Serratia marcescens. A pathogen of increasing clinical importance

Serratia infections: from military experiments to current practice

Serratia species, in particular Serratia marcescens, are significant human pathogens. S. marcescens has a long and interesting taxonomic, medical experimentation, military experimentation, and human clinical infection history. The organisms in this genus, particularly S. marcescens, were long thought to be nonpathogenic. Because S. marcescens was thought to be a nonpathogen and is usually red pigmented, the U.S. military conducted experiments that attempted to ascertain the spread of this organism released over large areas. In the process, members of both the public and the military were exposed to S. marcescens, and this was uncovered by the press in the 1970s, leading to U.S. congressional hearings. S. marcescens was found to be a certain human pathogen by the mid-1960s. S. marcescens and S. liquefaciens have been isolated as causative agents of numerous outbreaks and opportunistic infections, and the association of these organisms with point sources such as medical devices and various solutions given to hospitalized patients is striking. Serratia species appear to be common environmental organisms, and this helps to explain the large number of nosocomial infections due to these bacteria. Since many nosocomial infections are caused by multiply antibiotic-resistant strains of S. marcescens, this increases the danger to hospitalized patients, and hospital personnel should be vigilant in preventing nosocomial outbreaks due to this organism. S. marcescens, and probably other species in the genus, carries several antibiotic resistance determinants and is also capable of acquiring resistance genes. S. marcescens and S. liquefaciens are usually identified well in the clinical laboratory, but the other species are rare enough that laboratory technologists may not recognize them. 16S rRNA gene sequencing may enable better identification of some of the less common Serratia species.

Effects of temperature, nutrients, organic matter and coral mucus on the survival of the coral pathogen, Serratia marcescens PDL100

Serratia marcescens is an enteric bacterium that causes white pox disease in elkhorn coral, Acropora palmata; however, it remains unclear if the pathogenic strain has adapted to seawater or if it requires a host or reservoir for survival. To begin to address this fundamental issue, the persistence of strain PDL100 was compared among seawater and coral mucus microcosms. Median survival time across all conditions ranged from a low of 15 h in natural seawater [with a first-order decay constant (k) = -0.173] at 30°C to a maximum of 120 h in glucose-amended A. palmata mucus (k = -0.029) at 30°C. Among seawater and mucus microcosms, median survival time was significantly greater within Siderastrea siderea mucus compared with seawater or mucus of Montastraea faveolata or A. palmata (P < 0.0001). In seawater, the addition of phosphate and especially glucose resulted in significant improvements in survival (P < 0.001), while only the addition of glucose resulted in significant improvement in survival in A. palmata mucus (P < 0.0001). Increasing the temperature of seawater to 35°C resulted in a significantly slower decay than that observed at 30°C (P < 0.0001). The results of this study indicate that PDL100 is not well-adapted to marine water; however, survival can be improved by increasing temperature, the availability of coral mucus from S. siderea and most notably the presence of dissolved organic carbon.

Endogenous Serratia marcescens endophthalmitis with dark hypopyon: case report and review

A case of endogenous Serratia marcescens endophthalmitis in a patient with diabetes, end-stage renal disease, and an indwelling venous catheter is reported. The patient presented with a tan hypopyon and elevated intraocular pressure. Diagnosis was established by positive blood, vitreous, conjunctival, and catheter tip cultures. After a deteriorating course the eye was enucleated. Gross and histopathologic examination revealed the presence of a dark hypopyon with iris necrosis and pigment dispersion and possible spontaneous globe perforation. This is the eleventh reported case of endogenous Serratia endophthalmitis. Previous association of a pink hypopyon and of pigmented vitreous fluid and Serratia endophthalmitis has been reported. This is the first case of dark hypopyon in endogenous Serratia marcescens endophthalmitis reported in the medical literature. Previous entities associated with dark hypopyon have been limited to intraocular melanoma and Listeria monocytogenes endophthalmitis. Dark hypopyon in the appropriate clinical setting may be useful in aiding diagnostic and therapeutic decisions.

Combination of biotyping and electrophoretic patterns of esterases for differentiation of nosocomial Serratia marcescens strains

A total of 292 Serratia marcescens strains isolated in seven Belgian hospitals between 1986 and 1992 were submitted to both biotyping by carbon source utilization and esterase electrophoresis typing. The strains were assigned to 11 biotypes (290 isolates) or were auxotrophic (2 isolates), whereas the various electrophoretic patterns of their esterases produced 54 zymotypes. The two typing methods correlate well, since biotypes embraced more than one zymotype, while each zymotype was restricted to a single biotype. Esterase electrophoretic patterns represent a potent marker for delineating outbreaks of nosocomial infections, whereas biotyping appears to be an appropriate method for screening of strains.

Pink hypopyon: a sign of Serratia marcescens endophthalmitis

Endogenous bacterial endophthalmitis in infants is uncommon. We recently examined and treated an infant who presented with pink hypopyon which followed a Serratia marcescens septicaemia. Culture of the aspirate from the anterior chamber showed no red blood cells, and grew Serratia marcescens, which was also isolated from the tip of the child's umbilical artery catheter. The presence of a pink hypopyon in the absence of hyphaema may suggest the diagnosis of Serratia marcescens endophthalmitis.

Immunophysical characterization of human isolates of Serratia marcescens

The immunophysical characteristics of 29 Serratia marcescens strains isolated from hospitalized patients in three different cities were studied. Their outer membrane antigens were compared by solid-phase radioimmunoassay inhibition, and their proteinase K-treated, whole-cell lysates were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analysis. The strains had a limited number of unique outer membrane lipopolysaccharide (LPS) and capsular polysaccharide (K) antigens. By solid-phase radioimmunoassay inhibition, these strains could be divided into four distinct LPS and five K antigenic groups. By SDS-PAGE, the LPS groups could be further divided into three distinct SDS-PAGE core polysaccharide profiles and five distinct O-side-chain polysaccharide profiles. Immunoblot analysis with rabbit antiserum confirmed the limited heterogeneity of these isolates. Of the strains tested, no PAGE profile was unique to blood or nonblood isolates or to organisms collected from a given hospital. Variability of O and core PAGE profiles was not a function of organism growth cycle. Five representative Serratia strains were tested by SDS-PAGE and immunoblot analysis and in a bactericidal assay with normal human serum. We found that (i) the normal human serum had antibodies to the LPS of each of the strains, (ii) the anti-LPS antibody measured by immunoblot did not correlate with the level of bactericidal activity in the normal human serum, (iii) three of four sepsis isolates were serum sensitive, (iv) two Serratia strains serum sensitive in log-phase growth became serum resistant in late stationary-phase growth and under limiting nutrient conditions, and (v) no LPS PAGE profile distinguished serum-sensitive from serum-resistant strains.

Serratia bacteremia

During a 6-yr period, 146 patients at our institution had Serratia bacteremia (3.8% of the total number of episodes of bacteremia), with an incidence of 1.24/1000 admitted patients. We chose a random group of 50 cases for clinical analysis in the present study. The disease was community-acquired in 8% of the cases and nosocomially-acquired in the remaining 92%. The bacteremia was unimicrobial in 84% and part of a polymicrobial bacteremia in 16% of the episodes. The most frequently isolated species of the Serratia genus was S. marcescens. Portals of entry, in decreasing order of frequency, were: urinary, unknown, respiratory, and surgical wound infections. Clinically, the most frequent finding was fever (100%). Shock occurred in 28% of the patients, and none of our cases showed evidence of disseminated intravascular coagulation. We found 62% of Serratia isolates resistant to gentamicin. Overall mortality was 38% and factors associated with a poor prognosis were: severity of the underlying disease, critical clinical situation at onset of bacteremia, presence in the intensive care unit (I.C.U.), occurrence of shock or polymicrobial bacteremia, portal of entry in the respiratory tract, and inadequate treatment.

A serratial protease causes vascular permeability reaction by activation of the Hageman factor-dependent pathway in guinea pigs

The 56-kilodalton (56K) protease isolated from a culture filtrate of Serratia marcescens caused vascular permeability enhancement followed by edema formation when injected into guinea pig peripheral corneas and subconjunctival space or skin. The character and the mechanism of permeability enhancement were analyzed in vivo. The enhancement was maximum at 5 to 10 min. The permeability reaction increased exponentially by the amount of enzyme used. The enhancement of permeability induced by the 56K protease was not affected by treatment with an antihistamine but was greatly augmented by simultaneous injection of a kinin potentiator, Glu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro-OH (SQ 20,881). Furthermore, the permeability activity of the protease, but not the amidolytic activity, was inhibited by soybean trypsin inhibitor, a well-known inhibitor of plasma kallikrein, as well as by corn trypsin inhibitor, the best inhibitor of activated Hageman factor. Results of these in vivo studies indicate that the permeability-enhancing reaction induced by the 56K protease is caused by activation of the Hageman factor-dependent pathway in the tissue. The permeability-increasing activity of the 56K protease was parallel with the enzyme activity. Serratial lipopolysaccharide did not produce a permeability enhancement reaction within 30 min when injected into guinea pig skin. These results are consistent with the results of recent in vitro experiments in which activation of the purified Hageman factor but not of prekallikrein by the 56K protease was elucidated (Matsumoto et al., J. Biochem. (Tokyo) 96:739-749, 1984). Thus, the molecular mechanism described above appears to be operative in the pathogenesis of corneal edema and chemosis, which is induced by S. marcescens, in addition to the direct tissue destruction by the protease.

Subacute constrictive pericarditis from Serratia marcescens bacteremia

A case report of subacute constrictive pericarditis associated with disseminated Serratia marcescens infection and bacteremia in a patient with chronic tubulointerstitial nephritis and uremia is described. Although not substantiated by clinical history, the renal pathologic features were similar to those of ethylene glycol-induced tubulointerstitial nephritis. The patient did not have a history of heroin addiction. The importance of predisposing factors such as uremia, invasive vascular procedures, tracheal intubation, peritoneal dialysis, and pericardiocentesis in Serratia infection in susceptible persons is discussed, as are possible roles of uremia, pericardiocentesis, and pericardiotomy in the pathogenesis of constrictive pericarditis in the present case.

Pathologic patterns of Serratia marcescens pneumonia

To characterize the pulmonary lesions caused by Serratia marcescens, the authors reviewed all autopsy-culture-proven cases of S. marcescens pneumonia occurring at their hospital between 1968 and mid-1980. In 16, S. marcescens was the only organism cultured from the lungs during life or at autopsy. This report describes primarily these pure infections. Two histopathologic reactions were seen. Nine non-neutropenic patients had acute, hemorrhagic bronchopneumonia, seven with microabscesses and two with larger cavities. In seven, distinctive vasculitis was apparent in vessels larger than 75 microns in diameter; intramural gram-negative rods were identified in two. Seven immunosuppressed patients had diffuse neutropenic pneumonitis resembling diffuse alveolar damage, with extensive intra-alveolar fibrinous exudates and pulmonary hemorrhage. In two patients, bacteria without cellular reaction were present. In patients with prolonged infections, focal areas of intra-alveolar organization and bronchiolitis obliterans accompanied both patterns. Since the incidence of nosocomial S. marcescens infection is increasing and since pneumonia caused by this organism is recognizable histologically, autopsy cultures positive for S. marcescens should not be disregarded.

Characterization of rabbit corneal damage produced by Serratia keratitis and by a serratia protease

The structural alterations elicited in the rabbit corneal stroma by experimental Serratia marcescens keratitis and by a highly purified serratia protease preparation were compared by gross observation, biochemical analyses, and electron microscopic examination of the affected tissue. Acute inflammation, liquefactive necrosis of the cornea, and descemetocele formation occurred during the development of the infection and after the intracorneal injection of submicrogram amounts of the protease. In vitro incubation of insoluble corneal stromal tissue with the bacterium or with the protease resulted in solubilization of the stromal proteoglycan ground substance; however, specific collagenase activity was not detected. Electron microscopic examination of corneas damaged by the bacterial infection and by the protease revealed loss of ruthenium red staining of the proteoglycan ground substance and dispersal of ultrastructurally normal collagen fibrils. Thus, our findings indicate that the major corneal damage which occurs during serratia keratitis and after the injection of the serratia protease is caused by solubilization and loss of the ground substance of the tissue. In addition, the observation that the major structural alterations observed during serratia keratitis can be reproduced by the bacterial protease supports the idea that the enzyme is involved, at least in part, with the production of severe corneal damage by the bacterium.

The increasing isolation of Serratia species from clinical specimens

A 14-month survey was undertaken in a diagnostic bacteriology laboratory to determine the incidence of Serratia spp. in routine clinical specimens. Gram-negative organisms with enterobacteria-like colonies were tested by a simple screening procedure. Fifty-eight strains of S. marcescens and two strains of S. liquefaciens were isolated from 59 patients. The strains were usually non-pigmented and exhibited multiple antibiotic resistance. Serotyping and determination of bacteriocine sensitivity patterns revealed that the majority of infections were sporadic, although episodes of cross-infection did occur. S. marcescens was considered to contribute significantly to morbidity and mortality in 53% of patients and appears to be of increasing importance in hospital-acquired infections.

Detection of Serratia outbreaks in hospital

Infections due to Serratia marcescens were studied in 23 different hospitals. A retrospective study was done in 4 hospitals; all isolates were compared by serological typing, antibiograms, bacteriocin production, and bacteriocin sensitivity. 2 of the hospitals were having cross-infection problems due to antibiotic-resistant strains, but the other 2 had little or no cross-infection. Outbreaks were studied in 19 other hospitals. 9 of these outbreaks were classified as "common source" since contaminated "sterile solutions" were incriminated as the cause in each. One hospital had a "pseudo-outbreak," in which Serratia from E.D.T.A. blood-collecting tubes contaminated blood-cultures as they were collected. All 10 of these strains from common-source outbreaks were generally sensitive to antibiotics. Outbreaks in 9 other hospitals resulted from cross-infection and were caused by strains which were very resistant to antibiotics. Guidelines for detecting outbreaks are given and control measures are suggested.

[Antibody detection in infections with Serratia marcescens (author's transl)]

A report is given on the detection by agglutination and precipitation of antibodies against homologous strains in infections with Serratia marcescens. The results of the investigation indicate that antibody formation is likely if invasive forms are present. The agglutination titers were between 1:40 and 1:640. It can be presumed that, in addition to the patient's antibodies against the O antigen, antibodies are also formed against certain antigens with the character of ferments or toxins.

Antibiogram and lipid analysis of a pigmented strain of Serratia marcescens and its nonpigmented variants

Antibiograms and lipid analyses of Serratia marcescens pigmented strain 08 and its nonpigmented variants are compared. The overall lack of significant differences between pigmented and nonpigmented strains suggests that the role of pigment formation may not be related to antibiotic susceptibility.

Antibiograms and lipid contents of pigmented and nonpigmented strains of Serratia marcescens

The antibiogram of pigmented 08 and nonpigmented Bizio strains of Serratia marcescens was determined. Their lipid content was also analyzed.

Hydrolysis of casein: a differential aid for the indentification of Serratia marcescens

Through the hydrolysis of casein, a cultural characteristic has been established in the preliminary identification of Serratia marcescens. Compared against 438 strains of the families, Pseudomonadaceae and Enterobacteriaceae, this organism has a reproducible capability to decompose casein, while most other Gram-negative bacilli failed to produce any hydrolysis, or, at the most, hazy zones only. Routine use has shown this to be a valuable differential aid in the identification of Serratia marcescens.

Lipid content of antibiotic-resistant and -sensitive strains of Serratia marcescens

The lipid content of antibiotic-resistant, nonpigmented strain (Bizio) and antibiotic-sensitive, pigmented strain (08) of Serratia marcescens was studied. The resistant strain contains at least three times more total extractable lipid and phospholipid than the sensitive strain. Lysophosphatidylethanolamine, phosphatidylserine, lecithin, phosphatidylglycerol, phosphatidylethanolamine, and polyglycerolphosphatide were identified in the phospholipid fractions of both strains.

Hazard inherent in microbial tracers: reduction of risk by the use of Bacillus stearothermophilus spores in aerobiology

The use of a "biological tracer" forms an essential part of many aerobiological experiments. Where release of such tracers is likely to result in deliberate or inadvertent human exposure, safety becomes a primary consideration in the selection of the tracer organism. Of the three most commonly used organisms, namely Bacillus subtilis, Escherichia coli, and Serratia marcescens, only the first comes near to satisfying the need for nonpathogenicity and even it has been incriminated as a cause of human infection, sometimes with a fatal outcome. The relevant characteristics of B. stearothermophilus were, therefore, investigated. Because it can grow only at elevated temperatures (minimum 41 C; optimum 56 C), it should not pose a threat to human health and this view is supported by experimental evidence to be presented. It is extremely easy to grow and maintain in the laboratory, and spore suspensions are easily prepared and stored. It withstands the stresses of aerosolization and sampling and its stability in the aerosol state compares favorably with that of B. subtilis var. niger.

Epidemiological surveillance of Serratia marcescens infections by bacteriocin typing

During 10 months, 155 isolates of Serratia marcescens were cultured from 105 patients, of whom 49 were considered to have significant infection. The 155 isolates were typed by bacteriocin sensitivity, and 137 (88.4%) were assigned to 37 provisional bacteriocin groups; 18 isolates were nontypable. No major outbreaks of nosocomial infection were demonstrable; however, there were four chronologically separate minor episodes of cross-infection that involved two or three patients per room or unit, respectively.