Hemagglutination (fimbriae) and hydrophobicity in adherence of Serratia marcescens to urinary tract epithelium and contact lenses

Genome evolution and plasticity of Serratia marcescens, an important multidrug-resistant nosocomial pathogen

Serratia marcescens is an important nosocomial pathogen that can cause an array of infections, most notably of the urinary tract and bloodstream. Naturally, it is found in many environmental niches, and is capable of infecting plants and animals. The emergence and spread of multidrug-resistant strains producing extended-spectrum or metallo beta-lactamases now pose a threat to public health worldwide. Here we report the complete genome sequences of two carefully selected S. marcescens strains, a multidrug-resistant clinical isolate (strain SM39) and an insect isolate (strain Db11). Our comparative analyses reveal the core genome of S. marcescens and define the potential metabolic capacity, virulence, and multidrug resistance of this species. We show a remarkable intraspecies genetic diversity, both at the sequence level and with regards genome flexibility, which may reflect the diversity of niches inhabited by members of this species. A broader analysis with other Serratia species identifies a set of approximately 3,000 genes that characterize the genus. Within this apparent genetic diversity, we identified many genes implicated in the high virulence potential and antibiotic resistance of SM39, including the metallo beta-lactamase and multiple other drug resistance determinants carried on plasmid pSMC1. We further show that pSMC1 is most closely related to plasmids circulating in Pseudomonas species. Our data will provide a valuable basis for future studies on S. marcescens and new insights into the genetic mechanisms that underlie the emergence of pathogens highly resistant to multiple antimicrobial agents.

Role of hydrophobicity in adhesion of wild yeast isolated from the ultrafiltration membranes of an apple juice processing plant

The role of cell surface hydrophobicity in the adhesion to stainless steel (SS) of 11 wild yeast strains isolated from the ultrafiltration membranes of an apple juice processing plant was investigated. The isolated yeasts belonged to four species: Candida krusei (5 isolates), Candida tropicalis (2 isolates), Kluyveromyces marxianus (3 isolates) and Rhodotorula mucilaginosa (1 isolate). Surface hydrophobicity was measured by the microbial adhesion to solvents method. Yeast cells and surfaces were incubated in apple juice and temporal measurements of the numbers of adherent cells were made. Ten isolates showed moderate to high hydrophobicity and 1 strain was hydrophilic. The hydrophobicity expressed by the yeast surfaces correlated positively with the rate of adhesion of each strain. These results indicated that cell surface hydrophobicity governs the initial attachment of the studied yeast strains to SS surfaces common to apple juice processing plants.

Bacterial cell attachment, the beginning of a biofilm

The ability of bacteria to attach to surfaces and develop into a biofilm has been of considerable interest to many groups in numerous industries, including the medical and food industry. However, little is understood in the critical initial step seen in all biofilm development, the initial bacterial cell attachment to a surface. This initial attachment is critical for the formation of a bacterial biofilm, as all other cells within a biofilm structure rely on the interaction between surface and bacterial cell for their survival. This review examines what are believed to be some of the most important aspects involved in bacterial attachment to a surface.

Isolation rate of non-hemagglutinating strains of Serratia marcescens from clinical specimens in a general hospital: comparison of serotypes O2 and O14

Given the absence of recent reports on the isolation rate of Serratia marcescens by pili type, clinical isolates from respiratory and urinary tract specimens--prime loci of infection by this organism--were subjected to examination. The 123 S. marcescens strains (serotype O2, 67 strains, serotype O14, 56 strains) used in this study were isolated from inpatients at Showa University Fujigaoka Hospital during the 5 years from April 1997 to March 2002. Higher rates of S. marcescens O2 with mannose-resistant (MR)/K Klebsiella-like pili were detected among the respiratory tract-derived strains. On the other hand, more non-hemagglutinating O14 strains were found among the urinary tract-derived strains. Analysis by study phase revealed a rise in the isolation rate of non-hemagglutinating strains, from 0-17.4% for O2 strains and 34.5%-66.7% for O14 strains, between phase I (April 1997 to March 1999) and phase II (April 1999 to March 2002) of the study. In order to examine the increasing non-hemagglutinating strains in detail, the 28 serotype O14 non-hemagglutinating strains, and 8 strains with only mannose-sensitive (MS) pili were subjected to genotyping by pulsed-field gel electrophoresis (PFGE), revealing the presence of 10 clones with disparate genotypes. The A1 strain isolated at the highest frequency was non-hemagglutinating in all cases and possessed the same genotype, indicating proliferation within the hospital over the 5 years of the study. These results indicate that non-hemagglutinating strains were transmitted among patients within the hospital.

Contribution of the hydrophobic effect to microbial infection

The hydrophobic effect has been known for decades. Numerous researchers have invoked the hydrophobic effect to explain how pathogens adhere to tissues. In some cases, inhibition of adhesion can be brought about by low concentrations of aromatic compounds, such as p-nitrophenol or tryptophan. Because the hydrophobic effect has been considered to be nonspecific, the molecular biology of adhesive hydrophobins has not been studied in as much detail as lectin adhesins. The literature provides compelling evidence that a large number of bacterial and fungal pathogens depend on hydrophobic interactions for successful colonization of a host. Several laboratories are now developing effective antiadhesins, based on inhibition of hydrophobic interactions between the host and the pathogen.

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.

The role of Serratia marcescens in soft contact lens associated ocular infections. A review

Serratia marcescens is a Gram negative rod which for a century and a half was considered a harmless saphrophyte. However, medical technology and the use of antibacterial agents have created ecological niches for this bacterium, which is now a medical problem. The bacterium is encountered in connection with contact lens keratitis, often associated with contaminated contact lens solutions. The concentrations of chlorhexidin and thiomersal required in contact lens solution to suppress the bacterium have been proved toxic to the eye. Modern contact lens solutions with biguanids have rapid killing kinetics, while in solutions with polyquaternium S. marcescens can survive in reduced numbers for up to 72 hours. The adherence of a specific isolate of Serratia to hydrogel lenses increased with decreased water content of the lenses. However, there has been no correlation between hydrophobicity markers or hemagglutinins and adherence to contact lenses or urinary tract epithelium. When handling medical plastic devices, such as contact lenses, strictly enforced hygiene remains the most important method to combat environmental bacteria such as Serratia marcescens.

Culture conditions affect cytotoxin production by Serratia marcescens

Cytotoxins have been implicated in the pathogenesis of bacterial infections. In this study, the influence of different culture conditions was evaluated on cytotoxin production of Serratia marcescens. Parameters such as culture media, incubation temperature, starting pH of culture medium, aeration, anaerobiosis, carbon sources, iron concentration in he culture media, and release of cell-bond toxin by polymyxin B were investigated. The data suggest that this cytotoxin is predominantly extracellular and is not induced by iron limitation. Aerobic culture with shaking resulted in higher cytotoxicity than static aerobic or anaerobic culture. Bacteria grown in glucose, sucrose or galactose were more cytotoxic than those grown in inositol or maltose. The culture conditions that were identified as optimal for cytotoxin production by Serratia marcescens were incubation temperature ranging from 30 to 37 degrees C, in medium adjusted pH 8.5, with shaking. This work will contribute to further studies on the identification of this cytotoxic activity.

Effects of silver on adherence of bacteria to urinary catheters: in vitro studies

Strains of Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Enterococcus faecalis, and Klebsiella pneumoniae, mostly from complicated urinary tract infections, showed reduced adherence to silver-treated silicone or latex catheters as compared with latex or silicone catheters. The relative degrees of cell adherence to catheters at 2 h or 18 h, as indicated by radiolabeled cell assays, were in general agreement with growth rate-reduction assays and scanning-electron-microscopy data. For strains of E. coli, the correlation between cell hydrophobicity and degree of adherence to catheters was not significant. Antibiotic resistance (tetracycline, sulfathiazine, neomycin, kanamycin) and silver resistance were not associated. The radiolabel adherence procedure provided a quantitative method for evaluating the relative antimicrobial efficacy of silver-treated catheters.

Adherence of Serratia marcescens, Serratia liquefaciens, Pseudomonas aeruginosa and Staphylococcus epidermidis to blood transfusion bags (CPD-SAGMAN sets)

The adherence of 4 isolates of Serratia marcescens, 1 isolate of Serratia liquefaciens, 1 of Pseudomonas aeruginosa, and 2 of Staphylococcus epidermidis to blood transfusion sets (CPD-SAGMAN) consisting of bags and connecting tubing was tested. All strains adhered well to the connecting tubes (polyvinyl chloride) from the transfusion sets from 3 manufacturers. Three isolates from a Swedish outbreak of septicaemia associated with contaminated blood bags showed greater adherence than an isolate from a urinary tract infection. There was no significant adherence of S. marcescens to the blood bags. In general, there were no significant differences in the adherence of a given isolate to the plastics from different manufacturers. Appropriate hygienic procedures for the production of transfusion sets appear to be of greater importance than differences in the plastic material as regards the incidence of transfusion-related bacteremia.