Development of a new set of phages as an epidemiological marker in Staphylococcus epidermidis causing nosocomial infections

Genomics of staphylococcal Twort-like phages--potential therapeutics of the post-antibiotic era

Polyvalent bacteriophages of the genus Twort-like that infect clinically relevant Staphylococcus strains may be among the most promising phages with potential therapeutic applications. They are obligatorily lytic, infect the majority of Staphylococcus strains in clinical strain collections, propagate efficiently and do not transfer foreign DNA by transduction. Comparative genomic analysis of 11 S. aureus/S. epidermidis Twort-like phages, as presented in this chapter, emphasizes their strikingly high similarity and clear divergence from phage Twort of the same genus, which might have evolved in hosts of a different species group. Genetically, these phages form a relatively isolated group, which minimizes the risk of acquiring potentially harmful genes. The order of genes in core parts of their 127 to 140-kb genomes is conserved and resembles that found in related representatives of the Spounavirinae subfamily of myoviruses. Functions of certain conserved genes can be predicted based on their homology to prototypical genes of model spounavirus SPO1. Deletions in the genomes of certain phages mark genes that are dispensable for phage development. Nearly half of the genes of these phages have no known homologues. Unique genes are mostly located near termini of the virion DNA molecule and are expressed early in phage development as implied by analysis of their potential transcriptional signals. Thus, many of them are likely to play a role in host takeover. Single genes encode homologues of bacterial virulence-associated proteins. They were apparently acquired by a common ancestor of these phages by horizontal gene transfer but presumably evolved towards gaining functions that increase phage infectivity for bacteria or facilitate mature phage release. Major differences between the genomes of S. aureus/S. epidermidis Twort-like phages consist of single nucleotide polymorphisms and insertions/deletions of short stretches of nucleotides, single genes, or introns of group I. Although the number and location of introns may vary between particular phages, intron shuffling is unlikely to be a major factor responsible for specificity differences.

Epidemiological typing of clinically significant strains of coagulase-negative staphylococci

This study was undertaken to determine the characteristics of 202 isolates of coagulase-negative staphylococci (CNS) isolated from 78 patients (two-seven per patient) using biochemical identification, bacteriophage susceptibility patterns, reverse-typing, plasmid profiles, antimicrobial susceptibility testing and slime production. All the strains could be typed by using the six markers consecutively. In addition, we have been able to deduce the similarity of 58 strains from 24 patients by means of one marker or another (these are similar or different strains within one patient but not between one patient and another). The use of a combination of markers is the ideal method for typing the strains; thus making it possible to confirm if two or more isolates from the same patient are similar or not and if they produce infection or are simple contaminants.

Phage typing of coagulase-negative staphylococci

Seventy-nine staphylococcal strains isolated from blood cultures (57 coagulase-negative staphylococci (CNS) and 22 S. aureus) and 308 CNS isolated from the skin of healthy donors were phage typed. S. epidermidis and S. capitis were readily typed with 91 strains out of 124 and 24 strains out of 43 strains being successful. Species such as S. haemolyticus, S. hominis and S. simulans could be moderately phage typed. Others gave only a few strains capable of being typed, such as S. saprophyticus and S. sciuri. Under our experimental conditions the S. warneri, S. xylosus and S. cohnii could not be typed with our set of phages.

Comparative evaluation of a new molecular method for typing Staphylococcus epidermidis

The discriminatory powers of several techniques for typing Staphylococcus epidermidis were evaluated in an epidemiological study of bacteria isolated from intensive care patients and from neonates. Genomic DNA fingerprinting using BclI restriction endonuclease was an effective epidemiological marker. The distinct restriction fragment profiles produced with this enzyme were highlighted with specific probes in a Southern blot technique. Cloned Escherichia coli rRNA gene probes proved to have lower discriminatory power and be less suitable for intraspecies typing. However, a panel of random genomic Staphylococcus epidermidis DNA clones provided almost the same level of discrimination as the DNA fingerprinting technique and also provided a clearer profile. DNA and gene fingerprinting techniques were reproducible and highly discriminatory compared to typing based on antigen and plasmid profiles, antibiotic susceptibility patterns and biotypes.