Reduction In Minimum Inhibitory Concentration Research Articles

Activity of Mecillinam and Clavulanic Acid on ESBL Producing and Non- ESBL Producing Escherichia Coli Isolated From UTI Cases

Mecillinam is one of the very few oral antibacterial agents used against extended spectrum ?- lactamase (ESBL) producing Escherichia coli (E. coli) causing urinary tract infection (UTI)). It is reported that, resistance to mecillinam can be reversed to some extent by adding beta lactamase inhibitor like clavulanic acid. The present study was aimed to determine in-vitro activity of mecillinam and mecillinam-clavulanic acid combination on the susceptibility of ESBL producing and non-ESBL producing E. coli. Total 124 E. coli (78 ESBL positive and 46 ESBL negative) isolates from urine samples of patients with UTI were included in the study. Organisms were isolated from patients attending BIRDEM General Hospital from July 2012 to December 2012. ESBL production was tested by double disc synergy test. Minimum inhibitory concentration (MIC) of mecillinam and clavulanic acid against E. coli was determined by agar dilution method. Of the total E. coli isolates, 62.9% was ESBL positive and 37.1% was negative for ESBL. Out of ESBL positive isolates, 75.6% was sensitive to mecillinam while ESBL negative isolates showed the sensitivity as 67.4%. The sensitivity to mecillinam of ESBL positive and negative isolates increased to 85.9% and 86.9% respectively by addition of clavulanic acid with mecillinam. The MIC values of intermediate and resistant isolates converted to sensitive MIC range after addition of clavulanic acid with mecillinam. Conversion of resistance of ESBL producing isolates by adding clavulanic acid was also evident by the reduction of MIC50 and MIC90 from 4?g/ml to ?1 ?g/ml and from 128 ?g/ ml to 64 ?g/ml respectively. Similar trend of reduction of MICs was also observed in non-ESBLs. In conclusion, both ESBL positive and negative E. coli demonstrated considerable sensitivity to mecillinam and the sensitivity increased significantly (p<0.05) by adding clavulanic acid with mecillinam.Ibrahim Med. Coll. J. 2014; 8(2): 56-60

Microemulsification of clove essential oil improves its in vitro and in vivo control of Penicillium digitatum

Clove essential oil (CEO) is a promising alternative to chemical fungicides for postharvest decay control. However, relatively high concentrations required for in vivo microbial growth inhibition limit its application. Hence, this study aimed to strengthen the antifungal activity of CEO by loading it in microemulsion system. Two CEO microemulsions (ME-1, CEO/ethanol/Tween 80 = 1:2:7; ME-2, CEO/ethanol/Tween 80 = 1:3:6) were evaluated their antifungal activity against Penicillium digitatum in vitro and in navel oranges. Microemulsification of CEO caused a reduction of MIC (minimum inhibitory concentration) from 0.50 μl/ml to 0.25 μl/ml, while the MFC (minimum fungicidal concentration) remained unchanged at 0.50 μl/ml, indicating enhancement of only fungistatic activity. The decay incidence of navel oranges treated with ME-1 and ME-2 was significantly (p < 0.05) reduced by 34.51% and 20.93%, respectively, in comparison to that of pure oil treatment after 5 days' storage at 25 °C. In the vapor phase, CEO microemulsions had the best control of lesion diameter and decay development. Additionally, the improved antifungal activity of CEO microemulsions may be related to their stronger ability to suppress spore germination and germ tube elongation of P. digitatum. The enhanced control of postharvest green mold of navel oranges by CEO after microemulsification can broaden its application in food industry.

In vitro effectiveness of triterpenoids and their synergistic effect with antibiotics against Staphylococcus aureus strains.

Objectives:The aim of this study is to evaluate the effect of four triterpenoids such as oleanolic acid, ursolic acid, cycloastragenol, and beta-boswellic acid alone and in combination with antibiotics against Staphylococcus aureus strains.Materials and Methods:Sixteen clinical strains of S. aureus from infected wounds were isolated. Eight were methicillin-sensitive S. aureus (MSSA), and the other eight were methicillin-resistant S. aureus (MRSA). The activity was also seen in reference S. aureus American Type Culture Collection™ strains. The activity of all the triterpenoids and antibiotics against S. aureus was evaluated by broth microdilution method. The effectiveness was judged by comparing the minimum inhibitory concentrations (MICs) of the compounds with antibiotics. The combination of antibiotics with compounds was evaluated by their fractional inhibitory concentrations (FIC).Results:Against both clinical and reference MSSA strains, none of the compounds exhibited comparable activity to antibiotics vancomycin or cefradine except for ursolic acid (MIC 7.8 μg/ml). Against MRSA, all compounds (MIC 16–128 μg/ml) showed lesser activity than vancomycin (MIC 5.8 μg/ml). Among triterpenoid-antibiotic combinations, the most effective were ursolic acid and vancomycin against clinical strain MSSA (FICS 0.17). However, overall, different combinations between triterpenoids and antibiotics showed 95%–46% (P < 0.05) reduction in MICs of antibiotics compared to when antibiotics were used alone. Cefradine, a drug not suitable for treating MRSA (MIC = 45 μg/ml), showed a remarkable decrease in its MIC (87% P< 0.01) when it was used in combination with oleanolic acid or ursolic acid in both clinical and reference strains.Conclusion:The tested triterpenoids are relatively weaker than antibiotics. However, when used in combination with antibiotics, they showed remarkable synergistic effect and thus can help in prolonging the viability of these antibiotics against S. aureus infections. Furthermore, reduction in MIC of cefradine with oleanolic acid indicates their potential use against MRSA.

Pterostilbene Enhanced Anti-Methicillin Resistant &lt;i&gt;Staphylococcus aureus&lt;/i&gt; (MRSA) Activity of Oxacillin

Methicillin-resistant Staphylococcus aureus (MRSA) is a deadly pathogen that initially was limited to hospital and healthcare facilities but has gradually became a growing problem in healthy children and adults. Pterostilbene belongs to the phenylpropanoid phytoalexin which is involved in plant response to various pathogen and herbivores attack. The aim of this study is to evaluate the anti-MRSA action of pterostilbene in combination with selected antibiotics; vancomycin, linezolid and oxacillin against ATCC 43300 and ATCC 33591. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and fractional inhibitory concentration (FIC) index values were determined. Microbroth dilution technique and microdilution checkerboard (MDC) assay were employed. The MIC and MBC of pterostilbene against ATCC 33591 was 31.25 and 62.50 µg mL-1, respectively. While for ATCC 43300, the MBC value was also twice (62.50 µg mL-1) its MIC value of 31.25 µg mL-1. This indicated that pterostilbene was bacteriostatic against both MRSA strains. Our MIC/MBC study also showed that linezolid exhibited bacteriostatic action but, oxacillin and vancomycin were bactericidal. MDC study showed that pterostilbene-oxacillin combination exhibited lowest FIC value (0.56) against both MRSA strains which indicated partial synergistic interaction. On the other hand, pterostilbene was additive (FIC 1.00) in combination with vancomycin whereas pterostilbene-linezolid combination displayed indifference effect with FIC of 1.25 against both MRSA strains. Pterostilbene in combination with oxacillin partially enhanced anti-MRSA activity with twofold reduction in MIC of oxacillin by acting at different site at the bacterial cell wall from that of oxacillin but more specific to the site of action of vancomycin.

Azole resistance in Candida spp. isolated from Catú Lake, Ceará, Brazil: an efflux-pump-mediated mechanism.

Since, there is no study reporting the mechanism of azole resistance among yeasts isolated from aquatic environments; the present study aims to investigate the occurrence of antifungal resistance among yeasts isolated from an aquatic environment, and assess the efflux-pump activity of the azole-resistant strains to better understand the mechanism of resistance for this group of drugs. For this purpose, monthly water and sediment samples were collected from Catú Lake, Ceará, Brazil, from March 2011 to February 2012. The obtained yeasts were identified based on morphological and biochemical characteristics. Of the 46 isolates, 37 were Candida spp., 4 were Trichosporon asahii, 3 were Cryptococcus laurentii, 1 Rhodotorula mucilaginosa, and 1 was Kodamaea ohmeri. These isolates were subjected to broth microdilution assay with amphotericin B, itraconazole, and fluconazole, according to the methodology standardized by the Clinical and Laboratory Standards Institute (CLSI). The minimum inhibitory concentrations (MICs) of amphotericin B, itraconazole, and fluconazole were 0.03125–2 μg/mL, 0.0625 to ≥16 μg/mL, and 0.5 to ≥64 μg/mL, respectively, and 13 resistant azole-resistant Candida isolates were detected. A reduction in the azole MICs leading to the phenotypical reversal of the azole resistance was observed upon addition of efflux-pump inhibitors. These findings suggest that the azole resistance among environmental Candida spp. is most likely associated with the overexpression of efflux-pumps.

Reduction of minimum inhibitory concentrations in drug-resistant Mycobacterium tuberculosis isolates in the presence of efflux pump inhibitors

Reduction of minimum inhibitory concentrations in drug-resistant Mycobacterium tuberculosis isolates in the presence of efflux pump inhibitors

Role of efflux pumps inhibitor in decreasing antibiotic resistance of Klebsiella pneumoniae in a tertiary hospital in North India.

The contribution of efflux systems to drug resistance in Enterobacteriaceae is becoming increasingly appreciated. This study phenotypically analyzed the role of efflux mechanisms in resistance to ertapenem, doripenem, and tigecycline among clinical isolates of carbapenem-resistant Klebsiella pneumoniae (CRKP). Multidrug-resistant and carbapenem non-susceptible K. pneumoniae isolates were determined by disk diffusion test. Further susceptibility of these isolates to carbapenems, ceftriaxone, cefoperazone, ceftazidime, tigecycline, and colistin was determined by agar dilution assay, and CRKP was identified. While modified Hodge test was used to confirm carbapenemase production, the contribution of efflux mechanisms was determined by a minimum inhibitory concentration (MIC) reduction assay, and typing was done by enterobacterial repetitive intergenic consensus (ERIC) polymerase chain reaction (PCR). Of the 238 isolates of K. pneumoniae, 174 were multidrug resistant and 74 were CRKP. Forty of the CRKP were positive for carbapenemase production, while 43, 11, and 2 of the CRKP isolates had elevated MIC of ≥ 32 µg/mL for ertapenem, doripenem, and tigecycline, respectively. Twofold or higher MIC reduction to ertapenem, doripenem, and tigecycline was observed in 6, 28, and 27 isolates, respectively; however, non-susceptibility to ertapenem, doripenem and tigecycline was abolished in 2, 11, and 18 K. pneumoniae isolates, respectively. Nine clones of CRKP widely distributed within the hospital were obtained from ERIC PCR. Although colistin retained better activity against CRKP, efflux pumps contributed to increased MIC in ertapenem, doripenem, and tigecycline. Therefore, efflux systems are important aspects that should be explored in the fight against multidrug-resistant bacteria.

Modification of the susceptibility of gram-negative rods producing ESβLS to β-lactams by the efflux phenomenon.

The production of β-lactamases is the most important mechanism of Gram-negative rod resistance to β-lactams. Resistance to ceftazidime and cefepime in clinical isolates of Enterobacteriaceae (especially ESβL-positive E. coli and K. pneumoniae) and P. aeruginosa is life-threatening. However, all strains of the above mentioned species possess chromosomally encoded RND efflux pump systems in addition to β-lactamase production. The main goal of this study was to assess the role of efflux pump systems in cefepime and/or ceftazidime resistant phenotypes of ESβL-positive clinical strains of Enterobacteriaceae and P. aeruginosa. The influence of the efflux pump inhibitor PAβN on the minimum inhibitory concentration (MIC) values of tested cephalosporins was species-dependent. Generally, a significant reduction (at least four-fold) of β-lactam MICs was observed in the presence of PAβN only in the case of P. aeruginosa clinical isolates as well as the ESβL-producing transformant PAO1161 ΔampC. The usage of this agent resulted in the restoration of susceptibility to cefepime and/or ceftazidime in the majority of the P. aeruginosa ESβL-positive strains with low and moderate resistance to the above cephalosporins. Moreover, an outer membrane permeabilizing effect in the presence of PAβN was identified. Strain-dependent β-lactamase leakage upon PAβN or β-lactam treatment was demonstrated. The most important observation was the restoration of susceptibility of P. aeruginosa WUM226 to cefepime (MIC decrease from 32 to 4 mg/L) and ceftazidime (MIC decrease from 128 to 4 mg/L) in the presence of PAβN, which occurred despite an almost complete lack of β-lactamase leakage from bacterial cells. In conclusion, these data indicate that RND efflux pumps can modify the susceptibility to β-lactams in Gram-negative rods producing ESβLs. However, this phenomenon occurs only in P. aeruginosa strains and was not observed among E. coli and K. pneumoniae strains, representing the Enterobacteriaceae family.

Modulation of the antibiotic activity against multidrug resistant strains of 4-(phenylsulfonyl) morpholine

The compound 4-(Phenylsulfonyl) morpholine belongs to the class of sulfonamides, which are widely used in the treatment of a large number of diseases caused by microorganisms. This compound has a morpholine group, which is also known for its antimicrobial properties. The aim of the present study was to investigate the antimicrobial and modulating activity of 4-(Phenylsulfonyl) morpholine against standard and multi-resistant strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and strains of the fungi Candida albicans, C. tropicalis and C. krusei. Antimicrobial activity was assessed based on the minimum inhibitory concentration (MIC) using the microdilution method. MIC was ⩾1024μg/mL for all microorganisms. Regarding modulating activity, the most representative effect occurred with the combination of 4-(Phenylsulfonyl) morpholine at a concentration of 128μg/mL (MIC 1/8) and amikacin against P. aeruginosa 03, with a reduction in MIC from 312.5 to 39.06μg/mL.

Enzyme mediated-transesterification of verbascoside and evaluation of antifungal activity of synthesised compounds

Enzymatic acylation of verbascoside, a polyhydroxylated natural product, has been reported in this study using five different commercial lipases and taking p-nitrophenyl alkanoates as acyl donors. Out of these enzymes, the immobilised Candida antarctica lipase B was found as the enzyme of choice. Mono- and di-acylated products were formed, with mono as major product indicating high regioselective nature of such transformations. A series of acyl esters of verbascoside have been synthesised by this enzymatic transesterification methodology. The lipophilicity of the synthesised analogues was also checked. The analogues were further subjected to synergistic antifungal activity with amphotericin B (AmB) against Candida albicans. Fourfold reduction in minimum inhibitory concentration of AmB was observed with few synthesised analogues such as verbascoside 4″-octanoate (3b), verbascoside 4″-palmitate (3d) and verbascoside 4″,4′-dipalmitate (4d) at a concentration of 0.5 μg/mL.

In vitro synergistic activity of colistin and ceftazidime or ciprofloxacin against multidrug-resistant clinical strains of Pseudomonas aeruginosa.

Infections caused by multidrug resistant (MDR) Pseudomonas aeruginosa are difficult to treat. Antibiotic development is dwindling in recent years. In order to develop new alternate therapies antimicrobial activity of different antibiotic combinations are being studied in vitro and in vivo. Sub-inhibitory concentrations of colistin were tested in combination with ceftazidime or ciprofloxacin by the checkerboard method against 25 MDR strains of P. aeruginosa. Synergy was observed for ceftazidime or ciprofloxacin antibiotic combinations with colistin among 73.3% of MDR3 (R(AMK, GEN, TOB) R(CAZ) R(CIP)) strains and 100% of MDR4 (R(AMK, GEN, TOB) R(CAZ) R(CIP) R(TZP)) strains. 6.6% strains of MDR3 and 14.3% strains of MDR5 (R(AMK, GEN, TOB) R(CAZ) R(CIP) R(TZP) R(IPM)) phenotypes were inhibited by colistin and ceftazidime alone and 6.6% strains of MDR3 phenotypes were inhibited by colistin and ciprofloxacin alone. For the remaining strains, though synergy was not observed, significant reduction in minimum inhibitory concentration was evident. The results of this study are significant as sub-inhibitory concentrations of colistin have an advantage of reducing in vivo toxicity. These findings need further evaluation for clinical use.

A promising approach of overcoming the intrinsic resistance of Candida krusei to fluconazole (FLC)--combining tacrolimus with FLC.

Candida krusei is intrinsically resistant to fluconazole (FLC). This study aimed to investigate whether tacrolimus (FK506) could enhance the susceptibility of FLC against C. krusei. The tested strains included the following: five isolates with minimal inhibitory concentration (MIC) of 32 μg mL(-1), two with MIC of 256 μg mL(-1), and one with MIC of 512 μg mL(-1). MICs of FK506 and FLC alone and in combination were determined by checkerboard assay, with data analyzed by fractional inhibitory concentration index model. The time-kill curves were plotted to investigate the antifungal activity at 0, 6, 12, 24, and 48 h after drug exposure. The results revealed that FK506 reduced the resistance of all isolates obviously and degree of reduction in MICs varied with susceptibilities of strains. Addition of FK506 resulted in a fourfold and 16-fold downward shift in MICs of the isolates with MICs of 32 μg mL(-1) and of ≥ 256 μg mL(-1), respectively. The synergy was further confirmed by the time-kill assay. When they were in combination against CK4/CK9 with MIC of 32/256 μg mL(-1), there was a 2.25/2.03 log10 CFU mL(-1) decrease at 24 h compared with FLC alone, respectively. In conclusion, combination of FK506 and FLC may represent a promising approach of overcoming the intrinsic resistance of C. krusei to FLC.

English

This study investigated the loss of resistance of multidrug resistant (MDR) Pseudomonas aeruginosa strains after exposure to dilutions of acridine orange. Five pure axenic strains of P. aeruginosa coded PA1 to PA5 obtained from five infected human sources which included middle ear, urethra, trachea, wound and urine were obtained from the Medical Microbiology Department of the University of Benin Teaching Hospital, Nigeria and stocked on sterile Nutrient agar slants. Slant cultures were sub-cultured aseptically on sterile MacConkey and Blood agar plates and incubated aerobically at 37&deg;C for 24 h to confirm for P. aeruginosa. Gram staining and oxidase test were carried out on resulting colonies. Antibiotic sensitivity test was done by agar disc diffusion method on all confirmed strains on sterile Mueller-Hinton agar plates before and after treatment with acridine orange (AO). P. aeruginosa strains that showed &le;50.0% reduction in resistance markers (RM) after treatment with 0.35, 0.55, 0.75 and 0.95 &micro;g/ml dilutions of AO were noted. Minimum inhibitory concentration (MIC) assay was done using gentamicin on PA5 strain with all four dilutions. All five strains showed 100% resistance against augmentin, nalidixic acid, nitrofurantoin, cotrimoxazole, amoxicillin and tetracycline. Sensitivity was recorded for ofloxacin and gentamicin with 14.6&plusmn;9.5 and 8.4&plusmn;4.4 mm zones of inhibition, respectively for all the strains except strain PA3 which was resistant to 8 (100.0%) of antibiotics used. Strains PA1, PA2, PA4 and PA5 were each resistant to 6 (75.0%) of the antibiotics tested. There was loss of RM of 52.1&plusmn;18.6 and 54.7&plusmn;37.6% to ofloxacin after treatment with 0.35 and 0.55 &micro;g/ml dilutions, respectively by all MDR P. aeruginosa strains. Loss of RM to gentamicin by strains PA1, PA2, PA4 and PA5 after 0.35 &micro;g/ml acridine orange treatment was recorded as 0.0, 61.5, 58.3 and 60.0%, respectively with a mean&plusmn;standard error (SE) of 45.0&plusmn;15.0%. With 0.55 &micro;g/ml dilution, 97.6&plusmn;28.3% loss of RM was recorded while less than 45.0 and 35.0% loss of RM were recorded for 0.75 and 0.95 &micro;g/ml dilutions, respectively. Acridine orange dilutions of 0.35 and 0.55 &micro;g/ml recorded two-fold (5 &micro;g) and four-fold (2.5 &micro;g) reduction in MIC of gentamicin, respectively. The implications of these findings are discussed. Key words: Resistance loss, Pseudomonas aeruginosa, treatment, dilutions, acridine orange.

Possible Role of Curcumin as an Efflux Pump Inhibitor in Multi Drug Resistant Clinical Isolates of Pseudomonas aeruginosa.

Multidrug resistant non-fermenters are continuously increasing in hospital and ICU settings. One of the mechanisms of developing drug resistance is possession of efflux pump through which bacteria extrude antimicrobial agents and other toxic substances. If these efflux channels are blocked or inhibited, increased drug concentration can be achieved in a bacterial cell with optimal drug dose. Present study was aimed to investigate role of curcumin as efflux pump inhibitor (EPI) and to compare its activity with a known EPI like phe-arg-beta-naphthylamide (PAβN). A total of 170 clinical isolates of Pseudomonas aeruginosa were taken, antimicrobial susceptibility was performed by disc diffusion test and minimum inhibitory concentration (MIC) against selected drugs before and after adding known synthetic EPI, PAβN (20mg/L). Out of these, 30 multidrug resistant strains were taken and MIC was performed with curcumin (50mg/L) with and without selected drugs. Results : Significant reduction in MIC was observed after adding curcumin (50mg/L) with selected antimicrobial agents in 9/30 (30%) of multi drug resistant (MDR) isolates of Pseudomonas aeruginosa, while no change in MIC was observed when curcumin (50mg/L) was used alone, indicating its efflux pump inhibitor activity. This study suggests role of efflux pump in development of drug resistance which can be overcome by use of an efflux pump inhibitor, with more emphasis on compound like curcumin which will have less or no adverse effects if used in vivo.

Synthesis, optimization, and characterization of silver nanoparticles from Acinetobacter calcoaceticus and their enhanced antibacterial activity when combined with antibiotics

BackgroundThe development of nontoxic methods of synthesizing nanoparticles is a major step in nanotechnology to allow their application in nanomedicine. The present study aims to biosynthesize silver nanoparticles (AgNPs) using a cell-free extract of Acinetobacter spp. and evaluate their antibacterial activity.MethodsEighteen strains of Acinetobacter were screened for AgNP synthesis. AgNPs were characterized using various techniques. Reaction parameters were optimized, and their effect on the morphology of AgNPs was studied. The synergistic potential of AgNPs on 14 antibiotics against seven pathogens was determined by disc-diffusion, broth-microdilution, and minimum bactericidal concentration assays. The efficacy of AgNPs was evaluated as per the minimum inhibitory concentration (MIC) breakpoints of the Clinical and Laboratory Standards Institute (CLSI) guidelines.ResultsOnly A. calcoaceticus LRVP54 produced AgNPs within 24 hours. Monodisperse spherical nanoparticles of 8–12 nm were obtained with 0.7 mM silver nitrate at 70°C. During optimization, a blue-shift in ultraviolet-visible spectra was seen. X-ray diffraction data and lattice fringes (d =0.23 nm) observed under high-resolution transmission electron microscope confirmed the crystallinity of AgNPs. These AgNPs were found to be more effective against Gram-negative compared with Gram-positive microorganisms. Overall, AgNPs showed the highest synergy with vancomycin in the disc-diffusion assay. For Enterobacter aerogenes, a 3.8-fold increase in inhibition zone area was observed after the addition of AgNPs with vancomycin. Reduction in MIC and minimum bactericidal concentration was observed on exposure of AgNPs with antibiotics. Interestingly, multidrug-resistant A. baumannii was highly sensitized in the presence of AgNPs and became susceptible to antibiotics except cephalosporins. Similarly, the vancomycin-resistant strain of Streptococcus mutans was also found to be susceptible to antibiotic treatment when AgNPs were added. These biogenic AgNPs showed significant synergistic activity on the β-lactam class of antibiotics.ConclusionThis is the first report of synthesis of AgNPs using A. calcoaceticus LRVP54 and their significant synergistic activity with antibiotics resulting in increased susceptibility of multidrug-resistant bacteria evaluated as per MIC breakpoints of the CLSI standard.

Prevalence of Pseudomonas aeruginosa and Acinetobacter spp producing metallo-β-lactamase in a tertiary care hospital

Background: Hospital acquired infection (HAI) due to multidrug resistant pathogens are increasing day by day. Among which MBL producing Pseudomonas aeruginosa and Acinetobacter spp contribute a major portion of HAI. Aims: The objective is to determine the antibiotic susceptibility pattern of P. aeruginosa and Acinetobacter spp. showing imipenem resistance and prevalence of MBL producing strains among them in a tertiary care hospital. Materials and Methods: Over a period of 5 months in a tertiary care hospital, 60 Pseudomonas aeruginosa and 50 Acinetobacter spp. were isolated. These were tested phenotypically for detection of metallo-β-lactamase (MBL) production, by imipenem-ethylenediaminetetraacetic acid (EDTA) combined disc method and by four fold or more reduction of minimum inhibitory concentration (MIC) against imipenem with EDTA. Result and Conclusion: The prevalence of MBL producing Pseudomonas aeruginosa was found to be 41% and Acinetobacter spp. 22%. Antibiotic susceptibility tests revealed multidrug resistance for most antibiotics but 100% sensitivity for colistin. A big proportion of these positive strains were isolated from patients with multiple risk factors like prolonged hospital stay, indwelling urinary catheter, continuous mechanical ventilation, prolonged antimicrobial therapy, intravenous lines. The overall mortality rate among them was as high as 21%.

Modulation of the Antibiotic Activity by Extracts fromAmburana cearensisA. C. Smith andAnadenanthera macrocarpa(Benth.) Brenan

The aim of this study was to verify the possible interactions between ethanol extracts of Amburana cearensis A. C. Smith and Anadenanthera macrocarpa (Benth.) Brenan, combined with six antimicrobial drugs against multiresistant strains of Staphylococcus aureus and Escherichia coli isolated from humans. The antibacterial activity of the extracts was determined using the minimum inhibitory concentration (MIC). The microdilution assay was performed to verify the interactions between the natural products and the antibiotics using a subinhibitory concentration. The activity of amikacin associated with the extract of Anadenanthera macrocarpa against EC 27 was enhanced, demonstrating an MIC reduction from 128 to 4 μg/mL. Among the β-lactams, no potentiation on its activity was observed, with exception to the antagonism of the natural products with ampicillin against S. aureus 358.

Ciprofloxacin shows synergism with classical antifungals against Histoplasma capsulatum var. capsulatum and Coccidioides posadasii

This study evaluated the in vitro interaction between ciprofloxacin (CIP) and classical antifungals against Histoplasma capsulatum var. capsulatum in mycelial (n = 16) and yeast-like forms (n = 9) and Coccidioides posadasii in mycelial form (n = 16). This research was conducted through broth microdilution and macrodilution, according to Clinical Laboratory Standards Institute. Inocula were prepared to obtain from 0.5 × 10(3) to 2.5 × 10(4) cfu ml(-1) for H. capsulatum and from 10(3) to 5 × 10(3) cfu ml(-1) for C. posadasii. Initially, minimum inhibitory concentration (MIC) for each drug alone was determined. Then, these MICs were used as the highest concentration for each drug during combination assays. The procedures were performed in duplicate. For all combination assays, MICs were defined as the lowest concentration capable of inhibiting 80% of visible fungal growth, when compared to the drug-free control. Drug interaction was evaluated by paired sample t-Student test. The obtained data showed a significant MIC reduction for most tested combinations of CIP with antifungals, except for that of CIP and voriconazole against yeast-like H. capsulatum. This study brings potential alternatives for the treatment of histoplasmosis and coccidioidomycosis, raising the possibility of using CIP as an adjuvant antifungal therapy, providing perspectives to delineate in vivo studies.

Molecular characterization of the first fluoroquinolone resistant strains of Streptococcus agalactiae isolated in Brazil

Three isolates of Streptococcus agalactiae, recovered from residents of the metropolitan area of Rio de Janeiro with significant bacteriuria, were found to be resistant to levofloxacin. Determination of the minimal inhibitory concentration (MIC) confirmed one isolate as intermediate and two as resistant to levofloxacin. No reduction in levofloxacin MIC was observed with reserpine, indicating that resistance was not caused by an efflux mechanism. Typical point mutations were observed in the quinolone resistance determinant region of gyrA and parC. Other point mutations in parC generated novel altered codons: Ser80→Pro in the intermediate resistance isolate, and Gly128→Asp in a resistant isolate. Through molecular modeling, it was possible to observe that these novel substitutions might not play a role in resistance, since these amino acids were not involved in the antibiotic binding site. Pulsed field gel electrophoresis profiles revealed a non-clonal trend among these isolates. This is the first report of genetic characterization of levofloxacin-resistant S. agalactiae strains in Brazil.

Study of the Correlation of Imipenem Resistance with Efflux Pumps AdeABC, AdeIJK, AdeDE and AbeM in Clinical Isolates of Acinetobacter baumannii

Background: To investigate the role of efflux pumps AdeABC, AdeIJK, AdeDE and AbeM in reduced susceptibility to imipenem in clinical isolates of Acinetobacter baumannii. Methods: Susceptibility testing was conducted by the agar dilution method. The presence and expression of pump genes were analyzed by conventional PCR and real-time RT-PCR, respectively. Results: Most antibiotics, including carbapenem, aminoglycosides, fluoroquinolones and cephalosporins showed high minimum inhibitory concentration (MIC) values in imipenem-resistant A. baumannii (IRAB). After exposure to the efflux pump inhibitor Phe-Arg-β-naphthylamide, a 4- to 32-fold reduction of imipenem MICs was observed in 33 (66%) isolates of IRAB, while no significant decrease occurred in imipenem-susceptible A. baumannii (ISAB). The majority of IRAB isolates (>80%) were found to be positive for adeB, adeR, adeS, adeJ and abeM. Positive adeE was discovered in 6 isolates of IRAB and coexisted with adeB. Approximate 4-, 3- and 11-fold increases in adeB, adeJ and abeM expression were observed, respectively, in IRAB compared to those in ISAB. Conclusions: A variety of efflux pump systems, including AdeABC, AdeIJK and AbeM, seem to play important roles in the resistance to imipenem of A. baumannii. Moreover, this is the first time that adeE has been found to coexist with adeB in a small number of isolates of A. baumannii.