Comparison of Transcriptional Responses and Metabolic Alterations in Three Multidrug-Resistant Model Microorganisms, Staphylococcus aureus ATCC BAA-39, Escherichia coli ATCC BAA-196, and Acinetobacter baumannii ATCC BAA-1790, on Exposure to Iodine-Containing Nano-micelle Drug FS-1

Abstract

Iodine is one of the oldest antimicrobial agents. Until now, there have been no reports on acquiring resistance to iodine. Recent studies showed promising results on application of iodine-containing nano-micelles, FS-1, against antibiotic-resistant pathogens as a supplement to antibiotic therapy. The mechanisms of the action, however, remain unclear. The aim of this study was to perform a holistic analysis and comparison of gene regulation in three phylogenetically distant multidrug-resistant reference strains representing pathogens associated with nosocomial infections from the ATCC culture collection: Escherichia coli BAA-196, Staphylococcus aureus BAA-39, and Acinetobacter baumannii BAA-1790. These cultures were treated by a 5-min exposure to sublethal concentrations of the iodine-containing drug FS-1 applied in the late lagging phase and the middle of the logarithmic growth phase. Complete genome sequences of these strains were obtained in the previous studies. Gene regulation was studied by total RNA extraction and Ion Torrent sequencing followed by mapping the RNA reads against the reference genome sequences and statistical processing of read counts using the DESeq2 algorithm. It was found that the treatment of bacteria with FS-1 profoundly affected the expression of many genes involved in the central metabolic pathways; however, alterations of the gene expression profiles were species specific and depended on the growth phase. Disruption of respiratory electron transfer membrane complexes, increased penetrability of bacterial cell walls, and osmotic and oxidative stresses leading to DNA damage were the major factors influencing the treated bacteria. IMPORTANCE Infections caused by antibiotic-resistant bacteria threaten public health worldwide. Combinatorial therapy in which antibiotics are administered together with supplementary drugs improving susceptibility of pathogens to the regular antibiotics is considered a promising way to overcome this problem. An induction of antibiotic resistance reversion by the iodine-containing nano-micelle drug FS-1 has been reported recently. This drug is currently under clinical trials in Kazakhstan against multidrug-resistant tuberculosis. The effects of released iodine on metabolic and regulatory processes in bacterial cells remain unexplored. The current work provides an insight into gene regulation in the antibiotic-resistant nosocomial reference strains treated with iodine-containing nanoparticles. This study sheds light on unexplored bioactivities of iodine and the mechanisms of its antibacterial effect when applied in sublethal concentrations. This knowledge will aid in the future design of new drugs against antibiotic-resistant infections.

The Effect of Three Complexes of Iodine with Amino Acids on Gene Expression of Model Antibiotic Resistant Microorganisms Escherichia coli ATCC BAA-196 and Staphylococcus aureus ATCC BAA-39

“…All these facts indicate that the prime target of iodine released by the complexes was the bacterial cell wall, which degraded due to the oxidizing power of iodine and led to an increased penetrability of the affected cells for metal ions and other toxic compounds, including antibiotics. This finding is in agreement with the previous reports where an increased concentration of ROS in the cytoplasm of the microorganisms treated with FS-1 [ 8 , 9 , 10 ]. Abiotic stresses induce an increase in the level of ROS in the cellular cytoplasm resulting in the production of toxic methylglyoxal [ 32 ] and damaging intracellular lipids, proteins, and nucleic acids [ 33 ].…”

“…In order to reduce the intracellular influx of iodine bound to amino acids, the treated cultures down-regulate the activities of the uptake transporters and permeases of organic nitrogen-rich compounds. It appears that E. coli coped better with the prevention of the influx of iodine into cytoplasm than S. aureus , agreeing with the previous study when the drug FS-1 was used [ 9 ]. A deleterious effect of intracellular iodine caused the activation of synthesis of various chaperons and shock proteins in S. aureus that was not observed in the treated E. coli .…”

“…The gene expression patterns were also affected by the growth phases of the bacterial cultures when the complexes were applied. The dissimilarity of responses of the different tested bacterial pathogens at different growth phases was reported in a previous study with the therapeutic complex FS-1 [ 9 ]. It should be noted that Figure 5 presents a general overview of the affected metabolic pathways, which have to be verified in future studies.…”

“…The most common effect of the iodine-containing complexes used in this study was a strong up-regulation of the efflux pumps and detoxication enzymes such as copper transporter copA , multicopper oxidase cueO in E. coli ; zinc transporter zitB , heavy metal ion efflux pump zntA , and mercuric ion reductase merA2 in S. aureus ; and nfsA reductase in both microorganisms. The genes copA , cueO , and zitB were significantly up-regulated when the same model cultures were treated with the drug FS-1 [ 8 , 9 ]. Many other genes associated with the oxidation–reduction processes were also regulated ( Figure 4 ).…”

“…The iodine-containing complex FS-1, initially developed as a supplementary medicine against multidrug-resistant tuberculosis [ 6 ], has also shown the potential to reverse the antibiotic resistance of multidrug-resistant bacteria to antibiotic-susceptible phenotypes lasting at least for a few generations. This effect was demonstrated using three model multidrug-resistant microorganisms: Staphylococcus aureus ATCC BAA-39, Escherichia coli ATCC BAA-196, and Acinetobacter baumanni ATCC-1790 [ 7 , 8 , 9 ].…”