Efficacy of Vancomycin with Fosfomycin against Vancomycin-Resistant Enterococcus Strains Using Agar Dilution Method.

BACKGROUND: Enterococcus faecalis and Enterococcus faecium can cause community-acquired and nosocomial infections. Combination antibiotic therapies have a distinct advantage over monotherapies in terms of their synergistic effect. In the study, it was aimed to investigate in vitro activity of vancomycin combined with fosfomycin by agar dilution method against VRE strains. METHODS: A total of 30 clinical VRE strains were included in the study. Bacterial identifications of the strains were undertaken using conventional routine methods. The resistance to vancomycin was investigated using the broth microdilution method compared to fosfomycin by agar dilution method, and the results were interpreted in accordance with the CLSI guidelines. All experiments contained 25 mg/mL glucose-6-phosphate for fosfomycin. The fractional inhibitory concentration (FIC) indexes (FICI) were interpreted as synergism, FICI ≤ 0.5. Additionally, two strains in 30 VRE were studied to determine the time-kill curves to verify the synergistic results. Both antibiotics were studied at 1 x MIC in the tests. Viable counts were determined at 0, 4, 8, 12, and 24-hour intervals. Time-kill curves were constructed by plotting mean colony forming unit counts versus time. RESULTS: Susceptibility rate to fosfomycin was found at 16.6% (5/30). The MIC50,90 and MICrange values of antimi-crobials were 512, 512, and 512 - 1,024 mg/L for vancomycin, and 128, 128, and 64 - 160 mg/L for fosfomycin. The rate of synergism was found as 100%. CONCLUSIONS: The result shows that the combination of vancomycin with fosfomycin gives hope that it may be an option in the treatment of infections caused by VRE.

Efficacy of vancomycin in combination with various antimicrobial agents against clinical methicillin resistant Staphylococcus aureus strains.

BACKGROUND: Multi-drug resistant methicillin resistant Staphylococcus aureus (MRSA) strains that have been isolated frequently worldwide have difficulties in the treatment and therefore alternative choices for the treatment of the infections are required. The aim of the study was to evaluate the interaction of various antimicrobials in combination with vancomycin against MRSA. METHODS: Twenty five clinical MRSA strains isolated in 2016 were included in the study. The interaction between vancomycin and new generation/conventional antimicrobials against MRSA strains was analyzed by E-test. RESULTS: All of the strains tested was found to be susceptible to vancomycin, telavancin, dalbavancin, ceptobiprole, daptomycin, linezolid, quinupristin-dalfopristin, trimethoprim-sulfamethoxazole, rifampicin and tigecycline. The susceptibility rates of the isolates were found to be high, with the lowest rate (48%) against azithromycin. According to the fractional inhibitory concentration index results, synergistic interaction with vancomycin was determined with trimethoprim-sulfamethoxazole, azithromycin, linezolid, minocycline, dalbavancin, clindamycin in five, three, two, two, one, one and one strain(s), respectively. Additionally, all combinations studied showed additive interaction at high rates. CONCLUSIONS: The results of the study indicate that the use of vancomycin in combination with conventional and new generation antibiotics is promising.

In vitro efficacy of vancomycin combined with fosfomycin against Vancomycin-Resistant Enterococci strains.

OBJECTIVE: Enterococci have been isolated frequently worldwide and have difficulties in the treatment. Combination antibiotherapies have a distinct advantage over monotherapies in terms of their synergistic effect. In the study, it was aimed to investigate in vitro activity of vancomycin combined with fosfomycin against VRE strains. METHODS: A total of 30 VRE strains were included in the study. Bacterial identifications of the strains were undertaken using conventional routine methods. The resistance to agents tested was investigated by using the broth microdilution method. Glucose-6-phosphate (25 mcg/mL) for fosfomycin were used in all experiments. The activity of antibiotics in combination was assessed using a broth microcheckerboard. The fractional inhibitory concentration index (FICI) was interpreted as follows: synergism, FICI ≤0.5. Additionally, two strains in 30 VRE were studied to determine the time-kill curves to verify the synergistic results. For each strain, antibiotics were studied alone and in combination at the minimum inhibitory concentration (1xMIC) values. RESULTS: Susceptibility rate to fosfomycin was found at 26.6 % (8/30). The MIC50, MIC90 and MIC interval values of antimicrobials were 512, 512, and 512 - 1024 mcg/mL for vancomycin, and 128, 160, and 64 - 224 mcg/mL for fosfomycin, respectively. The rate of synergism was found as 100 % by both checkerboard and time-kill methods. CONCLUSION: The result shows that the combination of vancomycin with fosfomycin could be an alternative in the treatment of infections caused by VRE.

In vitro activity of daptomycin combined with dalbavancin and linezolid, and dalbavancin with linezolid against MRSA strains.

OBJECTIVES: Combination therapies have a distinct advantage over monotherapies in terms of their broad spectrum, synergistic effect and prevention of the emergence of drug resistance. In the present study, the in vitro antibacterial activity of daptomycin combinations with linezolid and dalbavancin, and dalbavancin with linezolid were evaluated against 30 clinical MRSA strains. METHODS: The MICs of all antibiotics were determined using microbroth dilution as described by the CLSI. The in vitro activities of antibiotics in combination were assessed by using a microbroth 'chequerboard' assay. The MIC values of all antibiotics determined were evaluated in accordance with the recommendations of the CLSI for daptomycin and linezolid, and the FDA for dalbavancin. RESULTS: All strains (100%) were found to be susceptible to daptomycin, dalbavancin and linezolid. The MIC50, MIC90 and MICrange values of these antibiotics were determined to be 1, 1 and 0.5-1 mg/L, 0.12, 0.12 and 0.03-0.12 mg/L, and 1, 2 and 1-2 mg/L, respectively. The rates of synergistic effects were 67% for daptomycin combined with dalbavancin and with linezolid, and 60% for dalbavancin combined with linezolid. CONCLUSIONS: The results of this study show that in vitro combinations of these new antimicrobials will be effective in the therapy of MRSA infections.

[In vitro activity of daptomycin against VRE and MRSA strains]. / Daptomisinin VRE ve MRSA suslarina in vitro etkinligi.

Infections with multidrug-resistant (MDR) gram-positive bacteria are gradually increasing in the world. Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are among the leading pathogens isolated from nosocomial infections. The increased use of vancomycin in the treatment has led to the development of isolates with reduced susceptibility and resistance. Daptomycin is a novel lipopeptide antibiotic which has a rapid bactericidal activity against infections caused by gram-positive bacteria including MRSA and VRE. The aim of this study was to evaluate the in vitro activity of daptomycin against VRE and MRSA strains isolated from clinical samples of hospitalized patients. A total of 229 isolates of which 118 were VRE and 111 were MRSA have been included in the study. All of the VRE strains were isolated from rectal swab samples and two of them were also resistant to linezolid with the MIC values of 8 µg/ml and 12 µg/ml. Bacterial identification was performed by conventional methods and susceptibility testing of daptomycin was performed by using the broth microdilution method as recommended by CLSI. The MIC values were interpreted according to CLSI susceptibility criteria for daptomycin. Daptomycin MIC50 and MIC90 values for VRE were found as 1 µg/ml and 2 µg/ml, respectively, with a MIC range of 0.125-2 µg/ml. Daptomycin MIC50 and MIC90 values for MRSA were determined as 0.12 µg/ml and 0.5 µg/ml, respectively, and the overall distribution of MIC values ranged between ≤ 0.032-1 µg/ml. All VRE including two linezolid-resistant strains and all MRSA strains (100%) were found susceptible to daptomycin. It was concluded that daptomycin is one of the few alternative agents for the treatment of infections caused by VRE and MRSA, nevertheless it was suggested that daptomycin MICs should better be monitored to prevent treatment failure due to the presence of non-susceptible strains and possible emergence of strains with decreased susceptibility during long-term therapy.

Activity of vancomycin combined with linezolid against clinical vancomycin-resistant Enterococcus strains.

Introduction: Because multi-drug-resistant Gram-positive bacteria have been isolated frequently worldwide and are difficult to treat, alternative treatment choices are required. Combination antibiotherapies have a distinct advantage over monotherapies in terms of their broad spectrum and synergistic effect. In the present study, it was aimed to investigate the in vitro activity of vancomycin combined with linezolid against clinical vancomycin-resistant enterococci (VRE) strains with high-level aminoglycoside resistance. Material and methods: A total of 30 randomly selected clinical VRE strains were studied. Susceptibility to agents tested was investigated using broth microdilution assay. The inoculum of strain was adjusted to approximately 5 × 105 CFU/ml in the wells. The results were interpreted in accordance with Clinical and Laboratory Standards Institute guidelines. In vitro activities of antibiotics in combination were assessed using the broth microcheckerboard technique. The fractional inhibitory concentration indexes (FICIs) were interpreted as follows: synergism, FICI ≤ 0.5; additive/indifference, FICI ≤ 0.5 - ≤ 4; antagonism, FICI > 4. Results: All strains were resistant to vancomycin and susceptible to linezolid. The MIC50,90 and MICrange values of antimicrobials were 512, 512, and 512-1024 µg/ml for vancomycin; 2, 2, and 2-4 µg/ml for linezolid. The rate of synergy was found to be 46.6% (14/30) for linezolid combined with vancomycin. No antagonism was observed. Conclusions: The results of the study suggest that this combination may contribute to the treatment of VRE infections for their synergistic effect and because no antagonism was observed.

[In vitro activity of linezolid and dalbavancin against vancomycin-resistant enterococci]. / Linezolid ve Dalbavansinin Vankomisine Dirençli Enterokok Suslarina Karsi In Vitro Aktivitesi.

The incidence of infections caused by multidrug resistant gram-positive bacteria is increasing worlwide. In addition, emergence and dissemination of glycopeptide resistance in enterococci has accelerated the need for the development of new antimicrobial agents for treatment. Linezolid which is an oxazolidinone and dalbavancin which is a second-generation, semi-synthetic lipoglycopeptid are important therapeutic options for infections caused by antimicrobial-resistant gram-positive pathogens. The aim of this study was to investigate the in-vitro antimicrobial activity of linezolid and dalbavancin against vancomycin- resistant enterococci (VRE). A total of 100 VRE strains, isolated from rectal swabs of patients hospitalized in Istanbul University Faculty of Istanbul Medicine between 2006-2007 were included in the study. All strains were identified as Enterococcus spp. by conventional methods and had minimum inhibitory concentrations (MICs) of ≥ 32 µg/ml for vancomycin. Vancomycin, linezolid and dalbavancin susceptibility testing was performed by broth microdilution method. For the quality control of the tests, S.aureus ATCC 29213 and E.faecalis ATCC 29212 were included in each run. Molecular identification of linezolid-resistant strains (n= 2) were done by 16S rRNA sequencing and resistance mechanisms were tested by 23S rRNA sequencing. Against VRE strains, MIC50, MIC90 and MIC ranges of linezolid and dalbavancin were found as 4, 4, 1-16 µg/ml and 32, 64, 0.25-128 µg/ml, respectively. Linezolid susceptibility, intermediate susceptibility and resistance rates were found as 32%, 66% and 2% in the same order. Linezolid-resistant two strains were identified as E.faecium, and this data was confirmed by Pasteur Institute. Both of those isolates had G2576T mutations in 23S rRNA genes. Because susceptibility breakpoint for dalbavancin has not been established by Clinical and Laboratory Standards Institute (CLSI) yet, susceptibility and resistance rates for dalbavancin were not indicated. According to the MIC results, linezolid was found to be the most effective antibiotic against VRE strains, and dalbavancin was found more effective than vancomycin. Additionally, our results showed that routine susceptibility testing of VRE strains isolated from hospitalized patients to linezolid was required.

In vitro activity of dalbavancin against staphylococci isolated in Istanbul, Turkey.

BACKGROUND: Staphylococci are a major cause of both community- and hospital-acquired infections. Dalbavancin is a new bactericidal second-generation lipoglycopeptide antibiotic to use in the treatment of multidrug-resistant staphylococcal infections. It is important to determine its activity against staphylococci isolated in Turkey. Dalbavancin has not yet been used in antimicrobial therapy in our country. METHOD: Dalbavancin was tested against a total of 453 staphylococcal strains by using the reference broth microdilution method. Organisms tested included: methicillin-resistant Staphylococcus aureus (MRSA; 237 strains), methicillin-susceptible S. aureus (MSSA; 144 strains) and methicillin- resistant coagulase-negative staphylococci (MR-CoNS; 72 strains). RESULTS: MIC(50) and MIC(90) values of dalbavancin against MRSA, MSSA and MR-CoNS were found as ≤0.008 and 0.25 mg/l; 0.016 and 0.125 mg/l; and 0.016 and 0.5 mg/l, respectively. The overall distribution of dalbavancin MIC values ranged from ≤0.008 to 2 mg/l. If the interpretive breakpoint MIC value is ≤1 mg/l, the susceptibility rates of MRSA, MSSA and MR-CoNS strains were determined as 99.6, 100 and 98.6%, respectively. CONCLUSION: The MIC results for dalbavancin have demonstrated a good activity against both methicillin-sensitive and -resistant staphylococci isolated from hospitalized patients.

In Vitro Synergistic Effect of Vancomycin Combined with Daptomycin Against Vancomycin-Resistant Enterococci.

New antimicrobial agents are being designed to treat infections of multidrug-resistant pathogens and have been introduced in the past few years, but there has been a worldwide increase in the incidence of vancomycin-resistant enterococci (VRE) infections, and treatment options are still limited. In this study, it was aimed to investigate the in vitro activity of vancomycin combined with daptomycin against 30 VRE strains. The minimum inhibitory concentration (MIC) values of antibiotics were determined using broth microdilution assay as described by the Clinical and Laboratory Standards Institute (CLSI). The activities of antibiotics in combination were assessed using a broth microcheckerboard method. In addition, 4 of the 30 strains were randomly selected to determine the time-kill curves at 1 × MIC concentrations and 2 of 4 strains at ½ × MIC concentrations. Viable counts were determined at 0-, 4-, 8-, 12-, 24-, 48-, and 72-hr intervals. This was accomplished by subculturing 0.1 mL from repetitive serial dilutions in Eppendorf tubes, followed by subculturing 0.1 mL from tubes onto Tryptic Soy Agar plates. All plates were incubated at 35°C for 24 hr. The synergistic effect was found 100% using the broth microcheckerboard method, and in strains tested using the time-kill method at both 1 × MIC and ½ × MIC concentrations. The results of this study suggest that this combination could be effective in the treatment of the VRE-associated infection.

Evaluation of the fluorescent treponemal antibody absorption test for detection of antibodies (immunoglobulins G and M) to Treponema pallidum in serologic diagnosis of syphilis.

We compared the fluorescent treponemal antibody-absorption (FTA-ABS) (immunoglobulin (Ig)G + IgM) assay with the (micro-) Treponema pallidum haemagglutination assay (TPHA), the T. pallidum particle agglutination assay (TPPA), the Murex syphilis ICE (ICE) enzyme-linked immunosorbent assay (ELISA), the Diesse Enzywell TP (TP) (ELISA) using 122 serum samples and the Western blot (WB) assay using 42 serum samples whose results were inharmonious with other tests. Additionally, the Captia syphilis-M (IgM) (ELISA) were performed. All sera had already been examined by the rapid plasma reagin (RPR) card test, a non-treponemal test and the TPHA, a treponemal test using routine screening tests. Agreements of the FTA-ABS with the TPHA test, the TPPA test, the ICE test and the TP test were 97.5%, 95.9%, 98.3% and 98.3%, respectively. The results suggest that the FTA-ABS test is a useful confirmatory test, but can be inadequate as a confirmatory test for serologic diagnosis of syphilis by giving equivocal and false-negative results even rarely.

In-vitro activity of ceftriaxone combined with newer agents against MRSA.

In this study, in vitro synergism in combinations of agents as ceftriaxone/dalbavancin, ceftriaxone/linezolid and ceftriaxone/daptomycin against MRSA strains were investigated. Thirty clinical MRSA strains were tested. The minimum inhibitory concentrations of all antibiotics were determined using reference broth microdilution method. In-vitro activities of antibiotics combined against the strains were tested using two-dimensional checkerboard microdilution method. Results were interpreted as follows: synergy = FICI ≤0.5; 'no interaction' effect = FICI ˃0.5-≤4; antagonism = FICI ˃4. The MIC50, MIC90 and MICrange of ceftriaxone, daptomycin, dalbavancin and linezolid were found as 128, 1024 and 16-2048 mg/L; 1, 1 and 0.5-1 mg/L; 0.12, 0.12 and 0.03-0.12 mg/L; and 1, 2 and 1-2 mg/L, respectively. Our results showed that the frequency of synergistic effects (FICI: ≤0.5) of three combinations were all at the same rate of 77% (23/30). No in vitro antagonism (FICI >4) was observed.

In vitro activity of daptomycin combinations with rifampicin, gentamicin, fosfomycin and fusidic acid against MRSA strains.

OBJECTIVES: Although new antimicrobial agents designed to treat infections with limited therapeutic options have been introduced in the past few years, resistant Gram positive cocci have continued to emerge and spread. Daptomycin is a cyclic lipopeptide antibiotic that has rapid bactericidal activity against broad spectrum of Gram positive bacteria, including methicillin resistant Staphylococcus aureus (MRSA). Antibiotics are sometimes used in combination in an attempt to prevent or delay the in vivo emergence of drug-resistant subpopulations of pathogenic organisms. The aim of the study was to evaluate in vitro activity of daptomycin combinations with rifampicin, gentamicin, fosfomycin, and fusidic acid against MRSA strains. METHODS: In total, 25 strains were tested. The minimum inhibitory concentrations of all antibiotics were determined using a microbroth dilution assay. The in vitro activities of antibiotics in combination were assessed using the microbroth checkerboard technique. With this method, the fractional inhibitory concentration index was interpreted as follows: synergism ≤0.5; additive/indifference >0.5-≤4; antagonism >4. RESULTS: According to the MIC values, all strains (100%) were susceptible to daptomycin, 16% (4/25) to rifampicin, 20% (5/25) to gentamicin, 44% (11/25) to fosfomycin, and 72% (18/25) to fusidic acid. Synergistic interaction of daptomycin in combinations with rifampicin, gentamicin, fosfomycin, and fusidic acid were found as 12%, 68%, 100% and 16%, respectively. No antagonism was observed. CONCLUSION: The combination of daptomycin with fosfomycin may be a promising alternative therapy of MRSA infections.

Auxo-, sero-, and opa-typing of Neisseria gonorrhoeae strains isolated in Istanbul, Turkey.

BACKGROUND: Typing methods are essential in understanding of the transmission dynamics of Neisseria gonorrhoeae. Several typing methods were described including opa-typing. GOALS: The goal of this study was to type all of the strains we isolated in the recent past by using auxo-, sero-, and opa-typing, and to compare the discriminatory power of these methods. STUDY: Auxotyping, serotyping, and opa-typing were performed for 56 N. gonorrhoeae strains isolated from male patients with urethritis. RESULTS: A total of 9 auxotypes and 33 serovars were detected. Combining the 2 systems, a total of 45 distinct auxotype/serovar (A/S) classes were identified. The most common A/S class was NR/Bsty (5 strains). Fifty-five distinct patterns were detected by opa-typing. Two strains that have been isolated 16 months apart gave identical patterns with opa-typing and their A/S class was also identical (NR/Bsty). Simpson's index of diversity was found as 0.664, 0.961, 0.987, and 0.999 for auxotyping, serotyping, A/S class, and opa-typing, respectively. CONCLUSIONS: Opa-typing is a potential useful method for typing N. gonorrhoeae as a result of its high discriminatory power, rapidity, ease and relatively lower cost.