Colonial variation in Serratia marcescens together with antibiotic resistance

A strain of Serratia marcescens, isolated from the blood cultures of a patient receiving antibiotics, exhibited 3 unstable properties. These properties were resistance to aminoglycosides, colony size and pigment production. While resistance to aminoglycosides was linked to colony size, pigment production appeared independent of the other 2 properties. When multiple variation of properties occurs in colonies isolated from clinical material, this still may represent a pure culture.     

Co-transduction mapping in Serratia marcescens

The linkage of 34 auxotrophic markers in strain HY of Serratia marcescens was studied by means of transductions with phages x and y. The markers could be ordered into 18 loci of different auxotrophies by transduction crosses with phage x (markers in trans-position) 17 of which showed to be linked to at least one of the other loci. A linear map of this section of the genome was constructed. It corresponds well to the map of 8 loci derived from transductive crosses (markers in cis-position) with phage y. Since a virion can transduce about 5 loci at the same time the map represents only a small section of the Serratia genome. No similarity to any part of the maps of Escherichia or Salmonella can be detected. It is discussed why most auxotrophic mutations which were induced by nitrosoguanidine map in this small genomic region.     

Cross-infection with Serratia marcescens

Cross-infection in a urological unit due to Serratia marcescens is reported. The bacteriology of the organism and its mode of spread are described. It is suggested that Serratia marcescens may be a more virulent organism than is generally believed, especially in situations in which there is an excess of mucus.     

Serratia marcescens meningitis.

A case of Serratia marcescens meningitis in a 66-year-old man is reported. The infection occurred 4 weeks after apparently successful otic surgery, and a nidus of infection in the middle ear was established at autopsy. This is the second case of S. marcescens meningitis following ear surgery reported in the English-language literature.     

Pulmonary infection with Serratia marcescens

A case of pulmonary infection, presenting with fever and productive cough (pseudohaemoptysis) was diagnosed as having infection with Serratia marcescens on performing culture and sensitivity tests. The organism was confirmed upto species level using the standard biochemical tests.     

Oxygen uptake by Serratia marcescens

Oxygen uptake was studied in cell suspensions of Serratia marcescens BIZIO supplied with various types of substrates. Of the polyols provided as substrates glycerol was the best stimulant of oxygen uptake followed by D-mannitol and sorbitol. D-xylitol and meso-inositol stimulated oxygen uptake only after a long lag. The hexose sugars as well as their phosphorylated derivatives were better than the pentoses as stimulants of oxygen uptake. Ammonium accelerated oxygen uptake in the presence of fructose, glucose or mannitol. Oxygen uptake in the presence of either glucose-l-phosphate or glucose-6-phosphate was independent of NADP⁺, indicating a non-enzymic system.     

The cell-bound hemolysin of Serratia marcescens contributes to uropathogenicity

The contribution of the cell-bound hemolysin of Serratia marcescens to uropathogenicity was studied in an experimental urinary tract infection in rats. The strain carrying the Serratia hemolysin colonized the urinary tract more and lead to a stronger inflammatory response compared to the isogenic hemolysin negative strain.     

The role of integrons in dissemination of antibiotic resistance

Bacteria can transfer genetic information to get protection against most antibiotics. The acquisition of resistance genes involves genetic mobile elements such as plasmids and transposons. Another genetic structures, named integrons, have been described and contain one or more gene cassettes located at a specific site. Integrons contain an intI gene encoding a site-specific recombinase belonging to the integrase family and a recombination site attI. A gene cassette includes an open reading frame and, at the 3'-end, a recombination site attC. Integration or excision of cassettes occurs by a site-specific recombination mechanism catalyzed by the integrase. However, insertion can rarely occur, at non-specific sites leading to a stable situation for the cassette. Cassettes are transcribed from a common promoter located in the 5'-conserved segment and expression of distal genes is reduced by the presence of upstream cassettes. Most gene cassettes encode antibiotic resistant determinants but antiseptic resistant genes have also been described. Integrons seem to have a major role in the spread of multidrug resistance in Gram-negative bacteria but integrons in Gram-positive bacteria have been recently described. Moreover, the finding of super-integrons with gene cassettes coding for other determinants (biochemical functions, virulence factors) in different Gram negative bacteria suggests that integrons are probably implied in bacterial genome evolution.     

The role of integrons in antibiotic resistance gene capture

Although recently discovered, integrons have played a primordial role in the evolution of bacterial genomes. They are best known as the genetic agents responsible for the capture and spread of antibiotic resistance determinants among diverse Gram-negative clinical isolates, and this activity is at the root of the antibiotic resistance phenomenon that has evolved over the last 60 years. The discovery of the ancestral chromosomal super-integrons, novel integron classes, and the multitude of gene cassettes they propagate solidify the crucial role of this system in adaptive bacterial evolution. Recent evidence suggests that evolutionarily old genetic recombination mechanisms for gene transfer have been adapted to the new antibiotic environment due to the heavy selective pressure of liberal antibiotic use in human medicine and animal husbandry.     

Evidence of an efflux pump in Serratia marcescens

Spontaneous mutants resistant to fluoroquinolones were obtained by exposing Serratia marcescens NIMA (wild-type strain) to increasing concentrations of ciprofloxacin both in liquid and on solid media. Frequencies of mutation ranged from 10(-7) to 10(-9). Active expulsion of antibiotic was explored as a possible mechanism of resistance in mutants as well as changes in topoisomerase target genes. The role of extrusion mechanisms in determining the emergence of multidrug-resistant bacteria was also examined. Mutants resistant to high concentrations of fluoroquinolones had a single mutation in their gyrA QRDR sequences, whereas the moderate resistance in the rest of mutants was due to extrusion of the drug.     

Identification of capsular antigens in Serratia marcescens.

Previous studies with 31 strains of Serratia marcescens, including 28 reference O-serotype strains, have indicated that 19 of them have an acidic polysaccharide which copurifies with lipopolysaccharide during phenol-water extraction. Polysaccharide in crude extracts from 18 of the 19 strains was precipitated with Cetavlon (hexadecyltrimethyl ammonium bromide), and capsules were demonstrated around these 18 strains by Indian ink exclusion zones. Capsule-antibody binding by the Quellung reaction suggested that the acidic polysaccharide formed the capsule around the bacterial cells. Anticapsular (anti-K) antibody was detected in reference O antisera which had been prepared against boiled whole cells. Cross-titration and absorption studies revealed 14 different K antigens among these strains.     

Clearance of Serratia marcescens from blood in mice: role of hydrophobic versus mannose-sensitive interactions.

In the present study, we examined the potential roles of cell surface hydrophobicity and mannose-sensitive (MS) interactions in blood clearance of Serratia marcescens in mice. Hydrophobic strain RZ, partially hydrophobic mutant 3162, and nonhydrophobic mutant 3164 were coinoculated into BALB/c male mice, and blood samples were plated out at different time intervals; colonies of the three strains were distinguished by their different morphologies. All three strains were cleared from the blood stream at similar rates, despite their large relative differences in cell surface hydrophobicity. Clearance from blood was subsequently studied by coinoculating two clinical isolates which differ in their abilities to adhere via MS interactions. MS+ strain 1785 was cleared much more rapidly than MS- strain 3255; moreover, in the presence of D-mannose, clearance of strain 1785 was inhibited to a rate similar to that of MS- strain 3255. When D-glucose was substituted for D-mannose, inhibition was not observed. The results suggest that MS, rather than hydrophobic, interactions are primarily responsible for the rapid clearance of S. marcescens from blood observed.