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.     

Biological activity of an antibiotic produced by Myxococcus coralloides.

A strain of Myxococcus coralloides was isolated which produced an antibiotic active against Gram-positive bacteria and also against Neisseria sp at high levels of antibiotic. The antibiotic was bactericidal on sensitive growing bacteria. It was inactive on non-growing cells and also on cells whose growth has been stopped by addition of chloramphenicol. Strains of S. aureus resistant to several antibiotics, including penicillin and ampicillin, were also sensitive to this antibiotic.     

Mechanisms of Proteus resistance to chloramphenicol]

Data on chloramphenicol sensitivity of clinical Proteus strains isolated within 1970--1975 and some mechanisms of their resistance to this antibiotic are presented. It was found that most of the Proteus strains (62.82 +/- 2.15 per cent) were resistant to chloramphenicol. 75 per cent of the isolates had resistance of transmissive character. Resistance of the Proteus cultures to chloramphenicol was not a stable feature and was lost during storage under laboratory conditions. Direct correlation between stability of the antibiotic resistance in the Proteus, the resistance level and the period of the culture storage was found. It was shown that the transmissive resistance to chloramphenicol in the Proteus cultures was due to synthesis of a highly active constituitive chloramphenicol-inactivating enzyme. Direct relation between the Proteus resistance level to chloramphenicol and the rate of the enzyme synthesis was noted. A number of the Proteus strains phenotypically sensitive to this antibiotic was capable of its inactivation. Still, the activity of the enzyme was low. The rate of the enzyme synthesis and the level of the acquired resistance in the chloramphenicol resistant mutants depended on the presence or absence of the enzyme in the cells of the initial sensitive strain. The capacity for chloramphenicol accumulation in a number of the chloramphenicol resistant mutants of the Proteus was decreased.     

Survival of orally administered isolated intestinalLactobacillus acidophilus in different parts of gastrointestinal tract of mice

A strain ofLactobacillus acidophilus (Strain HF) was isolated from human faeces. A chloramphenicol resistant strain (HFCm) and a strain (HFCmSm) restant to both chloramphenicol and streptomycin were developed from the isolated strain (HF). All the three strains showed similarin vitro susceptibility against host defence factors like gastric acid, bile salts and volatile as well as non-volatile fatty acids.In vivo tests were done by feeding these strains to mice. When the resistant strains were orally administered along with the antibiotic(s) they were stable up to 72 h     

A chromosomal chloramphenicol acetyltransferase determinant from a probiotic strain of Bacillus clausii

The mechanism of resistance to chloramphenicol was studied in four strains of Bacillus clausii included in a probiotic mixture, which is administered to humans for prevention of gastrointestinal side effects due to oral antibiotic therapy. By cloning experiments, a chloramphenicol acetyltransferase (CAT) gene, cat _Bcl , coding for a putative 228-amino acid CAT protein was identified in B. clausii SIN. The deduced amino acid sequence displayed from 31% to 85% identity with 56 CAT proteins from other Gram-positive bacterial strains. The cat _Bcl gene was also detected by PCR in the three other B. clausii strains resistant to chloramphenicol, whereas it was absent in the three control strains susceptible to chloramphenicol. Pulse-field gel electrophoresis of total DNA digested by I-CeuI followed by hybridization with a cat -specific probe as well as unsuccessful repeated attempts of in vitro transfer of chloramphenicol resistance to various recipient cells indicated that cat _Bcl was chromosomally located in all four resistant B. clausii strains.     

Chloramphenicol and expression of multidrug efflux pump in Enterobacter aerogenes

Chloramphenicol has been reported to act as an inducer of the multidrug resistance in Escherichia coli. A resistant variant able to grow on plates containing 64 microg/ml chloramphenicol was obtained from the Enterobacter aerogenes ATCC 13048-type strain. Chloramphenicol resistance was due to an active efflux of this antibiotic and it was associated with resistance to fluoroquinolones and tetracycline, but not to aminoglycoside or beta-lactam antibiotics. MDR in the chloramphenicol-resistant variant is linked to the overexpression of the major AcrAB-TolC efflux system. This overexpression seems unrelated to the global Mar and the local AcrR regulatory pathways.     

Mixed-infection of antibiotic susceptible and resistant Helicobacter pylori isolates in a single patient and underestimation of antimicrobial susceptibility testing

Antibiotic resistance among Helicobacter pylori has been increasing worldwide and has begun to affect the overall efficacy of current antibiotic regimens adversely. We examined 220 pairs of H. pylori isolates obtained from both the antrum and corpus of separate patients; 109 (50%) harbored antibiotic-resistant H. pylori: amoxicillin (0.5%), clarithromycin (5.9%), furazolidone (1.4%), metronidazole (45.5%), nitrofurantoin (1.4%), and tetracycline (6.8%). Heteroresistance among the two biopsy sites from each patient was present in 41 of the 109 patients (38%) with antibiotic resistant H. pylori (e.g. 34% with resistant strains would be misclassified as susceptible if a biopsy of the antrum alone used for antimicrobial susceptibility testing). DNA fingerprinting genotype analysis was carried out on the 41 pairs of isolates with heteroresistance. While different patients had different fingerprinting patterns, each pair of isolates showed identical or similar fingerprinting patterns. These results suggest that antibiotic-resistant H. pylori typically develop from pre-existing susceptible strain rather than coinfection with a different strain. The minor differences in genotype (degeneration of genotype) seen reflect one of the processes for development of genetic diversity in H. pylori. No biopsy single site can be considered representative for antimicrobial susceptibility testing.     

Influence of antibiotic selection on genetic composition of Escherichia coli populations from conventional and organic dairy farms

The widespread agricultural use of antimicrobials has long been considered a crucial influence on the prevalence of resistant genes and bacterial strains. It has been suggested that antibiotic applications in agricultural settings are a driving force for the development of antimicrobial resistance, and epidemiologic evidence supports the view that there is a direct link between resistant human pathogens, retail produce, farm animals, and farm environments. Despite such concerns, little is understood about the population processes underlying the emergence and spread of antibiotic resistance and the reversibility of resistance when antibiotic selective pressure is removed. In this study, hierarchical log-linear modeling was used to assess the association between farm type (conventional versus organic), age of cattle (calf versus cow), bacterial phenotype (resistant versus susceptible), and the genetic composition of Escherichia coli populations (E. coli Reference Collection [ECOR] phylogroup A, B1, B2, or D) among 678 susceptible and resistant strains from a previously published study of 60 matched dairy farms (30 conventional and 30 organic) in Wisconsin. The analysis provides evidence for clonal resistance (ampicillin resistance) and genetic hitchhiking (tetracycline resistance [Tet(r)]), estimated the rate of compositional change from conventional farming to organic farming (mean, 8 years; range, 3 to 15 years), and discovered a significant association between low multidrug resistance, organic farms, and strains of the numerically dominant phylogroup B1. These data suggest that organic farming practices not only change the frequency of resistant strains but also impact the overall population genetic composition of the resident E. coli flora. In addition, the results support the hypothesis that the current prevalence of Tet(r) loci on dairy farms has little to do with the use of this antibiotic.     

Analysis of antibiotic susceptibility and extrachromosomal DNA content of Ruminococcus albus and Ruminococcus flavefaciens

Seventeen Ruminococcus albus and Ruminococcus flavefaciens strains have been screened for naturally occurring antibiotic resistance, as determined by zones of inhibition from antibiotic disks. These strains were also examined for extrachromosomal DNA content. All strains screened are resistant to low levels (10-200 micrograms/mL) of streptomycin. In contrast to the previously reported data, we have found that R. flavefaciens C-94 is now susceptible to both kanamycin and tetracycline. However, R. flavefaciens FD-1 is not susceptible to kanamycin (minimum inhibitory concentration (MIC) = 40 micrograms/mL). Furthermore, R. albus 8 is resistant to tetracycline (MIC = 40 micrograms/mL), and erythromycin (MIC = 100 micrograms/mL). Six freshly isolated strains showed resistance to tetracycline (35-70 micrograms/mL), and all tetracycline-resistant strains also showed resistance to minocycline. None of these Ruminococcus determinants share homology with the streptococcal tetL, tetM, or tetN determinants. All 17 strains were screened for extrachromosomal DNA content. Nine different techniques for the detection and isolation of extrachromosomal DNA were tested. However, owing to difficulties in demonstrating or isolating plasmid DNA, it has not been possible to determine if these antibiotic resistance genes are plasmid borne. Evidence is presented to suggest that the presence of oxygen may affect the quality of the DNA obtained from Ruminococcus.     

Dynamics of drug resistance of Vibrio cholerae isolated from surface water reservoirs in Siberia and the Soviet Far East in 1976-1990]

In the study on antibiotic resistance 1383 strains of El Tor Vibrio cholerae isolated from surface water reservoirs in 12 administrative territories of the Siberia and Far East within a period of 15 years were tested. The following antibiotics were used: ampicillin, streptomycin, monomycin, polymyxin, tetracycline, chloramphenicol, rifampicin and nalidixic acid. The resistance was unstable and its pattern was wave-like according to annual changes in the biological cycle. It was especially evident in regard to ampicillin, streptomycin, monomycin and polymyxin. The highest numbers of the strains were resistant to polymyxin, ampicillin and streptomycin (up to 100 per cent in some years). The lowest numbers of the strains were resistant to chloramphenicol (0.4 per cent) and tetracycline (1.9 per cent). No strains resistant to rifampicin and nalidixic acid were isolated. In some cases the antibiotic resistance level depended on the geographical zone where the strain was isolated. A direct quantitative dependence of the resistance level on the MIC was observed: the lower the MIC of the drug was, the lower the number of the strains resistant to it was. Within the 15-year period there was no general tendency to increase the resistance in V. cholerae to the antibiotics used.     

Influence of Antibiotic Selection on Genetic Composition of Escherichia coli Populations from Conventional and Organic Dairy Farms

The widespread agricultural use of antimicrobials has long been considered a crucial influence on the prevalence of resistant genes and bacterial strains. It has been suggested that antibiotic applications in agricultural settings are a driving force for the development of antimicrobial resistance, and epidemiologic evidence supports the view that there is a direct link between resistant human pathogens, retail produce, farm animals, and farm environments. Despite such concerns, little is understood about the population processes underlying the emergence and spread of antibiotic resistance and the reversibility of resistance when antibiotic selective pressure is removed. In this study, hierarchical log-linear modeling was used to assess the association between farm type (conventional versus organic), age of cattle (calf versus cow), bacterial phenotype (resistant versus susceptible), and the genetic composition of Escherichia coli populations (E. coli Reference Collection [ECOR] phylogroup A, B1, B2, or D) among 678 susceptible and resistant strains from a previously published study of 60 matched dairy farms (30 conventional and 30 organic) in Wisconsin. The analysis provides evidence for clonal resistance (ampicillin resistance) and genetic hitchhiking (tetracycline resistance [Tet^r]), estimated the rate of compositional change from conventional farming to organic farming (mean, 8 years; range, 3 to 15 years), and discovered a significant association between low multidrug resistance, organic farms, and strains of the numerically dominant phylogroup B1. These data suggest that organic farming practices not only change the frequency of resistant strains but also impact the overall population genetic composition of the resident E. coli flora. In addition, the results support the hypothesis that the current prevalence of Tet^r loci on dairy farms has little to do with the use of this antibiotic.     

The survival of three strains of Arcobacter butzleri in the presence of lemon, orange and bergamot essential oils and their components in vitro and on food

AIMS: To test the effect of oils and vapours of lemon, sweet orange and bergamot and their components against three Arcobacter butzleri strains. METHODS AND RESULTS: The disc diffusion method was used to screen the oils and vapours against three strains of A. butzleri. In vitro bergamot was the most inhibitory essential oil (EO) and both citral and linalool were effective. On cabbage leaf, the water isolate was the least susceptible to bergamot EO, citral and linalool (1-2 log reduction), with the chicken isolate being the most susceptible (6-8 log reduction). However, the latter appeared not to be susceptible to vapours over 24 h although type strain and water isolate populations reduced by 8 logs. On chicken skin, the effectiveness of the oils was reduced compared with that on cabbage leaf. CONCLUSIONS: Bergamot was the most effective of the oils tested and linalool the most effective component. All strains tested were less susceptible in food systems than in vitro. SIGNIFICANCE AND IMPACT OF THE STUDY: Arcobacter isolates vary in their response to EO suggesting that the results of type strain studies should be interpreted with caution. Bergamot EO has the potential for the inhibition of this 'emerging' pathogen.     

Utilization of the Etest Assay for Comparative Antibiotic Susceptibility Profiles of Citrus Variegated Chlorosis and Pierce’s Disease Strains of Xylella fastidiosa

Xylella fastidiosa has a wide host range. Isolates of this bacterium that cause diseases in citrus (CVC) and grapes (PD) share 98% genome homology, and 95.7% amino acid identity. Drug resistance genes show a higher level of divergence and may be involved in the X. fastidiosa–host interaction. Antibiotic susceptibility of CVC and PD strains were compared utilizing the Etest strip method (AB Biodisk). Etest is applicable for fastidious slow-growing organisms due to its reproducibility. Results showed that the CVC strain was resistant to bacitracin, cefotaxime, and trimethoprim, and susceptible to chloramphenicol, erythromycin, gentamicin, kanamycin, streptomycin, and tetracycline. The PD strain was susceptible to all tested antibiotics, except kanamycin and trimethoprim. Both isolates produced a class C β-lactamase. These data support previous antibiotic studies and gene discrepancies found in the sequencing data of PD and CVC strains. These results demonstrate the efficacy of utilizing Etest assays for X. fastidiosa strains.     

Significance of determination of Shigella antibiotic resistance in bacteriological diagnosis of dysentery]

The results of the Shigella antibiotic susceptibility assay within 1995-2002 are presented. 1472 cultures from 1158 patients with intestinal infections and bacteria carriers were isolated. The isolates were tested for their susceptibility to tetracycline, chloramphenicol, gentamicin, kanamycin, ampicillin and ofloxacin. It was shown that S. flexneri and S. sonnei were resistant to tetracycline. The S. flexneri isolates were highly resistant to chloramphenicol (73.3 to 96.0%) while resistance to it in the isolates of S. sonnei varied from 7.7 to 88.5%. In this connection the Levin medium with tetracycline was used to increase the Shigella isolation. In the study of the culture media efficiency with respect to isolation of Shigella it was observed that the Levin medium with tetracycline provided higher rates of S. flexneri and S. sonnei isolation (2.3- and 1.7-fold increase respectively) vs. the Shigella isolation on the Ploskirev medium without the antibiotic.     

Antibiotic resistance in Streptococcus pneumoniae and Haemophilus influenzae. Report of a study group on bacterial resistance.

Twenty laboratories in England and Scotland took part in 1977 in a survey of antibiotic resistance in Streptococcus pneumoniae and Haemophilus influenzae. In Str pneumoniae 59 (6.8%) of the 866 strains studied were resistant to tetracycline and three to chloramphenicol, and one strain showed a decreased susceptibility to penicillin. The prevalence of resistance to tetracycline was lower than that found in a similar study performed in 1975. Nine hundred and fifty-two strains of H influenzae were examined: 15 (1.6%) were resistant to ampicillin (all were beta-lactamase producers) and 26 (2.7%) to tetracycline. Only two strains were resistant to chloramphenicol and two to trimethoprim. Sixty-three H influenzae strains were capsulated. Thirty-four of these were of Pittman type b, and antibiotic resistance, particularly to ampicillin, was more common in these than in other serotypes or non-typable strains. Some variation was seen in the resistance rate of both H influenzae and Str pneumoniae to tetracycline in strains from different centres, but too few were isolated to assess whether this represented a true geographical difference.     

Oxidative stress involved in the antibacterial action of different antibiotics

Staphylococcus aureus and Escherichia coli sensitive to chloramphenicol incubated with this antibiotic suffered oxidative stress with increase of anion superoxide (O2-). This reactive species of oxygen was detected by chemiluminescence with lucigenin. S. aureus, E. coli, and Enterococcus faecalis sensitive to ciprofloxacin exhibited oxidative stress when they were incubated with this antibiotic while resistant strains did not show stimuli of O2-. Other bacteria investigated was Pseudomonas aeruginosa, strains sensitive to ceftazidime and piperacillin presented oxidative stress in presence of these antibiotics while resistant strains were not stressed. Higher antibiotic concentration was necessary to augment O2- in P. aeruginosa biofilm than in suspension, moreover old biofilms were resistant to oxidative stress caused by antibiotics. A ceftazidime-sensitive mutant of P. aeruginosa, coming from a resistant strain, exhibited higher production of O2- than wild type in presence of this antibiotic. There was relation between antibiotic susceptibility and production of oxidative stress.     

Kinetics of induction and purification of chloramphenicol acetyltransferase from chloramphenicol-resistant Staphylococcus aureus

Plasmid-mediated chloramphenicol resistance in Staphylococcus aureus has been shown to involve acetylation of chloramphenicol by an enzyme induced by growth in the presence of the antibiotic and certain analogues. Analysis of the kinetics of induction has been complicated by (i) the intrinsic inhibitory effects of chloramphenicol on induced enzyme synthesis and (ii) the rapid disappearance of inducer after synthesis of the acetylating enzyme. The compound related to d-threo chloramphenicol which lacks a C(3) hydroxyl substituent (3-deoxychloramphenicol) is a potent inducer of chloramphenicol acetyltransferase but is ineffective as an antibiotic and is not a substrate for the enzyme. The availability of such a "gratuitous" inducer has simplified an analysis of the kinetics of induction of chloramphenicol acetyltransferase. The enzyme from induced bacteria has been purified to homogeneity and has been compared with the analogous enzyme present in E. coli which harbors a resistance transfer factor with the chloramphenicol resistance determinant.     

番茄斑萎病毒对多杀菌素抗性西花蓟马发育繁殖和药剂敏感性的影响

【目的】西花蓟马Frankliniella occidentalis (Pergande)是重要的入侵害虫,是番茄斑萎病毒（TSWV）最有效的传播媒介,TSWV对西花蓟马的生长发育有一定的影响。多杀菌素是防治西花蓟马最有效的药剂之一,但已有田间西花蓟马对多杀菌素产生抗药性的报道。TSWV对抗性西花蓟马是否也有影响及程度如何尚不清楚。本研究通过对此问题进行深入研究,以期为进一步了解TSWV对西花蓟马的影响提供依据。【方法】应用特定年龄-龄期及两性生命表的方法,研究用番茄斑萎病毒处理和未处理的多杀菌素抗性和敏感西花蓟马种群的生物学特性;用叶管药膜法测定不同处理种群对3种药剂（多杀菌素、甲氨基阿维菌素苯甲酸盐和虫螨腈）的敏感性变化。【结果】对于抗性品系,TSWV处理后西花蓟马的发育历期缩短,雌成虫寿命和产卵量略高,但与对照组差异不显著(P＞0.05),内禀增长率（r）和净生殖率（R₀）分别为0.0433 d^-1和2.210,显著高于对照组（分别为0.0356 d^-1和1.972）（P ≤ 0.001）。对于敏感品系,TSWV处理后西花蓟马的发育历期缩短,雌雄成虫寿命均显著延长（P ≤ 0.001）,产卵量也略有提高,R₀为4.125,显著高于对照组（3.979）（P ≤ 0.001）。TSWV处理后敏感和抗性西花蓟马对多杀菌素的敏感性没有发生明显变化,对甲氨基阿维菌素苯甲酸盐和虫螨腈的敏感性显著降低。【结论】番茄斑萎病毒对多杀菌素敏感和抗性西花蓟马均有直接有利影响,病毒处理的西花蓟马发育历期缩短,繁殖能力增强,成虫寿命延长,对药剂的敏感性降低。     

Identification of IAA-producing endophytic bacteria from micropropagated Echinacea plants using 16S rRNA sequencing

The presence of latent bacteria is a serious problem in plant tissue cultures. While endophytes are generally beneficial to plants in situ, they may affect culture growth under the modified conditions in vitro. The present study was undertaken to identify and characterize endophytic bacteria associated with the medicinal plant Echinacea in tissue culture. Based on classical microbiological tests and 16S rRNA analyses, it was found that endophytic bacteria associated with aseptically micropropagated Echinacea plantlets are representatives of several genera, Acinetobacter, Bacillus, Pseudomonas, Wautersia (Ralstonia) and Stenotrophomonas. Based on TLC and HPLC analyses, we found that Pseudomonas stutzeri P3 strain produces plant hormone, auxin (indole-3-acetic acid, IAA). Antibiotic resistance was also assessed as a virulence factor. The majority of endophytic bacteria were resistant to the antibiotic kanamycin, but susceptible to chloramphenicol. Recommendations for propagating Echinacea in vitro cultures involve the addition of chloramphenicol, tetracycline, and ampicillin, antibiotics that cause no side effects on these plant species.