Bug-eyed; eye infections caused by bacteria

This article is a brief introduction to the eye infections most commonly caused by bacteria together with their treatment.

Mechanism of uptake of the catecholic (7)-α-formamido cephalosporin BRL 41897A by klebsiella pneumoniae

The catecholic cephalosporin BRL 41897 A is resistant to β-lactamases and is taken up by bacteria via the iron transport system. The uptake of this antibiotic in E.coli uses the Fiu and Cir outer membrane proteins, whereas in P. aerugtnosa it enters via the pyochelin transport system. In this thesis mutants of K. pneumoniae resistant to BRL 41897A were isolated using TnphoA mutagenesis and used to study the mechanism of uptake of BRL 41897A by K. pneumoniae. The activity of BRL 41897A towards the parent strain (M10) was increased in iron depleted media, whereas no significant differences in the resistant (KSL) mutants were observed. Three mutants (KSL19, KSL38and KSL59) produced decreased amounts of certain iron-regulated outer membrane proteins. The uptake of 55Fe-BRL 41897A by M10 in iron-deficient medium was higher than in iron-rich medium. This result indicated the involvement of an iron transport system in the uptake of BRL 41897A by K. pneumoniae. Uptake by the KSL mutants in iron-deficient culture was higher than that by M10. This result, supported by analysis of outer membrane and periplasmic proteins of the KSL mutants, indicates that loss of one outer membrane protein can be compensated by over expression of other outer membrane and/or periplasmic proteins. However, the increased uptake of BRL 41897A by the KSL mutants did not reflect increased activity towards these strains, indicating that there are defects in the transport of BRL 41897A resulting in failure to reach the penicillin binding protein target sites in the cytoplasmic membrane. Southern blotting of chromosomal digests and sequencing in one mutant (KSL19) showed that only one copy of TnphoA was inserted into its chromosome. A putative TnphoA inserted gene in KSL19, designated kslA, carrying a signal sequence was identified. Transformation of a fragment containing the kslA gene into KSL19 cells restored the sensitivity to BRL 41897A to that of the parent strain. Data base peptide sequence searches revealed that the kslA gene in the KSL19 has some amino acid homology with the E. coli ExbD protein, which is involved in stabilisation of the TonB protein. 

Ecological studies on high-rate biological filters with special reference to microbial biosynthesis and nitrification

Pilot scale studies of high rate filtration were initiated to assess its potential as either a primary 'roughing' filter to alleviate the seasonal overloading of low rate filters on Hereford sewage treatment works - caused by wastes from cider production - or as a two stage high rate process to provide complete sewage treatment. Four mineral and four plastic primary filter media and two plastic secondary filter media were studied. The hydraulic loading applied to the primary plastic media (11.2 m3 /m3 .d) was twice that applied to the mineral media. The plastic media removed an average around 66 percent and the mineral media around 73 percent of the BOD applied when the 90 percentile BOD concentration was 563 mg/1. At a hydraulic loading of 4 m3 /m3 .d the secondary filters removed most of the POD from partially settled primary filter effluents, with one secondary effluent satisfying a 25 mg/1 BOD and 30 mg/1 SS standard. No significant degree of nitrification was achieved. Fungi dominated the biological film of the primary filters, with invertebrate grazers having little influence on film levels. Ponding did not arise, and modular media supported lower film levels than random-fill types. Secondary filter film levels were low, being dominated by bacteria. The biological loading applied to the filters was related to sludge dewaterability, with the most readily conditionable sludges produced by filters supporting heavy film. Sludges produced by random-fill media could be dewatered as readily as those produced by low rate filters treating the same sewage. Laboratory scale studies showed a relationship between log effluent BOD and nitrification achieved by biological filters. This relationship and the relationship between BOD load applied and removed observed in all filter media could he used to optimise operating conditions required in biological filters to achieve given effluent BOD and ammoniacal nitrogen standards.

The suitability of biodegradable poly(dl-lactide-co-glycolide)75:25 microspheres for the sustained release of antibiotics

Post-operative infections resulting from total hip arthroplasty are caused by bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa entering the wound perioperatively or by haemetogenous spread from distant loci of infection. They can endanger patient health and require expensive surgical revision procedures. Gentamicin impregnated poly (methyl methacrylate) bone cement is traditionally used for treatment but is often removed due to harbouring bacterial growth, while bacterial resistance to gentamicin is increasing. The aim of this work was to encapsulate the antibiotics vancomycin, ciprofloxacin and rifampicin within sustained release microspheres composed of the biodegradable polymer poly (dl-lactide-co-glycolide) [PLCG] 75:25. Topical administration to the wound in hydroxypropylmethylcellulose gel should achieve high local antibiotic concentrations while the two week in vivo half life of PLCG 75:25 removes the need for expensive surgical retrieval operations. Unloaded and 20% w/w antibiotic loaded PLCG 75:25 microspheres were fabricated using a Water in Oil emulsification with solvent evaporation technique. Microspheres were spherical in shape with a honeycomb-like internal matrix and showed reproducible physical properties. The kinetics of in vitro antibiotic release into newborn calf serum (NCS) and Hank's balanced salt solution (HBSS) at 37°C were measured using a radial diffusion assay. Generally, the day to day concentration of each antibiotic released into NCS over a 30 day period was in excess of that required to kill St. aureus and Ps. auruginosa. Only limited microsphere biodegradation had occurred after 30 days of in vitro incubation in NCS and HBSS at 37°C. The moderate in vitro cytotoxicity of 20% w/w antibiotic loaded microspheres to cultured 3T3-L1 cells was antibiotic induced. In conclusion, generated data indicate the potential for 20% w/w antibiotic loaded microspheres to improve the present treatment regimens for infections occurring after total hip arthroplasty such that future work should focus on gaining industrial collaboration for commercial exploitation.

Bacterial associations with salmonid eggs

Rainbow trout eggs Salmo gairdneri, Richardson, were incubated under a range of different environmental conditions. Recovery of bacteria from egg surfaces revealed that increased water temperature, slow water flow rates and high egg density all significantly increased egg surface bacterial populations. Live eggs were mainly colonized by Cytophaga sp., pseudomonas fluorescens and Aeromonas hydrophila. In contrast, dead eggs supported considerable numbers of fluorescent Pseudomonas sp. Analysis of potential nutrient sources for bacteria colonizing live egg surfaces revealed that small amounts of amino acids, phosphate and potassium may be lost by incubating eggs. Subsequently these nutrients were shown to be capable of supporting limited bacterial growth and reproduction. Dead eggs `leaked' increased amounts of the above nutrients which in turn supported higher bacterial numbers. In addition, biochemical analysis of eggs revealed amino acids and fatty acids that might be utilized by bacteria colonizing dead egg surfaces. Assessment of adhesion properties of bacteria frequently recovered from egg surfaces revealed high cell surface hydrophobicity as an important factor in successful egg colonization. Analysis of egg mortalities from groups of rainbow trout and brown trout (S.trutta L.) eggs maintained under two different incubation systems revealed that potentially a close correlation existed between egg surface bacterial numbers and mortalities in the egg during incubation. Innoculation of newly-fertilized eggs with bacteria demonstrated that groups of eggs supporting high numbers of P.fluorescens suffered significantly higher mortalities during the early part of their incubation. Exposure of incubating eggs to oxolinic acid, chlortetracycline and chloramphenicol demonstrated that numbers of bacteria on egg surfaces could be significantly reduced. However, as no corresponding increase in egg hatching success was revealed, the treatment of incubating eggs with antibiotics or antimicrobial compounds can not be recommended. In commercial hatcheries bacteria are only likely to be responsible for egg deaths during incubation when environmental conditions are unfavourable. High water temperatures, slow water flow rates and high egg density all lead to increased bacterial number of egg surfaces, reduced water circulation and low levels of dissolved oxygen. Under such circumstances sufficient amounts of dissolved oxygen may not be available to support developing embryos.

Recombinant protein subunit vaccine synthesis in microbes:a role for yeast?

Objectives Recombinant protein subunit vaccines are formulated using protein antigens that have been synthesized in heterologous host cells. Several host cells are available for this purpose, ranging from Escherichia coli to mammalian cell lines. This article highlights the benefits of using yeast as the recombinant host. Key findings The yeast species, Saccharomyces cerevisiae and Pichia pastoris, have been used to optimize the functional yields of potential antigens for the development of subunit vaccines against a wide range of diseases caused by bacteria and viruses. Saccharomyces cerevisiae has also been used in the manufacture of 11 approved vaccines against hepatitis B virus and one against human papillomavirus; in both cases, the recombinant protein forms highly immunogenic virus-like particles. Summary Advances in our understanding of how a yeast cell responds to the metabolic load of producing recombinant proteins will allow us to identify host strains that have improved yield properties and enable the synthesis of more challenging antigens that cannot be produced in other systems. Yeasts therefore have the potential to become important host organisms for the production of recombinant antigens that can be used in the manufacture of subunit vaccines or in new vaccine development.