Antimicrobial activity of Ca(OH)2 dental cements: an in vitro study

The effect of five commercial calcium hydroxide root canal medications (XR-SPAD, Calcicur, Hy-cal, Root-cal, Hypo-cal) and two calcium hydroxide mixtures (with water or glycerin) on the growth of (a) three anaerobic bacteria associated with endodontic infections; and (b) saliva bacterial strains was determined using the agar diffusion inhibitory test. Statistically significant zones of bacterial growth inhibition for all the bacteria tested were observed. Calcium hydroxide mixed with glycerin showed the largest zones of bacterial inhibition, whereas Root-cal was the least active. These results underline the necessity to evaluate the antibacterial potential of endodontic medications against the different bacterial strains commonly isolated from infected root canals.     

In vitro antimicrobial activity of different gutta-percha points and calcium hydroxide pastes

The aim of this study was to evaluate the antimicrobial activity of different trademarks and compositions of gutta-percha points and calcium hydroxide pastes used in endodontic therapy. The evaluated material consisted of gutta-percha points containing calcium hydroxide (Roeko), gutta-percha points containing chlorhexidine (Roeko), two conventional gutta-percha points (Endo Points and Roeko) and two calcium hydroxide pastes (Calen and Calen/PMCC). Antimicrobial tests included five species of microorganisms: Escherichia coli (ATCC10538), Staphylococcus epidermidis (ATCC12228), Staphylococcus aureus (ATCC6538), Pseudomonas aeruginosa (ATCC27853), and Micrococcus luteus (ATCC9341). The Agar diffusion method was employed. The plates were kept at room temperature for 2 h for prediffusion and then incubated at 37 degrees C for 24 h. The triphenyltetrazolium chloride gel was added for optimization and the zones of inhibition were measured. Statistical evaluation was carried out using analysis of variance and Tukey Test. The obtained results showed that all microbial species used in the study were inhibited by the gutta-percha points containing chlorhexidine and by the calcium hydroxide pastes (Calen and Calen/PMCC), with similar results (p > 0.05). No antimicrobial activity was observed for the other groups. It was concluded that the gutta-percha points containing chlorhexidine presented antimicrobial activity, whereas the gutta-percha points containing calcium hydroxide did not.     

Antimicrobial effect in vitro of chlorhexidine and calcium hydroxide impregnated gutta-percha points

The aim of this study was to evaluate the antimicrobial activity of points containing antiseptics used for temporary obturation in endodontics. Points containing calcium hydroxide (Roeko and Hygienic), and chlorhexidine (Roeko) were tested and gutta-percha points served as control (Meta Dental Corp.). The following microorganisms were studied: Streptococcus mutans (Sm), Enterococcus faecalis (Ef), Staphylococcus aureus (Sta), Candida albicans (Ca), Fusobacterium nucleatum (Fn) ATCC 25586, Porphyromonas gingivalis (Pg) ATCC 33277, and Prevotella intermedia (Pi) ATCC 25611. The experiments were organized in three stages: 1st stage: one point of each kind was placed on agar plates previously seeded with microorganisms. 2nd stage: Another group of points was immersed in broth for 24 hours and placed on the seeded agar. Samples were then incubated at 37 degrees in the conditions of oxygen and for the time required by each microorganism. The zones of bacterial inhibition around each point were measured. The pH values of the broths were recorded. 3rd stage: the immersion broths were inoculated with suspensions of microorganisms, incubated, seeded on plates by dissemination and incubated. CFU counts were performed. RESULTS: points containing chlorhexidine showed inhibition zones with every microorganism in the 1st stage and, in the 2nd stage, with most of the microorganisms studied, except for Fn and Pi. Calcium hydroxide containing points did not inhibit any of the microorganisms assessed. Broth pH values did not exhibit any changes. CFU counts of the broths in which chlorhexidine points had been immersed showed total inhibition for all the microorganisms. The differences between materials were statistically significant (p<0.05) (ANOVA). In the conditions of this study, chlorhexidine-containing points proved to be effective against most of the tested strains.     

Antibacterial efficacy of a new chlorhexidine slow release device to disinfect dentinal tubules

Dentinal tubules of 27 cylindrical bovine root specimens were infected with Enterococcus faecalis. In nine specimens, 5% chlorhexidine was placed in a slow-release device (Activ Point) for 7 days, in another nine irrigation with 10 ml of 0.2% chlorhexidine was used, and the remaining nine served as positive control. Powder dentin samples obtained from within the canal lumina using ISO 025 to 033 burs were examined for the presence of vital bacteria by inoculating brain-heart infusion plates and counting colony forming units. Results were analyzed using analysis of variance and covariance with repeated measures. Heavy bacterial infection was observed at the layer close to the lumen in the control specimens, decreasing rapidly from layer to layer up to the deepest layer tested (400-500 microm), which contained several hundred colony forming units. Viable bacteria in each layer of dentin were significantly reduced with chlorhexidine irrigation solution (p < 0.01) and were completely eliminated with the chlorhexidine slow-release device (p < 0.01).     

两种根管消毒药物体外抑菌作用的比较研究

目的：探讨氢氧化钙制剂ApexCal、2%洗必泰（CHX）及两者配伍制剂对感染根管内常见菌的体外抑制作用。方法：采用琼脂扩散实验测定ApexCal、2%CHX及ApexCal与2%CHX1∶1混合对粪肠球菌、粘性放线菌、牙髓卟啉单胞菌、牙龈卟啉单胞菌和中间普氏菌形成的抑菌环直径并进行统计学比较。结果：2%洗必泰的抑菌作用显著高于ApexCal,ApexCal/2%CHX的抑菌作用显著低于2%CHX,但对粪肠球菌的抑菌作用明显优于Apex-Cal。结论：2%CHX和ApexCal/2%CHX可以作为有效的根管消毒剂,具有临床实用价值。     

In vitro cytotoxicity of medicated and nonmedicated gutta-percha points in cultures of gingival fibroblasts

This investigation was designed to test the cellular toxicity of two medicated (Roeko activ point and Roeko Calcium Hydroxide) and four nonmedicated brands of gutta-percha (GP) points (Antaeos, DeTrey White, Roeko color, and Roeko Top color). The test points were transferred into a culture medium including the GP-point material with a concentration of 6 mg/ml, and eluates were obtained after 72 h. Five milliliters of each eluate were pipetted onto fibroblast cultures, incubated, and subsequently stained. Mitotic rates, cell densities, and the distribution of normal cells, pathologically altered and dead cells were determined and correlated with control cell cultures. Roeko activ point (containing chlorhexidine) resulted in the highest number of dead cells. The difference was statistically significant in comparison with all other materials. Concerning all parameters mentioned, the cytotoxicity of the points containing calcium hydroxide (Roeko Calcium Hydroxide) was not significantly different from all other points tested, with the exception of those containing chlorhexidine. All tested gutta-percha materials caused cytotoxic reactions in varying extents. Taking into consideration the limitations of an in vitro experiment, points containing calcium hydroxide and nonmedicated points seem to be the most recommendable products for clinical use.     

Antimicrobial activity of sodium hypochlorite and chlorhexidine by two different tests

The aim of this study was to evaluate the antimicrobial capacity of sodium hypochlorite (1% and 5%) and chlorhexidine (0.12%, 0.5% and 1%) with or without the addition of organic material (bovine serum albumin, BSA) against some bacterial samples (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Porphyromonas gingivalis and Fusobacterium nucleatum) using two activity tests (contact and diffusion agar tests). In the contact test (first model), bacterial samples were kept in contact with each irrigating solution for different time intervals: immediately (t(0)), 5 min (t(5)), 15 min (t(15)) and 30 min (t(30)). The agar diffusion test was the second model used. In half the specimens, 0.5% BSA was added to simulate organic tissue present in the root canal. Bacterial growth was evaluated for each microorganism and activity test. Each test was repeated 10 times. In the contact test, 0.12% chlorhexidine solution (CHX) did not eliminate E. faecalis at any tested time. CHX at 0.5% eliminated all strains except E. faecalis after immediate contact. All strains were eliminated by 1% CHX, 1% NaOCl and 5% NaOCl. BSA did not interfere with the antimicrobial activity of the irrigating solutions. In the agar diffusion test, all solutions exhibited zones of antimicrobial activity; however, BSA interfered with the antimicrobial activity of NaOCl and CHX. Under the condition of the contact test, the 0.12% CHX was ineffective in eliminating E. faecalis, while 0.5% CHX, 1% CHX, 1% NaOCl and 5% NaOCl showed antibacterial effectiveness against all the tested bacterial strains. The addition of an organic load interfered with the accuracy of the agar diffusion test.     

Efficacy of calcium hydroxide: chlorhexidine paste as an intracanal medication in bovine dentin

The purpose of this study was to evaluate the antibacterial efficacy of an intracanal medication composed of calcium hydroxide with 2% chlorhexidine. Dentin from 24 bovine incisors was used. The incisors were made into standardized cylindrical segments of dentin and infected with Enterococcus faecalis. They were then treated with an intracanal paste composed of calcium hydroxide and sterile water or an intracanal paste composed of calcium hydroxide and 2% chlorhexidine for 1 week. Dentin shavings were collected, suspended in solution, and spread on brain-heart infusion agar. After incubation, colony-forming units were enumerated. The amount of bacteria per mg of dentin was determined. The calcium hydroxide paste with 2% chlorhexidine was significantly more effective at killing E. faecalis in the dentinal tubules than calcium hydroxide with water.     

Residual antibacterial activity of chlorhexidine digluconate and camphorated p-monochlorophenol in calcium hydroxide-based root canal dressings

The purpose of this study was to evaluate the residual antibacterial activity of several calcium hydroxide [Ca(OH)2]-based pastes, placed in root canals of dogs' teeth with induced chronic periapical lesions. Root canals were instrumented with the ProFile rotary system and filled with 4 pastes: G1 (n=16): Ca(OH)2 paste + anesthetic solution; G2 (n=20): Calen paste + camphorated p-monochlorophenol (CMCP); G3 (n=18): Calen; and G4 (n=18): Ca(OH)2 paste + 2% chlorhexidine digluconate. After 21 days, the pastes were removed with size 60 K-files and placed on Petri plates with agar inoculated with Micrococcus luteus ATCC 9341. Pastes that were not placed into root canals served as control. After pre-diffusion, incubation and optimization, the inhibition zones of bacterial growth were measured and analyzed by Mann-Whitney U test at 5% significance level. All pastes showed residual antibacterial activity. The control samples had larger halos (p<0.05). The mean residual antibacterial activity halos in G1, G2, G3 and G4 were 7.6; 10.4; 17.7 and 21.4 mm, respectively. The zones of bacterial growth of G4 were significantly larger than those of G1 and G2 (p<0.05). In conclusion, regardless of the vehicle and antiseptic, all Ca(OH)2-based pastes showed different degrees of measurable residual antibacterial activity. Furthermore, unlike CMCP, chlorhexidine increased significantly the antibacterial activity of Ca(OH)2.     

In vitro study of the indirect action of calcium hydroxide on the anaerobic flora of the root canal

The aim of this study was to evaluate in vitro a possible mechanism involved in the antimicrobial action of calcium hydroxide, namely absorption of carbon dioxide from the roof canal. Twenty obligate and 20 facultative anaerobic bacteria isolated from infected root canals and identified to species level were used. For each bacterial species a standard concentration was achieved and 0.1 ml of the inoculum was spread on blood agar plates, which were consecutively incubated in an anaerobic chamber for 5–7 days. One experimental and one control group were studied: the experimental group included one plate with the bacterial species as well as one open plate containing 32 g calcium hydroxide paste at a mixing ratio of 6:4. Both plates were incubated in an anaerobic chamber for 72 h. The control group included only one plate containing the same bacterial species and was incubated under the same conditions. After a 72-h incubation, the number of the recovered bacteria were counted in both groups. Statistical analysis showed that the number of bacteria recovered from the control group was significantly lower than that of the experimental group, but no particular resistance of any bacterial species to calcium hydroxide could be detected. This finding strongly suggests that the ability of calcium hydroxide to absorb carbon dioxide may contribute to its antibacterial activity.     

Inactivation of root canal medicaments by dentine,hydroxylapatite and bovine serum albumin

AIM: This study examined and compared the inhibition of the antibacterial effect of saturated calcium hydroxide solution, chlorhexidine acetate and iodine potassium iodide by dentine, hydroxylapatite and bovine serum albumin. METHODOLOGY: Enterococcus faecalis strain A197A prepared to a suspension of 3 x 10(8) cells per ml in 0.5% peptone water was used. Fifty microL of saturated calcium hydroxide solution, 0.05% chlorhexidine acetate or 0.2/0.4% iodine potassium iodide were incubated at 37 degrees C with 28 mg dentine powder (DP), hydroxylapatite (HA) or bovine serum albumin (BSA) in 50 microL water for 1 h before adding 50 microL of the bacterial suspension. Samples for bacterial culturing were taken from the suspension 1 and 24 h after adding the bacteria. In further experiments, the amount of dentine was stepwise reduced from 28 mg 150 microL-1 to 2.8 mg 150 microL-1. RESULTS: Calcium hydroxide was totally inactivated by the presence of 28 mg of DP, HA or BSA. Chlorhexidine (0.05%) was strongly inhibited by BSA and slowed down by dentine. However, HA had little or no inhibitory effect on chlorhexidine. The antibacterial effect of 0.2/0.4% iodine potassium iodide on E. faecalis was totally inhibited by dentine (28 mg), but was practically unaffected by HA or BSA. A stepwise reduction of dentine from 28 mg 150 microL-1 to 2.8 mg 150 microL-1 was followed by a similar reduction of the inhibition of the antibacterial activity of chlorhexidine. Iodine potassium iodide was not inhibited at all with dentine amounts less than 28 mg. However, the effect of saturated calcium hydroxide solution was totally eliminated by dentine, in all four concentrations. CONCLUSION: Inhibition by dentine of the antibacterial activity of calcium hydroxide, chlorhexidine and iodine potassium iodide occurs by different mechanisms. Different components of dentine may be responsible for the inhibition of these three medicaments. Calcium hydroxide was particularly sensitive to inhibition by both inorganic and organic compounds.     

In situ antimicrobial effectiveness of chlorhexidine and calcium hydroxide: gel and paste versus gutta-percha points

The aim of this study was to determine the antibacterial effectiveness of either chlorhexidine or calcium hydroxide integrated in gutta-percha points compared with chlorhexidine or calcium hydroxide delivered as gel or paste, respectively. A total of 70 initially sterile roots with open accesses were carried for 1 week in the oral cavities of two volunteers. The roots were then removed, and samples were taken from the root canals for microbial analysis. The roots were medicated with calcium hydroxide paste, 5% chlorhexidine gel, or a chlorhexidine- or calcium hydroxide-containing gutta-percha point. The accesses were closed with bonding material, and the roots incubated for 1 week. After removal of the antimicrobial agents, roots were again checked for bacterial growth. One thioglycolate-soaked paper point was then introduced into each canal, and roots were incubated for 1 week more to observe bacterial regrowth. After 1 week of medication, the absolute bacterial count revealed significant differences compared with the controls. However, only the chlorhexidine-gel and the calcium hydroxide paste group showed no microbial colonization in a considerable number of samples after 1 and 2 weeks.     

Antimicrobial activity of extracts of calcium hydroxide points

The purpose of this study was to evaluate in vitro the antibacterial effect of calcium hydroxide points by using a broth dilution test. Extracts of calcium hydroxide points and a calcium hydroxide paste (Calasept) were tested by using 2 facultative anaerobic bacteria, Streptococcus mutans (ATCC 27352) and Enterococcus faecalis (ATCC 29212). Saline solution was used as a control. Each tested agent was kept in contact with the bacterial species used for the experiment for 5 minutes, 1 hour, 1 day, 2 days, and 5 days. Results showed that Calasept paste was effective in killing the tested bacteria, whereas calcium hydroxide points and saline showed bacterial survival in all experimental periods. It was concluded that calcium hydroxide points extract is not an effective antimicrobial agent against the tested bacteria.     

A comparison of the antimicrobial efficacy of three calcium hydroxide formulations on human dentin infected with Enterococcus faecalis

This study compared the antibacterial efficacy of three different formulations of calcium hydroxide by using human dentin specimens that were infected with Enterococcus faecalis. After exposure to three forms of calcium hydroxide (calcium hydroxide mixed with distilled water, calcium hydroxide mixed with 0.2% chlorhexidine, and calcium hydroxide mixed with camphorated paramonochlorophenol) for 7 days, dentin powder from the infected specimens was obtained and assessed for bacterial quantity by spectrophotometry. It was found that calcium hydroxide mixed with camphorated paramonochlorophenol killed all of the Enterococcus faecalis inside the dentinal tubules. This result was better than that obtained with calcium hydroxide mixed with distilled water or with 0.2% chlorhexidine (p < 0.05). Calcium hydroxide mixed with distilled water and calcium hydroxide mixed with 0.2% chlorhexidine were ineffective against these bacteria.     

自制氢氧化钙糊剂与临床常用根管消毒剂抗菌效果及细胞毒性的实验室性能比较

目的：依据ISO7406技术报告和中国医药行业标准YY0268-1995,前期实验室研制一种便于临床使用的氢氧化钙糊剂,与目前临床使用的根管消毒剂的抗菌效果及细胞毒性进行性能比较。方法：通过琼脂扩散法、培养基稀释法和四唑盐比色法（MTT）比较所研制的氢氧化钙糊剂（CHCM）与氢氧化钙/生理盐水、氢氧化钙牙胶尖（Roeko,Calcium Hydroxide Plus）、45%苯甲酚溶液（Ⅰ）和45%甲醛甲酚溶液（Ⅱ）的抗菌性和细胞毒性。结果：45%甲醛甲酚溶液（Ⅱ）的抗菌效果最好,氢氧化钙糊剂（CHCM）次之,氢氧化钙牙胶尖和氢氧化钙/生理盐水糊剂抗菌效果不如其他实验组。45%甲醛甲酚溶液（Ⅱ）在2、3、4d的细胞毒性程度为2级,在5 d为3级。氢氧化钙/生理盐水的细胞毒性程度为0级。氢氧化钙糊剂（CHCM）、氢氧化钙牙胶尖和45%苯甲酚溶液（Ⅰ）的细胞毒性程度为1级。结论：研制的氢氧化钙糊剂其生物安全性符合ISO7406技术报告和中国医药行业标准YY0268-1995中的有关要求,与氢氧化钙/生理盐水、氢氧化钙牙胶尖、45%苯甲酚溶液（Ⅰ）和45%甲醛甲酚溶液（Ⅱ）相比具有良好的抗菌效果和生物安全性。     

In vitro susceptibility of Candida albicans to four disinfectants and their combinations

AIM: The aim of this study was to evaluate the susceptibility of seven strains of Candida albicans to four disinfectants: iodine potassium iodide, chlorhexidine acetate, sodium hypochlorite and calcium hydroxide. In addition, all possible pairs of the disinfectants were tested in order to compare the effect of the combination and its components. METHODOLOGY: Filter paper discs were immersed in standardized yeast suspensions and then transferred to disinfectant solutions of different concentrations and incubated at 37 degrees C for 30 s, 5 min, 1 h and 24 h. After incubation the filter paper discs were transferred to vials with PBS and glass beads that were then vigorously shaken for dispersal of the yeast cells. PBS with resuspended yeasts was serially diluted 10-fold. Droplets of 25 microL from each dilution were inoculated on TSB agar plates and incubated in air at 37 degrees C for 24 h. The number of colony-forming units was then calculated from appropriate dilutions. RESULTS: C. albicans cells were highly resistant to calcium hydroxide. Sodium hypochlorite (5% and 0.5%) and iodine (2%) potassium iodide (4%) killed all yeast cells within 30 s, whilst chlorhexidine acetate (0.5%) showed complete killing after 5 min. Combinations of disinfectants were equally or less effective than the more effective component. All C. albicans strains tested showed similar susceptibility to the medicaments tested. CONCLUSIONS: This study indicates that sodium hypochlorite, iodine potassium iodide and chlorhexidine acetate are more effective than calcium hydroxide against C. albicans in vitro. However, combining calcium hydroxide with sodium hypochlorite or chlorhexidine may provide a wide-spectrum antimicrobial preparation with a long-lasting effect.     

Effectiveness of 2% chlorhexidine gel and calcium hydroxide against Enterococcus faecalis in bovine root dentine in vitro

AIM: To evaluate the effectiveness of 2% chlorhexidine gluconate gel and calcium hydroxide (Ca(OH)2) as intracanal medicaments against Enterococcus faecalis. METHODOLOGY: One hundred and eighty dentine tubes prepared from intact freshly extracted bovine maxillary central incisors were infected in vitro for 7 days with E. faecalis. The specimens were divided into four groups, according to the intracanal medicament used, as follows: Group 1: 2% chlorhexidine gluconate gel; Group 2: calcium hydroxide in a viscous vehicle (polyethyleneglycol 400); Group 3: 2% chlorhexidine gluconate gel + calcium hydroxide and Group 4: Brain Heart Infusion (BHI) broth (control group). The medicaments were placed into the canal lumen and left there for experimental times of 1, 2, 7, 15 and 30 days. After each period, irrigation with sterile saline to remove the medicament was performed and the canals were dried with sterile paper points. Dentine chips were removed from the canals with sequential sterile round burs at low speed. The samples obtained with each bur were immediately collected in separate test tubes containing BHI broth. The tubes were incubated at 37 degrees C and daily observed for microbial growth, visualized by the medium turbidity. RESULTS: Chlorhexidine gel alone completely inhibited the growth of E. faecalis after 1, 2, 7 and 15 days. Calcium hydroxide allowed microbial growth at all experimental times. The combination of chlorhexidine and Ca(OH)2 was effective after 1 and 2 days demonstrating 100% antibacterial action; however, its antibacterial activity reduced between 7 and 15 days. CONCLUSION: Under the conditions of this study, it can be concluded that 2% chlorhexidine gel alone was more effective against E. faecalis than calcium hydroxide (P < 0.05). However, its antibacterial activity depended on how long it remained inside the root canal.     

In vitro antibacterial effect of chlorhexidine added to glass-ionomer cements.

The aims of the present study were to investigate the antibacterial properties of glass-ionomer cements containing different concentrations of chlorhexidine and the possible release of chlorhexidine from the compound. Chlorhexidine gluconate or diacetate was mixed with glass-ionomer cements and tested in vitro against strains of Lactobacillus casei and mutans streptococci. A spectrophotometric test was used to monitor the release of chlorhexidine from the mixture. In a broth culture test, the higher the concentrations of chlorhexidine in the mixture, the longer the time of antibacterial effect on Streptococcus mutans and the greater the tendency of the material to deteriorate. Agar diffusion tests revealed bacterial inhibition in a dose-response manner. The tested bacterial strains were similarly inhibited and the antibacterial properties decreased with time. A minor portion of added chlorhexidine was released from the cement. The deterioration of the cements indicates that the material could be useful as a varnish-like chlorhexidine carrier.     

In vitro antibacterial effect of chlorhexidine added to glass-ionomer cements

Abstract— The aims of the present study were to investigate the antibacterial properties of glass-ionomer cements containing different concentrations of chlorhexidine and the possible release of chlorhexidine from the compound. Chlorhexidine gluconate or diacetate was mixed with glass-ionomer cements and tested in vitro against strains of Lactobacillus casei and mutans streptococci. A spectrophotometric test was used to monitor the release of chlorhexidine from the mixture. In a broth culture test, the higher the concentrations of chlorhexidine in the mixture, the longer the time of antibacterial effect on Streptococcus mutans and the greater the tendency of the material to deteriorate. Agar diffusion tests revealed bacterial inhibition in a dose-response manner. The tested bacterial strains were similarly inhibited and the antibacterial properties decreased with time. A minor portion of added chlorhexidine was released from the cement. The deterioration of the cements indicates that the material could be useful as a varnish-like chlorhexidine carrier.     

Susceptibility of various microorganisms to chlorhexidine.

The susceptibility to chlorhexidine of bacteria in aerobic, facultatively anaerobic and anaerobic isolates from clinical specimens of wounds, urine, saliva, and dental plaque was studied. Agar diffusion tests using 50 microng chlorhexidine discs and agar dilution tests were performed and the MIC values correlated with inhibition zone diameters. Anaerobic plaque strains were isolated and tested by the agar dilution method in an anaerobic glove box. Regression lines obtained for five agar media demonstrated a good correlation between zone diameters and MIC values. There was a broad range of susceptibility to chlorhexidine among both Gram-positive and Gram-negative strains. Low MIC values were noted for staphylococci, S. mutans, S. salivarius and E. coli, while strains of Proteus, Pseudomonas and Klebsiella were less susceptible. S. sanguis showed intermediate susceptibility with both low and high MIC values. Among the anaerobic isolates tested, the strains most susceptible to chlorhexidine were Propionibacterium and Selenomonas, While the least susceptible strains were Gram-negative cocci resembling Veillonella.