Extending the 30-minute rule for red cell units - investigation of the bacterial risk of 60-minute exposures to ambient temperature.

BACKGROUND AND OBJECTIVES: In the UK, a significant proportion of red cell units is discarded due to the 30-min rule governing out of temperature control. Studies have shown that repeated warming to ambient temperature has little impact on red cell quality or bacterial growth. We aimed to validate extension of the rule to 60 minutes by investigation of repeated same, and different, day exposures on bacterial growth. MATERIALS AND METHODS: Red cell units were seeded individually at 100-1000 cfu/ml with Yersinia enterocolitica, Serratia liquefaciens, Pseudomonas putida, Staphylococcus epidermidis, Enterobacter cloacae and Bacillus cereus. Test units were exposed to 30°C for 30 or 60 min on a single occasion at days 15, 17 and 21, or thrice on day 15 of a 35-day storage period. A 10-fold increase in bacterial counts in tests versus controls maintained in cold storage was considered indicative of significant bacterial proliferation. RESULTS: Exposure of units to 30°C for up to 60 min had no substantial impact on the growth of bacteria and all mesophiles declined steadily in tests and controls. Only P. putida showed a near significant elevation in count on exposure for 60 min at day 35. CONCLUSIONS: Extension of the out of temperature rule for red cells to 60 min will potentially not compromise patient safety, although exposures to ambient temperatures should be minimized. Units returned to storage must not be reissued for at least 6 hours and not be exposed to ambient temperatures on more than three occasions.

Serratia liquefaciens KM4 Improves Salt Stress Tolerance in Maize by Regulating Redox Potential, Ion Homeostasis, Leaf Gas Exchange and Stress-Related Gene Expression.

High salinity mitigates crop productivity and quality. Plant growth-promoting soil rhizobacteria (PGPR) improve plant growth and abiotic stress tolerance via mediating various physiological and molecular mechanisms. This study investigated the effects of the PGPR strain Serratia liquefaciens KM4 on the growth and physiological and molecular responsiveness of maize (Zea mays L.) plants under salinity stress (0, 80, and 160 mM NaCl). High salinity significantly reduced plant growth and biomass production, nutrient uptake, leaf relative water content, pigment content, leaf gas exchange attributes, and total flavonoid and phenolic contents in maize. However, osmolyte content (e.g., soluble proteins, proline, and free amino acids), oxidative stress markers, and enzymatic and non-enzymatic antioxidants levels were increased in maize under high salinity. On the other hand, Serratia liquefaciens KM4 inoculation significantly reduced oxidative stress markers, but increased the maize growth and biomass production along with better leaf gas exchange, osmoregulation, antioxidant defense systems, and nutrient uptake under salt stress. Moreover, it was found that all these improvements were accompanied with the upregulation of stress-related genes (APX, CAT, SOD, RBCS, RBCL, H⁺-PPase, HKT1, and NHX1), and downregulation of the key gene in ABA biosynthesis (NCED). Taken together, the results demonstrate the beneficial role of Serratia liquefaciens KM4 in improving plant growth and salt stress tolerance in maize by regulating ion homeostasis, redox potential, leaf gas exchange, and stress-related genes expression.

Interaction of macrophages with a cytotoxic Serratia liquefaciens human isolate.

Macrophages play key roles in host defense by recognizing, engulfing, and killing microorganisms. Understanding the response of macrophages to pathogens may provide insights into host defenses and the tactics used by pathogens to circumvent these defenses. In the present study, we investigated the interaction between a clinical isolate of Serratia liquefaciens and macrophages. S. liquefaciens strain HUMV-3250 triggers a fast and potent cytotoxic effect upon infection. This process requires the presence of live bacteria, adherence, and protein synthesis but not phagocytosis/bacterial internalization. Moreover, cytotoxicity assays, analysis of DNA integrity, immunofluorescence, and confocal, scanning, and time-lapse microscopy revealed that macrophage viability decreased rapidly with time upon challenge, and depends on the MOI used. Treatment of macrophages with caspase-1 inhibitors, or with specific inhibitors of phagocytosis, did not alter the infection outcome. Moreover, human macrophages exhibited similar cytotoxic changes after infection with this strain. Macrophages responded to this cytotoxic strain with a robust pattern of pro-inflammatory gene expression. However, phagocytosis attempts to engulf live bacteria were unsuccessful, and the phagocytes were unable to kill the bacteria. We conclude that macrophage cell death occurs rapidly as a result of necrotic events after close contact with S. liquefaciens. These results likely have important implications for understanding Serratia pathogenesis and host response to infection.

Estimating disease resistance in insects: phenoloxidase and lysozyme-like activity and disease resistance in the cricket Gryllus texensis.

An animal's ability to resist disease is usually estimated by measuring one or more components of the immune system. There is an assumption that these assays of immunity measure an animal's ability to mount an effective immune response. This paper tests this assumption by examining the relationship between two common estimates of insect immunocompetence, phenoloxidase and lysozyme-like enzyme activity, and resistance to three common insect bacterial pathogens: Serratia marcescens, Serratia liquefaciens, and Bacillus cereus. There was a correlation (Spearman's rs=0.33, p<0.001, n=190 pairs) between total phenoloxidase and baseline lysozyme-like activity within individuals. However, total phenoloxidase and baseline lysozyme-like activity levels did not predict which male crickets would survive any of the three bacterial challenges. Lysozyme-like activity increased after an immune challenge (Friedman, 33.72, p<0.001), and the greater the increase, the greater the chance that the cricket would survive S. marcescens (slope=0.15, chi 2=8.2, p=0.005) or B. cereus (slope=0.8, chi 2=6.4, p=0.01). The crickets with a greater total hemolymph protein concentration were also more likely to survive a challenge with any of the three bacterial pathogens than the crickets with lower total hemolymph protein concentrations (S. liquefaciens: slope=0.02, chi 2=9.2, p=0.002; B. cereus: slope=0.02, chi 2=6.5, p=0.01; S. marcescens: slope=0.03, chi 2=7.8, p=0.005). Because of the complexity of the immune system, empirical tests of the relationship between assays of immunity and resistance to a range of actual pathogens are important for correctly interpreting these measures.

The Yersinia HPI is present in Serratia liquefaciens isolated from meat.

AIMS: The aim of the study was to screen the Enterobacteriaceae flora of meat for the presence of bacteria harbouring the Yersinia high-pathogenicity island (HPI). METHODS AND RESULTS: Bacteria from 29 meat and 29 liver samples were isolated on violet-red bile glucose agar. A total of 197 isolates were screened for the presence of the irp2 gene, encoded within the HPI, by PCR. One isolate that was positive for irp2 gene was also positive for the fyuA, irp1, ybtP/ybtQ, ybtX/ybtS and int/asn tRNA genes by PCR. The presence of fyuA, irp1 and irp2 genes was confirmed by Southern hybridization. CONCLUSIONS: The isolate was identified as Serratia liquefaciens by sequencing of the 16S rRNA gene and by ribotyping. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of a Serratia harbouring the Yersinia HPI. Serratia is a frequently occurring Enterobacteriaceae genus in chill-stored meat.