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- Staphylococcal methicillin resistance expression under various growth conditions
- Lee, Yoo Nik , Poo Ha Ryoung , Lee, Young Ik
- J. Microbiol. 1997;35(2):103-108.
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Abstract
- To improve the detection of methicillin resistant staphylococci, lowered incubation temperature (30℃) and inclusion of sodium chloride in media have been empirically recommended. However, in this study, we found that sodium chloride in Peptone-Yeast Extract-K₂HPO₄(PYK) medium decreased methicillin minimum inhibitory concentrations. Divalent cations were shown to restore the expression of staphylococcal methicillin resistance. However, when it was determined by efficiency of plating, sodium chloride increased methicillin resistance expression on agar medium in which higher divalent cations were contained in the agar medium. The decrease of minimum inhibitory concentrations at 30℃ by sodium chloride occurred in Brain Heart Infusion but did not occur in other media investigated. Interestingly, both PYK and Brain Heart Infusion media had peptone, which contain cholic acids having detergent activities. Inclusion of sodium chloride in PYK caused a higher rate of autolysis. Penicillin binding protein 2a that has a low affinity to beta-lactam antibiotics, was highly inducible in methicillin resistant Staphylococcus epidermidis strains. In this study, we found that autolysins that are activated by the sodium chloride decreased the minimum inhibitory concentration at 30℃, and peptidoglycan is weakened due to the presence of methicillin. Peptone in the media may aggravate the fragile cells. However, stabilization due to the presence of divalent cations and production of penicilin binding protein 2a increase the survival of staphylococci.
- Suppressive Effects of Divalent Cations on Self-splicing Inhibition by Spectinomycin of Group 1 Intron RNA
- In Kook Park
- J. Microbiol. 1999;37(4):243-247.
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Abstract
- Effects of divalent cations on self-splicing inhibition by the antibiotic spectinomycin of the phage T4 thymidylate synthase intro (td) have been investigated. Ca^2+ ion at 1mM concentration suppressed splicing inhibition of spectinomycin by 10% and 50 uM Co^2+ ion also suppressed splicing inhibition of specinomycin by 10%. Mg^2+ ion at 6 mM concentration decreased splicing inhibition of spectinomycin by 42% while Mn^2+ ion decreased the splicing inhibition by 10%. Zn^2+ ion at 10 uM concentration lowered the splicing inhibition by spectinomycin of 15%. Of all divalent cations tested, Mg^2+ ion was the most effective in suppressing splicing inhibition by specinomycin whereas Ca^2+ ion was the least effective. The results suggest that spectinomycin may interact with specific and functional Mg^2+ -binding sites within intron RNA that lead to a displacement of Mg^2+ essential for catalytic activity.
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