Functional genomics reveals the toxin-antitoxin repertoire and AbiE activity in Serratia

Bacteriophage defences are divided into innate and adaptive systems. Serratia sp. ATCC 39006 has three CRISPR-Cas adaptive immune systems, but its innate immune repertoire is unknown. Here, we re-sequenced and annotated the Serratia genome and predicted its toxin-antitoxin (TA) systems. TA systems can provide innate phage defence through abortive infection by causing infected cells to 'shut down', limiting phage propagation. To assess TA system function on a genome-wide scale, we utilized transposon insertion and RNA sequencing. Of the 32 TA systems predicted bioinformatically, 4 resembled pseudogenes and 11 were demonstrated to be functional based on transposon mutagenesis. Three functional systems belonged to the poorly characterized but widespread, AbiE, abortive infection/TA family. AbiE is a type IV TA system with a predicted nucleotidyltransferase toxin. To investigate the mode of action of this toxin, we measured the transcriptional response to AbiEii expression. We observed dysregulated levels of tRNAs and propose that the toxin targets tRNAs resulting in bacteriostasis. A recent report on a related toxin shows this occurs through addition of nucleotides to tRNA(s). This study has demonstrated the utility of functional genomics for probing TA function in a high-throughput manner, defined the TA repertoire in Serratia and shown the consequences of AbiE induction.

Deciphering the molecular mechanisms of mother-to-egg immune protection in the mealworm beetle Tenebrio molitor

In a number of species, individuals exposed to pathogens can mount an immune response and transmit this immunological experience to their offspring, thereby protecting them against persistent threats. Such vertical transfer of immunity, named trans-generational immune priming (TGIP), has been described in both vertebrates and invertebrates. Although increasingly studied during the last decade, the mechanisms underlying TGIP in invertebrates are still elusive, especially those protecting the earliest offspring life stage, i.e. the embryo developing in the egg. In the present study, we combined different proteomic and transcriptomic approaches to determine whether mothers transfer a "signal" (such as fragments of infecting bacteria), mRNA and/or protein/peptide effectors to protect their eggs against two natural bacterial pathogens, namely the Gram-positive Bacillus thuringiensis and the Gram-negative Serratia entomophila. By taking the mealworm beetle Tenebrio molitor as a biological model, our results suggest that eggs are mainly protected by an active direct transfer of a restricted number of immune proteins and of antimicrobial peptides. In contrast, the present data do not support the involvement of mRNA transfer while the transmission of a "signal", if it happens, is marginal and only occurs within 24h after maternal exposure to bacteria. This work exemplifies how combining global approaches helps to disentangle the different scenarios of a complex trait, providing a comprehensive characterization of TGIP mechanisms in T. molitor. It also paves the way for future alike studies focusing on TGIP in a wide range of invertebrates and vertebrates to identify additional candidates that could be specific to TGIP and to investigate whether the TGIP mechanisms found herein are specific or common to all insect species.

Bacterial Actin-Specific Endoproteases Grimelysin and Protealysin as Virulence Factors Contributing to the Invasive Activities of Serratia

The article reviews the discovery, properties and functional activities of new bacterial enzymes, proteases grimelysin (ECP 32) of Serratia grimesii and protealysin of Serratia proteamaculans, characterized by both a highly specific "actinase" activity and their ability to stimulate bacterial invasion. Grimelysin cleaves the only polypeptide bond Gly42-Val43 in actin. This bond is not cleaved by any other proteases and leads to a reversible loss of actin polymerization. Similar properties were characteristic for another bacterial protease, protealysin. These properties made grimelysin and protealysin a unique tool to study the functional properties of actin. Furthermore, bacteria Serratia grimesii and Serratia proteamaculans, producing grimelysin and protealysin, invade eukaryotic cells, and the recombinant Escherichia coli expressing the grimelysin or protealysins gene become invasive. Participation of the cellular c-Src and RhoA/ROCK signaling pathways in the invasion of eukaryotic cells by S. grimesii was shown, and involvement of E-cadherin in the invasion has been suggested. Moreover, membrane vesicles produced by S. grimesii were found to contain grimelysin, penetrate into eukaryotic cells and increase the invasion of bacteria into eukaryotic cells. These data indicate that the protease is a virulence factor, and actin can be a target for the protease upon its translocation into the host cell.

Anti-cancer effects of recombinant arazyme from Serratia Proteomaculans

PURPOSE

Colorectal cancer is a lethal and prevalent type of cancer in both men and women worldwide, which can develop resistance to cancer chemotherapy. Developing an effective therapeutic agent is the most promising method for this life-threatening disease. The present study aimed to identify, clone, express and purify the recombinant arazyme (r-arazyme) of Serratia proteomaculans and evaluate the antitumor effect of r-arazyme in vitro.

METHODS

Bacterial strains and cell line, construction of expression vector and preparation of recombinant protein were prepared and then evaluated by western blot, cell culture, cell viability assay, lactate dehydrogenase release assay, cell apoptosis assay, caspase-3 and -9 activation assay, adhesion assay, matrigel invasion assay and reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

R-arazyme caused a great cytotoxic effect against human colorectal adenocarcinoma (HT29) cells in a dose-dependent manner, without any cytotoxic effect on human embryonic kidney cells 293 (HEK 293). In addition, r-arazyme could induce apoptosis in colorectal cancer cell lines via caspase-3 activation and the elevation of the Bax/Bcl-2 ratio. Further, r-arazyme inhibited cancer cells angiogenesis by significantly reducing the expression of angiogenesis-related genes such as VEGF, VEGFR-1, and VEGFR-2. Furthermore, r-arazyme could prevent invasion and adhesion of cancer cells. In general, the results may support the evidence that r-arazyme is a promising therapeutic candidate against cancer.

CONCLUSION

R-arazyme may play an important role in developing effective therapies against colorectal adenocarcinoma in humans, which results in reducing the overall morbidity and mortality related to colorectal cancer.

Resistance Trends and Epidemiology of Citrobacter-Enterobacter-Serratia in Urinary Tract Infections of Inpatients and Outpatients (RECESUTI): A 10-Year Survey

Background and objectives: Urinary tract infections (UTIs) are the third most common infections in humans, representing a significant factor of morbidity, both among outpatients and inpatients. The pathogenic role of Citrobacter, Enterobacter, and Serratia species (CES bacteria) has been described in UTIs. CES bacteria present a therapeutic challenge due to the various intrinsic and acquired resistance mechanisms they possess. Materials and Methods: The aim of this study was to assess and compare the resistance trends and epidemiology of CES pathogens in UTIs (RECESUTI) in inpatients and outpatients during a 10-year study period. To evaluate the resistance trends of isolated strains, several antibiotics were chosen as indicator drugs based on local utilization data. 578 CES isolates were obtained from inpatients and 554 from outpatients, representing 2.57 ± 0.41% of all positive urine samples for outpatients and 3.02 ± 0.40% for inpatients. E. cloacae was the most prevalent species. Results: The ratio of resistant strains to most of the indicator drugs was higher in the inpatient group and lower in the second half of the study period. ESBL-producing isolates were detected in 0-9.75% from outpatient and 0-29.09% from inpatient samples. Conclusions: Resistance developments of CES bacteria, coupled with their intrinsic non-susceptibility to several antibiotics, severely limits the number of therapeutic alternatives, especially for outpatients.

Glyphosate perturbs the gut microbiota of honey bees

Glyphosate, the primary herbicide used globally for weed control, targets the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzyme in the shikimate pathway found in plants and some microorganisms. Thus, glyphosate may affect bacterial symbionts of animals living near agricultural sites, including pollinators such as bees. The honey bee gut microbiota is dominated by eight bacterial species that promote weight gain and reduce pathogen susceptibility. The gene encoding EPSPS is present in almost all sequenced genomes of bee gut bacteria, indicating that they are potentially susceptible to glyphosate. We demonstrated that the relative and absolute abundances of dominant gut microbiota species are decreased in bees exposed to glyphosate at concentrations documented in the environment. Glyphosate exposure of young workers increased mortality of bees subsequently exposed to the opportunistic pathogen Serratia marcescens Members of the bee gut microbiota varied in susceptibility to glyphosate, largely corresponding to whether they possessed an EPSPS of class I (sensitive to glyphosate) or class II (insensitive to glyphosate). This basis for differences in sensitivity was confirmed using in vitro experiments in which the EPSPS gene from bee gut bacteria was cloned into Escherichia coli All strains of the core bee gut species, Snodgrassella alvi, encode a sensitive class I EPSPS, and reduction in S. alvi levels was a consistent experimental result. However, some S. alvi strains appear to possess an alternative mechanism of glyphosate resistance. Thus, exposure of bees to glyphosate can perturb their beneficial gut microbiota, potentially affecting bee health and their effectiveness as pollinators.

Context-dependent vertical transmission shapes strong endosymbiont community structure in the pea aphid, Acyrthosiphon pisum

Animal-associated microbiomes are often comprised of structured, multispecies communities, with particular microbes showing trends of co-occurrence or exclusion. Such structure suggests variable community stability, or variable costs and benefits-possibilities with implications for symbiont-driven host adaptation. In this study, we performed systematic screening for maternally transmitted, facultative endosymbionts of the pea aphid, Acyrthosiphon pisum. Sampling across six locales, with up to 5 years of collection in each, netted significant and consistent trends of community structure. Co-infections between Serratia symbiotica and Rickettsiella viridis were more common than expected, while Rickettsia and X-type symbionts colonized aphids with Hamiltonella defensa more often than expected. Spiroplasma co-infected with other endosymbionts quite rarely, showing tendencies to colonize as a single species monoculture. Field estimates of maternal transmission rates help to explain our findings: while Serratia and Rickettsiella improved each other's transmission, Spiroplasma reduced transmission rates of co-infecting endosymbionts. In summary, our findings show that North American pea aphids harbour recurring combinations of facultative endosymbionts. Common symbiont partners play distinct roles in pea aphid biology, suggesting the creation of "generalist" aphids receiving symbiont-based defence against multiple ecological stressors. Multimodal selection, at the host level, may thus partially explain our results. But more conclusively, our findings show that within-host microbe interactions, and their resulting impacts on transmission rates, are an important determinant of community structure. Widespread distributions of heritable symbionts across plants and invertebrates hint at the far-reaching implications for these findings, and our work further shows the benefits of symbiosis research within a natural context.

Differential genomic damage in different tumor lines induced by prodigiosin

Prodigiosin is a secondary metabolite produced by Serratia marcercens. As this pigment is suggested to be a cancer drug, genotoxicity studies are necessary. The aim of the present investigation was to evaluate the genotoxic effects of prodigiosin on tumoral and normal cell lines, NCIH-292, MCF-7 and HL-60. A normal line BGMK was used as control. Genomic damage induced by prodigiosin was observed in all tumor lines as well as the control line. The pigment induced the formation of micronuclei in tumor cells. The present data confirm the antitumor potential of prodigiosin. However, these findings also raise concerns regarding its target-specific action, as genotoxic effects on normal cells also occurred.

[ENTRY OF FACULTATIVE PATHOGEN SERRATIA GRIMESII INTO HELA CELLS. ELECTRON MICROSCOPIC ANALYSIS]

Facultative pathogens Serratia grimesii are able to invade eukaryotic cells where they have been found in vacuoles and free in the cytoplasm (Efremova et al., 2001; Bozhokina et al., 2011). However, efficiency of this invasion is low, and the mechanisms of the invasion related to the initial steps of the process are not known. In the present study, we have increased the invasion efficiency by incubation of HeLa cells with N-acetylcysteine (NAC) preceding the infection. In the NAC-pretreated cells, two modes of S. grimesii to enter HeLa cells were observed. In the most cases, the penetration of S. grimesii into the cell was consistent with the "zipper mechanism", involving specific interaction of bacterial invasin with a host cell surface receptor. However, in some cases, bacteria were trapped by membrane ruffling probably produced by injected bacterial proteins that trigger the bacterial uptake process, as described in the "trigger mechanism". Further elucidation of bacterial and cellular factors involved in the bacteria-host cell interaction should clarify whether two different mechanisms or a predominant one operate during S. grimesii invasion.

Molecular characterization of protease activity in Serratia sp. strain SCBI and its importance in cytotoxicity and virulence

A newly recognized Serratia species, termed South African Caenorhabditis briggsae isolate (SCBI), is both a mutualist of the nematode Caenorhabditis briggsae KT0001 and a pathogen of lepidopteran insects. Serratia sp. strain SCBI displays high proteolytic activity, and because secreted proteases are known virulence factors for many pathogens, the purpose of this study was to identify genes essential for extracellular protease activity in Serratia sp. strain SCBI and to determine what role proteases play in insect pathogenesis and cytotoxicity. A bank of 2,100 transposon mutants was generated, and six SCBI mutants with defective proteolytic activity were identified. These mutants were also defective in cytotoxicity. The mutants were found defective in genes encoding the following proteins: alkaline metalloprotease secretion protein AprE, a BglB family transcriptional antiterminator, an inosine/xanthosine triphosphatase, GidA, a methyl-accepting chemotaxis protein, and a PIN domain protein. Gene expression analysis on these six mutants showed significant downregulation in mRNA levels of several different types of predicted protease genes. In addition, transcriptome sequencing (RNA-seq) analysis provided insight into how inactivation of AprE, GidA, and a PIN domain protein influences motility and virulence, as well as protease activity. Using quantitative reverse transcription-PCR (qRT-PCR) to further characterize expression of predicted protease genes in wild-type Serratia sp. SCBI, the highest mRNA levels for the alkaline metalloprotease genes (termed prtA1 to prtA4) occurred following the death of an insect host, while two serine protease and two metalloprotease genes had their highest mRNA levels during active infection. Overall, these results indicate that proteolytic activity is essential for cytotoxicity in Serratia sp. SCBI and that its regulation appears to be highly complex.

Serratia odorifera mediated enhancement in susceptibility of Aedes aegypti for chikungunya virus

BACKGROUND & OBJECTIVES

The susceptibility of the mosquito to the invading pathogen is predominantly dictated by the complex interactions between the mosquito midgut and the surface proteins of the invading pathogen. It is well documented that the midgut microbiota plays an important role in determining the susceptibility of the mosquito to the pathogen. In the present study, we investigated the influence of Serratia odorifera, an endogenous cultivable midgut inhabitant of Aedes aegypti on the chikungunya virus (CHIKV) susceptibility to this mosquito.

METHODS

Ae. aegypti females free of gutflora were co-fed with CHIKV and either of the two midgut inhabitants namely, S. odorifeara and Microbacterium oxydans. CHIKV dissemination was checked on 10 th day post feeding (DPF) using indirect immunoflurescence assay and plaque assay. CHIKV interacting proteins of the mosquito midgut were identified using virus overlay protein binding assay and MALDI TOF/TOF analysis.

RESULTS

The observations revealed that co-feeding of S. odorifera with CHIKV significantly enhanced the CHIKV susceptibility in adult Ae. aegypti, as compared to the mosquitoes fed with CHIKV alone and CHIKV co-fed with another midgut inhabitant, M. oxydans. Virus overlay protein binding assay (VOPBA) results revealed that porin and heat shock protein (HSP60) of Ae. aegypti midgut brush border membrane fraction interacted with CHIKV.

INTERPRETATION & CONCLUSIONS

The results of this study indicated that the enhancement in the CHIKV susceptibility of Ae. aegypti females was due to the suppression of immune response of Ae. aegypti as a result of the interaction between S. odorifera P40 protein and porin on the gut membrane.

The stationary phase sigma factor, RpoS, regulates the production of a carbapenem antibiotic, a bioactive prodigiosin and virulence in the enterobacterial pathogen Serratia sp. ATCC 39006

Serratia sp. ATCC 39006 (S39006) is a Gram-negative bacterium that is virulent in plant (potato) and invertebrate animal (Caenorhabditis elegans) models. It produces two secondary metabolite antibiotics, a prodigiosin and a carbapenem, and the exoenzymes pectate lyase and cellulase. We showed previously that deletion of the RNA chaperone Hfq abolished antibiotic production and attenuated virulence in both animal and plant hosts. Hfq and dependent small RNAs (sRNAs) are known to regulate the post-transcriptional expression of rpoS, which encodes σ(S), the stationary phase sigma factor subunit of RNA polymerase. An S39006 hfq deletion mutant showed decreased transcript levels of rpoS. Therefore, in this study we investigated whether the phenotypes regulated by Hfq were mediated through its control of rpoS. Whereas loss of Hfq abolished prodigiosin and carbapenem production and attenuated virulence in both C. elegans and potato, characterization of an S39006 rpoS mutant showed unexpectedly elevated prodigiosin and carbapenem production. Furthermore, the rpoS mutant exhibited attenuated animal pathogenesis, but not plant pathogenesis. Additionally, a homologue of the Hfq-dependent sRNA, RprA, was identified and shown to regulate prodigiosin production in a manner consistent with its role in positively regulating translation of rpoS mRNA. Combined, these results demonstrate that Hfq regulation of secondary metabolism and plant pathogenesis is independent of RpoS and establishes RpoS and RprA as regulators of antibiotic production.

[Revealing the genetic determinants of Pks-pathogenicity island in clinical strains of enterobacteria]

AIM

Detection by PCR the frequency of clbB, clbN, clbA H clbQ genes of Pks-pathogenicity island in clinical strains ofenterobacteria.

MATERIALS AND METHODS

112 strains various genera and species of enterobacteria, including 16 museum and 96 clinical are investigated. Isolated strains represents Escherichia species (n = 68), Klebsiella (n = 16), Enterobacter (n = 9), Serratia (n = 7) and others minor species of Enterobacteriaceae family (n = 12). Fifty nine strains isolated from urine of urinary tract infection, 26 isolates from intestines of patients with dysbiosis and 11--from children with complications after a liver transplantation. A total bacterial isolates were screened by multiplex PCRforthe presence ofclbB, clbN, clbA and clbQ genes.

RESULTS

Among 41 uropathogenic E.coli it is revealed 15 (36,6%) Pks-positive strains carring all of clbB, clbN, clbA ? clbQ genes, that composed 27,1% from total number of the enterobacteria, isolates from urine. Among 44 clinical isolates of various species of enterobacteria only one Pks-positive strain K. pneumoniae was revealed. Strains enterobacteria, isolated at pyoinflammatory complications after liver transplantation (n = 11) and isolates from intestinal tract in dysbiosis (n = 26), were Pks-negative.

CONCLUSION

The clbB, clbN, clbA ? clbQ genes of the Pks-island which have been detected in 36,6 % E. coli urological strains are markers of pathogenicity of clinical isolates of extraintestinal origin and advisable of their detection by PCR.

Identification of an entomopathogenic bacterium, Serratia sp. ANU101, and its hemolytic activity

Four different bacterial colonies were isolated from an old stock of an entomopathogenic nematode, Steinernema monticolum. They all showed entomopathogenicity to final instar larvae of beet armyworm, Spodoptera exigua, by hemocoelic injection. However, they varied in colony form, susceptibility to antibiotics, and postmortem change of the infected host insects. Biolog microbial identification and 16S rDNA sequence analyses indicate that these are four different species classified into different bacterial genera. owing to high entomopathogenicity and a cadaver color of infected insect host, Serratia sp. was selected as a main symbiotic bacterial species and analyzed for its pathogenicity. Although no virulence of Serratia sp. was detected at oral administration, the bacteria gave significant synergistic pathogenicity to fifth instar S. exigua when it was treated along with a spore-forming entomopathogenic bacterium, Bacillus thuringiensis. The synergistic effect was explained by an immunosuppressive effect of Serratia sp. by its high cytotoxic effect on hemocytes of S. exigua, because Serratia sp. caused septicemia of S. exigua when the bacterial cells were injected into S. exigua hemocoel. The cytotoxic factor(s) was present in the culture medium because the sterilized culture broth possessed high potency in the cytotoxicity, which was specific to granular cells and plasmatocytes, two main immune-associated hemocytes in insects.

[The story on an intriguing actin-specific protease that turned out to be grimelysin, a member of a respectable family of thermolysin-like metalloproteinases]

The article describes a story of the discovery and properties of bacterial metalloproteinase ECP32 that cleaves actin at the only site between Gly42 and Val43. This site is intensively involved in the monomer-monomer contacts within actin filament. Cleavage with ECP32 results in a reversible loss of actin polymerizability. Therefore ECP cleaved actin has been a unique model to study mechanisms of actin polymerization and the filament dynamics. and the effects of actin-binding proteins on these processes, as well as to reveal allosteric effects in actin molecule and to determine three-dimensional actin structure that was previously determined only for the actin-ligand complexes. Furthermore, the non-pathogenic bacteria synthesizing ECP32 were shown to penetrate in eukaryotic cells rearranging their cytoskeleton. Biochemical analysis using the Vitek-2 system and sequencing of the 16S rRNA gene reidentified the ECP32-producing strain, previously identified as E. coli, as Serratia grimesii. Bacteria of a reference strain S. grimesii were found to express the gene of metalloprotease that cleaves actin similarly to ECP32. The gene was cloned, sequenced and expressed in E. coli. The protein encoded by this gene was named grimelysin. Grimelysin shared essential characteristics of ECP32: molecular weight, limited actin proteolysis, inhibition by chelating agents, cleavage site, and the N-terminal amino acids of the active enzyme published for ECP32. These data show that grimelysin and ECP32 seem to be the same protein. As it was demonstrated by confocal microscopy the bacteria capable of synthesizing natural or recombinant grimelysin acquire invasive phenotype. The data described here allow us to suggest that actin may be a target protein which proteolysis promotes bacterial invasion.

Virulence and prodigiosin antibiotic biosynthesis in Serratia are regulated pleiotropically by the GGDEF/EAL domain protein, PigX

Gram-negative bacteria of the genus Serratia are opportunistic human, plant, and insect pathogens. Serratia sp. strain ATCC 39006 secretes pectinases and cellulases and produces the secondary metabolites carbapenem and prodigiosin. Mutation of a gene (pigX) resulted in an extremely pleiotropic phenotype: prodigiosin antibiotic biosynthesis, plant virulence, and pectinase production were all elevated. PigX controlled secondary metabolism by repressing the transcription of the target prodigiosin biosynthetic operon (pigA-pigO). The transcriptional start site of pigX was determined, and pigX expression occurred in parallel with Pig production. Detailed quantitative intracellular proteome analyses enabled the identification of numerous downstream targets of PigX, including OpgG, mutation of which reduced the production of the plant cell wall-degrading enzymes and virulence. The highly pleiotropic PigX regulator contains GGDEF and EAL domains with noncanonical motifs and is predicted to be membrane associated. Genetic evidence suggests that PigX might function as a cyclic dimeric GMP phosphodiesterase. This is the first characterization of a GGDEF and EAL domain protein in Serratia and the first example of the regulation of antibiotic production by a GGDEF/EAL domain protein.

Fundamental factors affecting upper-room ultraviolet germicidal irradiation - part I. Experimental

The objective of this research was to study the factors that relate to the effectiveness of upper-room ultraviolet germicidal irradiation for inactivating airborne microorganisms. The work was conducted in a room-sized chamber designed and furnished for investigations of this nature. Nebulized Serratia marcescens, Bacillus subtilis spores, and vaccinia virus were used as test aerosols. Most data were collected from steady-state experiments comparing the number of viable organisms in the chamber air remaining with UV lamps turned on to the number with UV lamps turned off, but some decay experiments were conducted to compare the two methods. UV power level had a strong influence but was fully effective only in the presence of air mixing that produced vigorous vertical air currents. A conclusion of the study is that an upper-room ultraviolet installation is a complex system that requires careful integration of UV luminaires, UV power, and room ventilation arrangements.

Virulence of Serratia strains against Costelytra zealandica

Strains of Serratia spp. showed a high level of virulence when injected into the hemocoel of larvae Costelytra zealandica, with Serratia entomophila, S. plymuthica, and S. marcescens showing significantly higher virulence than S. proteamaculans. Toxicity was independent of the amber disease-causing plasmid pADAP, suggesting a generalized Serratia toxin.

[Persistense of mono- and associated cultures of conditionally pathogenic enterobacteria]

The comparative study of adhesive, hemolytic, DNA-ase, lecithinase, antilysozymic, anticomplementary activities of mono- and associated cultures of 57 Enterobacter spp., 61 Citrobacter spp. and 55 Serratia spp. strains, isolated from patients with pyoinflammatory, intestinal and urological diseases is carried out. Different variations of cocultivated bacteria including Enterobacter and Citrobacter, Enterobacter and Serratia, Citrobacter and Serratia are used. It was shown, that cocultivated Enterobacter, Citrobacter and Serratia bacteria increased the persistent properties of mixt cultures.

N-Acylhomoserine lactone-dependent cell-to-cell communication and social behavior in the genus Serratia

Members of the genus Serratia are increasingly responsible for nosocomial infections, the treatment of which may be complicated by the appearance of multi-antibiotic-resistant strains. Some but not all Serratia strains and species produce N-acylhomoserine lactones (AHLs), and possess luxR and luxI homologous genes. Phylogenetic comparisons have provided evidence for the lateral transfer of these quorum-sensing systems, and in at least one strain of S. marcescens, transfer via a complex transposon has been experimentally demonstrated. AHL-dependent quorum sensing in Serratia controls population surface migration, biofilm development, the biosynthesis of a carbapenem antibiotic and production of the red pigment, prodigiosin. Serratia also possesses LuxS and produces autoinducer-2 (AI-2) which appears to function as a second quorum-sensing system controlling many of the same phenotypes as the LuxR/AHL systems.

[Haemolytic and proteolytic properties of Serratia spp. rods]

For over fifty years Serratia spp. rods have increasingly been isolated from clinical specimens. The isolation has arisen mainly from hospitalised patients. The development of Serratia spp. infections is associated with predisposing factors of patients, occurrence in both natural settings and within the hospital environment and the virulence factors of bacteria. CDM medium with casein sodium salt, gelatine and Skim Milk were used to detect proteolytic properties. Over 95% of analysed strains produced gelatinase. Casein sodium salt was hydrolysed by 89,6% to 93,1% of strains depending on cultivation temperature. Skim Milk was hydrolysed by 78,5% to 84,7% of analysed Serratia spp. strains. Haemolytic properties of Serratia spp. rods were checked on a solid medium with human and sheep red blood cells at 22, 30, and 37 degrees C. The haemolysis of human erythrocytes at 37 degrees C was detected most frequently at 38,2%. There were no significant differences identified when cultivation temperature was observed.

The family of Serratia type pore forming toxins

The Serratia marcescens hemolysin represents the prototype of a growing family of pore forming toxins. The available bacterial genome sequences reveal Serratia hemolysin homologues in additional species. However, only S. marcescens hemolysin has been studied in great molecular detail. This family of toxins has nothing in common with the pore forming toxins of E. coli type (RTX toxins), the Staphylococcus aureus alpha-toxin or the thiol activated toxin of group A beta-hemolytic streptococci (Streptolysin O). Studies on erythrocytes, eukaryotic cells and artificial black lipid membranes, have shown that the mechanism of pore formation of ShlA is different form other pore forming toxins. The S. marcescens hemolysin proteins ShlB and ShlA, exhibit protein sequence homologues in Proteus mirabilis, Haemophilus ducreyi, Yersinia pestis, Yersinia enterocolitica, Edwardsiella tarda, Photorhabdus luminescens and Xylella fastidiosa . The family of Serratia type pore forming toxins show a unique secretory mechanism which has been described as a two partner secretion system (TPSS) or type V-secretion system. Not only Serratia type pore forming toxins are secreted via TPSS but also adhesins from Bordetella pertussis, Erwinia chrysanthemi and Haemophilus influenzae. The uniqueness of the Serratia family is underlined by the fact that activation of ShlA by ShlB strictly requires phosphatidylethanolamine as a cofactor. And, quite unusual, ShlA undergoes a conformational change during activation.

Pathogen-specific early mortality in very low birth weight infants with late-onset sepsis: a national survey

BACKGROUND

Late-onset sepsis (LOS) is an important cause of mortality among very low birth weight (VLBW) infants, and deaths occurring within 3 days after the onset of sepsis can probably be ascribed to sepsis. We examined the association of sepsis due to specific pathogens with the risk for early mortality after the onset of LOS, adjusted for perinatal and neonatal risk factors.

METHODS

From 1995 through 2001, information about 10,215 infants was gathered and deposited in the Israel National VLBW Infant Database. The study population was composed of 2644 infants, of which each had >or=1 events of LOS (totalling 3462 events). Logistic regression models were used to calculate the crude and adjusted risk for early mortality.

RESULTS

Early mortality was associated with 179 LOS events (5.2% of 3,462); the range of pathogens associated with these events included coagulase-negative staphylococci (CoNS), which were the cause of 1.8% of LOS events associated with early mortality, and Pseudomonas species, which were the cause of 22.6% of such events. Early mortality after LOS, adjusted for neonatal risk factors, was significantly associated with sepsis due to certain pathogens: Pseudomonas species (odds ratio [OR], 12.3); Klebsiella species (OR, 6.3); Serratia species (OR, 6.2); Escherichia species (OR, 4.3); Enterobacter species (OR, 4.1); and Candida species (OR, 3.2), compared with sepsis due to CoNS . In addition, lower gestational age, lower chronological age, small size for gestational age, and grade 3-4 intraventricular hemorrhage, each had an independent association with early mortality.

CONCLUSIONS

Klebsiella sepsis and Pseudomonas sepsis were associated with a 6.3-fold and 12.3-fold increased risk of early mortality, respectively, and accounted for 41.9% of all early deaths associated with LOS. Considering the aggressive nature of sepsis caused by these pathogens, empiric antibiotic therapy active against these organisms is worth consideration for VLBW infants with presumed LOS.

Cloning Serratia entomophila antifeeding genes--a putative defective prophage active against the grass grub Costelytra zealandica

Serratia entomophila and Serratia proteamaculans (Enterobacteriaceae) cause amber disease in the grass grub Costelytra zealandica (Coleoptera: Scarabaeidae), an important pasture pest in New Zealand. Larval disease symptoms include cessation of feeding, clearance of the gut, amber coloration, and eventual death. A 155-kb plasmid, pADAP, carries the genes sepA, sepB, and sepC, which are essential for production of amber disease symptoms. Transposon insertions in any of the sep genes in pADAP abolish gut clearance but not cessation of feeding, indicating the presence of an antifeeding gene(s) elsewhere on pADAP. Based on deletion analysis of pADAP and subsequent sequence data, a 47-kb clone was constructed, which when placed in either an Escherichia coli or a Serratia background exerted strong antifeeding activity and often led to rapid death of the infected grass grub larvae. Sequence data show that the antifeeding component is part of a large gene cluster that may form a defective prophage and that six potential members of this prophage are present in Photorhabdus luminescens subsp. laumondii TTO1, a species which also has sep gene homologues.

Quantification and kinetics of the decline in grass grub endopeptidase activity during initiation of amber disease

Amber disease in the grass grub (Costelytra zealandica White) (Coleoptera: Scarabaeidae), caused by strains of the bacteria Serratia entomophila or S. proteamaculans, is characterised by cessation of feeding and clearance of the midgut. Analysis of the midgut enzyme activity in diseased grass grub larvae showed that proteolytic activity was reduced to low levels. The endopeptidases, trypsin, elastase, and chymotrypsin, were all markedly reduced in activity whereas the exopeptidases (leucine-aminopeptidase and carboxypeptidase A and B) were much less affected. There was no effect on the non-proteolytic enzymes, esterase and alpha-amylase. Sequential analysis of enzyme levels in the gut during onset of disease showed that proteolytic activity dropped after cessation of feeding and preceded gut clearance. In starved, uninfected larvae enzyme activity levels remained high, indicating that decline in enzyme activity is not associated with absence of food and cessation of feeding, but with the onset of disease.

luxS mutants of Serratia defective in autoinducer-2-dependent ‘quorum sensing’ show strain-dependent impacts on virulence and production of carbapenem and prodigiosin

The enzyme LuxS is responsible for the production of autoinducer-2 (AI-2), a molecule that has been implicated in quorum sensing in many bacterial species. This study investigated whether there is aluxS-dependent signalling system in the Gram-negative bacteriaSerratiaspp.Serratia marcescensis a broad-host-range pathogen and an important cause of nosocomial infections. Production of AI-2 activity was detected inS. marcescensATCC 274 andSerratiaATCC 39006 and theirluxSgenes were sequenced.luxSmutants were constructed in these strains and were analysed to determine which phenotypes are regulated byluxSand therefore, potentially, by AI-2. The phenotypes of theluxSmutants included decreased carbapenem antibiotic production inSerratiaATCC 39006 and decreased prodigiosin and secreted haemolysin production inS. marcescensATCC 274. TheluxSmutant ofS. marcescensATCC 274 was also found to exhibit modestly reduced virulence in aCaenorhabditis elegansmodel. Finally, it was shown that the culture supernatant of a wild-type strain contains a signal, presumably AI-2, capable of complementing the prodigiosin defect of theluxSmutant of another strain, even when substantially diluted. It is concluded thatluxSmodulates virulence and antibiotic production inSerratia, in a strain-dependent manner, and that, for at least one phenotype, this regulation is via extracellular signalling.

Peripheral sequences of the Serratia entomophila pADAP virulence-associated region

Some strains of the Enterobacteriaceae Serratia entomophila and Serratia proteamaculans cause amber disease in the grass grub, Costelytra zealandica (Coleoptera: Scarabaeidae), an important pasture pest in New Zealand. The genes responsible for this disease reside on a large, 155-kb plasmid designated amber disease-associated plasmid (pADAP). Herein, we report the DNA sequencing of approximately 50 kb upstream and 10 kb downstream of the virulence-encoding region. Based on similarity with proteins in the current databases, and potential ribosome-binding sites, 63 potential ORFs were determined. Eleven of these ORFs belong to a type IV pilus cluster (pilL-V) and a further eight have similarities to the translated products of the plasmid transfer traH-N genes of the plasmid R64. In addition, a degenerate 785-nt direct repeat flanks a 44.7-kb region with the potential to encode three Bacillus subtilis Yee-type proteins, a fimbrial gene cluster, the sep virulence-associated genes and several remnant IS elements.

Use of the green fluorescent protein to monitor the fate of Serratia entomophila causing amber disease in the New Zealand grass grub, Costelytra zealandica

A series of constitutive green fluorescent protein (pGFPuv) derivatives of the bacterium Serratia entomophila (Enterobacteriaceae) were constructed, allowing the fate of cells causing amber disease ingested by the New Zealand grass grub (Costelytra zealandica, Coleoptera: Scarabaeidae) to be monitored. Examination of tissue and contents of the alimentary tract over time from ingestion, under fluorescence microscopy, revealed that the major site of S. entomophila colonisation in the grass grub is intestinal particulate matter. Visual examinations showed that wild type pathogenic strain persisted in high numbers in the grass grub intestinal tract, notably in the area of the hindgut, but the S. entomophila pADAP-free strain 5.6RC and the pADK mutant derivatives (pADK-4, -10, -13) that gave a non-feeding without gut clearance phenotype, were unable to colonise the gut. The indiscriminate colonisation of the intestinal tract particulate matter by pathogenic bacteria, rather than the colonisation of a specific site of activity, suggests that the bacterial toxins are induced and released from the bacteria while they live freely in the grass grub intestinal tract.

The characterization of upper-room ultraviolet germicidal irradiation in inactivating airborne microorganisms

In this study, we explored the efficacy of upper-room ultraviolet germicidal irradiation (UVGI) in reducing the concentration of Serratia marcescens and Mycobacterium bovis bacille Calmette-Guérin (BCG) aerosols in enclosed places. We constructed a facility (4.5 m x 3 m x 2.9 m) in which both ceiling- and wall-mounted UV fixtures (UV output: 10W and 5W respectively) were installed. The use of ceiling- and wall-mounted UV fixtures (total UV output: 15W) without mixing fan reduced the concentration of S. marcescens aerosols by 46% (range: 22-80%) at 2 air changes per hour (ACH) and 53% (range: 40-68%) at 6 ACH. The use of ceiling- and wall-mounted UV fixtures with mixing fan increased the UV effectiveness in inactivating S. marcescens aerosols to 62% (range: 50-78%) at 2 ACH and to 86% (81-89%) at 6 ACH. For BCG aerosols, UV effectiveness in inactivating BCG aerosols at 6 ACH were 52% (range: 11-69%) by ceiling-mounted UV fixture only (total UV output: 10W) and 64% (51-83%) by both ceiling- and wall-mounted UV fixtures (total UV output: 15W). Our results indicated that the equivalent ventilation rate attributable to upper-room UVGI for BCG aerosols ranged from 1 ACH to 22 ACH for ceiling-mounted UV fixtures and from 6.4 ACH to 28.5 ACH for ceiling- and wall-mounted UV fixtures. Both generalized linear and generalized additive models were fitted to all our data. The regression results indicated that the number of UV fixtures, use of mixing fan, and air exchange rate significantly affected UV effectiveness (p < 0.01, 0.01, 0.01 respectively). However, the strain difference (S. marcescens vs. BCG) appeared less important in UV effectiveness (p = 0.26). Our results also indicated that UV effectiveness increased at higher temperature ((italic)p(/italic) < 0.01), lower dry-bulb temperature ((italic)p(/italic) = 0.21), and colder air from a supply grill located near the ceiling (p = 0.22).

Plasmid-located pathogenicity determinants of Serratia entomophila, the causal agent of amber disease of grass grub, show similarity to the insecticidal toxins of Photorhabdus luminescens

Serratia entomophila and Serratia proteamaculans cause amber disease in the grass grub Costelytra zealandica (Coleoptera: Scarabaeidae), an important pasture pest in New Zealand. Larval disease symptoms include cessation of feeding, clearance of the gut, amber coloration, and eventual death. A 115-kb plasmid, pADAP, identified in S. entomophila is required for disease causation and, when introduced into Escherichia coli, enables that organism to cause amber disease. A 23-kb fragment of pADAP that conferred disease-causing ability on E. coli and a pADAP-cured strain of S. entomophila was isolated. Using insertion mutagenesis, the pathogenicity determinants were mapped to a 17-kb region of the clone. Sequence analysis of the 17-kb region showed that the predicted products of three of the open reading frames (sepA, sepB, and sepC) showed significant sequence similarity to components of the insecticidal toxin produced by the bacterium Photorhabdus luminescens. Transposon insertions in sepA, sepB, or sepC completely abolished both gut clearance and cessation of feeding on the 23-kb clone; when recombined back into pADAP, they abolished gut clearance but not cessation of feeding. These results suggest that SepA, SepB, and SepC together are sufficient for amber disease causation by S. entomophila and that another locus also able to exert a cessation-of-feeding effect is encoded elsewhere on pADAP.

Expression of the antifeeding gene anfA1 in Serratia entomophila requires rpoS

The rpoS gene of Serratia entomophila BC4B was cloned and used to create rpoS-mutant strain BC4BRS. Larvae of the New Zealand grass grub Costelytra zealandica infected with BC4BRS became amber colored but continued to feed, albeit to a lesser extent than infected larvae. Subsequently, we found that expression of the antifeeding gene anfA1 in trans was substantially reduced in BC4BRS relative to that in the parental strain BC4B. Our data show that a functional rpoS gene is vital for full expression of anfA1 and for development of the antifeeding component of amber disease.

Serratia ficaria: a misidentified or unidentified rare cause of human infections in fig tree culture zones

Serratia ficaria, an enterobacterium involved in the fig tree ecosystem, has been isolated from human clinical samples in rare instances, and its role as a pathogen is unclear. In 7 years, we have isolated S. ficaria from seven patients; it was the only pathogen in 4 patients, including a patient with septicemia described previously and three patients with gallbladder empyemas described in the present report. From March 1995 to July 1997, the incidence of biliary infections due to S. ficaria was 0.7%. We discuss the digestive carriage of this bacterium and its epidemiology with respect to the fig tree life cycle. Since fig trees grow around the Mediterranean as well as in the United States (California, Louisiana, Hawaii), S. ficaria should be more frequently isolated. In our experience, various strains have been misidentified or unidentified by commercial systems. Incorrect identification could be an additional explanation for the paucity of reported cases. S. ficaria produces nonpigmented, lactose-negative colonies which give off a potatolike odor. This odor is the primary feature of S. ficaria and must prompt reexamination of the identifications proposed by commercial systems. We tested 42 novel strains using three commercial systems: Vitek gram-negative identification (GNI) cards and API 20E and ID 32E strips (bioMérieux, Marcy-l'Etoile, France). The percentages of positivity that we have obtained were lower than those published previously for the following characteristics: lipase, gelatinase, DNase, and rhamnose. The best system for the recognition of S. ficaria is ID 32E, which correctly identified 27 of 42 strains. The API 20E system gave correct identifications for only two strains. S. ficaria was not present in the Vitek GNI card system database.

Serratia odorifera biogroup I: an emerging pathogen

Gram-negative bacteremia is a common cause of infection in hospitalized patients. Serratia sepsis is known to cause clinically significant morbidity and mortality. The most common species involved is Serratia marcescens. Clinicians have been uncertain as to the role of Serratia odorifera biogroup 1 as a human pathogen because most isolates have not been associated with invasive disease. In previous publications, 12 cases have been described in which S odorifera biogroup 1 caused sepsis. These observations verify the organism's role as a human pathogen.

Fatal reaction to transfusion of red-cell concentrate contaminated with Serratia liquefaciens

A 60-year-old woman undergoing surgery died from endotoxic shock and DIC after receiving a 19-day-old unit of optimal additive red-cell concentrate found contaminated with Serratia liquefaciens. No source of contamination could be found. This normally free-living organism is usually of low pathogenicity. It is a very unusual contaminant of stored donated blood, although it appears to be on the increase. When transfused, blood contaminated with S. liquefaciens always causes severe morbidity and is associated with a high death rate. This is the fifth report in the English literature.

Characterisation of virulence factors of Serratia strains isolated from foods

Out of 21 Serratia strains isolated from fresh juice and fish samples, five S. marcescens and two S. rubidaea caused lethality in mice on parenteral inoculation, but none through oral feeding. Three S. marcescens and one S. rubidaea produced heat-labile enterotoxin, detectible with the rabbit ligated ileal loop test, the mouse foot pad test and the vasopermeability factor test. Cell free culture filtrate (CFCF) of two enterotoxigenic S. mearcescens strains induced cytotoxic effect on a monolayer of Vero-cells, but CFCF of other enterotoxigenic strains could only induce cytotonic changes in Vero-cells. All strains possessed fimbriae type 3 while, only pathogenic strains had type 4 fimbriae and a colonization factor. All pathogenic Serratia strains were agglutinated at comparatively lower salt concentrations than non pathogenic strains (< 1.3 M), and had multiple drug resistance. Their public health significance is also discussed.

The amb2 locus from Serratia entomophila confers anti-feeding effect on larvae of Costelytra zealandica (Coleoptera: Scarabaeidae)

Serratia entomophila (Se) causes amber disease in the soil-dwelling pest, Costelytra zealandica (Cz). The disease presents two main signs: anti-feeding effect (AFE) and development of amber coloration (AC). To identify the genetic loci involved in pathogenicity, non-pathogenic (Path-) Se mutants were created by transposon (TnphoA) mutagenesis [Upadhyaya et al., J. Bacteriol. 174 (1992) 1020-1028]. The mutant UC24 lost the ability to produce amber disease signs and it was shown to contain a single TnphoA insertion. The TnphoA insertion site was mapped in a 5.3-kb DNA fragment, which was named amb2 locus. Cosmids containing amb2 fully restored AFE and partially restored AC in UC24. Escherichia coli (Ec) HB101 bearing the amb2 locus was able to cause AFE in a multiple-dose bioassay. SDS-PAGE analysis of the amb2 gene products produced in minicells showed the synthesis of two proteins of 16 and 19.5 kDa, named AnfA and AnfB. The genes encoding these proteins were mapped by deletion analysis. Pathogenicity tests with insect larvae fed with bacteria carrying the anfA and anfB gene regions separately showed that both regions are essential for AFE. It is proposed that the AnfA and AnfB proteins are virulence factors (toxin-like proteins) causing AFE in Cz.

Serratia rubidaea as an invasive pathogen

Serratia rubidaea biotype 1 was isolated from the bile and blood of a patient with a bile tract carcinoma obstructing the common bile duct and who underwent invasive procedures. The infection was cleared after adequate treatment with antibiotics.

Report of six cases of human infection by Serratia plymuthica

Serratia plymuthica is an uncommon cause of human infection. Only one case of chronic osteomyelitis and two cases of sepsis secondary to central venous catheter infection have been documented. We report the isolation of S. plymuthica from six patients. The organism was recovered from blood cultures in three cases in which the patients had lymphoblastic leukemia, lymphoma, or stroke. Two isolates were recovered from exudates (following knee and abdominal surgery). In the last case, the organism was isolated from the peritoneal fluid of a patient with cholecystitis. The infection was considered nosocomial in five cases and community acquired in the other.

Case report and review of septicemia due to Serratia ficaria

Serratia ficaria was first described in 1979 as part of the fig tree ecosystem (P.A.D. Grimont, F. Grimont, and M. P. Starr, Curr. Microbiol. 2:277-282, 1979). Since then, it has been isolated from clinical specimens from a few human patients (C. Bollet, J. Freney, P. de Micco, F. Grimont, and P.A.D. Grimont, Méd. Mal. Infect. 20:97-100, 1990; J.A. Brouillard, W. Hansen, and A. Compere, J. Clin. Microbiol. 19:902-904, 1984; H. Darbas, H. Jean-Pierre, G. Boyer, and M. Riviere, Méd. Mal. Infect. 23:269-270, 1993; V.J. Gill, J.J. Farmer, III, P.A.D. Grimont, M.A. Asbury, and C.L. McIntosh, J. Clin. Microbiol. 14:234-236, 1981; F.D. Pien and J.J. Farmer III, South. Med. J. 76:1591-1592, 1983; C. Richard, J. de Coquet, and C. Suc, Méd. Mal. Infect. 19:45-47, 1989), but the pathogenicity of S. ficaria was always questionable. We are reporting the case of an aged cancer patient who developed S. ficaria septicemia. The habitat of this organism and its potential role as a pathogen are discussed.

Identification of a Serratia entomophila genetic locus encoding amber disease in New Zealand grass grub (Costelytra zealandica)

Serratia entomophila UC9 (A1MO2), which causes amber disease in the New Zealand grass grub Costelytra zealandica, was subjected to transposon (TnphoA)-induced mutagenesis. A mutant (UC21) was found to be nonpathogenic (Path-) to grass grub larvae in bioassays and was shown, by Southern hybridization, to contain a single TnphoA insertion. This mutant failed to adhere to the gut wall (Adn-) of the larvae and also failed to produce pili (Pil-). A comparative study of the total protein profiles of wild-type S. entomophila UC9 and mutant UC21 revealed that the mutant lacked an approximately 44-kDa protein and overexpressed an approximately 20-kDa protein. Transfer of cosmids containing homologous wild-type sequences into mutant strain UC21 restored wild-type phenotypes (Path+, Pil+, and Adn+). One of the complementing cosmids (pSER107) conferred piliation on Pil- Escherichia coli HB101. The TnphoA insertion in UC21 was mapped within an 8.6-kb BamHI fragment common to the complementing cosmids, and we designated this gene locus amb-1. Six gene products with molecular masses of 44, 36, 34, 33, 20, and 18 kDa were detected in E. coli minicells exclusive to the cloned 8.6-kb fragment (pSER201A). The 44-kDa gene product was not detected in E. coli minicells containing the cloned mutant fragment. Saturation mutagenesis of this fragment produced four unlinked insertional mutations with active fusions to TnphoA. These active fusions disrupted the expression of one or more gene products encoded by amb-1. The 8.6-kb fragment cloned in the opposite orientation (pSER201B) expressed only a 20-kDa protein. We propose that these are the products of structural and/or regulatory genes involved in adhesion and/or piliation which are prerequisites in the S. entomophila-grass grub interaction leading to amber disease.

Serratia odorifera biogroup 1 causing an invasive human infection

Serratia odorifera biogroup 1 was isolated from the blood and urine of an alcoholic male with cirrhosis and signs of septic shock. The organism is rarely reported to occur in clinical specimens. This is the first case in which the organism was found to be responsible for invasive human infection.

Role of cell-bound hemolysin as a pathogenicity factor for Serratia infections

The hemolytic activities of clinical isolates of Serratia marcescens, of Serratia liquefaciens, and of Escherichia coli strains containing a cloned hemolysin gene of S. marcescens were determined. Hemolysis was induced only by cells and not by spent media. The hemolytically active bacteria induced the release of the leukotriene C4 and of much less leukotriene B4 from polymorphonuclear leukocytes, the release of histamine from rat mast cells, and chemoluminescence of neutrophils. The hemolytic activity was correlated with the response of the leukocytes, but quantitative differences were recorded with regard to the release of the inflammatory mediators. Therefore, other factors in addition to the hemolysin contribute to the stimulation of leukotriene generation and histamine release. It is concluded that the hemolysin via these inflammatory mediators can increase vascular permeability, edema formation, and granulocyte accumulation and thus contributes to the pathogenicity of Serratia species.