In Vitro Susceptibility of Corynebacterium diphtheriae to Thirteen Antibiotics

Fourteen isolates of Corynebacterium diphtheriae proved to be most susceptible to erythromycin and rifampin and were also inhibited by 11 other antibiotics tested.     

In Vitro Susceptibility of Selected Bacteria to Cefaclor

Cefaclor is an orally absorbed cephalosporin antibiotic chemically and pharmacologically similar to cephalexin. It appears to be more active than cephalexin against susceptible strains. The in vitro sensitivity of 230 clinical bacterial isolates to cefaclor was studied. Most isolates of S. aureus, K. pneumoniae, E. coli, and indole negative Proteus species were inhibited at clinically attainable serum and urine concentrations. Like cephalexin, cefaclor was less active against isolates of Enterobacter species, indole positive Proteus species and enterococci although many of these isolates were inhibited at concentrations achievable in urine.     

Susceptibility of Phytopathogenic Bacteria to Wheat Purothionins In Vitro

Purothionins are basic polypeptides with antimicrobial properties that are present in the endosperm of wheat and other cereal species. Susceptibility to wheat purothionins among phytopathogenic bacteria of the genera Pseudomonas, Xanthomonas, Agrobacterium, Erwinia, and Corynebacterium has been investigated. Sensitive strains have been found in all of these genera except Agrobacterium (the only strain of A. tumefaciens available proved to be resistant). Minimal inhibitory concentrations (MIC) with partially purified crude purothionins ranged from 1 μg/ml for C. sepedonicum (C.5) to 540 μg/ml for E. amylovora (E.3). Minimal bactericidal concentrations (MBC) were not higher than twice the MIC value, except for C. poinsettiae (C.4) (MBC/MIC = 8). Purothionins α and β, obtained by carboxymethyl-cellulose column chromatography, were tested against P. solanacearum (P.2) and X. phaseoli (X.2); α purothionin was more active than β against X.2, and β more active than α against P.2. This suggests a relationship between polypeptide sequence and specificity of action.     

In Vitro Susceptibility of Strains of Pseudomonas pseudomallei to Rifampin

Reported high activity of rifampin for Pseudomonas pseudomallei could not be verified by extensive in vitro tests conducted with 31 recently isolated strains. Minimal inhibitory concentrations of rifampin were 25 μg/ml for three strains and greater than 25 μg/ml for 28 strains. Rifampin had relatively poor in vitro activity when compared with tetracycline drugs and chloramphenicol antibiotics now commonly used for treating melioidosis.     

In Vitro Susceptibility of Neisseria gonorrhoeae to Nine Antimicrobial Agents

The in vitro action of nine antibiotics was tested by the agar streak method against 45 gonococcal strains isolated from penicillin-therapy failures. The penicillin susceptibility range of these strains was 0.003 to 1.32 μg/ml, and the tetracycline susceptibility range was 0.125 to 2.0 μg/ml. Minimal inhibitory concentrations of minocycline and doxycycline paralleled the activity of tetracycline and ranged from 0.125 to 1.0 μg/ml and 0.125 to 2.0 μg/ml, respectively. Rifampicin, with a narrow range of 0.5 to 1.0 μg/ml, inhibited 75% of the strains at 0.5 μg/ml. The range for cephaloridine and cephaloglycine was 0.5 to 20.0 μg/ml, but another cephalosporium derivative, cephalexin, exhibited greater activity in its range of 0.25 to 20.0 μg/ml. A semisynthetic penicillin, carbenicillin, with a range of 0.025 to 0.75 μg/ml, displayed more activity against the lower susceptible penicillin G gonococcal strains.     

In Vitro Susceptibility of Prototheca to pH and Salt Concentration

Prototheca sp. can assume high economic significance in the dairy industry and pose a potential risk for the public health. We investigated the in vitro susceptibility of Prototheca isolates retrieved from mastitic milk (P. zopfii and P. blaschkeae) to different pH buffers and salt concentrations using a microbroth assay adapted from the Clinical Laboratory Standards Institute guidelines. Different pH buffer solutions ranging from pH 1 to pH 12 and different sodium chloride concentrations, 4.5, 9 and 18%, were tested. P. zopfii strains presented an optimal growth between pH 5 and 9, a complete growth inhibition at pH 3, and limited growth at pH 1 and 12, whereas P. blaschkeae strains showed higher susceptibility to all pH values except for pH 3 where it demonstrated a moderate growth when compared to P. zopfii strains. When salinity was incremented, P. blaschkeae was more resistant than P. zopfii, although a reduction in growth for all strains of Prototheca was observed. This study demonstrated differences in the in vitro susceptibilities of P. zopfii and P. blaschkeae to different pH and salt concentrations and intend to be a contribution on the understanding of some of the physiologic features that can be associated with the survival of these microalgae in the environment.     

Susceptibility In Vitro and In Vivo of Pseudomonas pseudomallei to Rifampin and Tetracyclines

Tests were performed on 64 strains of Pseudomonas pseudomallei to compare rifampin, various tetracyclines, and other antibiotics for inhibitory activity in vitro. Rifampin minimum inhibitory concentration (MIC) values generally fell between 25 to 50 μg/ml. For deoxycycline, methacycline, tetracycline, and minocycline, MIC means ranged from 1.3 to 2.7 μg/ml. Delayed treatment tests in subacute mouse infections revealed a better rifampin activity than was expected from its weak activity in vitro, whereas of the others, minocycline appeared superior. None of these five antibiotics demonstrated fully curative effectiveness in terms of mouse survival or eradication of residual infection in organs.     

Spectra of Susceptibility of Neisseria meningitidis to Antimicrobial Agents In Vitro

The minimal inhibitory concentrations of 49 antimicrobial agents for 37 to 40 meningococcal strains freshly isolated from the nasopharynx of healthy carriers were determined. Coumermycin A(1) and rifampin were the most effective agents tested. The geometric mean values of the minimal inhibitory concentrations for coumermycin A(1) and rifampin were 0.0001 and 0.02 mug/ml, respectively.     

Susceptibility of Hippocampal and Cortical Neurons to Argon-Mediated In Vitro Ischemia

Abstract: Neurons from cerebral cortex and hippocampal CA1 sector exhibit a striking difference in vulnerability to transient ischemia. To establish whether this difference is due to the inherent (pathoclitic) properties of these neurons, the ischemic susceptibility was studied in primary cortical and hippocampal cultures by using a new model of argon-induced in vitro ischemia. Neuronal cultures were exposed at 37°C for 10–30 min to argon-equilibrated glucose-free medium. During argon equilibration, P o ₂ declined to <2.5 torr within 1 min and stabilized shortly later at ∼1.3 torr. After 30 min of in vitro ischemia, total adenylate was <45% and ATP content <15% of control in both types of culture. Cytosolic calcium activity increased from 15 to 50 n M . Reoxygenation of cultures after in vitro ischemia led to delayed neuronal death, the severity of which depended on the duration of in vitro ischemia but not on the type of neuronal cultures. Energy charge of adenylate transiently returned to ∼90% of control after 3 h, but ATP content recovered only to 40% and protein synthesis to <35%. Cytosolic calcium activity continued to rise after ischemia and reached values of ∼500 n M after 3 h. The new argon-induced in vitro ischemia model offers major advantages over previous methods, but despite this improvement it was not possible to replicate the differences in cortical and hippocampal vulnerability observed in vivo. Our study does not support the hypothesis that selective vulnerability is due to an inherent pathoclitic hypersensitivity.     

In Vitro Susceptibility of Atypical Mycobacteria To Rifampin

Atypical mycobacteria (209 strains) were examined for susceptibility to rifampin by the proportion method by using Middlebrook 7H-10 agar. All strains of Mycobacterium kansasii and tap-water scotochromogens were inhibited by 0.25 to 1 μg of the drug per ml. Seventy-six per cent of M. scrofulaceum and 61% of M. intracellulare strains were susceptible to 4 μg/ml or less; 5% of the former and 8% of the latter were resistant to 16 μg/ml. All strains of M. gastri and M. triviale and most strains of M. terrae were sensitive to 1 to 4 μg/ml. Two strains of M. borstelense were both inhibited by 8 μg/ml. Nearly all strains of M. fortuitum were resistant to the drug. The results of this study suggest that rifampin may be a valuable agent for the treatment of many atypical mycobacterial infections.     

In Vitro Susceptibility of Acanthamoeba Culbertsoni to Inhibitors of Folate Biosynthesis1

ABSTRACT. The effects of different sulphonamides, dihydrofolate reductase inhibitors and other inhibitors of folate metabolism on growth of Acanthamoeba culbertsoni in a chemically defined medium are reported. Among the sulphonamides, sulphamethoxazole and sulphadiazine were most effective followed by sulphanilamide and sulphaguanidine. Inhibition by each sulphonamide was reversed by p-aminobenzoic acid as well as folic acid. 7-Methylguanosine, a pteridine synthesis-inhibitor, did not inhibit multiplication of A. culbertsoni. Among the dihydrofolate reductase inhibitors, pyrimethamine blocked the amoebic growth at 100 μg/ml, while trimethoprim and cycloguanil palmoate failed to cause significant inhibition of growth even at 250 μg/ml. Metoprine inhibited amoebic growth completely at 50 μg/ml. Methotrexate and a thymidylate synthetase inhibitor 5-fluorouracil inhibited growth strongly, with IC₅₀ values (the concentration of the drug which causes 50% inhibition of the growth at 72 h) of 1.97 and 2.45 μg/ml, respectively. Inhibition by methotrexate, metoprine or 5-fluorouracil could not be reversed by folic acid, folinic acid, thymidine, or folinic acid plus thymidine. the results indicate unusual features in A. culbertsoni folate metabolism.     

In Vitro Susceptibility of Environmental Isolates of Exophiala dermatitidis to Five Antifungal Drugs

Several dematiaceous fungi frequently isolated from nature are involved in cases of superficial lesions to lethal cerebral infections. Antifungal susceptibility data on environmental and clinical isolates are still sparse despite the advances in testing methods. The objective of this study was to examine the activities of 5-flucytosine, amphotericin B, itraconazole, voriconazole and terbinafine against environmental isolates of Exophiala strains by minimum inhibition concentration (MIC) determination. The strains were obtained from hydrocarbon-contaminated soil, ant cuticle and fungal pellets from the infrabuccal pocket of attine gynes. Broth microdilution assay using M38-A2 reference methodology for the five antifungal drugs and DNA sequencing for fungal identification were applied. Terbinafine was the most active drug against the tested strains. It was observed that amphotericin B was less effective, notably against Exophiala spinifera, also studied. High MICs of 5-flucytosine against Exophiala dermatitidis occurred. This finding highlights the relevance of studies on the antifungal resistance of these potential opportunistic species. Our results also contribute to a future improvement of the standard methods to access the drug efficacy currently applied to black fungi.     

In Vitro Susceptibility of Candida Isolates from Organ Transplant Recipients to Newer Antifungals

Organ transplant recipients (OTR) are at higher risk of developing life-threatening infections. In this study, we tested 527 Candida isolates obtained from the oral and genital mucosa from OTR and healthy controls in order to monitor antifungal susceptibility patterns in this particular risk group. Testing was carried out in parallel for already marketed azoles and anidulafungin. Minimal inhibitory concentrations (MICs) were determined using the E-test^® for azoles and CLSI broth microdilution for anidulafungin. Overall, there was no difference in the distribution of Candida spp. for both groups, C. albicans being the most frequently isolated Candida sp. followed by C. glabrata. Also, there were only minor differences in the susceptibility patterns to all antifungal agents. All C. albicans isolates were fully susceptible to fluconazole and voriconazole. In C. glabrata, 2.2 % (n = 1) were resistant to fluconazole, and 82.6 % (n = 38) to itraconazole, and in C. krusei, 66.7 % (n = 2) were resistant in itraconazole. All strains were susceptible to voriconazole. Only fluconazole showed a higher rate of resistant C. glabrata isolates for OTR (3.7 %), whereas the control group showed only intermediate susceptible and no resistant isolates. As there are no breakpoints established for posaconazole by CLSI, breakpoints determined by EUCAST were used. A total of 87.9 % of C. albicans, 81.3 % of C. parapsilosis and 66.7 % of C. tropicalis were considered susceptible. C. glabrata and C. krusei showed higher MIC values and thus lesser susceptibility than the other Candida species. There were no differences observed between OTR and control groups. For anidulafungin, 99.8 % of C. albicans isolates were susceptible, 0.2 % were intermediate, whereas for C. glabrata, only 95.3 % were susceptible, 0.2 % were resistant and 4.5 % were interpreted as intermediate. Interestingly, the two resistant isolates were found in the control group. Also, the controls showed a marginally higher percentage of intermediate strains compared to the transplant patients. All in all, resistant isolates were only observed for C. glabrata of the control group.     

Micromethod (Spot-Plate) Determination of In Vitro Antibiotic Susceptibility

The spot-plate method for determining in vitro antibiotic susceptibility is a modified version of the standard tube dilution technique, with the same principle of twofold dilution. Results of the spot-plate method are compared with those of the standard tube dilution technique. It is proposed that the spot-plate method is an equally accurate, but more rapid and economical, technique for determining in vitro antibiotic susceptibility.     

Effects of Macrolide Antibiotics on Rat Embryonic Heart Function In Vitro

The Swedish Medical Product Agency (MPA) has listed erythromycin as a suggested human teratogen, causing cardiovascular malformations. It is further suggested that this may be a class effect of macrolide antibiotics. The proposed teratogenic mechanism is blockade of the human ether‐á‐go‐go‐related (hERG)/I_Kr current in the embryonic heart causing bradycardia and arrhythmia resulting in altered cardiac blood flow and/or embryonic hypoxia. To test this hypothesis, we examined the effect of three macrolide antibiotics on the function of the rat embryonic heart. Gestational day 13 rat embryos in vitro were exposed to erythromycin (25–500 μM), clarithromycin (25–500 μM), or azithromycin (100 μM to 1 mM) for 3 hr. The effect on the embryonic heart was monitored every hour. The results showed that erythromycin and clarithromycin caused a concentration‐dependent bradycardia. Twenty‐five micromolar was a no‐effect concentration for erythromycin and was close to a no‐effect concentration for clarithromycin. Azithromycin only caused significant bradycardia at 1 mM. Additional studies were performed with the embryos cultured at 40°C instead of 38°C, to mimic fever. The increased temperature increased the number of arrhythmias but did not worsen the drug‐induced bradycardia. The results support the concept that erythromycin and clarithromycin can adversely affect the embryonic heart but only at concentrations well outside expected embryonic exposure in the human