pathogenic bacteria have caused serious diseases and a lot of mortality in many nations , especially in the developing countries .
these agents usually spread quickly , and the most susceptibilities to them have been assigned to the immunocompromised persons , pregnant mothers , children , and older individuals ( 1 ) . along with the progressive resistance of bacteria to the current antibiotics as a result of irregular antibiotic consumption in medicine , the health and general hygiene of people are strongly at risk , and , therefore , to avoid this threat , identification and utilizing novel anti - bacterial compounds are required ( 2 ) . in the recent years
, experimental researches have introduced some thiazole derivatives as the multi - therapeutic effect compounds including anti - cancer , anti - inflammatory , and inhibitor of the parasites like leishmania and the fungi such as candida ( 36 ) . moreover ,
the anti - bacterial effects of these compounds have been proven on a wide range of pathogens like bacillus subtilis , staphylococcus aureus , pseudomonas aeruginosa , and klebsiella aerogenes so that their potency and broad spectrum activity have promised the researchers to replace them with out - dated drugs to which the bacteria are resisting ( 7 ) . also regarding the imidazole derivatives ,
many properties such as the anti - fungal , anti - viral , anti - parasitic , and in - vitro inhibition of cancer cells have been demonstrated , and studying the anti - bacterial effects of these compounds has emphasized their power to inhibit the bacteria such as enterococcus faecalis , staphylococcus aureus , and pseudomonas aeruginosa ( 811 ) .
the potent and wide range anti - bacterial properties of the thiazole and imidazole derivatives have generally made the anti - bacterial test to be among the initial experiments that are studied after synthesizing these agents . in this study
, we evaluated the in - vitro anti - bacterial effects of two novel imidazole and one new thiazole derivatives , which have recently been synthesized in iran , against the bacterial pathogens that are often transferred to the human body by means of food , and cause disease .
1 ) was incorporated into a three - phase process , and its chemical structure was verified by monocrystal x - ray diffraction , h nmr , c nmr , and ir spectroscopic techniques , element decomposition technique , and spectrophotometry .
this synthesized derivative was then dissolved in dmso ( 8000 g / ml ) ( 12 ) .
12 ) . 6 : ( e)-2-(5-acetyl-4-methylthiazol-2-yl)-2-[benzo[d]thiazol-2(3h)-ylidene]acetonitrile steps for synthesis of 3a  b imidazole derivatives ( derivatives from reference no . 13 ) .
3a : 2-(4-methylimidazolidin-2-ylidene ) malononitrile 3b : 2-(4,4-dimethylimidazolidin-2-ylidene ) malononitrile the 3a  b imidazole derivatives were synthesized in a mono - phase process from malononitrile ( 10 mm , 1.7 g ) and 2a  b diaminoalkanes ( 10 mm ) , and their chemical structures were confirmed by monocrystal x - ray diffraction , hnmr , cnmr , and ir spectroscopic techniques , element decomposition technique , and spectrophotometr y. these compounds were then dissolved in dmso ( 8000 g / ml ) ( 13 ) .
the tested bacteria were e. coli ( ptcc 1395 ) , s. dysenteriae ( ptcc 1188 ) , s. typhimurium ( ptcc 1596 ) , p. mirabilis ( ptcc 1076 ) , b. cereus ( ptcc 1665 ) , and l. monocytogenes ( ptcc 1297 ) ; they were obtained from the iranian research organization for science and technology ( irost ) .
each bacterium was cultured in a mueller - hinton agar medium , and incubated at 37 c for 24 h. henceforth , in a sterile medium and in a logarithmic growth phase , a concentration of 0.5 mcfarland ( 1.5  10 cfu / ml ) was obtained using a spectrophotometer and a standard mcfarland tube number 0.5 from each bacterium , which was assigned as the stock solution ( 14 ) .
the mic test was carried out in a sterile 96-well plate by broth microdilution as the clsi ( 15 ) standard .
first , 90 l of the muller - hinton broth medium ( merck , germany ) was added to each well .
then 100 l of the thiazole and imidazole derivatives ( in control groups , 100 l of penicillin and gentamycin antibiotics ( sigma ) with the primary concentration of 256 g / ml ) were added to the first well ( in which the concentration of derivatives was 4000 and concentration of antibiotics was 128 g / ml ) . after mixing , 100 l of this mixture
for a negative control , 100 l of the muller - hinton broth , 100 l of dmso , and 10 l of the bacterial suspension were added to the last well in each row .
the lucidity and turbidity in each well indicated the lack and existence of the bacterial growth , respectively .
the last well that did not show any turbidity by visual method was reported as mic ( 14 ) .
firstly , in the muller - hinton agar medium , the superficial bacterial culture was performed with a swab impregnated to the bacterial suspension .
then 20 l of the mic imidazole and thiazole derivatives obtained and also the antibiotics were shed on blank sterile disks .
after 24 h incubation at 37 c , the growth inhibition zone diameter was measured using a particular ruler .
the results of the growth inhibition zone diameter were provided as the average  standard deviation , and for the aim of analyzing the data , the spss statistical software ( version 22 ) was used ( 14 ) .
1 ) was incorporated into a three - phase process , and its chemical structure was verified by monocrystal x - ray diffraction , h nmr , c nmr , and ir spectroscopic techniques , element decomposition technique , and spectrophotometry .
this synthesized derivative was then dissolved in dmso ( 8000 g / ml ) ( 12 ) .
12 ) . 6 : ( e)-2-(5-acetyl-4-methylthiazol-2-yl)-2-[benzo[d]thiazol-2(3h)-ylidene]acetonitrile steps for synthesis of 3a  b imidazole derivatives ( derivatives from reference no . 13 ) .
3a : 2-(4-methylimidazolidin-2-ylidene ) malononitrile 3b : 2-(4,4-dimethylimidazolidin-2-ylidene ) malononitrile the 3a  b imidazole derivatives were synthesized in a mono - phase process from malononitrile ( 10 mm , 1.7 g ) and 2a  b diaminoalkanes ( 10 mm ) , and their chemical structures were confirmed by monocrystal x - ray diffraction , hnmr , cnmr , and ir spectroscopic techniques , element decomposition technique , and spectrophotometr y. these compounds were then dissolved in dmso ( 8000 g / ml ) ( 13 ) .
the tested bacteria were e. coli ( ptcc 1395 ) , s. dysenteriae ( ptcc 1188 ) , s. typhimurium ( ptcc 1596 ) , p. mirabilis ( ptcc 1076 ) , b. cereus ( ptcc 1665 ) , and l. monocytogenes ( ptcc 1297 ) ; they were obtained from the iranian research organization for science and technology ( irost ) .
each bacterium was cultured in a mueller - hinton agar medium , and incubated at 37 c for 24 h. henceforth , in a sterile medium and in a logarithmic growth phase , a concentration of 0.5 mcfarland ( 1.5  10 cfu / ml ) was obtained using a spectrophotometer and a standard mcfarland tube number 0.5 from each bacterium , which was assigned as the stock solution ( 14 ) .
the mic test was carried out in a sterile 96-well plate by broth microdilution as the clsi ( 15 ) standard .
first , 90 l of the muller - hinton broth medium ( merck , germany ) was added to each well .
then 100 l of the thiazole and imidazole derivatives ( in control groups , 100 l of penicillin and gentamycin antibiotics ( sigma ) with the primary concentration of 256 g / ml ) were added to the first well ( in which the concentration of derivatives was 4000 and concentration of antibiotics was 128 g / ml ) . after mixing ,
10 l of the bacterial suspension was added to each well . for a negative control , 100 l of the muller - hinton broth ,
100 l of dmso , and 10 l of the bacterial suspension were added to the last well in each row .
the lucidity and turbidity in each well indicated the lack and existence of the bacterial growth , respectively .
the last well that did not show any turbidity by visual method was reported as mic ( 14 ) .
firstly , in the muller - hinton agar medium , the superficial bacterial culture was performed with a swab impregnated to the bacterial suspension .
then 20 l of the mic imidazole and thiazole derivatives obtained and also the antibiotics were shed on blank sterile disks .
after 24 h incubation at 37 c , the growth inhibition zone diameter was measured using a particular ruler .
the results of the growth inhibition zone diameter were provided as the average  standard deviation , and for the aim of analyzing the data , the spss statistical software ( version 22 ) was used ( 14 ) .
in this study , the anti - bacterial effects of the 3a  b imidazole derivatives and compound 6 of thiazole were assessed for e. coli , s. dysenteriae , s. typhimurium , p. mirabilis , b. cereus , and l. monocytogenes by means of the growth inhibition zone diameter and mic measurements .
no inhibitory effect of the 3a  b imidazole derivatives against all of the tested bacteria was observed , and only compound 6 of thiazole had an inhibitory effect against s. dysenteriae , p. mirabilis , and l. monocytogenes , among the tested bacteria .
the inhibitory effect of this compound was recorded with the mic values of 1000 , 125 , and 1000 g/ ml , and the zone diameter values of 9.3  0.1 , 15.6  0.2 , and 8.1  0.0 mm for p. mirabilis , s. dysenteriae , and l. monocytogenes , respectively . in the anti - biogram test
performed , the most and least susceptibilities were recorded for b. cereus to gentamicin with the mic value of 0.5 g / ml , and for e. coli to penicillinwith the mic value of 64 g / ml ( tables 1 and 2 ) .
mic values ( g / ml ) for effects of thiazole and imidazole derivatives and antibiotics on tested bacteria .
growth inhibition zone diameter values ( mm ) for effects of thiazole and imidazole derivatives and antibiotics on tested bacteria .
thiazole and imidazole derivatives with high potencies of anti - bacterial activity could be some novel compounds that are used as antibiotics , and in many countries , are in focus of research fields . according to the results obtained for this work , the 3a  b compounds ( two imidazole derivatives ) lacked any inhibitory effect on the tested bacteria , whereas some of the imidazoline derivatives had the ability to inhibit pseudomonas and escherichia coli .
this difference in effect and inhibition potency of these substances is due to the presence of chlorine and phenyl compounds ( 15 ) . beside the lack of effects of the 3a  b derivatives , experiments proved the power of methylnitroimidazole to inhibit the growth of the enterobacteriaceae family such as proteus vulgaris and proteus mirabilis , and this compound could release free radicals that harm bacteria and kill them ; this ability was not observed for the 3a  b derivatives ( 16 ) .
compound 6 of thiazole could only inhibit s. dysenteriae , p. mirabilis , and l. monocytogenes among all the tested bacteria , and its inhibitory effect was much more on s. dysenteriae rather than p. mirabilis and l. monocytogenes .
in the recent studies , inhibition of the bacterial dna or enzymes has been proposed to be the influential mechanism for the inhibitory action of the thiazole derivatives .
inhibition of the bacterial enzyme eckasiii ( or fabh ) ( that is essential for the synthesis of fatty acids in gram negative and gram positive bacteria ) and the enzyme dna - gyrase ( that is needed to replicate the bacterial dna ) have been studied in some research works ( 17 , 18 ) .
noting that the quinolone - family antibiotics and the thiazole derivatives could inhibit the subunits a and b in dna - gyrase , respectively , is promising for the inhibition of the quinolone - resistant bacteria by the thiazole derivatives ( 18 ) .
an important feature in the structure of compound 6 of thiazole is the presence of benzothiazole , and researchers like maddila et al .
have paid attention to the anti - bacterial effects of the benzothiazole derivatives against escherichia coli ; the mic values in the range of 12.5200 g / ml have been evaluated for these compounds , suggesting that their possible potent activities are due to the presence of the chlorophenyl or pyrimidine ring in their structures ( 19 ) . in the experiment performed by patel et al .
the effects of the benzothiazole derivatives on escherichia coli , salmonella typhi , bacillus cereus , and shigella flexneri have been substantiated ; the chlorine and benzoimidazole connections are possibly involved in increasing the anti - bacterial effects of these substances ( 20 ) . in the study carried out by gilani et al .
the mic values in the range of 12.5200 g / ml have been reported , indicating the inhibitory effects of the benzothiazole derivatives against escherichia coli and staphylococcus aureus , in which the chlorine and chlorphenole connections are likely to be involved in increasing the anti - bacterial effects of these compounds ( 21 ) .
have shown the inhibitory effects of the benzothiazole derivatives bonded to cu and zn against staphylococcus aureus , escherichia coli , and bacillus subtilis , proving the potency of these benzothiazole derivatives by attaching to the dna molecules of the bacteria , inhibiting their activities ( 22 ) .
there has been a focus on the anti - bacterial activities of the thiazole derivatives in many research works , in which the growth inhibition zone diameter or mic or both have been measured . in this regard
in which they have shown the in - vitro anti - bacterial potency of the thiazole derivatives against bacillus subtilis , bacillus megaterium , escherichia coli , and pseudomonas aeruginosa by measuring the growth inhibition zone diameter ( 23 ) .
have proved the in - vitro potency of the thiazole derivatives to inhibit salmonella typhi , escherichia coli , klebsi - ella pneumoniae , vibrio cholera , and staphylococcus aureus by measuring the values for the growth inhibition zone diameter and mic ( 24 ) .
juspin et al . have carried out an experiment , in which the growth inhibition zone diameter and mic values were measured , and the in - vitro power of the thiazole derivatives to inhibit the activities of escherichia coli , pseudomonas aeruginosa , and staphylococcus aureus was confirmed ( 25 ) .
with respect to the inhibitory effect of the thiazole derivatives and their synergistic effect with other antibiotics , it is suggested to assess their therapeutic and toxic effect in laboratory animals , and is recommended to do more researches in order to better recognize these compounds and their possible functionality .
 background and objectives : bacterial resistance to antibiotics has motivated the researchers to evaluate the novel anti - bacterial compounds such as some thiazole and imidazole derivatives . thereby , in this work , we investigated the anti - bacterial effects of one new thiazole and two new imidazole derivatives on bacillus cereus , listeria monocytogenes , escherichia coli , salmonella typhimurium , proteus mirabilis and shigella dysenteriae.materials and methods : the thiazole and imidazole derivatives were dissolved in dmso . 
 the disk diffusion method was utilized to measure the growth inhibition zone diameter values , and the broth micro - dilution method was applied to determine the minimum inhibitory concentration ( mic ) values.results:the synthesized imidazole derivatives lacked any inhibitory effect against the tested bacteria . on the other hand , although the synthesized thiazole derivative showed no inhibitory effect against bacillus cereus , salmonella typhimurium , and escherichia coli , it inhibited the growth of proteus mirabilis , shigella dysenteriae , and listeria monocytogenes with the mic values of 1000 , 125 , and 1000 g / ml , respectively , and the growth inhibition zone diameter values of 9.3  0.1 , 15.6  0.2 , and 8.1  0.0 mm , respectively.conclusion:the anti - bacterial effect of the synthesized thiazole derivative on shigella dysenteriae , proteus mirabilis and listeria monocytogenes was proven . however , its inhibition effect against shigella dysenteriae was more than that against the others . 
 many in - vitro and in - vivo experiments are required to evaluate the effects of this compound on the bacteria and the human body . 
INTRODUCTION
MATERIALS AND METHODS
Synthesis of derivatives.
Preparing bacterial suspension.
Minimum inhibitory concentration (MIC) determination.
Growth inhibition zone diameter determination.
RESULTS
DISCUSSION
CONCLUSION