Serratia marcescens

Over the last 30 years, Serratia marcescens has become an important cause of nosocomial infection. There have been many reports concerning the identification, antibiotic susceptibility, pathogenicity, epidemiological investigations and typing of this organism. Accurate identification is important in defining outbreaks. The API 20E system has been used widely, but is not individually satisfactory. The growth of S. marcescens in the environment has been investigated in relation to water, disinfectants and plastics such as blood bags. Certain extracellular products are unique to S. marcescens. Pigment (prodigiosin) biosynthesis by S. marcescens has been investigated fully since the emergence of the organism as a cause of infection. Many other aspects of the pathogenicity and virulence of S. marcescens have been studied, including adherence and hydrophobicity, lipopolysaccharide (LPS) and extracellular products. Two modes of adhesion to host epithelial surfaces have been suggested. These are mannose-resistant (MR) pili and mannose-sensitive (MS) pili. LPS, which is responsible for the biological activity of endotoxin, has been investigated fully and 24 somatic antigens have been described. The production of different enzymes by S. marcescens as virulence factors has also been reported, including chitinase, lipase, chloroperoxidase and an extracellular protein, HasA. Antibiotics used to treat serratia infection include beta-lactam agents, aminoglycosides and fluoroquinolones and a variety of different resistance mechanisms have been demonstrated. Typing methods used to study the epidemiology of S. marcescens include biotyping, bacteriocin typing, phage typing, plasmid analysis, polymerase chain reaction amplification of enterobacterial repetitive intergenic consensus sequences (ERIC-PCR) and ribotyping. Serological typing has also been used and this method seems to be a suitable first-line typing method for S. marcescens, although some strains remain untypable. RAPD-PCR has also been applied to a small number of isolates and seems to be a promising method, especially for rapid monitoring of an outbreak and tracing the source of initial infection.     

L-Norvaline and L-homoisoleucine formation by Serratia marcescens,

Two unnatural amino acids were found as by-products in isoleucine fermentation from threonine by Serratia marcescens. These amino acids were identified as L-norvaline (2-aminopentanoic acid) and L-homoisoleucine (2-amino-4-methylhexanoic acid). Formation of L-norvaline and L-homoisoleucine was not observed when L-leucine was added to the medium. The leucine auxotroph derived from the isoleucine accumlator did not produce L-norvaline or L-homoisoleucine even during the accumulation of large amounts of isoleucine. It is suggested that L-norvaline and L-homoisoleucine formation is closely related to leucine biosynthesis.     

An epidemiological study of Serratia marcescens isolates from nosocomial infections by enzyme electrophoresis

Serratia marcescens isolates from 164 patients with suspected nosocomial infection in several hospitals in the greater Paris region were investigated by analysis of the electrophoretically demonstrable allelic variations of gene loci coding for five esterases and five other enzymes. All the loci were polymorphic and the mean number of alleles per locus was 6.1. A total of 72 distinctive electrophoretic types (ETs) representing multilocus genotypes was distinguished. The isolates were divided into two groups according to their resistance to antibiotics: 82 multiresistant isolates (MRI) and 82 relatively susceptible isolates (RSI). Seventy-two MRI (88%) were in four genetically related ETs: ET1, ET2, ET8 and ET9; ET1 was found in 48 isolates, whereas the remaining MRI were in 10 ETs, and all RSI in 61 ETs. Three ETs contained both MRI and RSI. The mean coefficients of genetic diversity for the 10 enzyme loci among ETs and isolates were smaller for MRI than for RSI, while the modal ET of MRI resembled that of RSI. The epidemiological significance of isolates varied according to their ET. Thus, isolates belonging to ET1, ET2 and ET8 were responsible for outbreaks or for sporadic infections, whereas isolates of other ETs were responsible for only sporadic infections. The temporal distribution of ET1 isolates among hospitals identified seven outbreaks in seven clinical departments.     

Nuclease overexpression mutants of Serratia marcescens

A family of mutants overexpressing the Serratia marcescens extracellular nuclease has been known for decades. A number of these alleles are characterized here at the molecular level, and the mutant genes are identified, yielding a likely model for their phenotype. The known mutations exert their effect indirectly on nucA expression by elevating the basal SOS response of the cell. Mutations have been found in xerC and uvrD, both of which result in partial SOS induction. A classic nucsu allele, that of strain W1050, is also likely to be in xerC.     

Pathology of Serratia marcescens mastitis in cattle

Microbiological, cytological, histopathological, and immunohistochemical investigations were carried out on four dairy cows affected by Serratia marcescens mastitis. The animals under study were from a herd of 120 lactating cows bred in the province of Rome. In the above herd, S. marcescens mastitis showed a prevalence of 20.8%. S. marcescens was the only bacterial agent isolated, prior to and after slaughter, from the teat milk, the mammary gland and the supramammary lymph nodes of the four cows under study. Cytologically, the four subjects exhibited high cell counts in their milk, with an average of up to 5,570,000 cells/ml in S.marcescens-infected quarters. Macroscopically, nodular lesions were apparent scattered throughout the mammary parenchyma, with enlargement of the regional lymph nodes. Histologically, a chronic, non-purulent mastitis, characterized by a marked fibrous tissue proliferation and the coexistence of corpora amylacea within the glandular alveoli, was observed in association with chronic hyperplastic lymphadenitis involving the supramammary lymph nodes of the four cows. Immunohistochemically, S. marcescens was demonstrated, by means of monoclonal antibodies, both in the mammary gland and in the supramammary lymph nodes from these four animals.     

Epidemiological survey of an outbreak of multiresistant Serratia marcescens by PCR-fingerprinting

During an outbreak of Serratia marcescens from May to November 1993 43 strains obtained from 27 ICU patients infected or colonized with multiresistant S. marcescens were genotypically characterized with random amplified polymerase chain reaction (RAPD-PCR)-fingerprinting. In addition, 43 epidemiologically unrelated control isolates were selected. PCR-fingerprinting identified ten different genotypes of S. marcescens among the outbreak related strains. One predominant genotype was demonstrated in 21/43 isolates of 11/27 patients. A cluster of this genotype was found in seven/eight patients on the cardiosurgical ICU. The epidemiologically unrelated strains all showed different genotypes as compared to the predominant type. This survey proved RAPD-PCR to be a highly discriminatory and reproducible method for epidemiological studies of S. marcescens strains in nosocomial outbreaks.     

The biological properties of Serratia marcescens bacteriophages]

Sixteen phages active against bacteria of the genus Serratia have been divided into 4 groups on the basis of the study of their biological properties. As a result, 5 typing phages have been selected, which permitted the typing of 77.3% of S. marcescens cultures under study, divided into 13 phage types.     

Specific phosphatidylethanolamine dependence of Serratia marcescens cytotoxin activity

A region of dorsomedial frontal cortex (DMFC) has been implicated in planning and executing saccadic eye movements; hence it has been referred to as a supplementary eye field (SEF). Recently, activity related to executing smooth-pursuit eye movements has been recorded from the DMFC, and microstimulation here has been shown to evoke smooth eye movements. This report documents neuronal activity present in smooth-pursuit tasks where the predictability of target motion was manipulated. The activity of many neurons in the DMFC reached a peak when a predictable change in target motion occurred. Furthermore, the peak activity of some cells was systematically shifted by manipulating the duration of the target event, indicating that the network these neurons were in could learn the temporal characteristics of new target motion. Finally, the activity of most neurons tested was greater when target motion was predictable than when it was unpredictable. The results suggest that the DMFC participates in planning smooth-pursuit eye movements based on past stimulus history.     

Production, purification and characterization of a 50-kDa extracellular metalloprotease from Serratia marcescens

The extracellular metalloprotease (SMP 6.1) produced by a soil isolate of Serratia marcescens NRRL B-23112 was purified and characterized. SMP 6.1 was purified from the culture supernatant by ammonium sulfate precipitation, acetone fractional precipitation, and preparative isoelectric focusing. SMP 6.1 has a molecular mass of approximately 50,900 Da by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE). The following substrates were hydrolyzed: casein, bovine serum albumin, and hide powder. SMP 6.1 has the characteristics of a metalloprotease, a pH optimum of 10.0, and a temperature optimum of 42 degrees C. The isoelectric point of the protease is 6.1. Restoration of proteolytic activity by in-gel renaturation after SDS-PAGE indicates a single polypeptide chain. SMP 6.1 is inhibited by EDTA (9 micrograms/ml) and not inhibited by antipain dihydrochloride (120 micrograms/ml), aprotinin (4 micrograms/ml), bestatin (80 micrograms/ml), chymostatin (50 micrograms/ml), E-64 (20 micrograms/ml), leupeptin (4 micrograms/ml), Pefabloc SC (2000 micrograms/ml), pepstatin (4 micrograms/ml), phosphoramidon (660 micrograms/ml), or phenylmethylsulfonyl fluoride (400 micrograms/ml). SMP 6.1 retains full activity in the presence of SDS (1% w/v), Tween-20 (1% w/v), Triton X-100 (1% w/v), ethanol (5% v/v), and 2-mercaptoethanol (0.5% v/v). The extracellular metalloprotease SMP 6.1 differs from the serratiopeptidase (Sigma) produced by S. marcescens ATCC 27117 in the following characteristics: isoelectric point, peptide mapping and nematolytic properties.     

Environmental reservoirs for Serratia marcescens intramammary infections in dairy cows

Via special media, Serratia marcescens isolates were found in 3 bedding pack samples and in 2 milking parlor floor samples, and in milk samples from 19 cows during an episode of mastitis in a dairy cow herd. Chromosomal digest patterns of isolated S marcescens were indistinguishable for 18 of the milk samples and all bedding pack samples. Our findings provide strong evidence that the bedding pack was the reservoir of S marcescens associated with the outbreak of intramammary infections. Additionally, our ability to match digest patterns of isolates in the bedding pack and milk confirms the theory that S marcescens is an environmental pathogen capable of causing mastitis.     

Aminoglycoside resistance patterns of Serratia marcescens strains of clinical origin

Aminoglycoside resistance patterns of 147 Serratia marcescens strains of clinical origin were studied. All strains analysed belonged to three different bacterial populations. The periods of study and the institutions the strains were isolated from correlated significantly with the resistance patterns shown by the strains. The most frequent resistance patterns found were the following: ACC (6')-I at the Hospital Infantil de México (Children's Hospital of México), and ANT (2') + AAC(6')-I at the Instituto Nacional de Pediatría (INPed or National Institute of Pediatrics) in Mexico City. Furthermore, the isolation frequency of aminoglycoside-sensitive strains decreased remarkably at the INPed over a 12-year period. These results suggest that there has been a selection of Serratia marcescens strains that are very resistant to aminoglycosides.     

Genetic analysis of the chitinase system of Serratia marcescens 2170

To carry out a genetic analysis of the degradation and utilization of chitin by Serratia marcescens 2170, various Tn5 insertion mutants with characteristic defects in chitinase production were isolated and partially characterized. Prior to the isolation of the mutants, proteins secreted into culture medium in the presence of chitin were analyzed. Four chitinases, A, B, C1, and C2, among other proteins, were detected in the culture supernatant of S. marcescens 2170. All four chitinases and a 21-kDa protein (CBP21) lacking chitinase activity showed chitin binding activity. Cloning and sequencing analysis of the genes encoding chitinases A and B of strain 2170 revealed extensive similarities to those of other strains of S. marcescens described previously. Tn5 insertion mutagenesis of strain 2170 was carried out, and mutants which formed altered clearing zones of colloidal chitin were selected. The obtained mutants were divided into five classes as follows: mutants with (i) no clearing zones, (ii) fuzzy clearing zones, (iii) large clearing zones, (iv) delayed clearing zones, and (v) small clearing zones. Preliminary characterization suggested that some of these mutants have defects in chitinase excretion, a negatively regulating mechanism of chitinase gene expression, an essential factor for chitinase gene expression, and a structural gene for a particular chitinase. These mutants could allow researchers to identify the genes involved in the degradation and utilization of chitin by S. marcescens 2170.     

Cloning and DNA sequence analysis of an aac(3)-Vb gene from Serratia marcescens

The AAC(3)-V resistance mechanism is characterized by high-level resistance to the aminoglycosides gentamicin, netilmicin, 2'-N-ethylnetilmicin, and 6'-N-ethylnetilmicin and moderate resistance levels to tobramycin. Serratia marcescens 82041944 contains an AA(3)-V resistance mechanism as determined from aminoglycoside resistance profiles. This strain, however, does not exhibit hybridization with a probe derived from the previously cloned aac(3)-Va gene, (R. Allmansberger, B. Br?u, and W. Piepersberg, Mol. Gen. Genet. 198:514-520, 1985). High-pressure liquid chromatography analysis of the acetylation products of sisomicin carried out by extracts of S. marcescens 82041944 have demonstrated the presence of an AAC(3) enzyme. We have cloned the gene encoding this acetyltransferase and have designated it aac(3)-Vb. Nucleotide sequence comparisons show that the aac(3)-Va and aac(3)-Vb genes are 72% identical. The predicted AAC(3)-Vb protein is 28,782 Da. Comparisons of the deduced amino acid sequences show 75% identity and 84% similarity between the AAC(3)-Va and AAC(3)-Vb proteins. The use of a DNA fragment internal to the aac(3)-Vb as a hybridization probe demonstrated that the aac(3)-Vb gene is very rare in clinical isolates possessing an AAC(3)-V mechanism.     

Suppression of murine experimental autoimmune hepatitis by T-cell vaccination or immunosuppression

Patients with autoimmune hepatitis (AIH) usually require immunosuppressive therapy for many years, if not for a lifetime. Experimental immunotherapy such as T-cell vaccination aims at manipulating the immune system in such a way that autoimmunity is specifically regulated to enable long-lasting correction of the disease process. We aimed to test the feasibility of T-cell vaccination as well as conventional immunosuppression in the murine model of experimental autoimmune hepatitis (EAH). EAH was induced in 5- to 7-week-old BALB/c mice by immunization with syngeneic liver homogenate in complete Freund's adjuvant. For T-cell vaccination, splenocytes were removed from animals 14 days after induction of EAH and from control animals, and activated in vitro by mitogen stimulation with Concanavalin A (Con A). Activated T cells were irradiated and injected at 5 x 10(7) cells per animal as T-cell vaccine. Immunosuppression in control animals was performed with prednisolone with or without azathioprine. T-cell vaccination with T cells from EAH animals, but not with irrelevant T cells, was able to protect animals from EAH, reducing the average disease severity from 2.2 (+/-0.3) to 0.5 (+/-0.3) (P < .01). T-cell vaccination was also able to treat EAH, because application of the vaccine 2 weeks after induction of the disease significantly reduced disease activity at week 4 from 2.4 (+/-0.4) to 1.1 (+/-0.2) (P < .05). Both passive transfer of disease and the capacity to protect by T-cell vaccination was mediated by CD4 T cells. Specific cellular recognition of activated disease-inducing T cells could be detected in vaccinated animals. Immunosuppressive drugs could also suppress EAH. Thus, T-cell vaccination in EAH is feasible and effective. Stimulation of a regulatory T-cell network is the likely mechanism of action by which T-cell vaccination can suppress EAH.     

Epidemiology of Serratia marcescens between 1987 and 1995 at Vall d'Hebron Hospital

BACKGROUND: Nosocomial infection have a relative high prevalence, which is necessary to reduce in order to improve the quality of patient care. The aims of this work is to study the behaviour of Serratia marcescens in our hospital as between 1987 and 1995. METHODS: Between February 1987 and March 1995 we detected 679 isolates of Serratia marcescens in 504 patients. We used serotype as first marker and phagotype as second, and evaluation of PGFE as a discriminator of doubtful strains was done. RESULTS: 35.8% of the strains were from the respiratory tract, 37.2% from urinary tract; and 11.7% were isolated in blood culture, among them 23.3% came form children younger than 7 years. We noticed a tendency to decrease the number of isolates along the studied period. The most frequent serotypes were O:6, O:3 and O:2; representing the 36.0% of the total. Serotypes O:6;14, O:4, O:5, O:11 and polyagglutinables accounted for 37% of the total. The frequency was variable from year to year, and the predominant serotypes were different in every one of the hospitals in which the center is divided. A 60% of the patients were hospitalized in the General Hospital Vall d'Hebron building, in ICU (20%) and in chirurgical services (25%). Ninety-six patients had more than one isolate, 91 of them (94.8%) can be classified by phenotypic test. The PFGE is discriminatory in three of the five unclassificable isolates. In more than 35% of the patients the strains isolated along the time are different. The 66.7% of the patients acquired Serratia strains in the same admission, and in some cases with few days of difference. We detected 17 cross infections, predominantly in ICUs. With PFGE we could discriminate isolates which produced cross infections between patient who are not in the same hospital. CONCLUSIONS: Although the prevalence of Serratia marcescens is diminishing, it is able to produce crossed infections that, in general, affected few patients. The serotype and phagotype discriminate 94.8% of isolates. The PFGE is high discriminatory and reproducible, only 6.8% of the 44 strains tested by this method can not be typed.     

Characterization of secretory intermediates of Serratia marcescens serine protease produced during its extracellular secretion from Escherichia coli cells

The Serratia marcescens serine protease (SSP; 66 kDa) is synthesized as a precursor (preproSSP; 112 kDa) composed of the NH2-terminal signal peptide of 27 amino acids, the mature protease part and a large COOH-terminal domain. When the SSP gene is expressed in Escherichia coli under the control of the tac promoter, the mature enzyme is excreted into the medium through the outer membrane, whereas preproSSP and two proteins, C-1 (40 kDa) and C-2 (38 kDa), processed from the COOH-terminal domain, are accumulated in the membrane fraction. Although treatment of the intact cells with trypsin caused slight truncation of C-1 and C-2, the main parts of C-1 and C-2, both of which are detected in the outer membrane, were resistant to trypsin, even after the cells had been osmotically shocked. Consistent with this, a high content of beta-sheet structure in C-2 was suggested by marked heat-modifiability, as determined by their electrophoretic mobilities on SDS-polyacrylamide gel. These findings suggest rigid integration of C-1 and C-2 in the outer membrane. Upon induction of the tac promoter, rapid excretion of SSP into the medium was first accompanied by the accumulation of C-1 in the outer membrane, which was followed by conversion of C-1 to C-2. PreproSSP was not detected during the accumulation of SSP in the medium, but it was gradually accumulated after the accumulation of SSP had reached a plateau. In addition, preproSSP still containing the intact NH2-terminal signal peptide was completely digested with trypsin when added to osmotically shocked cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Detection of cytotoxic activity on Vero cells in clinical isolates of Serratia marcescens

Cytotoxin production was studied in 60 Serratia marcescens strains isolated from hospitalized patients. Association of cytotoxic activity with serotype, source of isolation and presence of plasmids was also evaluated. Thirteen of the 60 S. marcescens strains produced a cytotoxic effect on Vero cells. These strains were isolated from distinct clinical sources and classified into seven different serotypes (O1:H7; O4:NM; O10:NT; O19:NM; O6,14:H4; O6,14:NM and O6,14:H1). No relationship was observed between cytotoxic activity and clinical source or serotypes of the strains. Plasmids from five cytotoxin-producing S. marcescens strains were transferred to E. coli K12/711. The transconjugants did not exhibit cytotoxicity, indicating that the cytotoxic effect is not plasmid-mediated among these strains. Although a cytotoxic activity was demonstrated in filtrates of some S. marcescens strains, further studies should be performed to assess the role of this toxin in pathogenesis.