ANTIFUNGAL ACTION OF STREPTOMYCIN-COPPER CHELATE AGAINST PHYTOPHTHORA INFESTANS ON TOMATO (LYCOPERSICON ESCULENTUM)

The antifungal protection afforded by streptomycin-copper chelate in vivo in greenhouse tests against Phytophthora infestans on tomato was found to be of the order of six times greater than that of streptomycin sulphate. The copper chelate also showed much greater resistance to simulated rainfall. Similar tests showed that streptomycin-copper chelate (in terms of streptomycin content) was from 2 1/2 to 5 times more effective as an antifungal prophylactic spray than zinc ethylene-bis(dithiocarbamate) (zineb), and some fifty times more active than copper oxychloride formulated as a commercial 50% wettable powder. These three materials showed roughly similar resistance to weathering by 'rainfall' and it was assumed therefore that 250 i.u./ml. streptomycin as streptomycin-copper chelate might be expected to give the same degree of protection against Phytophthora infestans in the field as would the usual field rates of usage of zineb and copper oxychloride.     

代谢工程改造L-半胱氨酸供给模块促地衣芽胞杆菌 高效合成杆菌肽

杆菌肽是一种主要由芽胞杆菌产生的广谱性抗生素,目前作为兽药广泛应用于畜禽养殖领域。前体氨基酸供应不足可能是限制微生物发酵高产杆菌肽的重要因素。文中以杆菌肽工业生产菌株——地衣芽胞杆菌Bacillus licheniformis DW2为出发菌株,研究l-半胱氨酸供给模块强化对杆菌肽合成的影响。首先,构建了l-半胱氨酸合成酶基因cysK强化表达菌株,杆菌肽效价相比于对照菌株提高了9.47%。接着,为提高l-半胱氨酸合成前体供给,对l-丝氨酸乙酰转移酶基因cysE和硫代硫酸盐/硫酸盐胞内转运蛋白基因cysP进行强化,杆菌肽产量分别提高了7.23%和8.52%。随后,结果表明转运蛋白TcyP负责从胞外向胞内转运胱氨酸,强化表达TcyP后胞内l-半胱氨酸浓度和杆菌肽效价分别提高了29.19%和7.79%。通过组合代谢工程育种,在整合表达了基因cysK基础上,利用强启动子PbacA分别替换基因cysP、cysE和tcyP原始启动子,得到工程菌株CYS4 (DW2::cysK-PbacA(cysP)- PbacA(cysE)-PbacA(tcyP)),杆菌肽效价达到910.02 U/mL,相比于出发菌株DW2 (747.71 U/mL) 提高了21.10%。最后,通过3 L发酵罐小试实验,进一步证实了强化l-半胱氨酸有利于杆菌肽合成。研究表明,强化胞内l-半胱氨酸供给水平是提高地衣芽胞杆菌中杆菌肽产量的有效策略,为杆菌肽工业生产提供了一株具有良好应用前景的菌株。     

Impact of feed supplementation with antimicrobial agents on growth performance of broiler chickens, Clostridium perfringens and enterococcus counts, and antibiotic resistance phenotypes and distribution of antimicrobial resistance determinants in Escherichia coli isolates

The effects of feed supplementation with the approved antimicrobial agents bambermycin, penicillin, salinomycin, and bacitracin or a combination of salinomycin plus bacitracin were evaluated for the incidence and distribution of antibiotic resistance in 197 commensal Escherichia coli isolates from broiler chickens over 35 days. All isolates showed some degree of multiple antibiotic resistance. Resistance to tetracycline (68.5%), amoxicillin (61.4%), ceftiofur (51.3%), spectinomycin (47.2%), and sulfonamides (42%) was most frequent. The levels of resistance to streptomycin, chloramphenicol, and gentamicin were 33.5, 35.5, and 25.3%, respectively. The overall resistance levels decreased from day 7 to day 35 (P < 0.001). Comparing treatments, the levels of resistance to ceftiofur, spectinomycin, and gentamicin (except for resistance to bacitracin treatment) were significantly higher in isolates from chickens receiving feed supplemented with salinomycin than from the other feeds (P < 0.001). Using a DNA microarray analysis capable of detecting commonly found antimicrobial resistance genes, we characterized 104 tetracycline-resistant E. coli isolates from 7- to 28-day-old chickens fed different growth promoters. Results showed a decrease in the incidence of isolates harboring tet(B), bla(TEM), sulI, and aadA and class 1 integron from days 7 to 35 (P < 0.01). Of the 84 tetracycline-ceftiofur-resistant E. coli isolates, 76 (90.5%) were positive for bla(CMY-2). The proportions of isolates positive for sulI, aadA, and integron class 1 were significantly higher in salinomycin-treated chickens than in the control or other treatment groups (P < 0.05). These data demonstrate that multiantibiotic-resistant E. coli isolates can be found in broiler chickens regardless of the antimicrobial growth promoters used. However, the phenotype and the distribution of resistance determinants in E. coli can be modulated by feed supplementation with some of the antimicrobial agents used in broiler chicken production.     

Effect of disinfectants on stability and transmissibility of R-plasmid in E. coli isolated from drinking water

Drug resistant enteropathogenic E. coli (EPEC, 086 serotype) isolated from contaminated piped drinking water supply (Fecal coliform 160/100 ml) was studied for effect of disinfectants (chlorine and UVB) on stability and transmissibility of R-plasmid. The strain was resistant to streptomycin and bacitracin and tolerant to multiple metal ions of Cd, Cr, Co, As, Ni, Zn and Hg. A plasmid of molecular size of 3.7 Kb was detected in the organism. After exposure to sublethal doses of disinfectants, complete elimination of resistances to streptomycin and Cr was observed. Partial loss of resistance to Hg due to chlorine was detected. Although UVB did not effected the pattern of transmissibility effect on frequency of transfer was observed. Surprisingly, in UVB irradiated cells, significantly enhanced rate of transfer was noted.     

Alterations inPseudomonas aeruginosa exoproducts by sub-MICs of some antibiotics

Aminoglycoside antibiotics, most effective at the level of 1/4 of the MIC, suppressed all the tested activities ofP. aeruginosa, except cytotoxicity. Proteinase activity was decreased to 60% (gentamicin) and 63% (streptomycin), permeability was reduced to 61% (gentamicin) and 73% (streptomycin), phospholipase C to 13% (gentamicin) and 51% (streptomycin) of the control values. Subinhibitory concentrations ofβ-lactams inhibited only phospholipase C activity to 89% (ticarcillin) and 64% (cefotaxim) of the control values. These antibiotics did not suppress the cytotoxic activity and increased protease activity up to 155% (ticarcillin) and 192% (cefotaxim) as well as permeability up to 121% (ticarcillin) and 154% (cefotaxim) of the control values.     

Kiwifruit ameliorates gentamicin induced histological and histochemical alterations in the kidney of albino mice

Gentamicin is an antibiotic used worldwide for treating Gram-negative bacterial infections. Gentamicin causes nephrotoxicity in up to 25% of therapeutic cases owing to increased production of free radicals. Kiwifruit are nutrient-dense fruits that have proven effective for ameliorating many pathological conditions caused by oxidative stress. We investigated the possible prophylactic and therapeutic effects of kiwifruit on the changes in renal histology and histochemistry caused by gentamicin. Intramuscular injection of mice with gentamicin for 10 consecutive days was nephrotoxic as indicated by epithelial vacuolization, glomerular atrophy and tubular necrosis. Necrotic tubule cells lost most of their polysaccharides and structural proteins. Co-administration of kiwifruit with gentamicin prevented nephrotoxic changes to a modest degree. When administered subsequent to gentamicin intoxication, kiwifruit ameliorated significantly the histological and histochemical alterations caused by gentamicin. Our findings support the use of kiwifruit in cases of acute renal injury due to gentamicin.     

Effects of various drugs on hemolytic activity of Streptococcus zymogenes

Drugs known to interrupt the chain of protein synthesis (streptomycin, chloramphenicol, ethidium bromide) appeared to affect production of the group D lysin by Streptococcus zymogenes by inhibiting growth. Drugs which block cell wall synthesis (vancomycin, bacitracin, d-cycloserine, and phosphonomycin) inhibited lytic activity by a mechanism independent of growth. Bacitracin appeared not to have a major effect on lysin production but elicited the production of an inhibitor of lytic activity.     

The metabolic stability of the enkephalins.

[Met⁵] and [Leu⁵]-enkephalins inhibit ³H-naloxone binding to brain opiate receptors much more effectively at 4°C than at 25°C. At 25°C several protease inhibitors potentiate the action of the enkephalins. Bacitracin is the most effective of these. In the presence of 100 μg/ml of bacitracin, the potencies of [Met⁵]- and [Leu⁵]-enkephalins are similar to those at 4°C. Some protease inhibitors, such as TLCK and TAME, are effective by themselves in inhibiting the binding of ³H-naloxone. Enkephalins with D-amino acids in the 2-position are equally effective at 0°C and at 25°C and their action is not potentiated by bacitracin. In particular, [D-Ala²]-enkephalins do not seem to be significantly degraded by the membrane enzymes which destroy the natural enkephalins.     

THE SYSTEMIC ACTION AGAINST PSEUDOMONAS MEDICAGINIS VAR. PHASEOLICOLA OF A STREPTOMYCIN SPRAY APPLIED TO DWARF BEANS

The prophylactic effect resulting from the localized application of streptomycin as a foliage spray on dwarf bean plants has been examined. Streptomycin sulphate solution applied to the primary leaves exhibited a marked and consistent systemic, antibacterial, prophylactic action even at sites as far removed from the point of application as the fourth trifoliate leaf. This systemic protection against the halo blight organism persisted for various periods up to a maximum of 11 days. Mannosidostreptomycin was much inferior to streptomycin in its systemic prophylactic action against halo blight.     

Survey of antimicrobial resistance in lactic streptococci.

A total of 26 strains of Streptococcus cremoris and 12 strains of Streptococcus lactis were challenged with 18 antimicrobial agents and with nisin in the Bauer-Kirby disk susceptibility test. All strains were susceptible to ampicillin, bacitracin, cephalothin, chloramphenicol, chlortetracycline, erythromycin, penicillin G, tetracycline, and vancomycin. All strains were resistant to trimethoprim, and almost all strains were resistant to sulfathiazole. Variability in resistance to gentamicin, kanamycin, lincomycin, nafcillin, neomycin, nisin, rifampin, and streptomycin was observed. MICs of these substances for the less susceptible strains were determined, and high-level resistance factors could not be detected, except in the case of nisin. S. lactis ATCC 7962 was resistant to at least 40-fold-higher concentrations of nisin (greater than 64 micrograms/ml) than most other strains tested. This strain was a potent nisin producer.     

Effectiveness ofRhizobium as modified by mutation for resistance to antibiotics

Many antibiotic-resistant mutants derived from effective strains ofRhizobium — mainlyR. leguminosarum andR. trifolii showed some loss of effectiveness on the homologous host. The frequency and degree of such changes in effectiveness depended on the type of antibiotic-resistance involved in the mutations. Resistance to streptomycin, spiramycin, chloramphenicol, or the tetracycline group of antibiotics was associated with little or no change. Resistance to D-cycloserine, novobiocin, vancomycin, bacitracin or penicillin was accompanied by partial or full loss of effectiveness in about one-half of the mutants. Full loss of effectiveness occurred most frequently among mutants selected for resistance to viomycin or neomycin. In contrast, restoration of the ability for effective symbiosis occurred in prototrophic revertants of a non-nodulating, purine-requiring mutant. Alteration of cell-wall characteristics is suggested as a possible basis for decrease of effectiveness among mutants resistant to those antibiotics, notablyD-cycloserine, which are known to inhibit cell-wall synthesis.This investigation was supported by a Public Health Service research career development award (1-K3-GM-22, 594) and research grant (GM-12131) from the National Institutes of Health.     

Survey of antimicrobial resistance in lactic streptococci

A total of 26 strains of Streptococcus cremoris and 12 strains of Streptococcus lactis were challenged with 18 antimicrobial agents and with nisin in the Bauer-Kirby disk susceptibility test. All strains were susceptible to ampicillin, bacitracin, cephalothin, chloramphenicol, chlortetracycline, erythromycin, penicillin G, tetracycline, and vancomycin. All strains were resistant to trimethoprim, and almost all strains were resistant to sulfathiazole. Variability in resistance to gentamicin, kanamycin, lincomycin, nafcillin, neomycin, nisin, rifampin, and streptomycin was observed. MICs of these substances for the less susceptible strains were determined, and high-level resistance factors could not be detected, except in the case of nisin. S. lactis ATCC 7962 was resistant to at least 40-fold-higher concentrations of nisin (greater than 64 micrograms/ml) than most other strains tested. This strain was a potent nisin producer.     

The effect of different oral antibiotics on the gastrointestinal microflora of a wild rodent (Aethomys namaquensis)

Gut sterilization via the oral administration of antibiotics facilitates physiological studies of the nutritionally important relationship between intestinal microflora and the host. However, the composition of gut flora is extremely variable, and as a result, the efficacy of antibiotics in achieving gut sterilization varies considerably between species. We tested the effectiveness of three antibiotic cocktails in sterilizing the gut of a rodent pollinator, the Namaqua rock mouse (Aethomys namaquensis). The cocktails were (1) streptomycin sulfate and bacitracin (previously used with domestic mice and rats), (2) chloramphenicol and bacitracin (based on antibiotic screening tests performed on faecal flora) and (3) Baytril 10% oral solution (a veterinary antimicrobial agent containing enrofloxacin). We tested for antibiotic inactivation by determining bacterial viability through fluorescence staining of faecal samples. We also tested techniques to maintain sterility during antibiotic treatment without the benefit of a laminar flow cabinet. Antibiotics were administered orally in food and water consumed ad libitum over 4 consecutive days. Antibiotic effectiveness was assessed by culturing anaerobic bacteria from faecal samples collected before and after each antibiotic treatment. Treatment with Baytril 10% oral solution eliminated or significantly reduced faecal flora, whereas other antibiotics did not. This study clearly demonstrates the importance of testing the effectiveness of antibiotics before their use in studies that involve antibiotic-treated subjects, particularly if these are species previously untested.     

The prophylactic administration of interleukin-2 increases the survival of mice with an acute intra-abdominal infection caused by Staphylococcus aureus]

The effect of RIL-2 on the survival of mice with acute Staphylococcus aureus strain 5/2 intra-abdominal [correction of intraperitoneal] infection was studied. RIL-2 was ineffective when administered simultaneously with the LD100 dose of bacteria. Antibiotics (gentamycin or combination of penicillin and streptomycin) administered in the same fashion cured 100% of animals. However, RIL-2 proved to be effective when administered simultaneously with LD70 dose of bacteria. The prophylactic course of RIL-2 consisting of repeated injections on days 3, 2 and 1 before the challenge with LD100 dose of bacteria also resulted in the marked increase of the survival of mice. The hypothetical mechanisms of action and the prospects of RIL-2 application are discussed.     

Distribution of Streptococcal Groups in Clinical Specimens with Evaluation of Bacitracin Screening

During a 2-year period, 4,968 strains of beta-hemolytic streptococci were examined for the clinical source distribution and bacitracin sensitivity of each group. In the upper respiratory tract, groups A (51.7%) and C (20.4%) accounted for most of the isolates, and in wounds and exudates group A (79.1%) made up most of the isolates. Group B (71.2%) was the major component of isolates from the genitorinary tract and, while composing 29.3% of the lower respiratory tract isolates, competed with group A (18.8%) and the nongroupables (22.8%) for supremacy. Bacitracin screening showed that 0.5% of group A streptococci were resistant, and sensitive non-group A isolates were group B (2.6%), group C (6.0%), group G (8.0%), and the nongroupables (2.2%). It was found that those groups which were most predominant in wounds and the upper respiratory tract gave the highest rate of false positives with bacitracin, whereas the predominant group of the genitourinary tract gave the lowest rate of false positives.     

Antibiotic Therapy of Staphylococcal Infections

The antibiotic treatment of staphylococcal infections remains a problem. Isolation of the organism and sensitivity testing are necessary in the choice of antibiotic. Penicillin G is the most effective penicillin against non-penicillinase-producing staphy-lococci; for the penicillinase producers there is very little to choose between the semisynthetic penicillins, methicillin, cloxacillin, nafcillin and oxacillin. For patients who are hypersensitive to penicillin, the bacteriostatic drugs (erythromycin, novobiocin, tetracycline, chloramphenicol, oleandomycin) are useful for mild infections, while for more severe illness the bactericidal drugs (vancomycin, ristocetin, kanamycin, bacitracin, neomycin) have been used successfully. Acute staphylococcal enterocolitis is probably best treated by a semisynthetic penicillin. Other antibiotics which have been found useful, with clinical trials, for staphylococcal infections are cephalosporin, fucidin, cephaloridine and lincomycin. The latter drug has been reported of value in the treatment of osteomyelitis. There is little justification for the prophylactic use of antibiotics to prevent staphylococcal infection. Surgical drainage is still an important adjunct in the treatment of many staphylococcal infections.     

Seed treatment for the control of halo-blight of beans (Pseudomonas phaseolicola)

Streptomycin and kasugamycin were applied as soaks, slurries or dusts to dwarf bean seeds either naturally (internally) infected or externally contaminated with Pseudomonas phaseolicola. Slurries of streptomycin (2–5 g a. i./kg seed) or kasugamycin (0–25 g a.i./kg seed) were the most effective treatments against both types of infection and were generally non-phytotoxic at these rates. Combined analysis of eight field experiments made over a 3 yr period showed that on average both compounds applied in slurries reduced primary infection from infected seeds by 98 %. The method thus shows considerable promise as a commercial control treatment.     

The Pharmacotherapy of the Depressive Syndrome

Three therapeutic modalities have proved effective in the treatment of depressive syndromes: electroconvulsive therapy (ECT), pharmacotherapy and psychotherapy. ECT gives the most reliable and most rapid results but may be contraindicated in certain cases. Psychotherapy is limited in its application to the reactive aspects of a depression. Pharmacotherapy is currently the most widely applied treatment of depression. Two classes of drugs are available which are effective in about 60% of depressed patients: the monoamine oxidase inhibitors and tricyclic compounds. Their mechanism of action is probably related to the regulation of the biogenic amine balance in the brain. The distinction between antipsychotic and antidepressant drugs is not as sharp as was formerly assumed. Maintenance pharmacotherapy has been shown to have prophylactic value in preventing relapses.     

Frequency of R Factor-mediated Multiple Drug Resistance in Klebsiella and Aerobacter

A comparative study was done on the transfer frequency of R factors from 90 strains of multiple drug-resistant Aerobacter and 81 strains of Klebsiella to Escherichia coli CSH-2 (F(-), met(-), pro(-), Nal-r). The most common resistance patterns for the Aerobacter isolants were ampicillin streptomycin chloramphenicol tetracycline and ampicillin streptomycin chloramphenicol tetracycline kanamycin neomycin; for the Klebsiella isolants, the most common resistance pattern was ampicillin kanamycin streptomycin tetracycline chloramphenicol neomycin. R factors were isolated from 14.1% of the Aerobacter strains; 61.5% of these R factors harbored R determinants for ampicillin streptomycin tetracycline. R factors were isolated from 79.1% of the Klebsiella strains; four R factors were isolated with significant frequency; streptomycin chloramphenicol kanamycin neomycin, 37.5%; ampicillin streptomycin tetracycline kanamycin neomycin, 14.1%; ampicillin streptomycin tetracycline, 12.5%; and streptomycin chloramphenicol tetracycline, 12.5%.Chloramphenicol, kanamycin, and neomycin resistance was rarely transferred from the Aerobacter strains, although over 50% of the clinical isolants possessed resistance to these antibiotics. In contrast, over 75% of the Klebsiella strains transferred resistance to chloramphenicol, kanamycin, neomycin. Highest frequency of transferred resistance to individual drugs in the Aerobacter strains was to streptomycin (14.8%), whereas in the Klebsiella group resistance to four drugs was transferred at a very high frequency: streptomycin (80.8%), chloramphenicol (78.5%), kanamycin (76.4%), and neomycin (75.9%).     

Aminoglycoside resistance rates, phenotypes, and mechanisms of Gram-negative bacteria from infected patients in upper Egypt

With the re-emergence of older antibiotics as valuable choices for treatment of serious infections, we studied the aminoglycoside resistance of Gram-negative bacteria isolated from patients with ear, urinary tract, skin, and gastrointestinal tract infections at Minia university hospital in Egypt. Escherichia coli (mainly from urinary tract and gastrointestinal tract infections) was the most prevalent isolate (28.57%), followed by Pseudomonas aeruginosa (25.7%) (mainly from ear discharge and skin infections). Isolates exhibited maximal resistance against streptomycin (83.4%), and minimal resistance against amikacin (17.7%) and intermediate degrees of resistance against neomycin, kanamycin, gentamicin, and tobramycin. Resistance to older aminoglycosides was higher than newer aminoglycosides. The most common aminoglycoside resistance phenotype was that of streptomycin resistance, present as a single phenotype or in combination, followed by kanamycin-neomycin as determined by interpretative reading. The resistant Pseudomonas aeruginosa strains were capable of producing aminoglycoside-modifying enzymes and using efflux as mechanisms of resistance. Using checkerboard titration method, the most frequently-observed outcome in combinations of aminoglycosides with β-lactams or quinolones was synergism. The most effective combination was amikacin with ciprofloxacin (100% Synergism), whereas the least effective combination was gentamicin with amoxicillin (53.3% Synergistic, 26.7% additive, and 20% indifferent FIC indices). Whereas the studied combinations were additive and indifferent against few of the tested strains, antagonism was never observed. The high resistance rates to aminoglycosides exhibited by Gram-negative bacteria in this study could be attributed to the selective pressure of aminoglycoside usage which could be controlled by successful implementation of infection control measures.