Effect of antibiotics on the human intestinal flora in mice

Antibiotics used during selective decontamination were studied for their effect on the human intestinal flora in mice. Polymyxin B and neomycin were found to eliminate Escherichia coli from the gastrointestinal tract but did not alter total numbers of obligate anaerobes. Neomycin induced an increase of the percentage of gram-negative obligate anaerobes. Cephradine did not affect the numbers of obligate and facultative anaerobes but increased the percentage of gram-negative obligately anaerobic rods in the flora. The selective effect of polymyxin B and neomycin on the flora is accounted for by a relative insusceptibility of the anaerobic flora as compared with E. coli. Low concentrations of polymyxin B and neomycin were detected in caecal supernatants. This was found to be due to strong binding of both antibiotics to the solid fraction of intestinal contents.     

Effect of selective media on recovery of obligately anaerobic gram-negative rods from human faeces

Total numbers and gross composition of the anaerobic human faecal flora were compared using non-selective and selective media. Combinations of selective agents to suppress the gram-negative part of the flora such as vancomycin and neomycin, vancomycin and kanamycin, or kanamycin and bile were found to reduce total numbers of recovered obligately anaerobic gram-negattive rods by 50–75%. With reference to experiments with penicillin as selective agent, underlying mechanisms for this phenomenon are discussed. It is concluded that selective media should not be used for quantitative enumeration of anaerobic gram-negative rods from the faecal flora.     

Bacteriological findings in patients with bone marrow transplantation (Karl Marx University Leipzig, 1985-1987)

The results of the bacteriological surveillance cultures for 26 patients with bone marrow transplantation (Karl Marx University Leipzig, G.D.R., 1985-1987) are presented. 5.9% of all surveillance cultures contained facultatively pathogenic germs (with Pseudomonas aeruginosa as the most frequent representative, which was the reason of a sepsis in two patients). Coagulasenegative Staphylococci and other germs with an obscure pathogenicity were isolated upon a large scale, especially from the mucous membrane regions. There are hints, that above all special strains of coagulasenegative Staphylococci "colonize" the patient's body (also for longer periods) and turn into the blood too. During the total decontamination intestinal anaerobic flora is absent. After closing of total decontamination Clostridium perfringens is the first detectable anaerobic species. During the selective decontamination systemic applications of antibiotics are able to obliterate anaerobic findings for certain periods. Recommendations for an effective arrangement of the surveillance cultures of bone marrow transplantation patients are given.     

DNA-methyltransferase activities in Streptomyces antibioticus

Abstract To quantitate ammonia production by the intestinal flora, ammonia levels in arterial blood and the venous effluent of the small and large bowel of conventional, selectively decontaminated, germ-free and gnotobiotic rats were measured.
When the anaerobic flora was removed by decontamination a significant decrease in ammonia levels was observed in the effluent of both the small and large intestine. Decontamination of aerobic flora did not result in depression of ammonia production. Gnotobiotic rats colonised with an anaerobic flora or with a mixed aerobic and anaerobic flora, showed a slight increase in ammonia levels. No increase in ammonia production was observed when rats were colonised with aerobic flora. These results indicate that the Enterobacteriaceae were not responsible for ammonia generation.
The increase in ammonia levels after colonisation with anaerobic or mixed anaerobic/aerobic flora did not completely restore ammonia levels, despite reaching bacterial counts which were comparable to those in conventional rats. This may be explained by the limited number of species with which the rats were colonized. The finding that aerobic flora does not significantly contribute to ammonia production suggests that neomycin, known to be exclusively effective against aerobic flora, must have other effects to explain improvement of hepatic encephalopathy.     

细菌耐药影响肠道菌群及其宿主免疫调控

抗生素在养殖业、医疗业及制药业的广泛应用导致环境中的细菌耐药性日益严重,环境中的抗生素及耐药细菌一旦进入人体肠道,将破坏肠道菌群稳态,对人体健康造成威胁,而残存于饮食中的环境污染物则加剧了细菌耐药造成的人体健康影响。文中在总结大量文献的基础上,阐述了细菌耐药对人体和动物肠道菌群的影响机制及其相关的机体免疫调控,以环境中影响人体肠道菌群获得耐药性的来源作为切入点,阐述抗生素和耐药细菌进入人体肠道后对人体肠道菌群结构和耐药基因组成的影响,以及与人体免疫和免疫调节相关疾病之间的相关机制,并对今后的研究方向进行了展望。     

Binding to faeces and influence on human anaerobes of antimicrobial agents used for selective decontamination

The degree of binding of ampicillin, cephradine, co-trimoxazole, gentamicin, nalidixic acid, neomycin, polymyxin B and tobramycin by faecal substance as well as the influence of these antibiotics on human intestinal obligate anaerobes was investigated. In contrast to ampicillin, cephradine, co-trimoxazole and nalidixic acid, the nonabsorbable antibiotics polymyxin B and neomycin were bound to a considerable degree by human faeces. The binding of tobramycin and gentamicin to the solid part of faeces was less effective. The inhibitory effect of co-trimoxazole, gentamicin, nalidixic acid, neomycin, polymyxin B and tobramycin on the human obligate anaerobes was weak as compared with ampicillin and cephradine. Drugs which effectively eliminate Enterobacteriaceae from the gastrointestinal tract and which have a moderate effect on obligate anaerobes, like polymyxin B, are particularly suitable for selective decontamination of the gastrointestinal tract. The strong inactivating binding of aminoglycosides and polymyxin B to faeces accounts for the relatively high oral dose needed for a suitable faecal concentration.     

Hydrolysis of iodothyronine glucuronides by obligately anaerobic bacteria isolated from human faecal flora

Abstract 35 bacterial strains isolated from the human faecal flora were screened for hydrolysis of the glucuronides of 3,3',5-triiodothyronine and 3,3'-diiodothyronine. Two Gram-positive obligately anaerobic strains possessed glucuronidase activity. These strains probably belong to the genus Eubacterium , but ethanol was produced in high concentrations during glucose fermentation, which makes final classification difficult. Considering the number of bacteria in the intestinal flora (> 10⁸/ml) and the biliary excretion of iodothyronine conjugates, the strains must be able to hydrolyse a major part of the total daily intestinal supply of these iodothyronine metabolites. The study extends previous observations with faecal suspensions of human and rat origin [24]. The relevance of bacterial β-glucuronidase activity for a possible enterohepatic circulation of iodothyronines is discussed.     

Antimicrobial resistance of bacteria isolated from slaughtered and retail chickens in South Africa

Animal feed is increasingly being supplemented with antibiotics to decrease the risk of epidemics in animal husbandry. This practice could lead to the selection for antibiotic resistant micro-organisms. The aim of this study was to determine the level of antibiotic resistant bacteria present on retail and abattoir chicken. Staphylococci, Enterobacteriaceae, Salmonella and isolates from total aerobic plate count were tested for resistance to vancomycin, streptomycin, methicillin, tetracycline and gentamicin using the disc diffusion susceptibility test; resistance to penicillin was determined using oxacillin. Results from the antibiotic code profile indicated that many of the bacterial strains were displaying multiple antibiotic resistance (MAR). A larger proportion of resistance to most antibiotics, except for vancomycin, was displayed by the abattoir samples, therefore suggesting that the incidence of MAR pathogenic bacteria was also higher in the abattoir samples. This resistance spectrum of abattoir samples is a result of farmers adding low doses of antibiotics to livestock feed to improve feeding efficiency so that the animals need less food to reach marketable weight. The lower incidence of MAR pathogenic bacteria in the retail samples is a result of resistance genes being lost due to lack of selective pressure, or to the fact that the resistant flora are being replaced by more sensitive flora during processing. The use of subtherapeutic levels of antibiotics for prophylaxis and as growth promoters remains a concern as the laws of evolution dictate that microbes will eventually develop resistance to practically any antibiotic. Selective pressure exerted by widespread antimicrobial use is therefore the driving force in the development of antibiotic resistance. This study indicated that a large proportion of the bacterial flora on fresh chicken is resistant to a variety of antibiotics, and that resultant food-related infections will be more difficult to treat.     

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.     

Impact of an urban effluent on antibiotic resistance of riverine Enterobacteriaceae and Aeromonas spp

In order to evaluate the impact of an urban effluent on antibiotic resistance of freshwater bacterial populations, water samples were collected from the Arga river (Spain), upstream and downstream from the wastewater discharge of the city of Pamplona. Strains of Enterobacteriaceae (representative of the human and animal commensal flora) (110 isolates) and Aeromonas (typically waterborne bacteria) (118 isolates) were selected for antibiotic susceptibility testing. Most of the Aeromonas strains (72%) and many of the Enterobacteriaceae (20%) were resistant to nalidixic acid. Singly nalidixic acid-resistant strains were frequent regardless of the sampling site for Aeromonas, whereas they were more common upstream from the discharge for enterobacteria. The most common resistances to antibiotics other than quinolones were to tetracycline (24.3%) and beta-lactams (20.5%) for Enterobacteriaceae and to tetracycline (27.5%) and co-trimoxazole (26.6%) for Aeromonas. The rates of these antibiotic resistances increased downstream from the discharge at similar degrees for the two bacterial groups; it remained at high levels for enterobacteria but decreased along the 30-km study zone for Aeromonas. Genetic analysis of representative strains demonstrated that these resistances were mostly (enterobacteria) or exclusively (Aeromonas) chromosomally mediated. Moreover, a reference strain of Aeromonas caviae (CIP 7616) could not be transformed with conjugative R plasmids of enterobacteria. Thus, the urban effluent resulted in an increase of the rates of resistance to antibiotics other than quinolones in the riverine bacterial populations, despite limited genetic exchanges between enterobacteria and Aeromonas. Quinolone resistance probably was selected by heavy antibiotic discharges of unknown origin upstream from the urban effluent.     

The digestive tract in immunocompromised patients: importance of maintaining its resistance to colonization,especially in hospital in-patients and those taking antibiotics

The colonization resistance (CR) of the gastrointestinal tract to potential pathogens depends partly on factors within the host but to a greater extent on the normal (anaerobic) gut flora. Its strength varies between individuals. These individual differences in resistance to colonization by pathogenic microorganisms may explain differences in susceptibility to infection. CR is lowered by remission-inducing treatment (radiation and/or chemotherapy) in leukaemia, but more severely by certain antibiotics. Development (by selection or transfer) of resistance to these antibiotics may lead to overgrowth and penetration of the mucosal lining by the overgrowing (potentially) pathogenic bacteria. Other antibiotics however, if sufficiently dosed, have been found to eliminate (potential) pathogens selectively without decreasing CR. This selective decontamination of the gastrointestinal tract has been successfully used prophylactically in neutropenic patients but needs to be monitored bacteriologically. It should perhaps be used more widely in the hospital to control development and spread of antibiotic-resistant strains.     

微生态学与后抗生素时代

本文简述了抗生素产生的历史背景,和对人类感染性疾病作出的贡献。但由于抗生素的泛用、滥用和过度治疗,引起了机体的菌群失调、二重感染和更为严重的细菌耐药性。为解决抗生素的弊端,解决菌群失调等问题,促使了微生态学的兴起和发展。本文还阐述了细菌耐药性的现状及危害,细菌产生耐药性的动因,后抗生素时代对细菌的防控措施。提出用微生态制剂、肠道正常菌群、中药、抗菌肽、噬菌体、研制新型抗菌药和规范用药等措施,防控细菌感染。同时阐述了常用中药的抗菌谱,及与微生态制剂合并应用的可能性。     

Effects of dietary antibiotics on intestinal microflora in broiler chickens

Changes were examined in the intestinal microflora in broiler chickens fed a diet containing antibiotics to obtain fundamental information on the mechanisms of beneficial effect of the antibiotics upon livestock production. Three antibiotics (colistin, bacitracin, and enramycin) were employed as feed additives. Experiments were conducted with broiler chickens in two ways. In one way dietary antibiotics were fed continually at levels approved for use as feed additives for a long term. In the other they were fed the same antibiotics for a short term. Significant changes in microflora were observed mainly in such bacterial groups as aerobic bacteria and Lactobacillus. In the long term administration, three possible modes of variance in the bacterial flora were postulated: Changes directly related to the antibacterial spectrum of antibiotics. Antagonistic changes related to an ecological balance in the bacterial flora. Changes in quantitative balance of bacteria constituting each bacterial group. The change in the intestinal microflora during administration of the antibiotic diet was expressed as a complex form of these transition modes. In the short term administration, it was demonstrated that the effect of the antibiotic diet lingered even 7 days after administration. This suggests that antibiotics used as feed additives may possibly affect the stability of the intestinal microflora.     

The intestinal microflora during the first weeks of life

Bacterial colonization of the neonatal gastrointestinal tract begins during birth when the neonate comes into contact with the maternal cervical and vaginal flora. In infants delivered by Caesarean section, bacteria colonizing the neonate gastrointestinal tract are provided by the environment. The first bacteria encountered in the majority of healthy infants, are facultative anaerobes, which remain predominant during the first 2 weeks of life. Among them, Staphylococcus, Enterobacteriaceae and Streptococcus were the genera most commonly isolated from the newborn faecal flora at birth. Facultative anaerobic bacteria are followed closely by Bifidobacterium sp. Clostridium perfringens is present within 2 days with an increase incidence in newborns delivered by a Caesarean section. Clostridium perfringens seems to be the precursor for installation of other anaerobic putrefactive bacteria, as Bacteroides and other Clostridium sp. The impact of Caesarean section and the period and quality of hospitalization are mainly implicated in changes of the normal newborn flora. Feeding seems to modulate the colonization pattern. In humans, breast milk plays a role in passive immunization of the neonatal intestine, and contains factors that promote the growth of Bifidobacterium bifidum in the intestinal flora. Formula feeding seems to promote implantation and persistence of Clostridium perfringens, and clearly enhances intestinal colonization of C. difficile in newborns.     

乳酸杆菌制剂对应用抗生素大鼠体内TLR2 mRNA转录水平及相关因素影响的研究

目的动态观察乳酸杆菌制剂对应用抗生素大鼠肠道菌群结构和TLR2 mRNA转录水平的影响。方法采用细菌培养法定量检测肠道双歧杆菌、乳酸杆菌、肠杆菌和肠球菌;利用反转录聚合酶链反应技术测定大鼠肠黏膜组织、肠系膜淋巴结、肝脏和脾脏细胞TLR2 mRNA转录水平。结果应用抗生素可致肠道菌群失调和TLR2 mRNA转录水平的早期受抑制。乳酸杆菌制剂干预可迅速提高肠道乳酸杆菌数量,及早扶正肠道菌群结构,减轻由于应用抗生素引起的Toll样受体mRNA转录受抑程度。结论乳酸杆菌制剂早期干预可及早扶正肠道菌群结构,减轻TLR2 mRNA转录水平受抑制程度,为临床合理应用抗生素,早期益生菌干预提供理论依据。     

抗生素对新生大鼠肠道菌群和肠道免疫发育的影响

目的通过建立动物模型,探讨口服抗生素对新生大鼠肠道菌群的变化及肠道免疫发育的影响。方法选用30只7日龄新生SD大鼠,随机分为3组：抗生素组（A）、益生菌干预组（B）及对照组（C）,每组10只,A组给予头孢克洛灌胃,B组先给头孢克洛灌胃,2h后再灌长双歧杆菌,C组每天灌以等量的生理盐水,持续2周后处死大鼠,留取盲肠内容物按照张秀荣方法进行肠道菌群检测,免疫组化方法进行肠组织CD4、CD8的测定。结果A组与B、C组相比,革兰阳性杆菌占肠道总细菌数比例明显下降,革兰阴性杆菌及革兰阳性球菌占总细菌数比例明显升高,差异均有显著性（P〈0．05）;A组肠组织中CD4、CD8表达程度受到抑制,与B、C组相比差异有显著性（P〈0．05）,B、C两组所有的指标差异均无显著性。结论抗生素的应用会抑制肠道菌群的正常定植,引起菌群紊乱,进而影响肠道免疫系统发育。     

Human flora-associated (HFA) animals as a model for studying the role of intestinal flora in human health and disease

Although the intestinal flora in animals plays an important role in health and disease, there is little direct information regarding the role of the human intestinal flora. By inoculating germfree animals with human faeces, the major components of the human flora can be transferred into the ex-germfree animals, i.e. human flora-associated (HFA) animals. HFA animals therefore provide a stable model for studying the ecosystem and metabolism of the human intestinal flora. Results with HFA animals suggest the role of the human intestinal flora is somewhat different from the role of the animal flora in conventional experimental animals. Studies using HFA animals, therefore, will provide much needed information on the precise role of the intestinal flora in relation to humans. HFA animals also can be used as models to investigate the interactions between the human intestinal flora, host factors, dietary manipulations, and therapeutics, such as probiotics, prebiotics, and antibiotics.     

海参多糖对小鼠肠道菌群紊乱的恢复作用

目的探究海参多糖对抗生素所致小鼠肠道菌群失衡的调整作用。方法超声浸提法提取海参多糖,硫酸-苯酚法测定多糖含量;通过抗生素连续灌胃1周,构建小鼠肠道紊乱模型;将18只昆明种小鼠随机分为正常对照、自然恢复和海参多糖干预组(每组6只),定期留取粪便,采用PCR-DGGE技术获得肠道菌群分子指纹图谱,进行相似性、多样性及主要差异条带序列的分析。结果提取海参多糖的浓度为1.92 mg/mL;正常对照组小鼠肠道菌群以有益菌,即乳杆菌属和梭菌属占主导地位;而在抗生素干预后,这两种菌的含量明显下降,并伴随检测出致病性卟啉单胞菌属;经海参多糖处理后,有益菌含量有所恢复,有害菌含量降低。结论海参多糖对抗生素所致实验小鼠肠道菌群紊乱有一定的恢复作用。     

Hydrolysis of iodothyronine conjugates by intestinal bacteria

Glucuronide and sulfate conjugation are important pathways in the peripheral metabolism of thyroid hormone. These reactions occur predominantly in the liver, and especially the glucuronides are excreted in the bile. Although an enterohepatic circulation after intestinal hydrolysis of iodothyronine conjugates is suggested by several authors, substantial proof has not been presented so far. In the present paper experimental work from our group is reviewed. The studies showed that fecal suspensions of human or rat origin hydrolysed iodothyronine conjugates, whereas oral administration of antibiotics to rats strongly reduced this capacity. Obligately anaerobic intestinal bacteria were found to be responsible for the hydrolysis and several species belonging to the major residents of the intestinal flora of man and rat could be isolated and identified. Recent studies with conventional and decontaminated rats produced strong support for the existence of an enterohepatic circulation of thyroid hormone. Our findings are discussed in connection with other relevant studies on this subject.     

Hydrolysis of iodothyronine conjugates by intestinal bacteria

Abstract Glucuronide and sulfate conjugation are important pathways in the peripheral metabolism of thyroid hormone. These reactions occur predominantly in the liver, and especially the glucuronides are excreted in the bile. Although an enterohepatic circulation after intestinal hydrolysis of iodothyronine conjugates is suggested by several authors, substantial proof has not been presented so far.
In the present paper experimental work from our group is reviewed. The studies showed that fecal suspensions of human or rat origin hydrolysed iodothyronine conjugates, whereas oral administration of antibiotics to rats strongly reduced this capacity. Obligately anaerobic intestinal bacteria were found to be responsible for the hydrolysis and several species belonging to the major residents of the intestinal flora of man and rat could be isolated and identified.
Recent studies with conventional and decontaminated rats produced strong support for the existence of an enterohepatic circulation of thyroid hormone. Our findings are discussed in connection with other relevant studies on this subject.