Iron,as the fourth largest metal element in the earth's crust,has been used as an important nutrient element in the evolution of various organisms to participate in important biological processes such as photosynthesis,nitrogen fixation,methanogenesis,hydrogen production and consumption,respiration,tricarboxylic acid cycle,oxygen transport,gene regulation and DNA synthesis^[4]。 Microbes are no exception,and almost all bacterial pathogens require iron for normal survival and reproduction,so vertebrates have evolved a variety of iron-nutritional immune mechanisms(Figure 1)to limit bacterial iron acquisition from the host in order to combat bacterial invasion^[5⇓~7]。

In vertebrates,iron exists mainly in the form of heme(protoporphyrin)complexed with a Fe²⁺）in the tetrapyridine ring,and heme exists in red blood cells.Even if the red blood cells rupture,the released heme will be rapidly bound by haptoglobin and hemagglutinin,so it is difficult for bacteria to obtain sufficient iron nutrition from this way.In addition,part of the iron is stored in eukaryotic cells in the form of ferritin,so it may be accessible to bacteria only after lysis of the host cell.Both dead cells and bacteria are phagocytosed by macrophages,and iron in macrophages may be used by intracellular bacteria.For this reason,NRAMP1 protein located on the phagosomal membrane of macrophages pumps Fe²⁺out of the phagosome to reduce bacterial access to Fe^2+[8]。 In addition,at physiological pH(7.0),extracellular soluble Fe²⁺（0.1 mol/L）will be oxidized to insoluble Fe³⁺（10^-18mol/L）,which is bound by transferrin with very high affinity,and free Fe³⁺can also bind to lactoferrin.Lactoferrin is a globular glycoprotein of the transferrin family,found in secretions such as breast milk,tears,and saliva,as well as in the granules of polymorphonuclear leukocytes,and is a key component of the mucosal immune response to infection^[9]。

Take E.coli as an example,each E.coli has 10⁵~10⁶iron atoms,so if the bacteria need 10⁹cell/mL concentration to infect the host,then the bacteria need 10¹⁸iron atoms per liter per generation,and in a solution of pH 7,the number of iron atoms per liter can be reduced.The solubility of ferric iron is only 10⁷iron atoms/liter,so in order to survive in the host,bacteria have evolved a variety of iron-nutrient immune evasion mechanisms(Figure 2)to obtain iron nutrients,mainly including iron ion uptake channels and heme uptake channels^[10][5⇓~7]。

Because iron is an indispensable nutrient for bacterial growth,it can inhibit bacterial growth by blocking bacterial iron metabolism.Gallium is a transition metal element that has shown therapeutic,diagnostic,and imaging potential in many diseases,including cancer and bacterial infections.The antibacterial effect of Ga³⁺stems from the fact that its ionic radius is almost the same as that of Fe³⁺,so it can replace Fe³⁺（in biological systems such as iron transporters and iron-requiring enzymes that depend on Fe³⁺(Fig.3).However,in the physiological environment,iron exists in the form of reduced Fe²⁺and oxidized Fe³⁺,and the two valence States of iron ions can be freely converted while playing a catalytic or electron transfer function.Unlike iron ions,gallium ions do not have a divalent state and cannot be reduced Ga³⁺,and when added to iron-requiring enzymes,they inactivate Fe³⁺dependent reduction and oxidation processes that are essential for bacterial survival and proliferation^[14]。 In addition,the iron available to bacteria in the host is very limited,so feeding bacterial Ga³⁺can effectively block the iron metabolism of bacteria,thereby inhibiting their growth or killing bacteria 。

In the study of Chitambar et al.,it was determined by radiolabeling that Ga(NO₃)₃could block the absorption of⁵⁹Fe by L1210 cells and inhibit the proliferation of bacteria^[15]。 In Ga³⁺treated cells,the electron spin resonance(ESR)signal of the ribonucleic acid reductase M₂subunit in the cytosolic extract was significantly suppressed;However,the ESR signal returned to normal within 10 min of exposure of these cytoplasmic extracts to ammonium ferric sulfate,a result that confirms that Ga³⁺can inhibit DNA synthesis by specifically limiting the amount of iron required for ribonucleic acid reductase M₂subunit activity 。

Pyochelin is a siderophile produced by the pathogen Pseudomonas aeruginosa.Porcaro et al.Studied the electronic properties and coordination chemistry of the Fe³⁺and Ga³⁺coordination sites in Pyochelin metal complexes by synchrotron radiation induced X-ray electron spectroscopy and X-ray absorption spectroscopy.It was demonstrated that iron and gallium have the same valence in the Pyochelin complex and have the same octahedral coordination geometry,in addition to the finding that the proximity distributions of iron and gallium are similar,strongly supporting a similar coordination chemistry at the origin of the biomimetic behavior of gallium^[17]。 CRISPR/cas9-based genetic mutagenesis studies showed that Pyochelin-facilitated uptake and ABC transporters are the two major pathways of P.Aeruginosa Ga³⁺internalization,and the crystal structure revealed that Ga³⁺and Fe³⁺fully occupy the same metal site of the periplasmic iron-binding protein HitA of the ABC transporter system^[18]。

As can be seen from the iron uptake pathway of bacteria(Fig.4),in addition to the direct use of free iron ions,bacteria can also obtain iron through the uptake of heme,so the analog of heme replaced by gallium,gallium protoporphyrinⅨ(Ga-PP),can also play the role of iron blocking.Because of its similarity to heme,Ga-PP can enter bacteria through the heme uptake channel of bacteria,but the gallium ion in Ga-PP can not carry out redox reaction,so Ga-PP cannot replace heme to participate in important enzymatic activities,resulting in the inactivation of heme-requiring enzymes and the inhibition or death of bacteria。

One heme acquisition system of P.Gingivalis consists of HmuR and HmuY proteins.Olczak et al.Used HmuY,HmuR,and HmuY-HmuR mutants to evaluate the role of HmuY and HmuR proteins in metalloporphyrin acquisition^[19]。 Iron porphyrin IX can support the growth of Porphyromonas gingivalis In a manner similar to heme.in contrast,cobalt(Ⅲ),gallium(Ⅲ),and copper(Ⅱ)protoporphyrin IX exhibit antibacterial activity against Porphyromonas gingivalis,and in the case of HmuY,HmuR,and HmuY-HmuR mutations in PorphyromorphAll metalloporphyrins can inhibit the growth of bacteria,therefore,HmuY protein may not be directly involved in the transport of free metalloporphyrins into bacterial cells,but it may also play a protective role against metalloporphyrin toxicity by binding excess metalloporphyrin compounds.in addition,some studies have confirmed that the antibacterial activity of Ga-PP is related to the production of superoxide dismutase and ROS^[20]。 Ga-PP may also inhibit bacterial growth by targeting cytochrome^[21]。

Unlike traditional antibiotics,which are specifically targeted by bacteria,the targets of IBAT are broad,multi-site and non-specific,and it is difficult for bacteria to prevent the uptake of iron Blockers through mutation.In addition,it takes a great deal of evolution for bacteria to give up their need for iron,and iron blockers act as"Trojans"for nutritional iron.blockers such as gallium and porphyrin gallium are actively ingested by bacteria as urgently needed,so it is difficult for bacteria to become resistant to iron-blocking therapy。

In 1986,Hubbard et al.Reported that reducing the iron content in the medium would limit the growth of Escherichia coli,resulting in the decrease of bacterial respiration rate,non-heme iron and cytochrome levels.Adding Ga³⁺to the iron-deficient medium would further reduce the production of bacteria.Therefore,it was considered that Ga³⁺would affect the low-affinity iron transport system of bacteria^[22]。 Later,Al-Aoukaty et Al.Found that the addition of gallium citrate to the medium could delay the growth phase of Pseudomonas fluorescens,while the addition of Fe³⁺to the medium or the consumption of gallium ions in the medium could reverse this result,and gallium-containing substances were found in the bacterial secretions,which further proved that gallium could be ingested by bacteria and affect bacterial growth^[23]。

Rzhepishevska et al.compared the different bactericidal activities of desferrioxamine gallium and gallium citrate,and studied the effect of the anionic complex of gallium on its antibacterial activity,and found that gallium citrate showed better antibacterial effect than desferrioxamine gallium both in vitro and in vivo,and the Ga³⁺in the form of gallium citrate was more absorbed by Pseudomonas aeruginosa than the Ga³⁺in the form of desferroxamine gallium^[24]。 Metabolomic analysis was used to study the effect of gallium citrate on bacterial cells,and it was found that Ga³⁺could reduce the concentration of glutamate,which was the key metabolite of Pseudomonas aeruginosa,and the concentration of other amino acids was also reduced,indicating that Ga³⁺affected multiple biosynthetic pathways of bacteria 。

Thompson et al.Tested the effect of topical administration of gallium citrate in the treatment of wounds infected by Klebsiella pneumoniae,and showed that wounds infected by Klebsiella pneumoniae healed faster and inflammation was significantly reduced after gallium citrate treatment compared with untreated controls^[25]。

DeLeon et al.Subcutaneously injected gallium malate as low as 25 mg/kg body weight into mice acutely infected with heat-damaged Pseudomonas aeruginosa,which resulted In the survival of all infected mice.gallium maltoate significantly reduced the colonization of Pseudomonas aeruginosa,Staphylococcus aureus,and Acinetobacter baumannii in mice with thermal injury.in addition,gallium maltoate prevented the spread of Pseudomonas aeruginosa infection from the injury site to the whole body^[14]。 in addition,gallium malate has inhibitory activity against drug-resistant bacteria,such as methicillin-susceptible Staphylococcus aureus,methicillin-resistant Staphylococcus aureus,methicillin resistant Staphylococcus epidermidis,and methicillin resistant Staphylococcus epidermidis In planktonic or biofilm^[26]。

gallium maltoxide has also been used as a coating agent for antimicrobial delivery.yaws is an infectious disease transmitted by direct skin contact.Local application of Gallium malate to rabbits with yaws with damaged skin can effectively reduce the number of Treponema pallidum,the pathogen of yaws^[27]。 in addition,when the wound of horse is infected by Staphylococcus aureus,the external application of 0.5%gallium malate can reduce the number of bacteria In the wound,reduce the granulation tissue around the wound,and significantly promote the healing of horse wound^[28]。

Mycobacterium tuberculosis and Mycobacterium avium complex can survive and reproduce in mononuclear macrophages,but antibiotics can not enter macrophages and intracellular bacteria,resulting in antibiotic resistance of intracellular bacteria.Based on the accumulation of Ga³⁺in mononuclear phagocytes and the report that Ga³⁺can not carry out redox cycle by replacing Fe³⁺,thus destroying the iron-dependent metabolic pathway of bacteria,Olakanmi et al studied the effects of Ga³⁺on iron acquisition and iron-dependent metabolic pathway of mycobacteria.It was also found that the complex of Ga³⁺and transferrin(Ga-Tf)produced Fe³⁺reversible concentration-dependent growth inhibition of MAC in Mycobacterium tuberculosis and human macrophages,which proved for the first time that Ga³⁺had an inhibitory effect on intracellular bacteria^[29]。

Transferrin or 2,2'-dipyridyl can limit the iron in the medium and significantly inhibit the growth of Echinococcus baumannii in vitro,and Ga(NO₃)₃alone has a certain inhibitory effect on the growth of Helicobacter baumannii and reduces the burden of Helicobacter baumanii in the lungs of mice,but its bacteriostatic effect is weakened in the presence of serum or transferrin^[30]。

Ga(NO₃)₃inhibits P.Aeruginosa biofilm formation and has been shown to be effective in murine lung and airway infection models^[31,32]。 In order to improve the bacteriostatic effect of Ga³⁺on Pseudomonas aeruginosa,Frangipani et al.Studied the complexation of Ga³⁺with a variety of siderophores and synthetic chelating agents,and found that Ga³⁺complexed with pyochelin at a ratio of 1:2 could inhibit the growth of Pseudomonas aeruginosa more effectively than Ga(NO₃)₃,suggesting that the pyochelin translocator enhanced the ability of Ga³⁺to enter cells^[33]。 In addition,the combination of Ga(NO₃)₃encapsulated in liposome and gentamicin can significantly improve the antibacterial effect of gentamicin on clinical isolates of Pseudomonas aeruginosa^[34]。

Benefiting from the fact that Ga(NO₃)₃has been approved by FDA for the treatment of hypercalcemia of malignancy,the results of phase I clinical trials demonstrate that systemic Ga(NO₃)₃therapy can improve lung function in patients with cystic fibrosis and chronic Pseudomonas aeruginosa lung infection^[35]。 More importantly,bacterial resistance to Ga(NO₃)₃develops slowly compared with antibiotics^[35]。 Later,Olakanmi et al reported that Ga-Tf and the complex of Ga³⁺and lactoferrin(Ga-Lf)could inhibit the growth of Francisella tularensis and Francisella neoformans,significantly reduce the activity of bacterial catalase and superoxide dismutase,and increase the sensitivity of bacteria to hydrogen peroxide,which has great potential in the treatment of pulmonary F.tularensis infection^[36]。

Valappil et al.Prepared phosphate glass doped with gallium（Ga₂O₃）by melt quenching technology,and found that the glass could dissolve and release Ga³⁺.The inhibition zone experiment proves that the bacteriostatic agent has bacteriostatic effect on Escherichia coli,Pseudomonas aeruginosa,Staphylococcus aureus,methicillin-resistant Staphylococcus aureus and Clostridium difficile,and the bacteriostatic effect on Pseudomonas aeruginosa is the best^[37]。 Phosphate glass containing Ga³⁺was prepared by magnetron sputtering to form a high surface energy coating with a thickness of about 400 or 1400 nm.The coating showed good antibacterial effect against Staphylococcus aureus and Escherichia coli through gallium ion release mechanism,and had good cytocompatibility,which had great potential as an implant coating in vivo^[38]。 Gallium can also be modified on the surface of titanium metal by anodic spark deposition technology,or added to titanium alloy by metallurgical method to endow titanium with antibacterial properties and maintain high bone fusion ability^[39][40]。 Gallium-doped chitosan can be prepared into antibacterial coatings for medical implants and instruments by electrophoretic deposition^[41,42]。

Xu et al.Prepared gallium-loaded antibacterial artificial dermis scaffold by using Ga³⁺and collagen solution.In vitro antibacterial test showed that Ga³⁺had good antibacterial performance and did not affect cell proliferation.In vivo experiment,the artificial dermis scaffold could prevent rat wound infection and showed good biocompatibility^[43]。

Xie et al.Synthesized a nanoparticle with gallium ion and photosensitizer indocyanine green,which can act on bacteria by combining photodynamic and iron blocking mechanisms.The photodynamic effect can destroy the bacterial cell membrane and promote the endocytosis of Ga³⁺.It shows the synergistic effect of killing multi-drug resistant bacteria and destroying biofilm,and shows a significant therapeutic effect on infectious liver abscess and keratitis in vivo experiments.At the same time,the ultra-fine nanoparticles can be quickly removed through the renal pathway to ensure biocompatibility^[44]。

In 1999,Stojiljkovic et al.Reported a comparative study of the antibacterial activity of complexes of various metals(gallium,iron,magnesium,cobalt,manganese,silver,palladium,tin,zinc,indium,antimony,copper,nickel,platinum,gadolinium,rubidium and titanium)and protoporphyrinⅨ(PP)against Yersinia enterocolitica,methicillin-resistant Staphylococcus aureus and Staphylococcus erythematosus.The antibacterial activity of Ga-PP was the highest,and the antibacterial effect of Ga-PP was found to be much better than that of Ga³⁺and PP,and the minimum inhibitory concentration was 1%of that of Ga³⁺and PP(Fig.5 )^[20]。 Ma et al.Later found that in addition to Ga-PP,meso-protoporphyrin gallium(Ga-MP)also had a good inhibitory effect on Staphylococcus epidermidis and Pseudomonas aeruginosa,and encapsulated it in a porous polyether polyurethane membrane,which could effectively maintain drug release for at least 3 months.Implanting this material into mice could effectively prevent the implant from being infected by biofilm and significantly improve the survival rate of mice^[45]。 Later,it was reported that Ga-PP and Ga-MP had better antibacterial activity than Ga(NO₃)₃against Acinetobacter baumannii biofilm^[46]。 in addition,when Ga-PP and Ga-MP were encapsulated into single emulsion F127 copolymer nanoparticles,the porphyrin gallium nanoparticles could be taken up by macrophages and maintained antibacterial activity In the cells for 3 days,which could significantly improve the survival rate of Caenorhabditis elegans infected by Pseudomonas aeruginosa and Pseudomonas baumannii^[47]。 Gallium 5,10,15,20-tetrakis(4-methoxyphenyl)chloroporphyrin(Ga-MeOTP)was also encapsulated in F127 nanoparticles,which had a better duration of activity than free Ga-MeOTP in Mycobacterium avium-infected macrophages^[48]。

Acinetobacter baumannii can spread outside the lung and cause fatal bacteremia.de L Léséleuc et al.Found that Acinetobacter baumannii strain LAC-4 is resistant to Ga(NO₃)₃.LAC-4 contains a heme oxygenase gene and expresses a highly efficient heme consumption system.Ga-PP was found to block the heme consumption system of the strain in vitro,completely eliminating the growth advantage of LAC-4 and its tolerance to Ga(NO₃)₃.In vivo experiments showed that intraperitoneal injection of Ga-PP could treat mice with pulmonary infection and prevent the dissemination of LAC-4 outside the lungs,significantly reducing the mortality after infection^[49]。

In vitro broth culture,Ga-PP showed significantly superior ability to inhibit Mycobacterium abscessus than Ga(NO₃)₃,relative to the small differences in inhibitory activity of different gallium salts against clinical isolates of Mycobacterium abscessus.Especially for Mycobacterium abscessus in human macrophages,the activity of Ga-PP is 20 times higher than that of Ga(NO₃)₃,which has great potential for the treatment of Mycobacterium abscessus^[50]。

Hijazi et al.Systematically studied the antibacterial activity of Ga(NO₃)₃,gallium maltate and Ga-PP against ESKAPE species(Enterococcus faecium,Staphylococcus aureus,Klebsiella pneumoniae,Acinetobacter baumannii,Pseudomonas aeruginosa and Enterobacter),and at the same time,considering the influence of iron content in the medium on the antibacterial test results,The antibacterial activity of iron blockers was also compared in standard MHB medium,iron-deficient MHB medium(DMHB),and RPMI-1640 medium supplemented with 10%human serum(RPMI-HS),in which low iron content and serum supplementation better mimic the in vivo environment^[51]。 In MHB and DMHB media,the antibacterial activity of Ga(NO₃)₃and gallium maltoate was limited,except that Ga-PP had antibacterial activity against Staphylococcus aureus and Acinetobacter baumannii;However,in RPMI-HS medium,the antibacterial activity of Ga(NO₃)₃and gallium malate was very obvious,while Ga-PP lost its antibacterial activity,which may be due to the binding of albumin in serum to Ga-PP and counteracting its inhibitory effect.In addition,they found that the presence of multiple heme absorption systems strongly affected the sensitivity of Baumannia to Ga-PP;Ga(NO₃)₃and gallium maltoate only showed bacteriostatic effect,while Ga-PP had bactericidal effect on sensitive strains 。

In the chitosan hydrogel,the antibacterial activity of the combination of Ga-PP and Deferiprone against Pseudomonas aeruginosa and Staphylococcus aureus small colony variant biofilms is significantly better than that of Ga-PP alone,When combined with ciprofloxacin or gentamicin,the combined efficacy of the three compounds exceeds the activity of any single compound,and this anti-biofilm strategy can be used for the treatment of local biofilm-associated infections^[52,53]。

Our research group obtained a water-soluble zwitterionic porphyrin by modifying super-hydrophilic zwitterionic groups on water-insoluble PP molecules.Based on this idea,we modified various hydrophilic groups on Ga-PP to synthesize and optimize a cationic porphyrin gallium heme biomimetic molecule(Ga-CHP)with good water solubility and best antibacterial property(Fig.6)^[54]。 When Ga-CHP was used in IBAT,it showed broad-spectrum and efficient antibacterial activity against Gram-positive bacteria,Gram-negative bacteria,and even multidrug-resistant bacteria,and it was not easy to cause drug resistance.in vivo experiments showed that Ga-CHP could accumulate at the site of infection in mice and significantly promote wound healing^[55]。 in addition,Ga-CHP was used to treat macrophage infection,and Ga-CHP was micropinocytosed into macrophages in an energy-dependent manner,and only 1.6μM of Ga-CHP was required to kill Staphylococcus aureus in macrophages.Ga-CHP treatment significantly reduced The bacterial burden in the abdominal cavity and organs of mice infected with Ga-CHP.in addition,because Ga-CHP is an excellent water-soluble photosensitizer,Ga-CHP-based IBAT can inactivate bacterial catalase(a heme-requiring enzyme),thereby preventing the removal of hydrogen peroxide in bacteria(Fig.7).Under blue light irradiation,combined photodynamic antimicrobial therapy(PDAT)increased the intracellular ROS content by 2.3 times.the combined effect of IBAT and PDAT showed a synergistic effect of 1+1>2.Ga-CHP-based IBAT and PDAT act synergistically in mouse wound anti-infective therapy,significantly outperforming either IBAT or PDAT treatment alone^[55]。 Finally,Ga-CHP was loaded into zwitterionic hydrogel to prepare an antifouling and antibacterial bifunctional contact lens,which can not only resist protein,bacteria and biofilm adhesion,but also release Ga-CHP continuously.99.9%of planktonic bacteria and mature biofilm were killed.With the help of natural sunlight,the symptoms of bacterial keratitis in mice were significantly relieved after wearing the contact lens for 7 days through iron-blocking and photodynamic antibacterial therapy^[56]。

In order to study the relationship between porphyrin molecular structure and antibacterial activity,a series of gallium porphyrin analogues with different charges and heme biomimetic properties(Fig.8)were carefully designed and synthesized.Ga-CHP showed the best inhibitory ability against both Staphylococcus aureus and Escherichia coli,and its MBC against the two bacteria was 12.5μmol/L and 25μmol/L,respectively.Although gallium nitrate has some antibacterial effect,it is much lower than Ga-CHP,especially for E.coli.The positively charged Ga-CHP showed higher antibacterial activity against Staphylococcus aureus and Escherichia coli than the negatively charged Ga-PP and the electroneutral zwitterion-modified gallium porphyrin(Ga-ZMP).It may be that the positively charged cationic group in Ga-CHP helps to improve the targeting ability of porphyrin gallium antibacterial agents to bacteria,and then improve their antibacterial activity.The heme biomimetic structure is another key for bacteria to be able to take up Ga-CHP smoothly.Although gallium tetramethylpyridylporphyrin(Ga-TMP)contains four cationic groups,its antibacterial effect is not better than that of Ga-CHP with two cationic groups.Ga-TMP has better targeting to bacteria,but lacks similarity with heme.Ga-TMPcan not be ingested by bacteria through the heme uptake system,which is the key to its poor antibacterial effect.In contrast,despite the electrostatic repulsion between Ga-PP and bacteria,Ga-PP can still be taken up by bacteria through the heme uptake system after co-culture with bacteria for a long time due to its high similarity to heme.The gallium ion complexed in the porphyrin ring is another key to its antibacterial action.Compared with CHP,Ga-CHP showed better antibacterial effect against S.Aureus and E.Coli,although both compounds had similar bacterial targeting ability and heme biomimetic structure.When Ga-CHP enters the cytoplasm of bacteria through the heme uptake system,it will bind to heme-requiring enzymes(such as catalase),but because Ga-CHP is loaded with Ga³⁺,it can not replace the function of Fe³⁺to participate in the redox reaction of enzyme activity,resulting in bacterial death 。

Compared with traditional antibiotics,iron-blocking antibacterial agents have the advantages of not easy to produce drug resistance and can effectively inhibit drug-resistant bacteria.In collaboration with Grinholc of the University of Gdansk in Poland,our research group has studied in detail the inhibitory ability of Ga-CHP against clinical isolates of ESKAPE pathogens(Enterococcus faecalis,Staphylococcus aureus,Klebsiella pneumoniae,Acinetobacter baumannii,Pseudomonas aeruginosa and Enterobacter).the results showed that Ga-CHP had a significant inhibitory effect on all drug-resistant bacteria,and the bacteriostatic ability was further improved after photodynamic therapy.In addition,Grinholc et al confirmed that Ga-CHP had a significant therapeutic effect on atopic dermatitis(AD)caused by drug-resistant Staphylococcus aureus^[57][57]。

Gallium ion and gallium porphyrin disrupt iron uptake by bacteria in different ways,so the combination of gallium ion and gallium porphyrin blockers may increase the inhibitory effect on bacteria.Choi et al showed that the synergistic combination of Ga-PP and Ga(NO₃)₃was bacteriostatic against Klebsiella pneumoniae and methicillin-resistant Staphylococcus aureus and bactericidal against Pseudomonas aeruginosa under iron-limited conditions.The combination of the two significantly disrupted K.Pneumoniae and P.Aeruginosa biofilms on plasma-coated surfaces and improved the survival of C.Elegans infected with K.Pneumoniae or P.Aeruginosa^[16]。 In addition,the combination of Ga-PP and colistin,or the combination of Ga(NO₃)₃and colistin also showed synergistic activity against Klebsiella pneumoniae and Pseudomonas aeruginosa.Choi et al.Subsequently reported that the combination of Ga-PP and Ga(NO₃)₃also had synergistic inhibitory activity against the growth of Mycobacterium avium,Mycobacterium abscessus,and Mycobacterium tuberculosis,with the strongest inhibitory activity against Mycobacterium abscessus^[58]。 Activity assays showed that Ga(NO₃)₃and Ga-PP inhibited both catalase and aconitase at high concentrations,but had a synergistic effect on M.Abscessus aconitase activity.After intranasal administration,the number of Mycobacterium abscessus bacteria in mice treated with the combination of Ga(NO₃)₃and Ga-PP was significantly lower than that in untreated or single-drug treated mice.These findings suggest that Ga(NO₃)₃and Ga-PP have a significant synergistic effect on several important human bacterial pathogens through dual inhibition of iron and heme metabolism 。