Microwave-assisted synthesis of antimicrobial dihydropyridines and tetrahydropyrimidin-2-ones: novel compounds against aspergillosis

Ten 4-aryl-1,4-dihydropyridine and three 4-aryl-1,2,3,4-tetrahydropyrimidin-2-one derivatives have been synthesized and examined for their activity against pathogenic strains of Aspergillus fumigatus and Candida albicans. Although none of the three compounds belonging to pyrimidin-2-one series showed any activity against two pathogens, two of the compounds of the dihydropyridine series, that is, diethyl 4-(4-methoxyphenyl)-2,6-dimethyl-1,4-dihydropyridin-3,5-dicarboxylate and dimethyl 4-(4-methoxyphenyl)-2,6-dimethyl-1,4-dihydropyridin-3,5-dicarboxylate, exhibited significant activity against A. fumigatus in disc diffusion, microbroth dilution and percent spore germination inhibition assays. The most active diethyl dihydropyridine derivative exhibited a MIC value of 2.92 microg/disc in disc diffusion and 15.62 microg/ml in microbroth dilution assays. The MIC(90) value of the most active compound by percent germination inhibition assay was found to be 15.62 microg/ml. The diethyl dicarboxylate derivative of dihydropyridine also exhibited appreciable activity against C. albicans. The in vitro toxicity of the most active diethyl dihydropyridine derivative was evaluated using haemolytic assay, in which the compound was found to be non-toxic to human erythrocytes even at a concentration of 625 microg/ml. The standard drug amphotericin B exhibited 100% lysis of erythrocytes at a concentration almost 16 times less than the safer concentration of the most active dihydropyridine derivative.     

Synthesis and antifungal activity of substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles

Series of substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles derivatives have been synthesized and examined for their activity against pathogenic strains of Aspergillus fumigatus (ITCC 4517), Aspergillus flavus (ITCC 5192) Aspergillus niger (ITCC 5405) and Candida albicans (ITCC No 4718). All synthesized compounds showed mild to moderate activity, except for 2-substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles 6a-d. The most active 1-(4-chlorophenyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole 4c exhibited a MIC value of 5.85 microg/disc against A. fumigatus and 11.71 microg/disc against A. flavus and A. niger in disc diffusion assay. Anti-Aspergillus activity of active compound 4c by microbroth dilution assay was found to be 15.62 microg/ml in case of A. fumigatus and 31.25 microg/ml with A. flavus and A. niger. The MIC90 value of the most active compound by percent germination inhibition assay was found to be 15.62 microg/ml against A. fumigatus. The MIC90 values of substituted-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indoles against C. albicans ranged from 15.62 to 250 microg/ml. The in vitro toxicity of the most active 1-(4-chlorophenyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2-a]indole 4c was evaluated using haemolytic assay, in which the compound was found to be non-toxic to human erythrocytes up to a concentration of 312.50 microg/ml. The standard drug amphotericin B exhibited 100% lysis at a concentration of 37.5 microg/ml.     

In-vitro activity of 5-fluorocytosine against 1,021 Spanish clinical isolates of Candida and other medically important yeasts

The aim of this study was to determine the prevalence of primary resistance to 5-fluorocytosine (5FC) among clinical isolates of yeasts in Spain where this drug is not currently available for therapy. We have tested the in vitro activity of 5FC against 1,021 recent yeast clinical isolates, including 522 Candida albicans, 140 Candida parapsilosis, 68 Candida glabrata, 41 Candida dubliniensis, 50 Candida guilliermondii, 34 Candida tropicalis, 28 Candida krusei, 20 Candida famata, 11 Cryptococcus neoformans, 5 Cryptococcus albidus, 43 Rhodotorula spp., 24 Trichosporon spp., 5 Saccharomyces cerevisiae, 9 Pichia spp., and 21 isolates from other 11 yeast species. The MICs were determined by the ATB Fungus agar microdilution test (bioMerieux, France) and the following interpretive breakpoints were used: susceptible, > 4 microg/ml; intermediate, 8 to 16 microg/ml; resistant, > 32 microg/ml. 5FC was very active against Candida spp. and other medically important yeasts as 852 (83.4%) of the studied isolates were susceptible (MIC < 4 microg/ml). The species most susceptible to 5FC were C. dubliniensis (100%of isolates; MIC90, 0.25 microg/ml), C. famata (100% of isolates; MIC90, 0.25 microg/ml), C. guilliermondii (98%of isolates; MIC90, 0.25 microg/ml), C. glabrata (95.5% of isolates; MIC90, 0.25 microg/ml), and C. neoformans (90.9% of isolates; MIC90, 2 microg/ml). Primary resistance to 5FC was very uncommon, and a MIC > 32 microg/ml, indicator of in vitro resistance, was observed in 106 isolates (10.4%): 77 C. albicans (16.5% of isolates; MIC90, > 128 microg/ml), 9 C. parapsilosis (6.4% of isolates; MIC90, 8 microg/ml), 4 C. albidus (80% of isolates, MIC50, > 128 microg/ml), 3 C. glabrata (4.4% of isolates; MIC90, 0.25 microg/ml), 3 C. tropicalis (8.8% of isolates; MIC90, 4 microg/ml), 2 C. krusei (7.1% of isolates; MIC90, 8 microg/ml), 2 Rhodotorula spp. (4.6% of isolates, MIC90, 1 microg/ml), 8 Trichosporon spp. (33.3% of isolates; MIC90, 64 microg/ml), and 1 C. lipolytica (50% of isolates). Interestingly, most C. albicans (67 out of 77 isolates) resistant to 5FC were serotype B isolates.     

The inheritance of thiabendazole resistance in Haemonchus contortus.

Haemonchus contortus worm populations isolated from naturally infected sheep at the Pastoral Research Laboratory, Armidale, N.S.W., were found to contain approximately 20% of worms resistant to a 50 mg/kg dose of thiabendazole. Following 3 generations of selection with 50 mg/kg thiabendazole the number of worms removed by the anthelmintic was too small to detect differences between treated and control groups. After more than 15 generations of selection, matings between males from the selected strain and non-resistant females produced resistant males and females in equal numbers. Thus, thiabendazole resistance does not appear to be sex-linked. A dose--response assay on the F2 adults indicated that worms from female resistant x male non-resistant crosses were more resistant than F2 adults of the reciprocal cross. An in vitro technique that identified thiabendazole-resistant eggs by their ability to hatch in a solution containing thiabendazole and 0.1% NaCl solution was also used to study the inheritance of resistance. F1 eggs had similar LC50's to the resistant parents. F2 and back-cross eggs from an original mating of thiabendazole-resistant females x non-resistant males had a higher LC50 than F2 and back-cross eggs from the reciprocal mating, indicating a degree of matroclinous inheritance of resistance. However, the resistant parents had tolerances to thiabendazole exceeding those of F2. F3 eggs had a resistance distribution that ranged from that of the resistant to the non-resistant parent. No significant deviation from linearity was observed in any of the dose--response lines. These results indicate that thiabendazole resistance in H. contortus worms is inherited as an autosomal and semi-dominant trait.     

Antifungal susceptibility of epigallocatechin 3-O-gallate (EGCg) on clinical isolates of pathogenic yeasts

This is the first report to investigate the antifungal susceptibility of 21 clinical isolates of seven Candida species to epigallocatechin 3-O-gallate (EGCg) and to compare with six antifungal agents, amphotericin B (AMPH), fluconazole (FLCZ), flucytosin (5FC), itraconazole (ITCZ), micafungin (MCFG), and miconazole (MCZ), using a method following the National Committee for Clinical Laboratory Standards (NCCLS) M27-A guidelines. Among the tested species, Candida glabrata exhibited the highest susceptibility to EGCg (MIC50, 0.5-1 microg/ml and MIC90, 1-2 microg/ml) compared favorably with FLCZ, although they were slightly less susceptible than to AMPH, 5FC, MCFG, ITCZ, and MCZ. Candida guilliemondii and Candida parapsilosis (MIC50, 1-4 microg/ml and MIC90, 2-16 microg/ml) were also susceptible to EGCg, although they appear to be slightly less susceptible to EGCg than C. glabrata and the other antifungal agents tested. Moreover, the susceptibility of Candida krusei strains (MIC50, 2 microg/ml and MIC90, 4-8 microg/ml) to EGCg was approximately 2- to 8-fold higher than those of 5FC and FLCZ. Our data indicate that EGCg can inhibit clinically pathogenic Candida species, although the concentrations of EGCg for antifungal susceptibility were slightly higher than those of tested antifungal agents on the whole. Based on these results, we suggest that EGCg may be effectively used as a possible agent or adjuvant for antifungal therapy in Candidiasis.     

1,2,3]Triazolo[4,5-h]quinolones. A new class of potent antitubercular agents against multidrug resistant Mycobacterium tuberculosis strains

In this preliminary study we report the activity of 3-methyl-9-substituted-6-oxo-6,9-dihydro-3H-[1,2,3]-triazolo[4,5-h]quinolone-carboxylic acids and their esters as a new class of antiinfective agents against MDR Mycobacterium tuberculosis. In antitubercular screening against H37Rv and 11 clinically isolated strains of M. tuberculosis several derivatives (1o,3a,c,i,j,p) showed MIC(90) in the range 0.5-3.2 microg/mL. 3c showed no cytotoxicity and proved to be the most potent derivative exhibiting MIC(90)=0.5 microg/mL against all M. tuberculosis strains and infected human macrophages (J774-A1) tested.     

Antimicrobial susceptibility patterns of unusual nonfermentative gram-negative bacilli isolated from Latin America: report from the SENTRY Antimicrobial Surveillance Program (1997-2002)

The antimicrobial susceptibility of 176 unusual non-fermentative gram-negative bacilli (NF-GNB) collected from Latin America region through the SENTRY Program between 1997 and 2002 was evaluated by broth microdilution according to the National Committee for Clinical Laboratory Standards (NCCLS) recommendations. Nearly 74% of the NF-BGN belonged to the following genera/species: Burkholderia spp. (83), Achromobacter spp. (25), Ralstonia pickettii (16), Alcaligenes spp. (12), and Cryseobacterium spp. (12). Generally, trimethoprim/sulfamethoxazole (MIC50, < 0.5 microg/ml) was the most potent drug followed by levofloxacin (MIC50, 0.5 microg/ml), and gatifloxacin (MIC50, 1 microg/ml). The highest susceptibility rates were observed for levofloxacin (78.3%), gatifloxacin (75.6%), and meropenem (72.6%). Ceftazidime (MIC50, 4 microg/ml; 83.1% susceptible) was the most active beta-lactam against B. cepacia. Against Achromobacter spp. isolates, meropenem (MIC50, 0.25 microg/ml; 88% susceptible) was more active than imipenem (MIC50, 2 microg/ml). Cefepime (MIC50, 2 microg/ml; 81.3% susceptible), and imipenem (MIC50, 2 microg/ml; 81.3% susceptible) were more active than ceftazidime (MIC50, >16 microg/ml; 18.8% susceptible) and meropenem (MIC50, 8 microg/ml; 50% susceptible) against Ralstonia pickettii. Since selection of the most appropriate antimicrobial agents for testing and reporting has not been established by the NCCLS for many of NF-GNB species, results from large multicenter studies may help to guide the best empiric therapy.     

Semen cryopreservation of small abalone (Haliotis diversicolor supertexa)

Methods for cryopreserving spermatozoa and maximizing fertilization rate in Taiwan small abalone, Haliotis diversicolor supertexa, were developed. The gametes (spermatozoa and eggs) of small abalone were viable 3 h post-spawning, with fertilization, and development rate decreasing with time. A minimum of 10(2) cell/ml sperm concentration and a contact time of 2 min between gametes is recommended for artificial insemination of small abalone eggs. Eight cryoprotectants, dimethyl sulfoxide (DMSO), dimethyl acetamide (DMA), ethylene glycol (EG), propylene glycol (PG), butylene glycol (BG), polyethylene glycol, glycerol and methanol, were tested at concentrations between 5 and 25% to evaluate their effect on motility of spermatozoa exposed to cryoprotectant for up to 60 min at 25 degrees C before freezing. The least toxic cryoprotectant, 10% DMSO, was added to artificial seawater (ASW) to formulate the extender for freezing. Semen was diluted 1:1 with the extender, inserted into 1.5 ml microtubes and frozen using a cooling rate between -3.5 and -20 degrees C/min to various transition temperatures (0, -30, -60, -90 and -120 degrees C), followed by transfer and storage in liquid nitrogen (-196 degrees C). The microtubes were thawed from +45 to +145 degrees C/min. Spermatozoa, cooled to -90 degrees C at a cooling rate of -12 or -15 degrees C/min and then immersed in liquid nitrogen, had the best post-thaw motility. Post-thaw sperm motility was markedly reduced compared to fresh sperm. More frozen-thawed spermatozoa are required to achieve fertilization rates comparable to those achieved using fresh spermatozoa.     

Ancylostoma caninum: the finger cell neurons mediate thermotactic behavior by infective larvae of the dog hookworm

Bhopale, V. M., Kupprion, E. K., Ashton, F. T., Boston, R., and Schad, G. A. 2001. Ancylostoma caninum: The finger cell neurons mediate thermotactic behavior by infective larvae of the dog hookworm. Experimental Parasitology 97, 70-76. In the amphids (anteriorly positioned, paired sensilla) of the free-living nematode Caenorhabditis elegans, the so-called finger cells (AFD), a pair of neurons, each of which ends in a cluster of microvilli-like projections, are known to be the primary thermoreceptors. A similar neuron pair in the amphids of the parasitic nematode Haemonchus contortus is also known to be thermoreceptive. The hookworm of dogs, Ancylostoma caninum, has apparent structural homologs of finger cells in its amphids. The neuroanatomy of the amphids of A. caninum and H. contortus is strikingly similar, and the amphidial cell bodies in the lateral ganglia of the latter nematode have been identified and mapped. When the lateral ganglia of first-stage larvae (L1) of A. caninum are examined with differential interference contrast microscopy, positional homologs of the recognized amphidial cell bodies in the lateral ganglia of H. contortus L1 are readily identified in A. caninum. The amphidial neurons in A. caninum were consequently given the same names as those of their apparent homologs in H. contortus. It was hypothesized that the finger cell neurons (AFD) might mediate thermotaxis by the skin-penetrating infective larvae (L3) of A. caninum. Laser microbeam ablation experiments with A. caninum were conducted, using the H. contortus L1 neuronal map as a guide. A. caninum L1 were anesthetized and the paired AFD class neurons were ablated. The larvae were then cultured to L3 and assayed for thermotaxis on a thermal gradient. L3 with ablated AFD-class neuron pairs showed significantly reduced thermotaxis compared to control groups. The thermoreceptive function of the AFD-class neurons associates this neuron pair with the host-finding process of the A. caninum infective larva and shows functional homology with the neurons of class AFD in C. elegans and in H. contortus.     

A membrane associated glutamate binding protein from Caenorhabditis elegans and Haemonchus contortus

1. A glutamate binding protein has been identified in membrane preparations from the free living nematode, Caenorhabditis elegans, and from the parasitic nematode, Haemonchus contortus. 2. This putative glutamate receptor was solubilized with 30 mM octyl-B-glucoside and partially purified by anion exchange and gel filtration chromatography. 3. An 80-fold purification with recovery of 75% of the glutamate binding activity was achieved. 4. The soluble C. elegans binding protein displayed a Kd for glutamate of 0.1 microM, in close agreement with the findings for the membrane associated binding protein. 5. Quisqualate was capable of displacing glutamate from the soluble C. elegans receptor, again in agreement with previous findings for the membrane bound receptor. 6. The fact that a parasitic nematode, Haemonchus contortus, also possesses this putative glutamate receptor, strengthens the case for using C. elegans as a model system for the study of parasitic nematode neuromuscular physiology.     

Antimicrobial activity of organic extracts isolated from Aplysina fistularis (Demospongiae: Aplysinidae)

Organic extracts of the sponge Aplysina fistularis (Pallas 1766) were tested for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus) and Gram negative bacteria (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa). The minimal inhibitory concentration (MIC) and toxic activity of extract were determined. Susceptibility trials of organic fractions obtained by VLC: Hexane, EtOAc and CHCl3 showed that EtOAc fraction has antibacterial activity against E. coli, while CHCl3 fraction inhibited E. coli and S. aureus growth. The later refractioning of EtOAc fraction and the biodirected assays showed that fractions F12 and F13 of EtOAc/Hex and EtOAc F14 were bioactive against Gram positive and Gram negative bacteria. Only EtOAc/MeOH Sf2 from subfractionig of EtOAc F14 produced inhibition for E. coli and S. aureus. In Sf2 EtOAc/MeOH, MIC was moderate for S. aureus (MIC > 256 g/ml). F4 CHCl3/MeOH produced a high inhibition in S. aureus (MIC = 0.125 g/ml) and for E. coli (MIC > 16 g/ml). F10 CHCl3/MeOH showed a moderate activity against S. aureus (MIC > 128 g/ml) and low activity against E. coli (MIC = 512 g/ml). F10 CHCL3/MeOH did no present toxic activity against Artemia salina. The fractiorts F4 CHCL3/MeOH and Sf2 EtOAc/MeOH were toxic for this organism when the concentration was higher than 100 microg/ml. LC50 in both cases was 548.4 and 243.4 microg/ml respectively. Secondary metabolites of medium polarity obtained from A. fistularis have a wide spectrum of anti bacterial activity. Toxicity analysis suggests that only F10 CHCL3/MeOH has potential as an antimicrobial agent for clinical use.     

Anticariogenic activity of macelignan isolated from Myristica fragrans (nutmeg) against Streptococcus mutans

The occurrence of dental caries is mainly associated with oral pathogens, especially cariogenic Streptococcus mutans. Preliminary antibacterial screening revealed that the extract of Myristica fragrans, widely cultivated for the spice and flavor of foods, possessed strong inhibitory activity against S. mutans. The anticariogenic compound was successfully isolated from the methanol extract of M. fragrans by repeated silica gel chromatography, and its structure was identified as macelignan by instrumental analysis using 1D-NMR, 2D-NMR and EI-MS. The minimum inhibitory concentration (MIC) of macelignan against S. mutans was 3.9 microg/ml, which was much lower than those of other natural anticariogenic agents such as 15.6 microg/ml of sanguinarine, 250 microg/ml of eucalyptol, 500 microg/ml of menthol and thymol, and 1000 microg/ml of methyl salicylate. Macelignan also possessed preferential activity against other oral microorganisms such as Streptococcus sobrinus, Streptococcus salivarius, Streptococcus sanguis, Lactobacillus acidophilus and Lactobacillus casei in the MIC range of 2-31.3 microg/ml. In particular, the bactericidal test showed that macelignan, at a concentration of 20 microg/ml, completely inactivated S. mutans in 1 min. The specific activity and fast-effectiveness of macelignan against oral bacteria strongly suggest that it could be employed as a natural antibacterial agent in functional foods or oral care products.     

Cultivation of Haemonchus contortus (Nematoda: Trichostrongylidae) from infective larvae to the adult male and the egg-laying female

The parasitic nematode Haemonchus contortus was cultured in vitro to the adult male and the egg-laying female. Gastric contents from 2 cannulated calves and 2 sheep as well as extracts of stomach mucosa from both hosts were added to a mixture of API-1 culture medium and Fildes' reagent (a pepsin digest of defibrinated bovine blood) adjusted to pH 6.4 for the first week and pH 6.8 thereafter. The gas phase was 85% N2:5% O2:10% CO2. Best results were obtained when API-1 culture medium plus Fildes' reagent was supplemented with ovine gastric contents. Adult males up to 10 mm were obtained, and they produced and stored sperm at about 28 days in culture. Spermatozoa were never seen in the uteri of females grown in vitro. After 36 days in culture, female worms up to 16 mm were obtained which produced and layed eggs. Some of the eggs underwent division up to the 8-cell stage but did not develop further. No live larvae were observed at a stage earlier than the fourth. Presumably, this was because no matings were observed, although large clumps of worms did occur in the culture medium and mating might have occurred. The growth of adults from young to mature phases of this stage included: for the female, oogenesis and laying of eggs; for the male, development of paired sclerotized spicules, and spermatogenesis with the production of spermatozoa.     

Isoniazid resistance of exponentially growing Mycobacterium smegmatis biofilm culture

Biofilm growth of Mycobacterium smegmatis was found to be unaffected at an isoniazid concentration that inhibited growth of planktonic bacilli (i.e. at isoniazid minimum inhibitory concentration=10 microg ml(-1)). Significant growth (50% of drug-free control) of biofilms was observed at up to 40 microg ml(-1) and the MIC for biofilm growth showed an increase to up to 80 microg ml(-1) isoniazid. Thus, the biofilm growth modus appears to be a strategy for replicating bacilli to evade the onslaught of antibacterials.     

In vitro susceptibilities of Candida spp. to Panomycocin, a novel exo-beta-1,3-glucanase isolated from Pichia anomala NCYC 434

Panomycocin, the killer toxin of Pichia anomala NCYC 434 (K5), is a 49 kDa monomeric glycoprotein with exo-beta-1,3-glucanase activity (patent pending). In this study we evaluated the in vitro activity of panomycocin against a panel of 109 human isolates of seven different pathogenic Candida spp. using microdilution and time-kill methods. Panomycocin was most active against C. tropicalis, C. pseudotropicalis and C. glabrata with MIC(90) values of 1 microg/ml. It displayed significant activity against C. albicans and C. parapsilosis with MIC(90) values of 4 and 2 microg/ml, respectively. For C. krusei, the MIC(90) value was 8 microg/ml. Panomycocin was fungicidal against all the tested Candida spp. The MFC values were only one or 2 dilutions higher than the MICs with the exception of C. krusei isolates with MFCs greater than or equal to 4xMIC. Results of this study indicated that panomycocin could be considered as a natural antifungal agent against Candida infections and has significant potential for further investigation.     

Evaluation of broad-spectrum anthelmintic activity in a novel assay against Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis in the gerbil Meriones unguiculatus

The gerbil Meriones unguiculatus, infected with three species of nematodes, each located in a separate part of the gastrointestinal tract, provided a reliable laboratory assay for the evaluation of broad-spectrum anthelmintic activity. Gerbils harbouring 6-day-old infections of Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis were given selected broad-spectrum anthelmintics by gavage. Three benzimidazoles, thiabendazole, oxfendazole and albendazole, a tetrahydropyrimidine, morantel, an imidazothiazole, levamisole hydrochloride, a macrocyclic lactone, ivermectin and an experimental natural product, paraherquamide, were active against all three nematodes at various dosages. Trichostrongylus colubriformis was most sensitive to levamisole hydrochloride, morantel, thiabendazole and paraherquamide whereas ivermectin, oxfendazole and albendazole were more effective against H. contortus. All compounds were active against the caecal nematode T. sigmodontis although it was less sensitive than T. colubriformis. Haemonchus contortus was more sensitive than T. sigmodontis to all anthelmintics tested except thiabendazole.     

Prevalence of anthelmintic resistance in gastrointestinal nematodes of dairy goats under extensive management conditions in southwestern France

The occurrence of benzimidazole (BZ) and levamisole resistance was investigated in 18 randomly selected dairy goat herds located in southwestern France and characterized by extensive management. On each of the 18 farms, 45 adult goats were randomly allocated into three groups of 15 animals each: an untreated control group, a group that was orally administered fenbendazole (10 mg kg(-1) body weight) and a group that received orally a levamisole drench (12 mg kg(-1) body weight). Individual faecal egg counts and pooled larval cultures were done 10 days after anthelmintic treatment. Naive lambs were infected with larvae obtained from control and fenbendazole treated groups and were necropsied 35 days after infection for worm recovery. Faecal egg count reductions (FERC) were calculated for fenbendazole and levamisole and, when less than 95 per 100, were considered as indicative of anthelmintic resistance. An in vitro egg hatch test (EHT) was conducted with thiabendazole on eggs isolated from pooled faeces of fenbendazole treated goats in nine farms. Faecal egg count reductions indicated the occurrence of benzimidazole resistance in 15 out of 18 farms. Among these farms, nine had EHT values above 0.1 microg thiabendazole ml(-1) confirming the benzimidazole resistance status. Levamisole resistance was detected in two farms through FECR. Based on necropsy results, the prevalence of benzimidazole resistance was higher in Trichostrongylus colubriformis, medium in Haemonchus contortus and lower in Teladorsagia circumcincta. In nine farms the benzimidazole resistance was monospecific whereas multispecific resistance was found in the six remaining farms. A negative relationship was found between FECR for fenbendazole and the average number of anthelmintic treatments given per year on the farm. Despite extensive management including a low number of treatments, the prevalence of benzimidazole resistance was very high suggesting that the repeated and sometimes exclusive use of benzimidazole drugs, even at low frequency, is probably the main cause in developing nematode resistance in dairy goat herds. The importance of other factors such as under-dosing or buying animals already carrying resistant nematodes are discussed.     

Effectiveness of the antibiotics chloramphenicol and rifampin in the treatment of Streptococcus pneumoniae-induced meningitis and systemic infections

Streptococcus pneumoniae, a common pathogen in pediatric infections, has become resistant to penicillin and make these infections difficult to treat. Rifampin and chloramphenicol have been recommended as alternative therapies, since they are less costly and more accessible to communities with limited resources. However, their use may be restricted by the differing levels of resistance found in target populations. The objective was to determine minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) for chloramphenicol and rifampin in strains of S. pneumoniae. These strains were newly isolated from children under age 5 that had demonstrated systemic infections and meningitis. A subgroup of 107 isolates of S. pneumoniae was selected from 324 strains isolated during a period of 2 years (1994-1996). Among these isolates, 60 were penicillin-resistant and 47 were susceptible; 53 isolates were from children with meningitis. MIC and MBC for chloramphenicol and rifampicin were obtained by standard methods recommended by the National Committee for Clinical Laboratory Standards (NCCLS). S. pneumoniae ATCC strain 49619 served as the control. An isolate was considered susceptible to chloramphenicol when MIC = 4 microg/ml and resistant when MIC = 8 microg/ml. A strain was considered susceptible to rifampin when MIC = 1 microg/ml and resistant when MIC = 4 microg/ml. MBC was determined by recording the lower concentration of the antibiotic that inhibited 99.9% of the initial inoculum. Chloramphenicol resistance was found in 21% of the 107 isolates. In the group susceptible to penicillin, 11% were resistant to chloramphenicol and in the group resistant to penicillin 28% was resistant to chloramphenicol as well. MBC was found > 4 microg/ml in 28% of the isolates susceptible to penicillin and in 60% of the resistant isolates. No isolates were found resistant to rifampin. However, 2 penicillin resistant isolates showed CBM > 1 microg/ml to rifampin, and one with CIM = 1 microg/ml had a MBC to rifampicin of 16 microg/ml. Meningitis isolates showed higher CIM and CBM than the group of total isolates. These data suggest that chloramphenicol is not recommended for invasive infections caused by S. pneumoniae in Colombia. Rifampin is a more effective therapy in combination with other antibiotics for treatment of this kind of infections. Further studies are necessary to clarify the significance of low levels of MBC to rifampin found in some strains, since this may affect the efficacy of therapies that include this antibiotic.     

Synthesis and biological evaluation of new N-(2-hydroxy-4(or 5)-nitro/aminophenyl)benzamides and phenylacetamides as antimicrobial agents

A new series of N-(2-hydroxy-4(or 5)-nitro/aminophenyl)benzamide and phenylacetamide derivatives (1a-1n, 2a-2n) were synthesized and evaluated for antibacterial and antifungal activities against Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, and their drug-resistant isolate. Microbiological results indicated that the compounds possessed a broad spectrum of activity against the tested microorganisms at MIC values between 500 and 1.95 microg/ml. Benzamide derivative 1d exhibited the greatest activity with MIC values of 1.95, 3.9, and 7.8 microg/ml against drug-resistant B. subtilis, B. subtilis, and S. aureus, respectively.