16 The following figure is generated from data collected from an experiment in which the Minimum Inhibitory Concentration MIC of a series of antiseptics and disinfectants was determined against Staphylococcus aureus Gram positive E coli Gram negative and Pseudomonas aeruginosa Gram negative Use the figure below to determine which of the following statements is TRUE TABLE 6 MIC of some antiseptics and disinfectants against gram positive and gram negative bacteria Chemical agent Benzalkonium chloride Benzethonium chloride Cetrimide Chlorhexidine Hexachlorophene Phenol o Phenylphenol Propamine isethionate Dibromopropamidine isethionate Triclosan S aureus 0 5 0 5 4 0 5 1 0 5 2 000 100 2 1 0 1 MIC ng ml for E coli P aeruginosa 50 32 16 1 12 5 2 000 500 64 4 5 250 250 64 128 5 60 250 2 000 1 000 256 32 300 Based on references 226 and 440 MICs of cationic agents for some MRSA strains may be higher see Table 10 a Generally lower concentrations of disinfectants antiseptics are necessary to kill Gram positive organisms when compared to Gram negative organisms b E coli is resistant to Triclosan c Cetrimide is not an effective disinfectant d Hexachlorophene is bacteriostatic for Gram positive organisms but bacteriocidal when used against Gram negative organisms 17 Which best describes microaerophiles a They require both atmospheric oxygen and CO levels to grow b They cannot grow in the presence of oxygen c They can grow in the presence of oxygen but will not use oxygen d They require oxygen to grow but the levels must lower than the concentration typically