Fractional Bactericidal Concentration Research Articles

Synergistic Bactericidal Effects of Quaternary Ammonium Compounds with Essential Oil Constituents.

Antimicrobial tolerance is a significant concern in the food industry, as it poses risks to food safety and public health. To overcome this challenge, synergistic combinations of antimicrobials have emerged as a potential solution. In this study, the combinations of two essential oil constituents (EOCs), namely carvacrol (CAR) and eugenol (EUG), with the quaternary ammonium compounds (QACs) benzalkonium chloride (BAC) and didecyldimethylammonium chloride (DDAC) were evaluated for their antimicrobial effects against Escherichia coli and Bacillus cereus, two common foodborne bacteria. The checkerboard assay was employed to determine the fractional inhibitory concentration index (FICI) and the fractional bactericidal concentration index (FBCI), indicating the presence of bactericidal, but not bacteriostatic, synergy in all QAC-EOC combinations. Bactericidal synergism was clearly supported by Bliss independence analysis. The bactericidal activity of the promising synergistic combinations was further validated by time-kill curves, achieving a >4-log10 reduction of initial bacterial load, which is significant compared to typical industry standards. The combinations containing DDAC showed the highest efficiency, resulting in the eradication of bacterial population in less than 2-4 h. These findings emphasize the importance of considering both bacteriostatic and bactericidal effects when evaluating antimicrobial combinations and the potential of EOC-QAC combinations for sanitization and disinfection in the food industry.

A hope for ineffective antibiotics to return to treatment: investigating the anti-biofilm potential of melittin alone and in combination with penicillin and oxacillin against multidrug resistant-MRSA and -VRSA.

The emergence and rapid spread of multi-drug resistant (MDR) bacterial strains, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus (VRSA), have posed a significant challenge to the medical community due to their ability to form biofilm and develop resistance to common antibiotics. Traditional antibiotics that were once effective in treating bacterial infections are now becoming increasingly ineffective, leading to severe consequences for patient outcomes. This concerning situation has called for urgent research to explore alternative treatment strategies. Recent studies have shown that antimicrobial peptides (AMPs) hold promise as effective agents against biofilm-associated drug-resistant infections as well as to enhance the efficacy of conventional antibiotics. Accordingly, we aimed to investigate the antimicrobial and antibiofilm effects of melittin AMP, both alone and in combination with penicillin and oxacillin, against biofilm-forming MDR-MRSA and -VRSA. In this study, we investigated the kinetics of biofilm formation and assessed various parameters related to the antimicrobial and antibiofilm efficacy of melittin and antibiotics, both alone and in combination, against MDR-MRSA and -VRSA. The antimicrobial parameters included the Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC), Fractional Inhibitory Concentration Index (FICi), Fractional Bactericidal Concentration Index (FBCi), and the antibiofilm activity of melittin and antibiotics indicated by the Minimum Biofilm Inhibitory Concentration (MBIC), Minimal Biofilm Eradication Concentration (MBEC), Fractional Biofilm Inhibitory Concentration Index (FBICi), and Fractional Biofilm Eradication Concentration Index (FBECi). The MIC results showed that all S. aureus isolates were resistant to penicillin (≥0.25 μg/mL), and 66% of isolates were resistant to oxacillin. The geometric means of the MIC values for penicillin, oxacillin, and melittin were 19.02, 16, and 1.62 μg/ml, respectively, and the geometric means of the MBC values for penicillin, oxacillin, and melittin were 107.63, 49.35, and 5.45 μg/ml, respectively. The study revealed that the combination indexes of melittin-penicillin and melittin-oxacillin, as determined by FIC values against all isolates, were 0.37 and 0.03, respectively. Additionally, melittin-penicillin and melittin-oxacillin exhibited combination indexes based on FBC values against all isolates at 1.145 and 0.711, respectively. Besides, melittin inhibited the biofilm formation of all S. aureus isolates, with MBIC values ranging from 10 to 1.25 μg/mL, and MBEC values ranging from 40 to 10 μg/mL. Generally, the combination indexes of melittin-penicillin and melittin-oxacillin, determined using FBIC values against all isolates, were 0.23 and 0.177, respectively. Moreover, melittin-penicillin and melittin-oxacillin typically had combination indexes based on FBEC values against all isolates at 5 and 2.97, respectively. In conclusion, our study provides evidence that melittin is effective against both planktonik and biofilm forms of MRSA and VRSA and exhibits significant synergistic effects when combined with antibiotics. These results suggest that melittin and antibiotics could be a potential candidate for further investigation for in vivo infections caused by MDR S. aureus. Furthermore, melittin has the potential to restore the efficacy of penicillin and oxacillin antibiotics in the treatment of MDR infections. Applying AMPs, like melittin, to revive beta-lactam antibiotics against MRSA and VRSA is an innovative approach against antibiotic-resistant bacteria. Further research is needed to optimize dosage and understand melittin mechanism and interactions with beta-lactam antibiotics for successful clinical applications.

The combination of allicin with domiphen is effective against microbial biofilm formation.

Microorganisms in biofilms are particularly difficult to control because of their increased survival and antibiotic resistance. Allicin and domiphen were employed to inhibit the microbial growth and biofilm formation of Staphylococcus aureus, Escherichia coli, and Candida albicans strains. Broth microdilution method and checkerboard assay were conducted to determine the efficacy of allicin combined with domiphen against S. aureus, E. coli, and C. albicans. Microbial biofilm formation was measured using the crystal violet staining method and fluorescence microscopy. And the total viable count of the biofilm cells on material surface after the treatment with antimicrobial reagents was calculated with the plate count technique. The two drugs showed synergistic effects against the pathogens with a fractional bactericidal concentration of less than 0.38. The combination of 64 μg/mL allicin with 1 μg/mL domiphen dispersed over 50% of the biofilm mass of S. aureus, E. coli, and C. albicans. In addition, the drug combination reduced the total viable counts of E. coli and C. albicans biofilm cells on stainless steel and polyethylene surfaces by more than 102 CFU/mL. The combination of allicin and domiphen is an effective strategy for efficiently decreasing biofilms formation on various industrial materials surfaces.

Synergistic Antimicrobial Effect of Antimicrobial Peptides CATH-1, CATH-3, and PMAP-36 With Erythromycin Against Bacterial Pathogens.

With the increasing bacterial resistance to traditional antibiotics, there is an urgent need for the development of alternative drugs or adjuvants of antibiotics to enhance antibacterial efficiency. The combination of antimicrobial peptides (AMPs) and traditional antibiotics is a potential alternative to enhance antibacterial efficiency. In this study, we investigated the synergistic bactericidal effect of AMPs, including chicken (CATH-1,−2,−3, and -B1), mice (CRAMP), and porcine (PMAP-36 and PR-39) in combination with conventional antibiotics containing ampicillin, tetracycline, gentamicin, and erythromycin against Staphylococcus aureus, Salmonella enteritidis, and Escherichia coli. The results showed that the minimum bactericidal concentration (MBC) of CATH-1,−3 and PMAP-36 was lower than 10 μM, indicating that these three AMPs had good bacterial activity against S. aureus, S. enteritidis, and E. coli. Then, the synergistic antibacterial activity of AMPs and antibiotics combination was determined by the fractional bactericidal concentration index (FBCI). The results showed that the FBCI of AMPs (CATH-1,−3 and PMAP-36) and erythromycin was lower than 0.5 against bacterial pathogens, demonstrating that they had a synergistic bactericidal effect. Furthermore, the time-killing kinetics of AMPs (CATH-1,−3 and PMAP-36) in combination with erythromycin showed that they had a continuous killing effect on bacteria within 3 h. Notably, the combination showed lower hemolytic activity and cytotoxicity to mammal cells compared to erythromycin and peptide alone treatment. In addition, the antibacterial mechanism of CATH-1 and erythromycin combination against E. coli was studied. The results of the scanning electron microscope showed that CATH-1 enhanced the antibacterial activity of erythromycin by increasing the permeability of bacterial cell membrane. Moreover, the results of bacterial migration movement showed that the combination of CATH-1 and erythromycin significantly inhibits the migration of E. coli. Finally, drug resistance analysis was performed and the results showed that CATH-1 delayed the emergence of E. coli resistance to erythromycin. In conclusion, the combination of CATH-1 and erythromycin has synergistic antibacterial activity and reduces the emergence of bacterial drug resistance. Our study provides valuable information to develop AMPs as potential substitutes or adjuvants for traditional antibiotics.

Highly Synergistic Effects of Melittin With Vancomycin and Rifampin Against Vancomycin and Rifampin Resistant Staphylococcus epidermidis.

Methicillin-resistant Staphylococcus epidermidis (MRSE) strains are increasingly emerging as serious pathogens because they can be resistant to many antibiotics called multidrug resistance (MDR) that limit the therapeutic options. In the case of vancomycin- and rifampin-resistant MDR-MRSE, the physicians are not allowed to increase the doses of antibiotics because of severe toxicity. Accordingly, we investigated the synergistic activity of melittin antimicrobial peptide with vancomycin and rifampin against vancomycin-resistant, and rifampin-resistant MDR-MRSE isolates. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), fractional inhibitory concentration index (FICi), and fractional bactericidal concentration index (FBCi) of antimicrobial agents against isolates were determined. Coagulate activities and serum and salt stability as well as melittin cytotoxicity on the human embryonic kidney (HEK) 293 cells and human red blood cells (RBCs) at their synergistic concentrations. MIC and MBC values for melittin were in the range of 0.312–2.5 and 0.312–5, respectively. Results also showed that the interaction of melittin with drugs was highly synergistic in which the geometric means of FICi and FBCi were < 0.5. Induced synergism led to a decrease in melittin, rifampin, and vancomycin concentrations by 8–1,020, 2–16, and 4–16-folds, respectively. This phenomenon caused a reduction in melittin toxicity by which the synergistic concentration of melittin needed to kill bacteria did not show cytotoxicity and hemolytic activity. Besides, no coagulation activity was found for the synergistic and alone concentrations of melittin in both Prothrombin Time (PT) and Partial Thromboplastin Time (PTT). Interestingly, the antibacterial activity of melittin in Mueller Hinton Broth (MHB) containing human serum did no significant differences between MIC and MBC values of melittin in MHB and MHB containing 10% human serum. The present findings showed that the therapeutic index of melittin was improved by 32.08- and 12.82-folds when combined with vancomycin and rifampin, respectively. Taken together, the obtained data show that melittin alone was effective against MDR-MRSE isolates and this antimicrobial peptide showed highly synergistic effects with vancomycin and rifampin without causing toxicity. Therefore, the combination of melittin and traditional antibiotics could be a promising strategy for the treatment of infections caused by MDR-MRSE.

Assessment of the efficacy of clofazimine alone and in combination with primary agents against Mycobacterium tuberculosis in vitro

The chemotherapeutic regimens of patients with drug-susceptible (DS)- tuberculosis (TB) comprise four primary anti-TB drugs: rifampicin (RMP), isoniazid (INH), ethambutol (EMB) and pyrazinamide (PZA), administered for six-to-nine months. These drug regimens target the various microbial populations that include actively replicating (AR), slow-replicating (SR) and non-replicating (NR) organisms. Clofazimine (CFZ) has showed benefit in shortening DS-TB treatment in vivo from six to four months when used in combination with this regimen in murine models of experimental infection. However, its antimicrobial efficacy when used in combination with the primary drugs against the various microbial populations of Mycobacterium tuberculosis has not been demonstrated. In the current in vitro study, the inhibitory and bactericidal activities of CFZ in combination with the primary anti-TB drugs, RMP, INH and EMB against the AR and SR organisms in planktonic and biofilm-forming cultures, respectively, were evaluated by fractional inhibitory concentration index (FICI) and fractional bactericidal concentration index (FBCI) determinations, using the Loewe Additivity Model. In planktonic cultures, CFZ demonstrated synergistic growth inhibitory activity in combination with RMP and INH individually and collectively. With respect to bactericidal activity, CFZ exhibited synergistic activity only in a two-drug combination with RMP. However, in biofilm-forming cultures, all CFZ-containing anti-TB drug combinations exhibited synergistic inhibitory and bactericidal effects, particularly in combination with RIF and INH. Clofazimine exhibited synergistic effects in combination with primary anti-TB drugs against both planktonic and biofilm-forming cultures, showing potential benefit in augmenting treatment outcome when used during standard TB chemotherapy.

Potentiation of β-Lactams against Methicillin-Resistant Staphylococcus aureus (MRSA) Using Octyl Gallate, a Food-Grade Antioxidant.

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to a number of antibiotics of clinical importance and is a serious threat to public health. Since bacteria rapidly develop resistance even to newly discovered antibiotics, this study aimed to develop drug potentiators to enhance the antibacterial activity of existing antibiotics for the control of MRSA. Based on our previous studies, screening of antimicrobial synergy was conducted with gallic acid and its derivatives using checkerboard assays. Antimicrobial synergy was confirmed with MRSA isolates from clinical cases. Combinations of penicillin, ampicillin, and cephalothin with octyl gallate (OG), an antioxidant approved by the US Food and Drug Administration (FDA), consistently exhibited synergistic bacteriostatic and bactericidal activities against MRSA, rendering MRSA sensitive to β-lactams. The fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) indices exhibited that the antimicrobial effects of OG were synergistic. The results of a permeability assay showed that OG significantly increased the permeability of the bacterial cell wall. Despite the intrinsic resistance of MRSA to β-lactams, the findings in this study demonstrated that OG enhanced the activity of β-lactams in MRSA and sensitized MRSA to β-lactams, suggesting that OG can be used as a drug potentiator to control MRSA using existing antibiotics.

Silver Nanoparticles Enhance Antimicrobial Efficacy of Antibiotics and Restore That Efficacy against the Melioidosis Pathogen

Melioidosis is an infectious disease caused by Gram-negative bacillus bacteria Burkholderia pseudomallei. Due to the emerging resistance of B. pseudomallei to antibiotics including ceftazidime (CAZ), the development of novel antibiotics and alternative modes of treatment has become an urgent issue. Here, we demonstrated an ability to synergistically increase the efficiency of antibiotics through their combination with silver nanoparticles (AgNPs). Combinations of four conventional antibiotics including CAZ, imipenem (IMI), meropenem (MER), and gentamicin sulfate (GENT) with starch-stabilized AgNPs were tested for their antibacterial effects against three isolates of B. pseudomallei. The combination of each antibiotic with AgNPs featured fractional inhibitory concentration (FIC) index values and fractional bactericidal concentration (FBC) index values ranging from 0.312 to 0.75 µg/mL and 0.252 to 0.625 µg/mL, respectively, against the three isolates of B. pseudomallei. The study clearly showed that most of the combinatorial treatments exhibited synergistic antimicrobial effects against all three isolates of B. pseudomallei. The highest enhancing effect was observed for GENT with AgNPs. These results confirmed the combination of each antibiotic with AgNPs restored their bactericidal potency in the bacterial strains that had previously been shown to be resistant to the antibiotics. In addition, morphological changes examined by SEM confirmed that the bacterial cells were severely damaged by combinations at the FBC level. Although bacteria produce fibers to protect themselves, ultimately the bacteria were killed by the antibiotic–AgNPs combinations. Overall, these results suggest the study of antibiotic–AgNPs combinations as an alternative design strategy for potential therapeutics to more effectively combat the melioidosis pathogen.

Antimicrobial activity of three essential oils (cinnamon, manuka, and winter savory), and their synergic interaction, against Listeria monocytogenes

AbstractEssential oils (EOs) are categorized as having antimicrobial, insecticidal, and antioxidant activities. For their antibacterial activity, EOs are widely studied as alternatives to antibiotics in human and veterinary medicines. The inhibitory and bactericidal activities of three EOs (Cinnamomum zeylanicum, Leptospermum scoparium, and Satureja montana) were determined against Listeria monocytogenes ATCC 7644. The chemical compositions of the EOs were determined through gas chromatography mass spectrometry (GC‐MS). Essential oils were tested alone or in binary and ternary combinations for both their inhibitory and their bactericidal activities. Binary and ternary mixtures were tested through a chequerboard assay, and thus fractional inhibitory and fractional bactericidal concentration indices were obtained in relation to the activity of each EO alone. The chemical composition of each EO had different percentages of the main classes of compounds. EOs showed high levels of monoterpenes (hydrocarbons and oxygenated), sesquiterpenes (hydrocarbons and oxygenated), and phenylpropanoids for winter savory, manuka, and cinnamon, respectively. Several synergistic activities against Listeria monocytogenes were demonstrated in binary and ternary mixtures of the EOs. Mixtures of the EOs tested showed potential for use as antibacterial products; moreover, because of the synergistic activities the mixtures could be used in lower quantities than individual EOs on their own.

Antibacterial effects of vancomycin in combination with methicillin against methicillin-resistant and methicillinsensitive Staphylococcus aureus

Background and aims: Staphylococcus aureus is considered as a frequent cause of infections. Therefore, antibacterial agents including β-lactam are normally used to treat these infections while the emergence of antibiotic resistance is one of the major clinical problems in this respect. Accordingly, combination antibacterial therapy is one way to alleviate this problem. As a result, the present study aimed to investigate the combined effects of vancomycin and methicillin on clinical isolates of methicillin-resistant S. aureus (MRSA) and methicillinsensitive S. aureus (MSSA). In addition, a series of follow-up studies were performed to evaluate the antibacterial activity. Methods: The current cross-sectional study was conducted on 40 hospitalized patients from various clinical samples such as pus/wound swabs, blood, urine and sputum during a 6-month period in 2017. To this end, the antibacterial activities of vancomycin and methicillin, alone and in combination were investigated against MRSA and MSSA. Eventually, the inhibitory effects of vancomycin and methicillin alone and in combination were studied on the growth profile of MRSA and MSSA, as well as the expression of mecA gene. Results: Based on the results, the significant synergistic and partial synergistic activity with fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) indexes ranged from 0.27-0.938 and 0.313-0.844, respectively, in the combination of vancomycin and methicillin in MRSA and MSSA isolates. Further, the obtained data indicated that the combination of vancomycin and methicillin had a synergistic effect against MRSA isolates (P&lt;0.01). The expression levels of the mecA gene were down-regulated by 5.25- fold in the combination of vancomycin and methicillin in MRSA isolate (P&lt;0.001). Conclusion: In general, these events may reflect the potential uses of vancomycin and methicillin combination against MRSA. However, a greater understanding of the underlying molecular mechanisms of vancomycin and methicillin in combination could contribute to the development of therapeutic strategies.

Single and combined antimicrobial efficacies for nine metal ion solutions against Klebsiella pneumoniae, Acinetobacter baumannii and Enterococcus faecium

Infection caused by Klebsiella pneumoniae, Acinetobacter baumannii and Enterococcus faecium can be difficult to treat. New biocidal products are needed in order to reduce the transmission of such bacteria from surfaces to patients. This fundamental study aimed to investigate the antimicrobial efficacy of nine metal ion solutions (yttrium, indium, niobium, titanium, tantalum, rhodium, ruthenium, zinc and gallium) using zone of inhibition (ZoI), minimum inhibitory concentration (MIC) and minimum bactericidal concentrations (MBC). Fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) assays were used to determine antimicrobial activities of various combinations. The rhodium metal ion solution when applied singly demonstrated the best antimicrobial efficacies against all the bacteria tested. FICs indicated that the rhodium/ruthenium combination was either synergistic or additive against all three tested bacteria. This metal ion combination also exhibited synergistic activity against E. faecium following in FBCs. Our data presented indicated the potential of the rhodium and/or ruthenium metal ions for antisepsis, disinfection and for incorporation into hygienic surfaces.

Core-shell magnetic nanoparticles display synergistic antibacterial effects against Pseudomonas aeruginosa and Staphylococcus aureus when combined with cathelicidin LL-37 or selected ceragenins.

Core–shell magnetic nanoparticles (MNPs) are promising candidates in the development of new treatment methods against infections, including those caused by antibiotic-resistant pathogens. In this study, the bactericidal activity of human antibacterial peptide cathelicidin LL-37, synthetic ceragenins CSA-13 and CSA-131, and classical antibiotics vancomycin and colistin, against methicillin-resistant Staphylococcus aureus Xen 30 and Pseudomonas aeruginosa Xen 5, was assessed alone and in combination with core–shell MNPs. Fractional inhibitory concentration index and fractional bactericidal concentration index were determined by microdilution methods. The potential of combined therapy using nanomaterials and selected antibiotics was confirmed using chemiluminescence measurements. Additionally, the ability of tested agents to prevent bacterial biofilm formation was evaluated using crystal violet staining. In most conditions, synergistic or additive effects were observed when combinations of core–shell MNPs with ceragenins or classical antibiotics were used. Our study revealed that a mixture of membrane-active agents such as LL-37 peptide or ceragenin CSA-13 with MNPs potentialized their antibacterial properties and might be considered as a method of delaying and overcoming bacterial drug resistance.

Carnosic acid acts synergistically with gentamicin in killing methicillin-resistant Staphylococcus aureus clinical isolates

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) is resistant to different commonly used antibiotics, stressing the need for further strategies to treat this human pathogen with worldwide prevalence. The use of phytochemicals within the current pharmacology is a promising approach to enhance the antimicrobial activity of common antibiotics in the battle against these bacteria. PurposeThe purpose of this study was to determine the antimicrobial effectiveness of carnosic acid, the major constituent of Rosmarinus officinalis L. leaves, in combination with gentamicin against multi-drug resistant MRSA clinical isolates obtained from pediatric patients with bacteremia. Materials and methodsAnti-MRSA activity was studied using the broth microdilution assay and time–kill method. Combinations of subinhibitory concentrations of carnosic acid and gentamicin were examined using the checkerboard method. ResultsCarnosic acid exhibited a good antibacterial activity against all multidrug-resistant MRSA clinical isolates tested, which are resistant to four up to nine antibiotics. In addition, the combination of carnosic acid with gentamicin not only decreased the minimal inhibitory concentration (MIC) of both by 4- to 5-fold, but also improved the bactericidal potency of the common antibiotic by 32- to 40-fold against both gentamicin-susceptible and gentamicin-resistant MRSA clinical isolates. A clear bactericidal synergistic activity between carnosic acid and gentamicin in killing multidrug-resistant MRSA clinical isolates with a fractional bactericidal concentration index (FBCI) of 0.28–0.35 was demonstrated. ConclusionsOur findings show the potential use of carnosic acid in combination with gentamicin as a promising alternative for the control of healthcare-associated infections caused by multidrug-resistant MRSA.

Efficacy of cryptdin-2 as an adjunct to antibiotics from various generations against salmonella.

Emerging drug resistance in Salmonella coupled with the recent poor success rate of antibiotic discovery programs of the pharmaceutical industry is a cause for significant concern. It has forced the scientific community to look for alternative new classes of antimicrobial compounds. In this context, combinations of antimicrobial peptides (AMPs) and conventional antibiotics have gained interest owing to their versatile applications. The present study was therefore planned to evaluate the synergistic effects, if any, of cryptdin-2, a mouse Paneth cell alpha-defensin, in combination with four different antibiotics i.e. ciprofloxacin, ceftriaxone, cefotaxime and chloramphenicol, which are conventionally used against Salmonella. Minimum bactericidal concentrations of the selected antimicrobial agents were determined by micro and macro broth dilution assays. In-vitro synergy between the agents was evaluated by fractional bactericidal concentration index (checkerboard test) and time-kill assay. Cryptdin-2-ciprofloxacin, cryptdin-2-ceftriaxone and cryptdin-2-cefotaxime combinations were found synergistic as evident by in vitro assays. This synergism provides an additional therapeutic choice by allowing the use of conventional antibiotics in conjunction with AMPs against MDR Salmonella.

New non-alcoholic formulation for hand disinfection

Hand washing is considered as the single most important strategy to prevent infections. World health organization (WHO) defines hand hygiene as a primary issue of personal care with particular reference to hospital personnel and health facility workers. In this work, we investigated a new combination for hand disinfection as an alternative to alcohol-based and chlorhexidine products. The new combination of 5-pyrrolidone-2-carboxylic acid (PCA) and copper sulphate pentahydrate (CS) was tested upon different bacterial species that normally colonize hands, including Staphylococcus aureus, methicillin resistant S. aureus (MR S. aureus), Staphylococcus epidermidis, multidrug resistant S. epidermidis (MDR S. epidermidis), Streptococcus pyogenes, Streptococcus agalactiae, Escherichia coli, Candida albicans and three clinical isolates: MR S. aureus, MDR S. epidermidis, and an E. coli strain. Minimal inhibitory concentrations (MICs), Minimal bactericidal concentrations (MBCs), fractional inhibitory concentration (FIC) indices, and fractional bactericidal concentration (FBC) indices were evaluated. Ethanol 70% V/V, isopropanol 60% V/V, and 4% w/V chlorhexidine solution were used as reference hand disinfectants. Copper sulphate pentahydrate was very effective against all tested microorganisms: The MIC and MBC for CS ranged from 781 mg/l against S. pyogenes to 12500 mg/l against E. coli strains and C. albicans. In addition, PCA exhibited a good antimicrobial activity, in particular, against S. pyogenes and S. agalactiae. The combination of CS and PCA showed a strong synergistic effect and all FIC indices were ≤0·500. The combination of CS and PCA were more effective than ethanol 70% V/V and isopropanol 60% V/V. In addition to antimicrobial activity, the new formulation possesses peculiar features such as residual activity and moisturizing effect. This work identifies a new strategy for hand disinfection.

An in vitro synergetic evaluation of the use of nisin and sodium fluoride or chlorhexidine against Streptococcus mutans

The objective of this study is to investigate the synergetic action between nisin and sodium fluoride or chlorhexidine against Streptococcus mutans, a primary cariogenic pathogen. In the antibacterial assay, a synergetic effect on S. mutans was found between nisin and sodium fluoride, but there was no interaction between nisin and chlorhexidine by the checkerboard, the fractional inhibitory concentration (FIC) and the fractional bactericidal concentration (FBC) tests. S. mutans survival rates showed a significant decline after treatment with a combination of nisin and sodium fluoride in a time-kill study. Scanning electron microscopy showed that the damage to S. mutans with the combined nisin and sodium fluoride treatment was the most severe among all of the different single and combined antimicrobial treatments. Furthermore, in the antibiofilm test, nisin in combination with sodium fluoride produced a stronger bactericidal effect on a S. mutans biofilm for 4h and 16h compared with sodium fluoride alone by confocal laser scanning microscopy. Nisin in combination with sodium fluoride exerted a high bactericidal effect on S. mutans and thereby has the potential to be used as an effective drug combination to prevent dental caries.

In VitroandIn VivoSynergistic Effects of Cryptdin 2 and Ampicillin against Salmonella

In view of the emergence of multidrug-resistant Salmonella strains, there is a need for therapeutic alternatives. To reduce the dose of antibiotic required in order to decrease the associated side effects, the present study was aimed at evaluating the synergism between cryptdin 2 (a Paneth cell antimicrobial peptide) and ampicillin (Amp) against Salmonella enterica serovar Typhimurium. The synergy was evaluated in terms of the fractional bactericidal concentration (FBC) index, time-kill assay results (in vitro), macrophage functions, i.e., intracellular killing, lipid peroxidation, superoxide dismutase activity, and generation of nitrite (ex vivo), and decreases in CFU of salmonellae in livers, spleens, and small intestines of infected mice treated with cryptdin 2 and/or Amp (in vivo). In vitro synergism between the two agents was observed on the basis of the FBC index and time-kill assays. When the agents were used in combination, ex vivo studies revealed an enhanced effect on macrophage functions, particularly exhibiting a synergetic effect in terms of SOD levels. In vivo synergy was indicated by larger log unit decreases in all target organs of mice treated with the combination than those for the drugs used alone. These results point toward the possible use of cryptdin 2 as an adjunct to ampicillin and may help in developing alternate strategies to combat Salmonella infections.

Synergy of Nitric Oxide and Silver Sulfadiazine against Gram-Negative, Gram-Positive, and Antibiotic-Resistant Pathogens

The synergistic activity between nitric oxide (NO) released from diazeniumdiolate-modified proline (PROLI/NO) and silver(I) sulfadiazine (AgSD) was evaluated against Escherichia coli, Enterococcus faecalis, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis using a modified broth microdilution technique and a checkerboard-type assay. The combination of NO and AgSD was defined as synergistic when the fractional bactericidal concentration (FBC) was calculated to be <0.5. Gram-negative species were generally more susceptible to the individual antimicrobial agents than the Gram-positive bacteria, while Gram-positive bacteria were more susceptible to combination therapy. The in vitro synergistic activity of AgSD and NO observed against a range of pathogens strongly supports future investigation of this therapeutic combination, particularly for its potential use in the treatment of burns and chronic wounds.

Efficacy of concurrent application of chlorhexidine gluconate and povidone iodine against six nosocomial pathogens

Chlorhexidine gluconate (CHG) and povidone iodine (PI) are rarely used concurrently despite a lack of evidence regarding functional incompatibility of these agents. CHG and PI, alone and combined, were evaluated against Staphylococcus aureus (methicillin-susceptible S aureus [MSSA] and methicillin-resistant S aureus [MRSA]), Staphylococcus epidermidis (MRSE), Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli using checkerboard microbroth dilution techniques. Minimum bactericidal concentration (MBC) was the concentration (percent wt/vol) that reduced bacterial burden ≥ 5-log(10) colony-forming units/mL at 2 hours when compared with bacterial densities in growth controls. Fractional bactericidal concentration indexes (FBCIs) were calculated to determine CHG and PI compatibility. Additionally, tissue plugs from freshly excised porcine vaginal mucosa were infected with S aureus (MSSA), treated for 2 hours with CHG 3%, PI 5%, or CHG 3% and PI 5% combined and then viable bacteria on the tissue plugs enumerated. In broth, CHG demonstrated dose-dependent bactericidal activity, whereas PI activity was all-or-none. All isolates studied were similarly susceptible to CHG (MBCs: 0.0078% ± 0.0019%, 0.0069% ± 0.0026%, 0.0024% ± 0.0005%, 0.0024% ± 0.0005%, 0.0059% ± 0.0%, and 0.0029% ± 0.0%, respectively). The MBCs of PI were identical (0.625%) for all isolates. Overall, FBCI calculations showed indifference. Treatment of MSSA-infected porcine tissue for 2 hours demonstrated that the CHG-PI combination was superior to either antiseptic alone. FBCIs, determined in broth culture, indicate that combining CHG and PI had no negative impact on antisepsis. Moreover, data from an ex vivo porcine mucosal infection model suggest a potential benefit when combining the 2 antiseptic agents.

In vitro activity and synergy of bismuth thiols and tobramycin against Burkholderia cepacia complex.

To determine the susceptibility of Burkholderia multivorans and Burkholderia cenocepacia to bismuth-thiols (BTs), and to examine the synergistic effects of tobramycin and subinhibitory concentrations of BTs against these organisms. The susceptibilities of 25 clinical isolates each of B. multivorans and B. cenocepacia to six BTs were measured by broth dilution in accordance with NCCLS protocols. Ten strains were selected to evaluate the antimicrobial interaction between BTs and tobramycin. Fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) indices were calculated to assess synergy. B. multivorans and B. cenocepacia showed a wide range of susceptibilities to BTs. Bismuth ethanedithiol (BisEDT) was one of the more potent BTs against these organisms (MIC50 7.8 microM), and was selected for synergy studies. Selected strains were highly resistant to tobramycin. The addition of subinhibitory concentrations of BisEDT (2 microM) reduced the MIC and MBC of tobramycin against all strains, achieving synergy in many instances. The FIC index was in the range 0.28-0.66 and the FBC in the range 0.12-0.85. Most strains became susceptible to tobramycin at clinically achievable concentrations in the presence of non-toxic BisEDT levels. Treatment with subinhibitory BisEDT and tobramycin reduces the MICs and MBCs for B. multivorans and B. cenocepacia. BTs may represent an important adjunctive therapy for resistant Burkholderia cepacia complex.