of isolates being highly resistant (MIC > 2 mg/L). - In addition, concern for... 

Lower respiratory tract infections account for a large proportion of prescribed antibiotics and, with emerging resistance to standard agents, the introduction of the fluoroquinolones, in particular ciprofloxacin, has provided a further component in the armamentarium. Ciprofloxacin is able to eradicate S. pneumoniae, H. influenzae, and M. catarrhalis readily. These findings suggest that the high respiratory tissue penetration of ciprofloxacin and the achievable minimum inhibitory concentrations lead to acceptable clinical outcomes in lower respiratory tract infections. 

Hardej et al. [22] have synthesized a series of rhodanine derivatives containing various substituents at the N3- and Cg-positions and tested for in vitro antibacterial activity against a panel of clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) strains. The anti-MRSA activity of compounds II (minimum inhibitory concentration (MIC)=3.9 pg/mL) and in (MIC=1.95 pg/mL) were significantly greater than that of the reference antibiotics penicillin G (MIC=31.25 pg/mL) and ciprofloxacin (MIC=7.8 pg/mL). 

Concern has been expressed about whether microorganisms could become resistant as a result of increased usage of antimicrobials, but it has been pointed out that they are different from antibiotics, because their attack on microorganisms is carried out by multiple mechanisms, and the development of resistance would therefore need more than one mutation. Moreover if the concentration of biocidal agent used in an inanimate material is higher than the minimum inhibitory concentration by a sufficiently large factor, any small decrease in susceptibility would be of little relevance. 

In the period following the Gorman and Ryan (1973) review, impressive advances were made. p-Lactam antibiotics were produced that possessed not only very low minimum inhibitory concentration (MIC) values against susceptible bacteria but also, in certain instances, significant activity against bacteria having pronounced resistance to the earlier compounds. 

Acute in vitro MIC (minimum inhibitory concentration) data were submitted for effects of narasin on a range of bacteria, but FEEDAP did not use these data in their calculation of the ADI. The JECFA " noted that there was no need to calculate a microbiological ADI as a faecal-binding study showed that most of the narasin in the gut is bound and inactive. In addition there is no risk of selection of resistance to antibiotics that are important for human medicine. Both FEEDAP and JECFA " calculated an ADI of 0.5mg/kgbw/day by applying a 100-fold safety factor to the NOEL of 0.5mg/kgbw/day from the one-year dog study. 

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