some of these mechanisms include metal efflux out of the cell , sequestration of heavy metals in complexes , and reduction of a metal to less toxic species [ 1 , 2 ] . metal efflux is seen in the case of cd which is detoxified in gram - negative bacteria by rnd - driven system like czc and ncc as zinc and nickel exporters , respectively . in gram - positive bacteria this metal efflux is done via cadmium - exporting p - type atpase as seen in cada pump in s. aureus . hg is transported inside the cells by specific uptake system which is rapidly reduced to abolish the toxic effects of hg on periplasmic proteins by reoxidation . in this way , mercury leaves the cell by passive diffusion and does not remain inside the cell [ 4 , 5 ] . the first detoxification step in gram - negative bacteria is attachment of periplasmic hg - binding protein merp to cations . it probably delivers toxic cations to the mercury transporter system which is subsequently transported into the cytoplasm . inside the cell , hg is reduced into hg by mera , related to the glutathione reductase system . mera protein is also involved in the reduction process of hg after cleavage by mera . multidrug resistance pumps ( mdr ) , responsible for the extrusion of chemically unrelated antimicrobial agents composes alternative resistance pathway . this process is mediated by active export of the toxic compounds by means of the proton motive forces . multidrug resistance to various organic cationic antiseptics and disinfectant compounds as cetyltrimethylammonium bromide ( cetrimide ) has been reported in various organisms including s. aureus , e. coli , and b. subtilis [ 7 , 8 ] . mutations leading to overexpression of the pumps have been identified in clinical isolates of multidrug - resistant strains . among these strains , this intrinsic multidrug resistance is attributed to the lowpermeability of outer membrane and expression of a number of broadlyspecific multidrug efflux ( mex ) pumps as mexab - oprm and mexxy - oprm [ 2 , 9 ] . these pumps are composed of three different peptides : mexa , a fusion membrane protein which apparently docks mexb to oprm , mexb translocase which belongs to the resistance nodulation division ( rnd ) family of solute / proton antiporters and oprm which is an outer membrane porin . the broad specificity of mdrs seems to be matched with the broad resistance of biofilms to antimicrobial agents . mdrs are mostly regulated by environmental factors exemplified by induced expression of e. coli emrab and rnd pump by drug substrate and stress , respectively . the presence of three additional efflux systems as mexcd - oprj , mexef - oprn , and mexjk - oprm due to overexpression of efflux genes by mutational events is addressed by other studies . however these pumps play different roles rather than drug efflux including export of the biocides , dyes , detergents , metabolic inhibitors , organic solvents , and molecules participated in bacterial cell - to - cell communication . in p. aeruginosa , the mexab - oprm multidrug efflux system exports a number of antimicrobial compounds such as -lactams and is responsible for its  intrinsic resistance  to antibiotics . the substrates for mexab - oprm include quinolones , tetracycline , and -lactams [ 2 , 9 , 12 ] . the effectiveness of uv light in biological inactivation aroused from observation of double stranded dna breaks occurred by uv ray . the break point is particularly between pyrimidine bases which alters base pairing and induces formation of new linkage between adjacent nucleotides on the same dna strand . many organisms developed reparative mechanisms to compensate destructive effects of uv radiation as nucleotide excision repair and photo reactivation . since uv radiation is widely used to sterilize operation rooms , utensils , and drinking water , the emergence of bacterial resistance will cause great hygiene problems . as mentioned above , various drug resistance mechanisms are involved in the emergence of pathogen - drug resistance . it is not unusual for pathogens to use combination of these resistance strategies against antimicrobial agents . understanding the synergistic effects of these resistance strategies helps us choose appropriate therapeutic agents against developed resistance . therefore , the aim of this study is to evaluate the prevalence of simultaneous resistance to the above - mentioned factors in some common resistant pathogens . standard bacterial strains were cultured in commercial culture medias as nutrient agar ( na ) , nutrient broth ( nb ) , trypticase - soy agar ( tsa ) , trypticase - soy broth ( tsb ) , muller hinton agar ( mha ) , eosin methylene blue ( emb ) , and macconkey agar . phg - ii and biochemical culture medias were also used for heavy metal resistance and identification of isolated bacteria , respectively . cadmium nitrate , sodium arsenate , and mercury nitrate were used as heavy metals in this study ( table 1 ) . in order to determine the sensitivity / resistance pattern of bacterial strains to antimicrobial agents , disk diffusion assay ( kirby - bauer method ) broth and agar dilution method was used for determination of minimum inhibitory concentration ( mic ) and minimal bactericidal concentration ( mbc ) . determination of the optimal concentration of antimicrobial compounds with the capacity to annihilate 99.9% of the microorganisms was performed using agar on plate method . bacterial resistance to cetrimide was assessed by replica - plating method using steer 's replicator [ 15 , 16 ] . various concentrations of heavy metals added to this medium in plates ( adjusted ph and 55c).then , 0.1  ml of microbial suspension in log - phase was spread on plates . different concentrations of heavy metals were used as follow : cadmium nitrate : 0.0370.0750.150.310.621.232.464.93 ( g / ml ) , mercury nitrate : 0.120.250.501.002.004.00 ( g / ml ) ,   sodium arsenate : 248163264128 ( mg / ml ) . resistance strains to chemical agents were based on the following relations : in s. aureus and e. coli , respectively , growth at the concentrations of 4.16 and 20.83  g / ml in screening method and p. aeruginosa , mic  400  g / ml ,   cadmium , mic  0.62  g / ml , mercury , mic  1  g / ml ,   arsenic , mic  4  mg / ml . the impact of uv ray ( uvc ) on the bacterial growth under laminar flow hood ( slee mains vlfs 636 ) was measured using photonmeter ( hausatech quantum sensor q spar ) . grew bacteria in tbs ( 24  h , 30  rpm ) were diluted in order to achieve approximately 1.5  10/ml bacteria . thereafter , bacterial cultures were exposed to uv radiation in different time intervals ( 0 , 30 , 60 , 120 , and 240 sec ) at the intensity of 0.25 j / ms . the coefficiencies of sensitivity to uv radiation were determined using the following formula : suv = ln [ ( cfu ) d/(cfu ) 0]/d where ( cfu ) 0 indicates the number of bacteria in the certain volume of control samples before uv radiation , ( cfu ) d indicates the number of bacteria in the same volume of sample after uv radiation , and d stands for applied dose in terms of j / m [ 15 , 20 ] . statistical analysis between different experimental assays the percentage of bacterial growth in the presence of different concentrations of cetrimide is demonstrated in figure 1 . the greatest mic and mbc values were 6.25  g / ml and 25  g / ml , 50  g / ml and 200  g / ml , and 400  g / ml and 800  g / ml for staphylococcus , e. coli , and p. aeruginosa , respectively . a significant difference ( p < 0.05 ) was observed between mic and mbc of staphylococcus and e. coli with p. aeruginosa strains . in general , the most prevalent metal resistance was against arsenate ( 95.92% ) , followed by cadmium ( 52.04% ) and mercury ( 36.73% ) ( table 2 ) . the rate of double metal resistance was 25.51% , 52.04% , and 36.67% for cd - hg , cd - as and hg - as , respectively . the rate of triple metal resistance ( cd - hg - as ) was 25.51 . comparison of coefficient of sensitivity to uv rays for the strains of staphylococcus , e. coli , and p. aeruginosa , are demonstrated in figures 24 . in order to evaluate bacterial resistance to uv ray , heavy metals and cetrimide - resistant strains were exposed to uv ray at intensity of 0.25 j / ms for 0 , 30 , 60 , and 120 and 240 second time spans ( figures 5 , 6 , and 7 ) . mean colony numbers grown in the culture medium after 240 seconds of uv radiation were 3.6 , 4.7 , and 6.9 in the strains of p. aeruginosa , e. coli , and staphylococci , respectively . mean numbers of the colonies after 120 seconds of uv irradiation were , respectively , 21.8 , 16.2 , and 13.5 in the strains of staphylococcus , e. coli and p. aeruginosa . there was a significant difference between staphylococcus and standard strains in each group after 60 seconds . such difference was not observed between standard strains , e. coli , and p. aeruginosa . after 240 seconds , there was a significant difference between staphylococcus and p. aeruginosa but not with e. coli . our data demonstrates that the staphylococcus , e. coli and p. aeruginosa have mean sensitivity coefficient to uv ray ( suv ) of 0.461 , 0.466 , and 0.476 , respectively , ( figures 35 ) . the mean colony number in all the strains under study is equal to 52.40 , 17.68 , and 5.46 in 60- , 120- , and 140- second time spans for staphylococcus , e. coli , and p. aeruginosa , respectively . thus , the difference between the colony numbers in 60 , 120 , and 240 seconds of uv radiation was not significant in all of the studied strains ( p > 0.05 , ci of 95% ) . presence of multidrug resistance pumps with capability to extrude chemically unrelated antimicrobial agents has been demonstrated in various living organisms . indeed , gram - negative bacteria exhibit low susceptibility to many antibiotics like penicillin , compared with gram - positive strains . it means ineffectiveness of its most effective gram - positive antibiotics for gram - negative bacteria . intrinsic resistance of gram - negative bacteria is mainly related to the presence of outer membrane barriers . these barriers act as narrow porin channels , which slows down penetration of even small hydrophilic solutes and low fluidity of lipopolysaccharide . there are some clues regarding the presence of other mechanisms besides outer membrane barriers even with species such as p. aeruginosa , which produce an outer membrane of exceptionally low permeability . rapid gain of equilibration across the outer membrane is partly attributed to the large surface - to - volume ratio in a small bacterial cell . therefore , the periplasmic concentrations of many antibiotics are expected to reach 50% of their external concentrations in 10 to 30 seconds in p. aeruginosa and in a much shorter time period than e. coli . additional mechanisms are therefore needed to explain intrinsic resistance like the hydrolysis of the earlier -lactam compounds by the periplasmic -lactamases encoded by chromosomal genes in many gram - negative bacteria . however , recent studies showed that multiple drug efflux pumps with broad specificities play a major role in intrinsic resistance of gram - negative bacteria . cetrimide , used widely as biocide and disinfectants , entered in the pathogen cell wall via outer membrane permeability porins . cetrimide resistance phenotype encoded by plasmid genes in e. coli was shown to be associated with altered composition of outer membrane lipopolysaccharide and diminished porin numbers . cetrimide resistance has been shown with staphylococcus , e. coli , and p. aeruginosa , similar to our findings . the greatest cetrimide resistance by p. aeruginosa seen in our study supports the finding regarding great gram - negative bacteria , mainly pseudomonas , resistance to cetrimide and multiple antibiotics , especially during nosocomial infections . generally , gram - negative bacteria are more biocide resistant than gram - positive bacteria , but it is not always the case . pattern of heavy metal resistance in our studied isolates remark the relative effectiveness of mercury rather than cadmium and specially arsenate for these isolates . great bacterial resistance against arsenate and cadmium makes them poor antimicrobial agents for these organisms , but new agents composed of mercury can be applied more effectively . interestingly , our data demonstrates that double ( mainly with mercury and cadmium ) or triple metal usage might be more effective because of the lower bacterial resistance to these heavy metals . application of ultraviolet spectrums , germicidal ( ultraviolet c ) and solar ( ultraviolet a and b ) , as adjunctive therapy for bioburdens have been previously documented . in our study , uv - radiation resistance in staphylococcus strains was higher than that of the other groups and the strains of e. coli have a higher resistance than p. aeruginosa . overall , our data demonstrates that the general bacterial resistance rate was higher among staphylococcus strains than e. coli strains . despite of the previously published data , regarding the greatest rate of multiple antimicrobial resistances in gram - negative bacteria , our results demonstrated greater general bacterial resistance in staphylococcus strains , a gram - positive bacterium . knowing the great antimicrobial resistance rate in gram - negative bacteria , it will be easy to understand the meaning of the greater rate of resistance among staphylococcus strains . these findings imply the very limited remained therapeutic options and consequently the need for finding new powerful antimicrobial agents .
widespread use of various antimicrobial agents resulted in the emergence of bacterial resistance . 
 mechanisms like direct efflux , formation , and sequestration of metals and drugs in complexes and antiporter pumps are some examples . 
 this investigation aims to investigate the resistance pattern of penicillin - resistant bacterial strains to some physicochemical agents . 
 sensitivity / resistance pattern of common bacterial strains to antimicrobial agents were evaluated by disk diffusion assay . 
 broth and agar dilution method were used for determination of minimum inhibitory concentration and minimal bactericidal concentration . 
 the impact of uv ray on the bacterial growth under laminar flow hood was measured using photonmeter . 
 our data demonstrates that the most prevalent metal resistance was against arsenate ( 95.92% ) , followed by cadmium ( 52.04% ) and mercury ( 36.73% ) . 
 there was significant difference between cetrimide resistances among studied microbial strains especially for p. aeruginosa ( p < 0.05 ) . 
 high rate of pathogen resistance to various antibacterial agents in our study supports previously published data . this great rate of bacterial resistance is attributed to the emergence of defense mechanisms developed in pathogens . the higher general bacterial resistance rate among staphylococcus strains rather than e. coli and p. 
 aeruginosa strains draws attention towards focusing on designing newer therapeutic compounds for staphylococcus strains .