Vairimorpha (Nosema) ceranae can promote Serratia development in honeybee gut: an underrated threat for bees?

The genus Serratia harbors opportunistic pathogenic species, among which Serratia marcescens is pathogenic for honeybees although little studied. Recently, virulent strains of S. marcescens colonizing the Varroa destructor mite's mouth were found vectored into the honeybee body, leading to septicemia and death. Serratia also occurs as an opportunistic pathogen in the honeybee's gut with a low absolute abundance. The Serratia population seems controlled by the host immune system, but its presence may represent a hidden threat, ready to arise when honeybees are weakened by biotic and abiotic stressors. To shed light on the Serratia pathogen, this research aims at studying Serratia's development dynamics in the honeybee body and its interactions with the co-occurring fungal pathogen Vairimorpha ceranae. Firstly, the degree of pathogenicity and the ability to permeate the gut epithelial barrier of three Serratia strains, isolated from honeybees and belonging to different species (S. marcescens, Serratia liquefaciens, and Serratia nematodiphila), were assessed by artificial inoculation of newborn honeybees with different Serratia doses (104, 106, and 108 cells/mL). The absolute abundance of Serratia in the gut and in the hemocoel was assessed in qPCR with primers targeting the luxS gene. Moreover, the absolute abundance of Serratia was assessed in the gut of honeybees infected with V. ceranae at different development stages and supplied with beneficial microorganisms and fumagillin. Our results showed that all tested Serratia strains could pass through the gut epithelial barrier and proliferate in the hemocoel, with S. marcescens being the most pathogenic. Moreover, under cage conditions, Serratia better proliferates when a V. ceranae infection is co-occurring, with a positive and significant correlation. Finally, fumagillin and some of the tested beneficial microorganisms could control both Serratia and Vairimorpha development. Our findings suggest a correlation between the two pathogens under laboratory conditions, a co-occurring infection that should be taken into consideration by researches when testing antimicrobial compounds active against V. ceranae, and the related honeybees survival rate. Moreover, our findings suggest a positive control of Serratia by the environmental microorganism Apilactobacillus kunkeei in a in vivo model, confirming the potential of this specie as beneficial bacteria for honeybees.

A highly specific Serratia-infecting T7-like phage inhibits biofilm formation in two different genera of the Enterobacteriaceae family.

Due to the emergence of multidrug-resistant bacteria, bacteriophages have become a viable alternative in controlling bacterial growth or biofilm formation. Biofilm is formed by extracellular polymeric substances (EPS) and is one of the factors responsible for increasing bacterial resistance. Bacteriophages have been studied as a bacterial control agent by use of phage enzymes or due to their bactericidal activities. A specific phage against Serratia marcescens was isolated in this work and was evaluated its biological and genomic aspects. The object of this study was UFV01, a bacteriophage belonging to the Podoviridae family, genus Teseptimavirus (group of lytic viruses), specific to the species S. marcescens, which may be related to several amino acid substitutions in the virus tail fibers. Despite this high specificity, the phage reduced the biofilm formation of several Escherichia coli strains without infecting them. UFV01 presents a relationship with phages of the genus Teseptimavirus, although it does not infect any of the E. coli strains evaluated, as these others do. All the characteristics make the phage an interesting alternative in biofilm control in hospital environments since small breaks in the biofilm matrix can lead to a complete collapse.

Addition of anaerobic electron acceptors to solid media did not enhance growth of 125 spacecraft bacteria under simulated low-pressure Martian conditions.

To protect Mars from microbial contamination, research on growth of microorganisms found in spacecraft assembly clean rooms under simulated Martian conditions is required. This study investigated the effects of low atmospheric pressure on the growth of chemoorganotrophic spacecraft bacteria and whether the addition of Mars relevant anaerobic electron acceptors might enhance growth. The 125 bacteria screened here were recovered from actual Mars spacecraft. Growth at 7 hPa, 0 °C, and a CO2-enriched anoxic atmosphere (called low-PTA conditions) was tested on five TSA-based media supplemented with anaerobic electron acceptors. None of the 125 spacecraft bacteria showed active growth under the tested low-PTA conditions and amended media. In contrast, a decrease in viability was observed in most cases. Growth curves of two hypopiezotolerant strains, Serratia liquefaciens and Trichococcus pasteurii, were performed to quantify the effects of the added anaerobic electron acceptors. Slight variations in growth rates were determined for both bacteria. However, the final cell densities were similar for all media tested, indicating no general preference for any specific anaerobic electron acceptor. By demonstrating that a broad diversity of chemoorganotrophic and culturable spacecraft bacteria do not grow under the tested conditions, we conclude that there may be low risk of growth of chemoorganotrophic bacteria typically recovered from Mars spacecraft during planetary protection bioburden screenings.

Combined biochar and metal-immobilizing bacteria reduces edible tissue metal uptake in vegetables by increasing amorphous Fe oxides and abundance of Fe- and Mn-oxidising Leptothrix species.

In this study, a highly effective combined biochar and metal-immobilizing bacteria (Bacillus megaterium H3 and Serratia liquefaciens CL-1) (BHC) was characterized for its effects on solution Pb and Cd immobilization and edible tissue biomass and Pb and Cd accumulation in Chinese cabbages and radishes and the mechanisms involved in metal-polluted soils. In the metal-containing solution treated with BHC, the Pb and Cd concentrations decreased, while the pH and cell numbers of strains H3 and CL-1 increased over time. BHC significantly increased the edible tissue dry weight by 17-34% and reduced the edible tissue Pb (0.32-0.46 mg kg-1) and Cd (0.16 mg kg-1) contents of the vegetables by 24-45%. In the vegetable rhizosphere soils, BHC significantly decreased the acid-soluble Pb (1.81-2.21 mg kg-1) and Cd (0.40-0.48 mg kg-1) contents by 26-47% and increased the reducible Pb (18.2-18.8 mg kg-1) and Cd (0.38-0.39 mg kg-1) contents by 10-111%; while BHC also significantly increased the pH, urease activity by 115-169%, amorphous Fe oxides content by 12-19%, and relative abundance of gene copy numbers of Fe- and Mn-oxidising Leptothrix species by 28-73% compared with the controls. These results suggested that BHC decreased edible tissue metal uptake of the vegetables by increasing pH, urease activity, amorphous Fe oxides, and Leptothrix species abundance in polluted soil. These results may provide an effective and eco-friendly way for metal remediation and reducing metal uptake in vegetables by using combined biochar and metal-immobilizing bacteria in polluted soils.

qPCR quantification of Carnobacterium maltaromaticum, Brochothrix thermosphacta, and Serratia liquefaciens growth kinetics in mixed culture.

Quantifying growth kinetics of specific spoilage microorganisms in mixed culture is required to describe the evolution of food microbiomes. A qPCR method was developed to selectively amplify individual meat spoilage bacteria, Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens, within a broth medium designed to simulate the composition of beef. An optimized method of DNA extraction was produced for standard curve construction. Method specificity was determined by individual single peaks in melt curves. Reaction efficiency for standard curves of C. maltaromaticum, B. thermosphacta and S. liquefaciens was high (R2 = 0.98-0.99), and linear quantification was achieved over a 5 log CFU/ml range. Coefficient of variation was calculated considering both threshold cycle (Ct) and bacterial concentration; the value did not exceed 14% for inter- or intra-runs for either method. Comparison of growth kinetic parameters derived from plate count and qPCR showed no significant variation (P > .05) for growth rate (GR) and maximum population density (MPD); lag phase duration (LPD) was not included in this comparison due to high innate variability. Log quantification of each isolate was validated in a mixed-culture experiment for all three species with qPCR and plate count differing less than 0.3 log CFU/ml (average 0.10 log CFU/ml, R2 = 0.98).

Effect of glucose, pH and lactic acid on Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens within a commercial heat-shrunk vacuum-package film.

Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens are common spoilage organisms found within the microbiome of refrigerated vacuum-packaged (VP) beef. Extending and predicting VP beef shelf-life requires knowledge about how spoilage bacteria growth is influenced by environmental extrinsic and intrinsic factors. Multifactorial effects of pH, lactic acid (LA) and glucose on growth kinetics were quantified for C. maltaromaticum, B. thermosphacta and S. liquefaciens within a heat shrink-wrapped VP commercial film containing a simulated beef medium. LA, pH, and undissociated lactic acid (UDLA) significantly affected bacterial growth rate (p < 0.001), whereas 5.55 mM glucose produced a marginal effect. At 1.12 mM UDLA, growth rate and maximum population density decreased 20.9 and 3.5%, 56 and 7%, and 11 and 2% for C. maltaromaticum, B. thermosphacta, and S. liquefaciens, respectively.

Transcriptomic responses of Serratia liquefaciens cells grown under simulated Martian conditions of low temperature, low pressure, and CO2-enriched anoxic atmosphere.

Results from previous experiments indicated that the Gram-negative α-proteobacterium Serratia liquefaciens strain ATCC 27592 was capable of growth under low temperature (0 °C), low pressure (0.7 kPa), and anoxic, CO2-dominated atmosphere-conditions intended to simulate the near-subsurface environment of Mars. To probe the response of its transcriptome to this extreme environment, S. liquefaciens ATCC 27592 was cultivated under 4 different environmental simulations: 0 °C, 0.7 kPa, CO2 atmosphere (Condition A); 0 °C, ~101.3 kPa, CO2 atmosphere (Condition B); 0 °C, ~101.3 kPa, ambient N2/O2 atmosphere (Condition C); and 30 °C, ~101.3 kPa, N2/O2 atmosphere (Condition D; ambient laboratory conditions). RNA-seq was performed on ribosomal RNA-depleted total RNA isolated from triplicate cultures grown under Conditions A-D and the datasets generated were subjected to transcriptome analyses. The data from Conditions A, B, or C were compared to laboratory Condition D. Significantly differentially expressed transcripts were identified belonging to a number of KEGG pathway categories. Up-regulated genes under all Conditions A, B, and C included those encoding transporters (ABC and PTS transporters); genes involved in translation (ribosomes and their biogenesis, biosynthesis of both tRNAs and aminoacyl-tRNAs); DNA repair and recombination; and non-coding RNAs. Genes down-regulated under all Conditions A, B, and C included: transporters (mostly ABC transporters); flagellar and motility proteins; genes involved in phenylalanine metabolism; transcription factors; and two-component systems. The results are discussed in the context of Mars astrobiology and planetary protection.

Listeria monocytogenes strains show large variations in competitive growth in mixed culture biofilms and suspensions with bacteria from food processing environments.

Interactions and competition between resident bacteria in food processing environments could affect their ability to survive, grow and persist in microhabitats and niches in the food industry. In this study, the competitive ability of L. monocytogenes strains grown together in separate culture mixes with other L. monocytogenes (L. mono mix), L. innocua (Listeria mix), Gram-negative bacteria (Gram- mix) and with a multigenera mix (Listeria + Gram- mix) was investigated in biofilms on stainless steel and in suspensions at 12 °C. The mixed cultures included resident bacteria from processing surfaces in meat and salmon industry represented by L. monocytogenes (n = 6), L. innocua (n = 5) and Gram-negative bacteria (n = 6; Acinetobacter sp., Pseudomonas fragi, Pseudomonas fluorescens, Serratia liquefaciens, Stenotrophomonas maltophilia). Despite hampered in growth in mixed cultures, L. monocytogenes established in biofilms with counts at day nine between 7.3 and 9.0 log per coupon with the lowest counts in the Listeria + G- mix that was dominated by Pseudomonas. Specific L. innocua inhibited growth of L. monocytogenes strains differently; inhibition that was further enhanced by the background Gram-negative microbiota. In these multispecies and multibacteria cultures, the growth competitive effects lead to the dominance of a strong competitor L. monocytogenes strain that was only slightly inhibited by L. innocua and showed strong competitive abilities in mixed cultures with resident Gram-negative bacteria. The results indicates complex patterns of bacterial interactions and L. monocytogenes inhibition in the multibacteria cultures that only partially depend on cell contact and likely involve various antagonistic and bacterial tolerance mechanisms. The study indicates large variations among L. monocytogenes in their competitiveness under multibacterial culture conditions that should be considered in further studies towards understanding of L. monocytogenes persistence in food processing facilities.

Bacteria can proliferate in thawed cryoprecipitate stored at room temperature for longer than 4 h.

Although key coagulation factor activities are maintained in thawed cryoprecipitate stored for up to 24 h at ambient temperature, several jurisdictions limit such storage to 4-6 h. Here, we separately spiked thawed cryoprecipitate units with four bacterial strains: Staphylococcus epidermidis, Serratia liquefaciens, Pseudomonas putida and Pseudomonas aeruginosa. No strains grew in the first 4 h of storage, but by 24 h, three of four exhibited up to 1000-fold proliferation. Pathogen inactivation technologies could be explored to mitigate the safety risk posed by extending storage of thawed cryoprecipitate at room temperature.

Evaluation of the spoilage potential of bacteria isolated from chilled chicken in vitro and in situ.

Microorganisms play an important role in the spoilage of chilled chicken. In this study, a total of 53 isolates, belonging to 7 species of 3 genera, were isolated using a selective medium based on the capacity to spoil chicken juice. Four isolates, namely Aeromonas salmonicida 35, Pseudomonas fluorescens H5, Pseudomonas fragi H8 and Serratia liquefaciens 17, were further characterized to assess their proteolytic activities in vitro using meat protein extracts and to evaluate their spoilage potential in situ. The in vitro studies showed that A. salmonicida 35 displayed the strongest proteolytic activity against both sarcoplasmic and myofibrillar proteins. However, the major spoilage isolate in situ was P. fragi H8, which exhibited a fast growth rate, slime formation and increased pH and total volatile basic nitrogen (TVBN) on chicken breast fillets. The relative amounts of volatile organic compounds (VOCs) originating from the microorganisms, including alcohols, aldehydes, ketones and several sulfur compounds, increased during storage. In sum, this study demonstrated the characteristics of 4 potential spoilage bacteria on chilled yellow-feather chicken and provides a simple and convenient method to assess spoilage bacteria during quality management.

[Evaluation of mixed biofilm formation between Candida albicans and a variety of bacterial species isolated from peripheral catheters at Tlemcen CHU. First study in Algeria]. / Évaluation du potentiel de formation de biofilms mixtes entre Candida albicans et quelques espèces bactériennes isolées de cathéters vasculaires périphériques au CHU de Tlemcen. Première étude en Algérie.

INTRODUCTION: Mixed-species biofilms constitute a reservoir of infection for a group of bacteria and yeasts that coexist on the same support. Peripheral venous catheters make up a good surface for the attachment of microorganisms that promote biofilm formation and this requires complex strategies for antimicrobial treatments. OBJECTIVE: No such studies on formation mixed biofilms have ever been conducted in Algeria. Therefore, we evaluated the potential for the formation of mixed-species biofilms by Candida albicans and some bacterial species isolated from peripheral vascular catheters at the University Hospital of Tlemcen, in Algeria. RESULTS: The results obtained showed that C. albicans have the potential to form mixed biofilms with three bacteria (Enterobacter cloacae, Bordetella spp. and Serratia liquefaciens) isolated from the same catheter as the yeasts. The amount of biofilms produced varies depending on the species and the composition of the growth medium. Observations by scanning electron microscopy showed that the structure of the mixed biofilm depends on the surface support the biofilm was formed on, and varies with the species. CONCLUSION: A competition was noted between bacteria and yeasts; it depends on the composition of the medium and its pH, which both play an important role in promoting the dominance of one over the other.

Quality and safety of red blood cells stored in two additive solutions subjected to multiple room temperature exposures.

BACKGROUND AND OBJECTIVES: Many international standards state that red blood cell (RBC) products should be discarded if left out of controlled temperature storage for longer than 30 min to reduce the risk of bacterial growth and RBC loss of viability. This study aimed to verify whether repeated short-time exposures to room temperature (RT) influence RBCs quality and bacterial proliferation. MATERIALS AND METHODS: Saline-adenine-glucose-mannitol (SAGM) and AS-3 RBC units were split and exposed to RT for 30 or 60 min on day 2, 7, 14, 21, and 42 of storage while reference units remained stored at 1-6°C. Red blood cell in vitro quality parameters were evaluated after each exposure. In a second experiment, SAGM and AS-3 RBC units were split and inoculated with Staphylococcus epidermidis (5 CFU/ml), Serratia marcescens (1 CFU/ml), and Serratia liquefaciens (1 CFU/ml). Reference units remained in storage while test units were exposed as described previously. Bacterial concentrations were investigated after each exposure. RESULTS: No differences were noticed between reference and test units in any of the in vitro parameters investigated. S. epidermidis did not grow in either reference or exposed RBCs. While S. marcescens did not grow in AS-3, bacterial growth was observed in RT-exposed SAGM RBCs on day 42. Similar growth was obtained for S. liquefaciens in the two additive solutions for both reference and test units. CONCLUSION: Short-time exposures to RT do not affect RBC quality and do not significantly influence bacterial growth. An expansion of the '30-minute' rule to 60 min should be considered by regulatory agencies.

Inactivation of Serratia liquefaciens on dry-cured ham by high pressure processing.

To quantify the inactivation of Serratia liquefaciens exerted by high pressure processing (HPP), slices of dry-cured ham were inoculated and processed combining different levels of technological parameters: pressure (347-852 MPa), time (2.3-15.8 min) and temperature (7.6-24.4 °C) according to a central composite design. Bacterial inactivation, as logarithmic reduction, indicated that S. liquefaciens was relatively sensitive to HPP. Six log reductions were achieved in a total of 10 trials combining pressures of 600 MPa or above with different holding times and temperatures. The inactivation of S. liquefaciens was analysed through the multiple regression analysis to generate a second order polynomial equation. Pressure and time were the two factors which significantly determined the inactivation of S. liquefaciens on dry-cured ham. Temperature did not significantly affect the lethality of the process. The response surface methodology was used to determine optimum process conditions to maximize the inactivation of S. liquefaciens in the experimental range tested. The maximum inactivation of S. liquefaciens in dry-cured ham was achieved by combining a pressure of 650 MPa with a holding time of 8 min. Combinations above these values (i.e. 750 MPa for 13 min) would not significantly improve the lethality of the process.

Growth of Serratia liquefaciens under 7 mbar, 0°C, and CO2-enriched anoxic atmospheres.

Twenty-six strains of 22 bacterial species were tested for growth on trypticase soy agar (TSA) or sea-salt agar (SSA) under hypobaric, psychrophilic, and anoxic conditions applied singly or in combination. As each factor was added to multi-parameter assays, the interactive stresses decreased the numbers of strains capable of growth and, in general, reduced the vigor of the strains observed to grow. Only Serratia liquefaciens strain ATCC 27592 exhibited growth at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres. To discriminate between the effects of desiccation and hypobaria, vegetative cells of Bacillus subtilis strain 168 and Escherichia coli strain K12 were grown on TSA surfaces and simultaneously in liquid Luria-Bertani (LB) broth media. Inhibition of growth under hypobaria for 168 and K12 decreased in similar ways for both TSA and LB assays as pressures were reduced from 100 to 25 mbar. Results for 168 and K12 on TSA and LB are interpreted to indicate a direct low-pressure effect on microbial growth with both species and do not support the hypothesis that desiccation alone on TSA was the cause of reduced growth at low pressures. The growth of S. liquefaciens at 7 mbar, 0°C, and CO2-enriched anoxic atmospheres was surprising since S. liquefaciens is ecologically a generalist that occurs in terrestrial plant, fish, animal, and food niches. In contrast, two extremophiles tested in the assays, Deinococcus radiodurans strain R1 and Psychrobacter cryohalolentis strain K5, failed to grow under hypobaric (25 mbar; R1 only), psychrophilic (0°C; R1 only), or anoxic (< 0.1% ppO2; both species) conditions.

Evaluating the 4-hour and 30-minute rules: effects of room temperature exposure on red blood cell quality and bacterial growth.

BACKGROUND: A 30-minute rule was established to limit red blood cell (RBC) exposure to uncontrolled temperatures during storage and transportation. Also, RBC units issued for transfusion should not remain at room temperature (RT) for more than 4 hours (4-hour rule). This study was aimed at determining if single or multiple RT exposures affect RBC quality and/or promote bacterial growth. STUDY DESIGN AND METHODS: Growth and RT exposure experiments were performed in RBCs inoculated with Serratia liquefaciens and Serratia marcescens. RBCs were exposed once to RT for 5 hours (S. liquefaciens) or five times to RT for 30 minutes (S. marcescens) with periodic sampling for bacterial counts. Noncontaminated units were exposed to RT once (5 hr) or five times (30 min each) and sampled to measure in vitro quality variables. RBC core temperature was monitored using mock units with temperature loggers. Growth and RT exposure experiments were repeated three and at least six times, respectively. Statistical analysis was done using mixed-model analysis. RESULTS: RBC core temperature ranged from 7.3 to 11.6°C during 30-minute RT exposures and the time to reach 10°C varied from 22 to 55 minutes during 5-hour RT exposures. RBC quality was preserved after single or multiple RT exposures. Increased growth of S. liquefaciens was only observed after 2 hours of continuous RT exposure. S. marcescens concentration increased significantly in multiple-exposed units compared to the controls but did not reach clinically important levels. CONCLUSION: Single or multiple RT exposures did not affect RBC quality but slightly promoted bacterial growth in contaminated units. The clinical significance of these results remains unclear and needs further investigation.

Sensory characteristics of spoilage and volatile compounds associated with bacteria isolated from cooked and peeled tropical shrimps using SPME-GC-MS analysis.

The spoilage potential of six bacterial species isolated from cooked and peeled tropical shrimps (Brochothrix thermosphacta, Serratia liquefaciens-like, Carnobacterium maltaromaticum, Carnobacterium divergens, Carnobacterium alterfunditum-like and Vagococcus penaei sp. nov.) was evaluated. The bacteria were inoculated into shrimps, packaged in a modified atmosphere and stored for 27 days at 8 °C. Twice a week, microbial growth, as well as chemical and sensory changes, were monitored during the storage period. The bacteria mainly involved in shrimp spoilage were B. thermosphacta, S. liquefaciens-like and C. maltaromaticum whose main characteristic odours were cheese-sour, cabbage-amine and cheese-sour-butter, respectively. The volatile fraction of the inoculated shrimp samples was analysed by solid-phase microextraction (SPME) and gas chromatography coupled to mass spectrometry (GC-MS). This method showed that the characteristic odours were most likely induced by the production of volatile compounds such as 3-methyl-1-butanal, 2,3-butanedione, 2-methyl-1-butanal, 2,3-heptanedione and trimethylamine.

Intraspecific genotypic richness and relatedness predict the invasibility of microbial communities.

Biological invasions can lead to extinction events in resident communities and compromise ecosystem functioning. We tested the effect of two widespread biodiversity measurements, genotypic richness and genotypic dissimilarity on community invasibility. We manipulated the genetic structure of bacterial communities (Pseudomonas fluorescens) and submitted them to invasion by Serratia liquefaciens. We show that the two diversity measures impact on invasibility via distinct and additive mechanisms. Genotypic dissimilarity of the resident communities linearly increased productivity and in parallel decreased invasion success, indicating that high dissimilarity prevents invasion through niche pre-emption. By contrast, genotypic richness exerted a hump-shaped effect on invasion and was linked to the production of toxins antagonistic to the invader. This effect peaked at intermediate richness, suggesting that high richness levels may increase invasibility. Invasibility could be well predicted by the combination of these two mechanisms, documenting that both genotypic richness and dissimilarity need to be considered, if we are to understand the biotic properties determining the susceptibility of ecosystems to biological invasions.

Effect of platelet additive solution on bacterial dynamics and their influence on platelet quality in stored platelet concentrates.

BACKGROUND: Platelet additive solutions (PASs) are an alternative to plasma for the storage of platelet concentrates (PCs). However, little is known about the effect of PAS on the growth dynamics of contaminant bacteria. Conversely, there have been no studies on the influence of bacteria on platelet (PLT) quality indicators when suspended in PAS. STUDY DESIGN AND METHODS: Eight buffy coats were pooled, split, and processed into PCs suspended in either plasma or PAS (SSP+, MacoPharma). PCs were inoculated with 10 and 100 colony-forming units (CFUs)/bag of either Serratia liquefaciens or Staphylococcus epidermidis. Bacterial growth was measured over 5 days by colony counts and bacterial biofilm formation was assayed by scanning electron microscopy and crystal violet staining. Concurrently, PLT markers were measured by an assay panel and flow cytometry. RESULTS: S. liquefaciens exhibited an apparent slower doubling time in plasma-suspended PCs (plasma-PCs). Biofilm formation by S. liquefaciens and S. epidermidis was significantly greater in PCs stored in plasma than in PAS. Although S. liquefaciens altered several PLT quality markers by Days 3 to 4 postinoculation in both PAS- and plasma-PCs, S. epidermidis contamination did not produce measurable PLT changes. CONCLUSIONS: S. liquefaciens can be detected more quickly in PAS-suspended PCs (PAS-PCs) than in plasma-PCs by colony counting. Furthermore, reduced biofilm formation by S. liquefaciens and S. epidermidis during storage in PAS-PCs increases bacteria availability for sampling detection. Culture-based detection remains the earliest indicator of bacterial presence in PAS-PCs, while changes of PLT quality can herald S. liquefaciens contamination when in excess of 10(8) CFUs/mL.

Effects of simulated Mars conditions on the survival and growth of Escherichia coli and Serratia liquefaciens.

Escherichia coli and Serratia liquefaciens, two bacterial spacecraft contaminants known to replicate under low atmospheric pressures of 2.5 kPa, were tested for growth and survival under simulated Mars conditions. Environmental stresses of high salinity, low temperature, and low pressure were screened alone and in combination for effects on bacterial survival and replication, and then cells were tested in Mars analog soils under simulated Mars conditions. Survival and replication of E. coli and S. liquefaciens cells in liquid medium were evaluated for 7 days under low temperatures (5, 10, 20, or 30 degrees C) with increasing concentrations (0, 5, 10, or 20%) of three salts (MgCl(2), MgSO(4), NaCl) reported to be present on the surface of Mars. Moderate to high growth rates were observed for E. coli and S. liquefaciens at 30 or 20 degrees C and in solutions with 0 or 5% salts. In contrast, cell densities of both species generally did not increase above initial inoculum levels under the highest salt concentrations (10 and 20%) and the four temperatures tested, with the exception that moderately higher cell densities were observed for both species at 10% MgSO(4) maintained at 20 or 30 degrees C. Growth rates of E. coli and S. liquefaciens in low salt concentrations were robust under all pressures (2.5, 10, or 101.3 kPa), exhibiting a general increase of up to 2.5 orders of magnitude above the initial inoculum levels of the assays. Vegetative E. coli cells were maintained in a Mars analog soil for 7 days under simulated Mars conditions that included temperatures between 20 and -50 degrees C for a day/night diurnal period, UVC irradiation (200 to 280 nm) at 3.6 W m(-2) for daytime operations (8 h), pressures held at a constant 0.71 kPa, and a gas composition that included the top five gases found in the martian atmosphere. Cell densities of E. coli failed to increase under simulated Mars conditions, and survival was reduced 1 to 2 orders of magnitude by the interactive effects of desiccation, UV irradiation, high salinity, and low pressure (in decreasing order of importance). Results suggest that E. coli may be able to survive, but not grow, in surficial soils on Mars.

Unexplained agglutination of stored red blood cells in Alsever's solution caused by the gram-negative bacterium Serratia liquefaciens.

Alsever's solution has been used for decades as a preservative solution for storage of RBCs. From October 2005 to January 2006, unexplained hemagglutination of approximately 10 to 20 percent of RBCs stored for several days in a modified version of Alsever's solution was noticed in quality control testing at the Canadian Blood Services Serology Laboratory. An investigation, including microbial testing, was initiated to determine the cause of the unexplained hemagglutination. The gram-negative bacterium Serratia liquefaciens was isolated from supernatant solutions of agglutinated RBCs. Further characterization of this strain revealed that it has the ability to form biofilms; presents high levels of resistance to chloramphenicol, neomycin, and gentamicin; and causes mannose-sensitive hemagglutination. The source of S. liquefaciens contamination in RBC supernatants was not found. However, this bacterium has not been isolated since January 2006 after enhanced cleaning practices were implemented in the serology laboratory where the RBCs are stored. This biofilm-forming, antibiotic-resistant S. liquefaciens strain could be directly linked to the unexplained hemagglutination observed in stored RBCs.