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reduction or elimination of microflora during root canal treatment is achieved by the combined effect of both chemomechanical preparation and intracanal medications .
the removal of microorganisms and other irritants from the confines of the root canal is conducted by means of the mechanical action of instruments and the flow and backflow of the irrigating solutions .
biopure mtad ( dentsply / tulsa , tulsa , ok , usa ) , which is a mixture of a tetracycline isomer , citric acid , and a detergent , has been recommended as a final rinse irrigant because of its antimicrobial properties and its ability to remove the smear layer .
aztreonam , which is a synthetic monocyclic beta - lactam antibiotic , has a molecular structure different from older beta - lactam antibiotics as it has a less complex nucleus .
metronidazole , a nitroimidazole compound , is a broad - spectrum antibiotic and exhibits activity against anaerobic bacteria and protozoa .
it demonstrates effective antibacterial activity against anaerobic cocci as well as gram - negative and gram - positive bacilli . in the treatment of periodontal disease , it has been used both topically and systemically .
the objective of this research was to assess and compare the antibacterial and antifungal effectiveness of biopure mtad , aztreonam , and metronidazole against obligate anaerobic bacteria , i.e. , bacteroides fragilis and propionibacterium acnes , facultative anaerobic bacteria , i.e. , enterococcus faecalis , and yeast , i.e. , candida albicans .
the microorganisms selected for this study , i.e. , b. fragilis atcc 25285 ( group 1 ) , p. acnes atcc 6921 ( group 2 ) , e. faecalis atcc 29212 ( group 3 ) , and c. albicans atcc 10231 ( group 4 ) , were obtained from the american type culture collection and stored at a temperature of 10c to 20c in a freezer .
strains of the selected microorganisms were reactivated in the respective media at a given temperature and time .
groups 1 and 2  activated in brain  heart infusion broth supplemented with hemin and menadione at 37c for 48 h. group 3  activated in brain  heart infusion broth for 24 h at 37c .
group 4  activated in sabouraud dextrose agar broth at 37c for 24 h. after the revival of microorganisms , four to five well - isolated colonies of each strain were picked up with a sterile loop , later dissolving them in respective test tubes containing 0.85% of 5 ml sterile saline to create a turbidity of 0.5 mcfarland scale ( 1.5  10 cfu / ml ) for the preparation of inoculum .
the resulting suspension was then spread on agar plates with the help of a sterile cotton swab in a form so that a lawn growth was observed .
the media used for the four groups were as follows : group 1  wilkins - chalgren agar plate ( himedia , mumbai ) .
group 2  brain  heart infusion medium ( himedia , mumbai ) with 1% glucose .
1 was used to prepare 6-mm diameter discs , which were later soaked in 40 l of normal saline and biopure mtad , respectively .
the company - made aztreonam and metronidazole antibiotic discs ( bd diagnostic , india ) were also used for the test .
these antibiotic discs were then aseptically transplanted to the agar plate formerly incubated with microorganisms . for group 1 and group 2 , agar plates biopure mtad , aztreonam , metronidazole , and normal saline containing discs , and for group 3 and group 4 , agar plates , biopure mtad , aztreonam , and normal saline prepared discs were transferred aseptically .
group 1 and group 2 agar plates were incubated in an anaerobic environment created using the anoxomat system ( mart microbiology bv , netherlands ) for 48 h. group 3 and group 4 plates were incubated for 48 h at 37c under the aerobic conditions , in an atmosphere of 10% co2 , in a co2 incubator ( new brunswick , usa ) .
antibiotic solution of biopure mtad was prepared by mixing powder and diluent . sterilized whatman paper no .
1 was used to prepare 6-mm diameter discs , which were later soaked in 40 l of normal saline and biopure mtad , respectively .
the company - made aztreonam and metronidazole antibiotic discs ( bd diagnostic , india ) were also used for the test .
these antibiotic discs were then aseptically transplanted to the agar plate formerly incubated with microorganisms . for group 1 and group 2 , agar plates biopure mtad , aztreonam , metronidazole , and normal saline containing discs , and for group 3 and group 4 , agar plates , biopure mtad , aztreonam , and normal saline prepared discs were transferred aseptically .
group 1 and group 2 agar plates were incubated in an anaerobic environment created using the anoxomat system ( mart microbiology bv , netherlands ) for 48 h. group 3 and group 4 plates were incubated for 48 h at 37c under the aerobic conditions , in an atmosphere of 10% co2 , in a co2 incubator ( new brunswick , usa ) .
the results obtained were statistically evaluated using one - way anova test and the intergroup comparison was done using bonferroni multiple comparison test . value of p < 0.001 was considered statistically significant . 

bacteroides fragilis ( group 1 ) [ tables 1a and b]propionibacterium acnes ( group 2 ) [ tables 2a and b]enterococcus faecalis ( group 3 ) [ tables 3a and b]candida albicans ( group 4 ) [ tables 4a and b ] . 
 
bacteroides fragilis ( group 1 ) [ tables 1a and b ] propionibacterium acnes ( group 2 ) [ tables 2a and b ] enterococcus faecalis ( group 3 ) [ tables 3a and b ] candida albicans ( group 4 ) [ tables 4a and b ] . effect of root canal irrigants and their values of zone of inhibition against bacteroides fragilis intergroup comparison of mean zone of inhibition size for the irrigants against bacteroides fragilis effect of root canal irrigants and their values of zone of inhibition against propionibacterium acnes intergroup comparison of mean zone of inhibition size of irrigants against propionibacterium acnes effect of root canal irrigants and their values of zone of inhibition against enterococcus faecalis intergroup comparison of mean zone of inhibition size for irrigants against enterococcus faecalis effect of root canal irrigants and their values of zone of inhibition against candida albicans intergroup comparison of mean zone of inhibition size of irrigants against candida albicans
disc diffusion technique , a well - established method for antimicrobial research , has been applied in this study .
this method has an advantage that chemical properties of tested medicaments do not alter during the procedure and also it is less technique sensitive .
anoxomat system was used for anaerobic culture in the current study as earlier research had shown that with the use of this system commendable growth is achieved , in terms of density and colony size .
evidently , the anoxomat method is considerably reliable and appears to support the growth of strict anaerobes efficiently . zone of inhibition around specimens was measured in the present study using a vernier caliper at three different points as done in previous studies . in the present study
tabulated results demonstrated that metronidazole produced the maximum zone of inhibition against b. fragilis [ graph 1 ] .
demonstrated that metronidazole was effective against b. fragilis , which is in agreement with the results obtained in the current study .
comparison of mean zone of inhibition of root canal irrigants against bacteroides fragilis antimicrobial efficacy against p. acnes in the existing study was shown to be maximum by metronidazole [ graph 2 ] .
effect of metronidazole on p. acnes has been reported with mixed findings in the literature .
gaetti - jardim jnior et al . determined the positive antibacterial effect of metronidazole against p. acnes , and the results obtained were in accordance with the present study .
similarly , effat khodeinae et al . demonstrated that 2% metronidazole showed adequate efficacy against p. acnes while evaluating the efficacy of 2% metronidazole gel against acne vulgaris .
in contrast to the above results , few studies reveal no effect of metronidazole against p. acnes .
comparison of mean zone of inhibition of root canal irrigants against propionibacterium acnes metronidazole is a potent bactericidal , which is efficacious against anaerobes that are composed of electron transport components , i.e. , ferredoxin , which are capable of donating electrons to metronidazole , developing highly reactive nitro radical anions that kill susceptible organisms by a radical - mediated mechanism .
this could be a possible reason for its high antimicrobial efficacy against b. fragilis and p. acnes . in the present study ,
metronidazole was not used to test antimicrobial efficacy for e. faecalis and c. albicans because it is ineffective against facultative anaerobes .
krishna et al . in their study demonstrated that 10% metronidazole was not effective against e. faecalis among the tested intracanal medicaments .
demonstrated that long - standing metronidazole therapy preferred the establishment of c. albicans in the oral cavity of rats . in the current study , maximum mean zone of inhibition against e.
faecalis was revealed by biopure mtad [ graph 3 ] , which is in accordance with several other studies .
newberry et al . in their study identified that seven out of the eight tested strains of e. faecalis growth were affected when mtad was used as a final irrigant .
however , results of this research are in contradiction to reports which refute the antimicrobial effect of mtad against e. faecalis .
comparison of mean zone of inhibition of root canal irrigants against enterococcus faecalis in the present study , antifungal effect against c. albicans was shown only by mtad this result obtained was in agreement with the result given by arslan et al . , who demonstrated antimicrobial action of mtad against c. albicans and e. faecalis .
the antifungal effect of mtad can be attributed to the better flow and penetration properties of doxycycline .
showed that mtad is ineffective against c. albicans and its substantivity may be altered when used in conjunction with naocl .
mtad in the current research has revealed substantial zone of inhibition against both b. fragilis and p. acnes .
this may be possibly due to the occurrence of doxycycline as earlier research has confirmed the action of doxycycline on b. fragilis and p. acnes in inhibiting the protein synthesis .
aztreonam in the present study showed significant antimicrobial efficacy against b. fragilis and mild antibacterial activity against e. faecalis but was completely inactive against p. acnes and c. albicans microorganisms .
aztreonam , a bactericidal antibiotic , acts by interrupting with the formation of the bacterial cell wall .
it causes lysis and death of gram - negative bacteria by binding to the penicillin - binding protein-3 ( pbp-3 ) , which might be the reason for its activity against b. fragilis .
poor affinity has been shown for the pbp-3 of gram - positive and anaerobic bacteria which could be the reason behind its mild activity against e. faecalis .
on the basis of results obtained in the current study , it may be stated that biopure mtad can be recommended as an effective alternative to the currently used root canal irrigants due to its superior antimicrobial properties against both aerobic and anaerobic microbial organisms as well as c. albicans .
metronidazole and aztreonam , on the other hand , are , however , not significantly efficacious against all strains of microbes commonly present in the root canal , thus limiting their use as an effective antimicrobial root canal irrigant .
although the present study was done with strict adherence to all the scientific protocols , still further studies are required to evaluate the efficacy of the different irrigants , which may further widen their horizon in the field of endodontics .
objective : this study aims to evaluate and compare the antimicrobial efficacy of three selected root canal irrigants ( biopure mtad , metronidazole , aztreonam ) against microbes commonly isolated from polymicrobial microbiota of root canal infection.materials and methods : this study was designed with four experimental groups ( group i  bacteroides fragilis , group ii  propionibacterium acnes , group iii  
 enterococcus faecalis , group iv  
 candida albicans ) based on the microbes selected for the study . 
 group i and group ii bacteria were used to compare and evaluate antimicrobial effect of biopure mtad , metronidazole , aztreonam , and normal saline . 
 group iii and group iv bacteria were used to compare and evaluate antimicrobial efficacy of biopure mtad , aztreonam , and normal saline . 
 normal saline was used as a control irrigant in this study . 
 agar disc diffusion method was applied to assess and compare the antimicrobial action of selected irrigants.results:metronidazole was found to be the most effective root canal irrigant against b. fragilis and p. acnes among the tested irrigants . 
 mean zone of inhibition against e. faecalis has been shown to be maximum by biopure mtad , followed by aztreonam . 
 antifungal effect against c. albicans was only shown by biopure mtad.conclusions:overall , biopure mtad is the most effective root canal irrigant as it has shown an antibacterial effect against all the tested microorganisms . 
 however , metronidazole showed maximum antibacterial effect against obligate anaerobes . 
 aztreonam also showed an antibacterial effect in the present study , raising its possibility to be used as a root canal irrigant in the future .