Effect of hydroacridine derivatives on the sensitivity of polyresistant strains of Staphylococcus aureus and Escherichia coli to antibiotics]

Sensitivity of 4 clinical strains of Staph. aureus and E. coli to 13 hydroacridine derivatives and their combinations with antibiotics, such as benzylpenicillin, ampicillin, semi-synthetic penicillins, streptomycin, chloramphenicol, tetracycline, chlortetracycline, monomycin, oleandomycin and erythromycin was studied. The highest bacteriostatic effect was observed on the use of perhydroactidine derivatives with benzylpenicillin or ampicillin with respect to polyresistant penicillinase-producing strains of Staph. aureus, resistance of which to these antibiotics was decreased 250--1000 times. Under the effect of the above compounds the staphylococcal resistance to chloramphenicol, tetracycline, chlortetracycline, oleandomycine and erythromycin decreased 2--66 times. The combinations of hydroacridine with the antibiotics, except 10-amino-trans-syn-trans-perhydroacridine had no effect on the resistance of the E. coli strains. The results of the combined effect of the above substances were associated with their chemical nature, the bacterial type and possibly the character of the strain resistance.     

Effect of trypsin on the activity of tetracycline, erythromycin and levomycetin]

Trypsin had an antimicrobial effect on Staph. aureus. Increasing of protein in the broth culture of the staphylococci was inhibited in the presence of 50 gamma/ml of trypsin by 42.8%. The activity of tetracycline, erythromycin and levomycetin increased, when they were used in combination with trypsin, the effect of the trypsin combinations with tetracycline or levomycetin was additive, while that of the combination with erythromycin was synergistic.     

Infectivity and sensitivity to antibiotics of Rickettsia prowazekii mutants of the low-pathogenic strain E cultured in chick embryos

Selection of mutants of a low pathogenic strain E of R. prowazekii is a trend in genetic investigation of this Rickettsia species and one of the approaches to stabilizing the strain avirulent properties with a purpose of using in vaccine prophylaxis of typhus. The mutants of R. prowazekii, strain E selected by the authors earlier were characterized with respect to their infective capacity for chick embryos (CE) and antibiotic sensitivity. It was found that the infective capacity for CE of the erythromycin resistant mutant induced by nitroso guanidine (EErrI) was by ID50 2-3 logarithms lower than that of the initial strain E. The infective capacity for CE of the rifampicin resistant mutant induced by nitroso guanidine (ERifrI) and the spontaneous erythromycin resistant mutant was similar to that of strain E. The ERifrI strain differed from the initial strain E by higher sensitivity to tetracycline and erythromycin and the EErrI strain differed from the initial strain E by higher sensitivity to tetracycline and rifampicin. It was shown that the biological properties of the nitroso guanidine-induced mutants resistant to rifampicin and erythromycin differed from those of the initial strain E and the properties of the spontaneous erythromycin resistant mutant were similar to those of the initial strain E.     

Changes in antibiotic sensitivity in strains of Staphylococcus aureus, 1952-78.

Two hundred strains of Staphylococcus aureus isolated from outpatients with infections of the skin and subcutaneous tissues were tested for sensitivity to penicillin, erythromycin, tetracycline, sodium fusidate, methicillin, clindamycin, chloramphenicol, and gentamicin. One hundred and sixty-three (81.5%) of the strains were resistant to penicillin and 16 (8%) resistant to tetracycline. Incidence of resistance to other antibiotics was low. No strain was resistant to chloramphenicol, gentamicin, or methicillin. When compared with results of earlier studies, there was an increase in the incidence of resistance to penicillin and tetracycline, but no appreciable increase in resistance to other antibiotics.     

Antibiotic resistance in strains of Listeria spp. from meat products

The susceptibility or resistance to 26 antimicrobial agents was determined for 64 strains of Listeria monocytogenes and 102 strains of L. innocua isolated from Italian meat products. Some strains of L. monocytogenes were found to be resistant to tetracycline, erythromycin, co-trimoxazole and clindamycin. No plasmids were found in any L. monocytogenes strain. Five strains of L. innocua contained a 7.9 kbp plasmid, but these isolates were not resistant to any antibiotic in common and treatment with curing agents could not eliminate resistance to antibiotics. These results suggest that antibiotic resistance was not likely to be plasmid mediated in our strains.     

E. coli resistance to antibiotics on the material studied and the structure of the antibiotic resistance of the strains]

Standard filter paper discs were used to determine the sensitivity of 943 strains of E. coli isolated in 1970-1974 from patients' purulent-inflammatory foci with respect to benzylpenicillin, streptomycin, levomycetin, tetracycline, erythromycin and monomycin. An increase in the specific weight of the cultures resistant to the 6 drugs from 4.7 +/- 1.7 per cent in 1970 to 16.0 +/- 2.6 per cent in 1974 was observed. Strains resistant to 5--6 antibiotis were more often isolated from the urine (64.6 per cent) and the wound content (48.9 per cent) and rarer from the abdominal cavity exudate (23.1 per cent), bile (28.0 per cent) and sputum (30.1 per cent). Most often certain combinations of resistance to benzylpenicillin, streptomycin, tetracycline and erythromycin were found in the E. coli strains tested.     

Mathematical model for the control and standardization of discs]

Analysis of tetracycline and erythromycin diagnostic discs manufactured in the USSR showed their conformity with the requirements of the USA Federal Register. Comparison of the antibiotic amounts extracting and diffusing from the discs showed that as an average 92 and 90 per cent of the extracted amounts of erythromycin and tetracycline respectively diffused into the agar. Subsequently, it is desirable that on control testing of the disc quality both the similarity of the antibiotic content in the discs and the real amount of the antibiotic diffusing into the agar should be considered. A statistically reliable correlation between the values of the growth inhibition zones around the discs with definite and constant amounts of erythromycin, tetracycline or oxacillin and different resistance levels for every staphylococcal strain was found. On the basis of such a control system it is possible to divide the staphyloccal strains into the groups with high, low and intermediate resistance levels to the above antibiotics. However, it is not possible to use such data for accurate calculation of the value of the minimum inhibitory concentration of unknown strains because of a high value of the main error.     

Interaction of aminoglycosides and the other antibiotic on selected bacterial strains

The aim of this study was to analyse the activity interaction of aminoglycosides (gentamicin, kanamycin, streptomycin and dihydrostreptomycin) when combined with other antibiotics (lincomycin, benzylpenicillin, amoxicillin, cephalexin, spectinomycin and erythromycin), on selected clinical bacterial strains. The checkerboard method has been selected from the traditional assays for the measurement of antibiotic interaction. Checkerboard results for all strains demonstrated synergism for nine cases (9/112--8%). Additive effects were predominant--73/112--65.2%. In 12.5% neutral effects were shown, but in 11.6% of combinations FIC indexes were not possible to calculate, because of the resistance of clinical strains to the highest concentration of at least one antibiotic. The best results were achieved for combinations of dihydrostreptomycin with procaine penicillin because of higher number of cases synergy effect was observed. Antagonism of aminoglycosides and beta-lactams in case of gentamicin and amoxicillin for E. coli and E. cloacea strains were shown. Potential activity for combination of streptomycin and erythromycin was shown.     

Antimicrobial resistance and genomic screening of clinical isolates of thermophilic Campylobacter spp. from south-east Queensland,Australia

AIM: To screen 90 clinical isolates of thermophilic Campylobacter species for putative resistance to ampicillin, erythromycin and tetracycline and perform numerical analysis to determine isolate relatedness. METHODS AND RESULTS: Disc diffusion, E-test MIC and agar dilution methods were performed. Disc diffusion testing showed 87 (97%) isolates appeared resistant to ampicillin at 10 microg; 14 (16%) resistant to tetracycline at 30 microg; and three (3.4%) resistant to erythromycin at 15 microg. E-test MICs showed a range of 0.5 to >256 mg l(-1) for ampicillin; 16 to >256 mg l(-1) for tetracycline; and >256 mg l(-1) for erythromycin. E-test showed 68% correlation (+/-1 log2 dilution) with agar dilution for ampicillin, 100% for erythromycin and 64% for tetracycline. Disc diffusion testing showed 100% correlation with agar dilution for erythromycin and tetracycline, and 77% for ampicillin. Numerical analyses of restriction endonuclease (RE) fragment profiles suggested a high level of isolate variation. CONCLUSION: The incidence of resistance of thermophilic Campylobacter spp. to erythromycin and tetracycline is low in south-east Queensland. SIGNIFICANCE AND IMPACT OF THE STUDY: Disc diffusion susceptibility testing may be used to screen thermophilic Campylobacter spp. for putative resistance to erythromycin and tetracycline. Agar dilution should be used to determine ampicillin susceptibility.     

Antimicrobial susceptibility of Campylobacter jejuni subsp. jejuni assessed by E-test and double dilution agar method in Southern Chile

The susceptibility patterns of 108 Campylobacter jejuni subsp. jejuni clinical strains, to six antimicrobial agents was determined by using the E-test and the double dilution agar methods. Using both methods, no strain was found to be resistant to ciprofloxacin, erythromycin and gentamicin, but two (1.8%) were resistant to tetracycline and all to aztreonam. Seven (6.5%) strains were resistant to ampicillin by the E-test and five (4.6%) by the double dilution agar method and by both methods. No great discrepancies were observed between both methods.     

Some properties of two erythromycin-dependent strains of Escherichia coli

Strains of Escherichia coli can be isolated that require erythromycin for growth. With one strain, AM, a range of antibiotics, including chloramphenicol, tetracycline, spectinomycin, kasugamycin and rifampicin, will substitute for erythromycin on solid and in liquid media; nalidixic acid supports growth in liquid but not on solid media. With a second strain, 103, chloramphenicol, tetracycline and spectinomycin support growth in liquid media but on solid medium only chloramphenicol substitutes for erythromycin. In media of higher than normal ionic strength, strain AM, but not strain 103, can grow in the absence of antibiotics. Possible reasons for these complex phenotypes are discussed.     

Combined action of penicillin, tetracycline and rifampicin on R. sibirica and R. prowazekii in experiments on chick embryos

The effect of combinations of penicillin, tetracycline and rifampicin on R. prowazekii (the causative agent of typhus) and R. sibirica (the causative agent of tick-borne rickettsiosis of the North Asia) was studied. It was shown that tetracycline and penicillin used in combination had a summation effect on both R. sibirica and R. prowazekii. The dose of each antibiotic was 2 times lower than the doses of the antibiotics used alone. However, R. sibirica was less sensitive to this combination than R. prowazekii: the minimum rickettsiocidic doses of the combination were 0.5 mg of tetracycline + 10000 units of penicillin per embryo with respect to R. sibirica and 0.1 mg of tetracycline + 10000 units of penicillin per embryo with respect to R. prowazekii. The combinations of rifampicin with penicillin or tetracycline in the concentrations used had no rickettsiocidic effect on either R. sibirica or R. prowazekii. However, it should be noted that these combinations had a synergistic action and provided a rickettsiostatic effect on R. prowazekii: the dose of rifampicin in its combination with penicillin was decreased 10 times and in the combination of rifampicin with tetracycline the doses of both rifampicin and tetracycline were decreased 10 times. Still, penicillin even in a dose of 20000 units per embryo had only a rickettsiostatic effect on R. sibirica and R. prowazekii.     

Identification and characterization of antibiotic resistance genes in Lactobacillus reuteri and Lactobacillus plantarum

Aims:  The study aimed to identify the resistance genes mediating atypical minimum inhibitory concentrations (MICs) for tetracycline, erythromycin, clindamycin and chloramphenicol within two sets of representative strains of the species Lactobacillus reuteri and Lactobacillus plantarum and to characterize identified genes by means of gene location and sequencing of flanking regions.
Methods and Results:  A tet (W) gene was found in 24 of the 28 Lact. reuteri strains with atypical MIC for tetracycline, whereas four of the six strains with atypical MIC for erythromycin were positive for erm (B) and one strain each was positive for erm (C) and erm (T). The two Lact. plantarum strains with atypical MIC for tetracycline harboured a plasmid-encoded tet (M) gene. The majority of the tet (W)-positive Lact. reuteri strains and all erm -positive Lact. reuteri strains carried the genes on plasmids, as determined by Southern blot and a real-time PCR method developed in this study.
Conclusions:  Most of the antibiotic-resistant strains of Lact. reuteri and Lact. plantarum harboured known plasmid-encoded resistance genes. Examples of putative transfer machineries adjacent to both plasmid- and chromosome-located resistance genes were also demonstrated.
Significance and Impact of the Study:  These data provide some of the knowledge required for assessing the possible risk of using Lact. reuteri and Lact. plantarum strains carrying antibiotic resistance genes as starter cultures and probiotics.     

Evaluation of anti-phytoplasma properties of surfactin and tetracycline towards lime witches' broom disease using real-time PCR

The anti-phytoplasma activities of surfactin (derived from Iranian native Bacillus subtilis isolates) and tetracycline towards Candidatus "Phytoplasma aurantifolia", the agent of lime Witches' broom disease, were investigated. HPLC was used to quantify the surfactin production in four previously characterized native surfactin-producing strains, and the one producing the highest amount of surfactin (about 1,500 mg/l) was selected and cultivated following optimized production and extraction protocols. Different combinations of purified surfactin and commercial tetracycline were injected into artificially phytoplasmainfected Mexican lime seedlings using a syringe injection system. An absolute quantitative real-time PCR system was developed to monitor the phytoplasma population shifts in the lime phloem during 3 months following the injections. The results revealed that the injections of surfactin or tetracycline had a significant inhibitory effect on Candidatus "P. aurantifolia". However, the combined treatment with both surfactin and tetracycline (1:1) resulted in the highest inhibition due to a synergic effect, which suppressed the phytoplasma population from about 2×10(5) to less than 10 phytoplasma units/g plant tissue.     

Comparison of Agar Dilution and Broth Microdilution Methods of Anaerobic Antimicrobial Susceptibility Testing using Several Veterinary Antibiotics against Clostridium perfringens Strains Originating from Porcine and Avian Sources

A broth microdilution and a reference agar dilution method was used to determine minimal inhibitory concentrations (MICs) of five veterinary antimicrobials when tested against 96 animal-derived and six American Type Culture Collection (ATCC) strains of Clostridium perfringens. These antimicrobials [bacitracin methylenedisalicylate (bacitracin-MD), tylosin, virginiamycin, erthromycin and tetracycline] are approved for use in animal feed at different levels for growth enhancement, control, and treatment of a variety of enteric diseases. For bacitracin-MD, MICs were higher using the broth microdilution method when compared to the agar dilution method. The two methods had the lowest agreement when using bacitracin-MD compared to the method agreements of other antimicrobials tested (only 34.3% of the C. perfringens tested within ±1 doubling dilution). Tylosin MICs were lower by the broth microdilution method but had better agreement between methods with 75.5% of the C. perfringens tested within ±1 doubling dilution. Good correlation between methods was found for virginiamycin, tetracycline, and erythromycin with 85.3, 76.5, 81.4% of the C. perfringens tested within ±1 doubling dilution, respectively. Differences in susceptibility to individual antimicrobials were found among the avian and porcine strains by both methods. For avian strains, bacitracin-MD, tylosin, and erthromycin MIC₉₀values had differences of at least four doubling dilutions between methods. There were biases toward higher bacitracin-MD and lower tylosin and erythromycin MIC₉₀values using the broth microdilution method. MIC₉₀values against porcine and ATCC strains were more comparable between methods for all five antimicrobials than those generated against avian strains but the biases were still present. Most animal-derived strains were inhibited by approved livestock feed levels of the antimicrobials. Caution should be used when evaluating the potential effectiveness of feed-based antimicrobials against C. perfringens when results are generated using an in vitro test that may not be in agreement with the reference agar dilution method.     

Transfer of erythromycin resistance in Staphylococcus aureus.

In the course of an outbreak of enteritis and conjunctivitis, Staphylococcus aureus was isolated from newborn infants. Strains cultured at a later phase of the outbreak differed from those found at the beginning in being resistant to several antibiotics, showing resistance to typing phages and releasing phages of the same lysis spectrum (10(9) p.f.u./ml after heating at 56 degrees C for 2 min). Transduction experiments with a strain and its cell-free lysate showed that inducible erythromycin resistance was transferable to strains isolated at the beginning of the outbreak and to laboratory strains. Plasmid origin of resistance was confirmed by (i) high transduction frequency; (ii) transduction to RN981 rec- mutants; (iii) kinetics of transduction; (iv) elimination of resistance. Mixed culture experiments yielded transductants at high frequency with resistance to erythromycin, streptomycin and tetracycline.     

Genetic, molecular, and functional analysis of Streptococcus faecalis R plasmid pJH1.

Streptococcus faecalis JH1 contains two conjugative plasmids, pJH1, an R plasmid that codes for resistance to kanamycin, streptomycin, erythromycin, and tetracycline, and pJH2, a hemolysin-bacteriocin plasmid. Strain JH1 was used as an antibiotic resistance donor in conjugation experiments with two plasmid-free S. faecalis recipient strains, JH2-2 and OG1-RF1. Plasmid pJH1 was purified from one transconjugant, DL77, and subjected to restriction endonuclease analyses. Five restriction enzymes, EcoRI, XbaI, BamHI, SalI, and XhoI, yielding 10, 9, 3, 2, and 2 fragments, respectively, were used to determine the size (80.7 kilobases) of pJH1 and to construct a restriction endonuclease map of the plasmid. Twenty-eight percent of the antibiotic-resistant transconjugants examined expressed only part of the resistance pattern (Kmr Smr Emr Tcr) associated with pJH1, that is, they were resistant to kanamycin, streptomycin, and erythromycin; to erythromycin and tetracycline; or to erythromycin or to tetracycline only. Most of these strains also produced hemolysin and bacteriocin, and several contained a hybrid plasmid consisting of pJH2 and specific segments of pJH1 DNA. Several of these hybrid plasmids, as well as a deletion derivative of pJH1 that coded for resistance to tetracycline but not to kanamycin, streptomycin, or erythromycin, were purified and used to confirm the arrangement of restriction endonuclease fragments on the pJH1 map and to locate the resistance determinants on this map.     

Action of Lincomycin on Staphylococci

On a solid medium, 0.1 to 1 μg/ml of lincomycin hydrochloride had a bacteriostatic effect upon 95 of 100 strains of staphylococci. Using cellophane transfers, we observed a bactericidal effect upon 54 of these strains after 3 to 14 hr of contact with 1 μg/ml. Five staphylococcal strains resistant to 100 μg/ml of lincomycin were also resistant to penicillin G, streptomycin, erythromycin, tetracycline, chloramphenicol (three strains), and rovamycin (three strains). Other staphylococcal strains resistant to methicillin, ampicillin, tetracycline, streptomycin, chloramphenicol, and erythromycin were sensitive to lincomycin.     

Characteristics of sheep-rumen isolates of Pseudomonas aeruginosa inhibitory to the growth of Escherichia coli O157

Screening facultative sheep-rumen bacteria which inhibit growth of Escherichia coli produced 11 strains of Pseudomonas aeruginosa. The isolates showed three different pulsed-field gel electrophoresis patterns and strains from different sheep produced pyocins that varied in strain specificity. Representative strains were resistant to ampicillin, methicillin, erythromycin, fusidic acid and augmentin, but not to tetracycline or nalidixic acid. Tested strains attached in large numbers to cultured rumen epithelial cells, potentially providing a means of survival in this ecosystem.     

高效降解石油外生菌根真菌的室内筛选

对7个外生菌根真菌菌株在不同石油浓度培养基中的生长及其对石油的降解作用进行了研究。结果表明:(1)不同菌株在同一石油浓度培养基中生长速度不同,同一菌株在不同石油浓度培养基中的生长速度亦不同。菌株010和菌株025在不同石油浓度培养基中生长速度均较其他菌株快。菌株010的菌丝干重随着石油浓度的增加而增加,当石油质量浓度为500 mg/L时,菌丝干重达到最大值,高于对照5.27%,石油对其生长产生了促进作用;当石油质量浓度为700 mg/L时,菌丝干重低于对照,随着石油质量浓度的升高,菌株生长呈下降趋势。石油质量浓度为100 mg/L时,菌株025生长最慢,菌丝干重低于对照9.1%。随着石油浓度的增加,菌株生长加快,当石油质量浓度为500 mg/L时,菌丝干重高于对照;当石油质量浓度为700 mg/L时,菌株025菌丝干重最高,高于对照25.65%。随着石油浓度的再度升高,菌株生长呈下降趋势。(2)不同菌株在同一石油浓度下对石油的降解能力不同,同一菌株在不同石油浓度下对石油的降解能力亦不同。菌株025对石油的降解能力最强,对石油的降解能力随着石油浓度的升高而提高。当培养基中石油质量浓度为900 mg/L时,菌株025对石油的降解率最高,达到73.65%。(3)菌株0100、09、035、LH004的菌丝生物量与对石油的降解能力呈正相关。