Diauxic lags explain unexpected coexistence in multi-resource environments

How the coexistence of species is affected by the presence of multiple resources is a major question in microbial ecology. We experimentally demonstrate that differences in diauxic lags, which occur as species deplete their own environments and adapt their metabolisms, allow slow-growing microbes to stably coexist with faster-growing species in multi-resource environments despite being excluded in single-resource environments. In our focal example, an Acinetobacter species (Aci2) competitively excludes Pseudomonas aurantiaca (Pa) on alanine and on glutamate. However, they coexist on the combination of both resources. Experiments reveal that Aci2 grows faster but Pa has shorter diauxic lags. We establish a tradeoff between Aci2's fast growth and Pa's short lags as their mechanism for coexistence. We model this tradeoff to accurately predict how environmental changes affect community composition. We extend our work by surveying a large set of competitions and observe coexistence nearly three times as frequently when the slow-grower is the fast-switcher. Our work illustrates a potentially common mechanism for the emergence of multi-resource coexistence despite single-resource competitive exclusions.

Large radicular cyst with both buccal and palatal cortical bones perforation secondary to vital pulp therapy failure

Radicular cyst as the most common odontogenic cyst usually arises from residual epithelial cells stimulated by inflammatory factors initiating by pulpal necrosis of a non-vital tooth. Radicular cyst is commonly asymptomatic, slow grower, and rarely invade near bony structures. Many treatment approaches are presented for a radicular cyst like surgical endodontic treatment, tooth extraction, enucleation, and marsupialization. In this case treatment plan compromised with root canal therapy and surgical enucleation of cystic lesion. This case report presents a large radicular cyst in a vital maxillary first molar with only one necrotic root canal secondary to direct pulp capping with mineral trioxide aggregate with buccal and palatal cortical bone perforation.

Propagation of Taxus baccata ‘Green Diamond’ by cutting

Buxus sempervirens and its varieties, such as ’Suffruticosa’, are popular plants of historic as well as modem gardens. The box tree moth (Cydalima perspectalis), one of its most aggressive pests, also appeared in Hungary in 2011. Taxus baccata is also a species with a great tradition in historic gardens. This species has outstanding longevity, a good self-renewing capacity and is easy to handle. It can create a dense and solid surface that could serve as a green wall or an excellent background to colourful shrubs and blooming plants. The ’Green Diamond’ variety of Taxus baccata boasting a spherical habit similar to Buxus sempervirens ’Suffruticosa’ is a slow-grower with small, dark green leaves and would be suitable to replace ’Suffruticosa’. It tolerates pmning well and has a good renewing capacity. Taxus baccata ’Green Diamond’ is currently propagated by grafting in Western European ornamental tree nurseries, which is however a costly and slow propagation method. As part of our work, we set the aim to work out the propagation method for Taxus baccata ’Green Diamond’ by cuttings. As part of our work, we examined the propagation of Taxus baccata ’Green Diamond’ by cutting in various plant growth mediums with the application of root stimulants in different concentrations.

Unusual Presentation for Unusual Infection: Disseminated Mycobacterium Avium-Intracellulare complex (MAC) in Patient with Sickle Cell Anemia Mimicking Blood Transfusion Reaction

Nontuberculous mycobacteria (NTM) are ubiquitous free living soil and water– borne organisms that cause numerous clinical syndromes including lymphadenitis, skin, soft tissue and pulmonary infections, however disseminated infection is almost exclusively in patient with severe immunocompromise (i.e:HIV, Hematological malignancy, and bone marrow transplant). Mycobacterium avium complex (MAC) is hard to diagnose as it is considered slow grower NTM. We describe a case of disseminated Mycobacterium avium-intracellulare complex infection in teenager with sickle hemoglobinopathy with unique presentation mimicking pRBCs transfusion reaction. Patient presented on three different occasions with tachycardia, hypotension and fever within 2-24 hours following pRBCs pheresis, all three episodes were investigated and were negative for transfusion reactions. Patient had central venous catheter (CVC), frequent admissions for vaso-occlusive painful episode, on hydrocortisone for adrenal insufficiency and off Hydroxyurea for two months. Diagnosis of mycobacterium avium complex bacteremia was confirmed by two positive blood cultures, whole body CT scan showed liver nodules, spleen nodules and lung nodules. Pulmonary dissemination was confirmed by Biopsy and culture, Lymphocyte markers showed severe lymphopenia with absolute CD4 count of 64. Patient underwent treatment with three month of four antibiotics followed by 9 months of three antibiotics with removal of the central line, follow up scan showed decrease size and numbers of nodules, patient started tolerating pheresis within one month of the antibiotics initiation. NTM infection should be added to the list of pathogens in sickle cell patients with CVCs and fever and should be considered in frequent pRBC transfusion like reaction with negative workup. Routine blood culture can identify rapid growing NTM but specific mycobacterial blood culture is required in case of other NTM species (slow grower). As dissemination almost always occurs in those with impaired cellular immunity, HIV testing and lymphocyte markers should be performed Removal of involved CVCs is essential for the treatment as well as appropriate antimicrobial medications. Disclosures No relevant conflicts of interest to declare.

Characterization of the growth dynamics and biofilm formation of Staphylococcus epidermidis strains isolated from contaminated platelet units

Bacterial contamination of platelet concentrates (PCs) poses the highest transfusion-associated infectious risk, with Staphylococcus epidermidis being a predominant contaminant. Herein, the growth dynamics of 20 S. epidermidis strains in PCs and regular media were characterized. Strains were categorized as fast (short lag phase) or slow (long lag phase) growers in PCs. All strains were evaluated for the presence of the biofilm-associated icaAD genes by PCR, their capability to produce extracellular polysaccharide (slime) on Congo red agar plates and their ability to form surface-attached aggregates (biofilms) in glucose-supplemented trypticase soy broth (TSBg) using a crystal violet staining assay. A subset of four strains (two slow growers and two fast growers) was further examined for the ability for biofilm formation in PCs. Two of these strains carried the icAD genes, formed slime and produced biofilms in TSBg and PCs, while the other two strains, which did not carry icaAD, did not produce slime or form biofilms in TSBg. Although the two ica-negative slime-negative strains did not form biofilms in media, they displayed a biofilm-positive phenotype in PCs. Although all four strains formed biofilms in PCs, the two slow growers formed significantly more biofilms than the fast growers. Furthermore, growth experiments of the two ica-positive strains in plasma-conditioned platelet bags containing TSBg revealed that a slow grower isolate was more likely to escape culture-based screening than a fast grower strain. Therefore, this study provides novel evidence that links S. epidermidis biofilm formation with slow growth in PCs and suggests that slow-growing biofilm-positive S. epidermidis would be more likely to be missed with automate culture.

Measurement and modelling of ordinary heterotrophic organism active biomass concentrations in anoxic/aerobic activated sludge mixed liquor

Ordinary heterotrophic organism (OHO) active biomass (ZBH) is a key parameter in models for activated sludge systems, which defines quantitatively the kinetic rates of relevant processes. However, ZBH has not been measured directly with consistent success: a simple respirometric batch test has provided varying correspondence between measured and theoretical concentrations. In this paper, the batch test is applied to mixed liquors drawn from well defined anoxic/aerobic parent systems at 10 and 20 d sludge ages, with consistent but poor correspondence between measured and theoretical values. In contrast, aerobic digestion batch tests on the same mixed liquors give good correspondences. It is concluded that the differences between theoretical and batch test measured values are due to the batch test method itself and its interpretation. It is found that the batch test conditions (particularly the substrate/ZBH ratio) influence the kinetic constants derived from the data, and hence the ZBH estimate. Two kinetic models with two competing OHO populations, a fast and a slow grower, are developed and applied to the batch tests and parent systems. The first model is based on kinetic selection only, while the second includes additional metabolic selection. Both models can account for the observations in the batch tests, but the second provides greater consistency between simulations of the parent systems and batch tests.

The Mycobactericidal Efficacy of Ortho-Phthalaldehyde and the Comparative Resistances of Mycobacterium bovis, Mycobacterium terrae, and Mycobacterium chelonae

Objectives:To assess the mycobactericidal efficacy of an agent relatively new to disinfection, ortho-phthalaldehyde (OPA) and to compare the resistances of threeMycobacteriumspecies.Mycobacterium bovis(strain BCG) was compared withMycobacterium chelonaeandMycobacterium terraeto investigate the feasibility of using either of the latter two species in tuberculocidal testing.M chelonae(a rapid grower) andM terrae(an intermediate grower) both grow faster and are less virulent thanM bovis(a slow grower).Design:The quantitative suspension protocol specified by the Environmental Protection Agency (EPA), the Tuberculocidal Activity Test Method (EPA test), was used throughout this study. Standard suspensions of all three species were prepared in a similar manner. Two suspensions ofM bovis,created in different laboratories, were used. These were tested against two concentrations of alkaline glutaraldehyde to provide reference data. Two concentrations of OPA were evaluated against all mycobacterial test suspensions. Four replicates of each organism-disinfectant combination were performed.Results:Results were assessed by analysis of variance.M terraewas significantly more resistant to 0.05% OPA than eitherM bovisorM chelonae.At 0.21% OPA,M terraewas slightly more susceptible than one test suspension ofM bovis,but not significantly different from the other.M chelonaewas significantly less resistant than the other species at both OPA concentrations. At their respective minimum effective concentration, OPA achieved a 6-log10 reduction ofM bovisin nearly one sixth the time required by glutaraldehyde (5.5 minutes vs 32 minutes).Conclusions:These data, along with other recent studies, lend support to the idea thatM terraemay be a suitable test organism for use in the tuberculocidal efficacy testing of disinfectants. They also confirm the relatively rapid tuberculocidal activity of OPA.