禽畜养殖粪便中多重抗生素抗性细菌研究

通过对新乡地区8家养猪场和11家养鸡场饲喂抗生素情况的调研,发现头孢氨苄、阿莫西林、卡那霉素、庆大霉素等4种抗生素是该地区被普遍使用的兽药抗生素。通过多点取样法和微生物培养技术对3家养鸡场和3家养猪场不同养殖时期的粪便进行单一抗生素和多重抗生素抗性细菌的检测,结果表明养鸡场堆置1周的粪便中抗头孢氨苄的细菌比例最高,达到65.90%,对所研究的3种和4种抗生素同时抗性的比例高达8.60%—12.51%和9.73%,明显高于饲喂中药的对照养鸡场样本检测结果(0.02%—2.73%和0.12%)。养猪场堆置1周的粪便中检测到抗头孢氨苄的细菌比例也是最高,达到49.12%上,但养猪场粪便中多重抗生素抗性细菌的比例明显低于养鸡场。同时研究发现,在两种养殖场中,幼龄期粪便中检测到的多重抗性细菌比例明显高于成熟期粪便,这可能与养殖过程中鸡、猪在幼龄期由于防病和促生长等因素而同时大剂量使用多种抗生素有关。     

Exposing plasmids as the Achilles' heel of drug-resistant bacteria

Many multidrug-resistant bacterial pathogens harbor large plasmids that encode proteins conferring resistance to antibiotics. Although the acquisition of these plasmids often enables bacteria to survive in the presence of antibiotics, it is possible that plasmids also represent a vulnerability that can be exploited in tailored antibacterial therapy. This review highlights three recently described strategies designed to specifically combat bacteria harboring such plasmids: inhibition of plasmid conjugation, inhibition of plasmid replication, and exploitation of plasmid-encoded toxin-antitoxin systems.     

Inhibited growth of common enteropathogenic bacteria in lactic-fermented cereal gruels

A natural lactic fermentation of mixtures of water and whole flour of either maize or high-tannin sorghum was obtained either before or after cooking to a weaning gruel: The preparations had a final pH of about 3.8 (range 3.67 to 4.00) and a ratio of lactic acid to acetic acid of 91 (w/w). The growth of added (about 10⁷ c.f.u./g gruel) Gram-negative intestinal pathogenic bacteria, enterotoxigenicEscherichia coli, Campylobacter jejuni, Shigella flexneri andSalmonella typhimurium, was strongly inhibited in the sour gruels, and the effect could primarily be explained by the low pH caused by the formation of lactic and acetic acids during the fermentation process. Of the added Gram-positive bacteria,Bacillus cereus andStaphylococcus aureus showed similar inhibited growth up to 7h after inoculation in the sour gruels. The strain ofStaphylococcus, however, showed only a continued reduction in growth in the fermented gruel samples, which had a viable lactic bacteria culture indicating the presence of a bacteriocin. This implies that a low pH (< 4.0) alone is not sufficient to sustain the inhibition of the growth ofStaphylococcus aureus. The survival studies were carried out at optimal temperatures for each respective enteropathogen.     

Salmonellae and other enteropathogenic bacteria in the intestines of wall geckos in Nigeria

The aerobic bacterial flora of the intestine of 150 wall geckos (Hemidactylus brookei) was investigated. A variety of bacteria was recovered including 35 isolates of Salmonella and several other species of Enterobacteriaceae, viz. Shigella sonnei—2, Edwardsiella tarda—4, Enterobacter spp—8, Citrobacter freundii—3, Serratia marcescens—3, Proteus spp—35, Klebsiella pneumoniae—13, and Escherichia coli—17, isolates. Eight Salmonella serotypes were identified, the predominant ones being S. hvittingfoss and S. typhimurium. The significance of these findings for the spread of human enteropathogens is discussed.     

Physiological assessment of bacteria using fluorochromes

This minireview focuses on the application of fluorogenic compounds in the detection of bacteria with particular emphasis on the assessment of physiological activity using epifluorescence microscopy. Microbiological applications of several related methods will also be reviewed.     

The interplay between Entamoeba and enteropathogenic bacteria modulates epithelial cell damage

Background

Mixed intestinal infections with Entamoeba histolytica, Entamoeba dispar and bacteria with exacerbated manifestations of disease are common in regions where amoebiasis is endemic. However, amoeba–bacteria interactions remain largely unexamined.

Methodology

Trophozoites of E. histolytica and E. dispar were co-cultured with enteropathogenic bacteria strains Escherichia coli (EPEC), Shigella dysenteriae and a commensal Escherichia coli. Amoebae that phagocytosed bacteria were tested for a cytopathic effect on epithelial cell monolayers. Cysteine proteinase activity, adhesion and cell surface concentration of Gal/GalNAc lectin were analyzed in amoebae showing increased virulence. Structural and functional changes and induction of IL-8 expression were determined in epithelial cells before and after exposure to bacteria. Chemotaxis of amoebae and neutrophils to human IL-8 and conditioned culture media from epithelial cells exposed to bacteria was quantified.

Principal Findings

E. histolytica digested phagocytosed bacteria, although S. dysenteriae retained 70% viability after ingestion. Phagocytosis of pathogenic bacteria augmented the cytopathic effect of E. histolytica and increased expression of Gal/GalNAc lectin on the amoebic surface and increased cysteine proteinase activity. E. dispar remained avirulent. Adhesion of amoebae and damage to cells exposed to bacteria were increased. Additional increases were observed if amoebae had phagocytosed bacteria. Co-culture of epithelial cells with enteropathogenic bacteria disrupted monolayer permeability and induced expression of IL-8. Media from these co-cultures and human recombinant IL-8 were similarly chemotactic for neutrophils and E. histolytica.

Conclusions

Epithelial monolayers exposed to enteropathogenic bacteria become more susceptible to E. histolytica damage. At the same time, phagocytosis of pathogenic bacteria by amoebae further increased epithelial cell damage.

Significance

The in vitro system presented here provides evidence that the Entamoeba/enteropathogenic bacteria interplay modulates epithelial cell responses to the pathogens. In mixed intestinal infections, where such interactions are possible, they could influence the outcome of disease. The results offer insights to continue research on this phenomenon.     

Lactobacillus johnsonii La1 shares carbohydrate-binding specificities with several enteropathogenic bacteria

The carbohydrate-binding specificities of the probiotic lactic acid bacterium Lactobacillus johnsonii La1 (a health-beneficial bacterial strain able to be incorporated into the human intestinal microflora) were investigated in vitro. First various soluble complex carbohydrates were tested as potential inhibitors of the strain adhesion onto Caco-2 intestinal epithelial cells, and then bacterial binding to glycolipids immobilized on TLC plates was probed. Two major carbohydrate-binding specificities of Lactobacillus johnsonii La1 were identified. A first one for an Endo-H treated yeast cell wall mannoprotein carrying mainly O:-linked oligomannosides, and a second one for the gangliotri- and gangliotetra-osylceramides (asialo-GM1). Similar carbohydrate-binding specificities are known to be expressed on cell surface adhesins of several enteropathogens, enabling them to adhere to the host gut mucosa. These findings corroborate the hypothesis that selected probiotic bacterial strains could be able to compete with enteropathogens for the same carbohydrate receptors in the gut.     

Physiological aspects of chitin catabolism in marine bacteria

Chitin, a carbohydrate polymer composed of alternating beta-1, 4-linked N-acetylglucosamine residues is the second most abundant organic compound in nature. In the aquatic biosphere alone, it is estimated that more than 10(11) metric tons of chitin are produced annually. If this enormous quantity of insoluble carbon and nitrogen was not converted to biologically useful material, the oceans would be depleted of these elements in a matter of decades. In fact, marine sediments contain only traces of chitin, and the turnover of the polysaccharide is attributed primarily to marine bacteria, but the overall process involves many steps, most of which remain to be elucidated. Marine bacteria possess complex signal transduction systems for: (1) finding chitin, (2) adhering to chitinaceous substrata, (3) degrading the chitin to oligosaccharides, (4) transporting the oligosaccharides to the cytoplasm, and (5) catabolizing the transport products to fructose-6-P, acetate and NH(3). The proteins and enzymes are located extracellularly, in the cell envelope, the periplasmic space, the inner membrane and the cytoplasm. In addition to these levels of complexity, the various components of these systems appear to be carefully coordinated by intricate regulatory mechanisms.     

Circulation flow of enteropathogenic bacteria in institutionalized children. I. An epidemiologic study

The circulation flow and maintenance of enteropathogenic bacteria were studied from May 1982 to April 1983 in a population of institutionalized children and adult staff contacts in the city of Rio de Janeiro, Brazil. Subjects were assigned to three groups: A and B, included, respectively, 105 and 46 children with diarrhea who were admitted in the institution in different periods, and group C with 82 adult contacts. Faecal cultures were positive in 35.2%, 39.1% and 19.7% of subjects of groups A, B, and C, respectively. It suggests that the transmission was probably fostered by the environment because of as high as 30% of faecal contamination was found in environmental samples. Higher rate of isolation and elevated antibodies levels pointed out that Escherichia coli (EPEC) was the prevalent agent. Shigella predominated in the serological tests. These findings suggest that the institution itself may play an important role in the epidemiology and transmission of enteric infections in the community.     

Bacteriocin activity of Pseudomonas sp. on enteropathogenic bacteria in an artificial aquatic system

The bacteriocin of Pseudomonas sp. strain R10 was active in vitro against several enteropathogenic bacteria: enterotoxigenic Escherichia coli, Salmonella typhimurium, Salmonella typhi, Shigella flexneri and Shigella sonnei. Pseudomonas sp. R10 was studied for 5 d in an aquatic system in the presence of strains of the enteropathogenic species mentioned. All the target strains were inhibited in the presence of bacteriocinogenic Pseudomonas sp. R10 and the highest antibacterial action was observed on the second day. Similar results were obtained with the partially purified bacteriocin, although the greatest bactericidal action, in all the studied target strains, was observed on the first day and the bacterial recounts were slightly higher overall.     

High heels as supernormal stimuli: How wearing high heels affects judgements of female attractiveness

There is a strong contemporary association between high heels and female sexuality. We investigated the hypothesis that one motivation for women wearing high heels is that it artificially increases the femininity of gait. We isolated the effects of heels on gait using point-light methodology. Females were recorded walking in flat shoes and high heels. Participants viewed point-light videos of the women wearing the two types of shoe. Participants judged the females in the heels condition as significantly more attractive (with a large effect size) than the females in the flat shoe condition. Biomechanical analyses revealed that wearing high heels led to increased femininity of gait including reduced stride length and increased rotation and tilt of the hips. We conclude that high heels exaggerate sex specific aspects of female gait and women walking in high heels could be regarded as a supernormal stimulus.     

Physiological responses of bacteria in biofilms to disinfection.

In situ enumeration methods using fluorescent probes and a radioisotope labelling technique were applied to evaluate physiological changes of Klebsiella pneumoniae within biofilms after disinfection treatment. Chlorine (0.25 mg of free chlorine per liter [pH 7.2]) and monochloramine (1 mg/liter [pH 9.0]) were employed as disinfectants in the study. Two fluorgenic compounds, 5-cyano-2,3-ditolyl tetrazolium chloride and rhodamine 123, and tritiated uridine incorporation were chosen for assessment of physiological activities. Results obtained by these methods were compared with those from the plate count and direct viable count methods. 5-Cyano-2,3-ditolyl tetrazolium chloride is an indicator of bacterial respiratory activity, rhodamine 123 is incorporated into bacteria in response to transmembrane potential, and the incorporation of uridine represents the global RNA turnover rate. The results acquired by these methods following disinfection exposure showed a range of responses and suggested different physiological reactions in biofilms exposed to chlorine and monochloramine. The direct viable count response and respiratory activity were affected more by disinfection than were the transmembrane potential and RNA turnover rate on the basis of comparable efficiency as evaluated by plate count enumeration. Information revealed by these approaches can provide different physiological insights that may be used in evaluating the efficacy of biofilm disinfection.