Serratia marcescens is a gram-negative environmental bacterium and opportunistic pathogen. S. marcescens expresses prodigiosin, a bright red and cell-associated pigment which has no known biological function for producing cells. We present here a kinetic model relating cell, ATP, and prodigiosin concentration changes for S. marcescens during cultivation in batch culture. Cells were grown in a variety of complex broth media at temperatures which either promoted or essentially prevented pigmentation. High growth rates were accompanied by large decreases in cellular prodigiosin concentration; low growth rates were associated with rapid pigmentation. Prodigiosin was induced most strongly during limited growth as the population transitioned to stationary phase, suggesting a negative effect of this pigment on biomass production. Mathematically, the combined rate of formation of biomass and bioenergy (as ATP) was shown to be equivalent to the rate of prodigiosin production. Studies with cyanide inhibition of both oxidative phosphorylation and pigment production indicated that rates of biomass and net ATP synthesis were actually higher in the presence of cyanide, further suggesting a negative regulatory role for prodigiosin in cell and energy production under aerobic growth conditions. Considered in the context of the literature, these results suggest that prodigiosin reduces ATP production by a process termed energy spilling. This process may protect the cell by limiting production of reactive oxygen compounds. Other possible functions for prodigiosin as a mediator of cell death at population stationary phase are discussed.Serratia marcescens is a ubiquitous environmental bacterium which has been isolated from soil, water, and insects (6). This organism has emerged as an important nosocomial pathogen associated with respiratory infections, urinary tract infections, sepsis, wound infections, and conjunctivitis among wearers of contact lenses (13,19,27). Environmental isolates of S. marcescens express the red, cell-associated pigment prodigiosin, but identification of most clinical isolates must rely on other biochemical markers because the majority are not pigmented (13,27).Prodigiosin has been traditionally known as a secondary metabolite: it has no clearly defined function in cellular metabolism (4). Several physiological processes in S. marcescens, including prodigiosin pigmentation and biofilm formation, are activated at high cell density by quorum-sensing mechanisms (26,28,30). Low phosphate concentrations and temperatures below 37°C favor strong pigmentation (29). At least 12 pigmentation (pig) genes (A through J; M and N), arranged as part of a larger pig operon, encode enzymes for prodigiosin biosynthesis. In addition, a suite of regulatory proteins provides fine genetic control at the level of transcription. Quorum-sensing regulation of pig operon expression is mediated by SmaR and SmaI (secondary metabolite activator) (24, 25). SmaR is a repressor with DNA binding activity (8); transcriptional repression is mi...

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Persistent small-cell lymphocytosis in dogs with a concurrent mediastinal mass has been associated with both thymoma and small-cell lymphoma. In thymomas, neoplastic thymic epithelial cells induce overproduction and release of polyclonal lymphocytes, whereas thymic lymphoma results in thymic effacement by a clonal expansion of neoplastic lymphocytes and subsequent leukemic phase of lymphoma. Flow cytometry has been used to differentiate these 2 entities by immunophenotyping mediastinal mass aspirates. It has been reported that cases with mediastinal masses in which ≥ 10% of the associated small-cell lymphocytes were double positive for CD4 and CD8 were thymomas, whereas masses associated with < 10% were suggestive of lymphoma. We report a unique case of thymoma-associated lymphocytosis lacking the classic CD4+CD8+ immunophenotype. Our findings suggest that there may be more diversity in the thymoma-associated lymphocyte immunophenotype than has been identified previously; immunophenotyping alone might not be sufficient to differentiate thymic small-cell lymphoma from thymoma-associated lymphocytosis. In dogs with mediastinal masses and peripheral lymphocytosis, employing a variety of testing modalities to avoid misdiagnosis is prudent. These modalities include cytologic and/or histologic evaluation, immunophenotyping, and clonality assessment.

Background: Neonatal foals are born essentially agammaglobulinemic and therefore must ingest colostrum or receive immunoglobulins to maintain health. Failure of passive transfer treatment involves administration of equine colostrum, plasma or commercial powdered colostrum (CPC). Anecdotal reports suggest a risk of anaphylaxis associated with plasma transfusion in neonates that received CPC prior to gut closure. Bovine serum albumin (BSA) in CPC may serve as a target for BSA-specific immunoglobulin E (IgE) in donor equine plasma. Objectives: To determine presence of BSA-specific IgE in samples collected post-routine vaccination in healthy horses, horses experiencing adverse vaccine reactions and commercial equine plasma. Study Design: Prospective Observational Methods: Serum was collected from 65 healthy horses at day 0, 14, 28, 90, 180, 270 and 365 post-vaccination, 26 horses after vaccine reaction at day 1, 180 or 270 post-vaccination, 4 horses not vaccinated and 10 horses from a commercial plasma donor herd. BSA-specific IgE was determined using enzyme-linked immunosorbent assay (ELISA). Results: BSA-specific IgE was not detected in non-vaccinated horses and was identified in all vaccinated horses. Younger horses demonstrated higher fold changes in post-vaccination BSA-specific IgE expression compared to older horses. No significant difference in BSA-specific IgE levels between commercial plasma donors and healthy horses was identified. No significant difference in post-vaccination anti-BSA IgE levels between reactor and healthy horses at day 180 and 270 post-vaccination were identified. Main Limitations: Small number of reactor horses at day 180 and 270 post-vaccination with most samples being collected 24 hours. There were no healthy horse samples for 24 hours post-vaccination; therefore, it was not possible to compare the two groups at this timepoint. Conclusions: Horses may express BSA specific IgE following vaccination. There may be risk of hypersensitivity type reaction when veterinarians administer commercial plasma to neonatal foals that have consumed CPC prior to gut closure.

SummaryBackgroundNeonatal foals are born essentially agammaglobulinaemic and therefore must ingest colostrum or receive immunoglobulins to maintain health. Failure of passive transfer treatment involves administration of equine colostrum, plasma or commercial powdered colostrum (CPC). Anecdotal reports suggest the risk of anaphylaxis associated with plasma transfusion in neonates receiving CPC prior to gut closure. Bovine serum albumin (BSA) in CPC may serve as a target for BSA‐specific immunoglobulin E (IgE) in donor equine plasma.ObjectivesTo determine the presence of BSA‐specific IgE in samples of commercial equine plasma, samples were collected following routine vaccination in healthy horses and horses experiencing adverse vaccine reactions.Study designProspective observational.MethodsSerum was collected from: 65 healthy horses at days 0, 14, 28, 90, 180, 270 and 365 post‐vaccination; 26 horses after vaccine reaction at days 1, 180 or 270 post‐vaccination; 4 horses not vaccinated; and 9 horses from a commercial plasma donor herd. BSA‐specific IgE was determined using enzyme‐linked immunosorbent assay.ResultsBovine serum albumin‐specific IgE was not detected in non‐vaccinated horses and was identified in all vaccinated horses. Younger horses demonstrated a trend for higher fold changes in post‐vaccination BSA‐specific IgE expression compared to older horses. No significant difference in BSA‐specific IgE levels between commercial plasma donors and healthy horses was identified. No significant difference in post‐vaccination BSA‐specific IgE levels between the reactor and healthy horses at days 180 and 270 post‐vaccination were identified.Main limitationsSmall number of reactor horses at day 180 and 270 post‐vaccination with most samples being collected 24 h. There were no healthy horse samples for 24 h post‐vaccination; therefore, it was not possible to compare the groups at this timepoint.ConclusionsHorses may express BSA‐specific IgE following vaccination. There may be a risk of hypersensitivity type reaction when veterinarians administer commercial plasma to neonatal foals consuming CPC prior to gut closure.