Genotyping of Staphylococcus epidermidis by small-fragment restriction endonuclease analysis and pulsed-field gel electrophoresis of genomic restriction fragments

Epidemiology and characterization ofStaphylococcus epidermidisisolates from humans, raw bovine milk and a dairy plant

Geographically relatedStaphylococcus epidermidisisolates from human patients (n=30), dairy farms (farmers and individual raw milk from cattle,n=36) and a dairy plant (n=55) were examined for epidemiological relatedness by pulsed-field gel electrophoresis and, usingin vitromethods, for the ability to produce biofilm and antimicrobial resistance. Methicillin-resistant isolates (MRSE) were also identified and characterized. Isolates from farmers and dairy cattle were found to be genetically related, while isolates from human patients were highly diverse. Some dairy plant isolates (18·2%) were closely related to those from dairy farms. Biofilm production and resistance to antimicrobial agents were most typical for isolates from human patients, of which 76·7% were MRSE. Methicillin resistance was also widespread in farm-related isolates (61·1%). This study indicates the possible transmission ofS. epidermidisbetween cattle and farmers. Dairy products were not proven to be an important source of either human infections or methicillin-resistant strains.

[Epidemiological profile of methicillin resistant Staphylococcus epidermidis with diminished sensitivity to teicoplanin and isolated from neutropenic patients at the National Center of Bone Marrow Transplantation in Tunis]

Fifty-seven methicillin resistant S. epidermidis with decreased susceptibility to teicoplanin were obtained from 14 neutropenic patients on a period of 11 months (19 February-31 December 1998) from essentially blood culture (30 strains) and ORL specimens (21 strains). The MIC90 of methicillin, gentamicin, ofloxacin and telcoplanin were respectively 1024, 1024, 512 and 32 mg/l. We applied pulsed field gel electrophoresis (PFGE) after Smal digestion to 21 isolates choosed between eight patients with multiple isolates (> two strains). For epidemiological control, a MetiR and TeicoR S. epidermidis isolated from blood culture taken from Caen CHU was include in study. Twenty-one isolates were separated by PFGE into eight group, from I to VIII. The control strain was classed in group IX. Group I include 14 strains which can be subdivised on three sub-types (differed by a single to three bands): seven strains have the pulsotype Ia and obtained respectively from five strains in transplantation unit and two strains in hematology unit. Two strains have the pulsotype Ib and isolated in the two units. Five strains have the pulsotype Ic and obtained also from transplantation unit (four strains) and hematology unit (one strain). All the other pulsotypes were identified in only one strain, frequently in association with the pulsotype I. Until recently, infections due to coagulase negative staphylococci have been regarded as endogenous in origin, these results with some pulsotype of S. epidermidis MetiR and TeicoR in the two separate units suggered a nosocomial origin, probably by medical staff transmission because no S. epidermidis TeicoR was isolated from environmental control during all the period.

Assessment of multiple coagulase-negative staphylococci isolated in blood cultures using pulsed-field gel electrophoresis

One of the criteria used to determine the clinical importance of coagulase-negative staphylococci (CNS) is the isolation of the bacteria from sequential blood cultures. Sequential isolates of CNS obtained from five immunocompromised patients over three months were genetically characterized by pulsed-field gel electrophoresis (PFGE). This typing method was compared to two first-line typing methods: determination of the species and of antibiotic susceptibility. In four patients the initial clinical evaluation changed because of the PFGE results several episodes of bacteremia would have been wrongly assessed if only the biotype and the antibiotype had been determined. Pulsed-field gel electrophoresis should therefore be used for CNS strains from immunocompromised patients or those suffering from chronic diseases with non-concordant biotype and anti-biotype.

Comparison of an improved RAPD fingerprinting with different typing methods for discriminating clinical isolates of Staphylococcus spp

Different epidemiological markers were used to characterize 2 Staphylococcus epidermidis and 8 Staphylococcus aureus strains isolated from patients with severe infections. We compared random amplified polymorphic DNA (RAPD) fingerprints, biotypes, antibiotic assays, plasmid profiles and chromosomal DNA restriction endonuclease analysis (REA). Data analysis based on numerical taxonomy methods indicates that RAPD and REA give similar results allowing a good discrimination of the two species and of each isolate. The RAPD method is easier and faster than REA, but the reproducibility of RAPD fingerprints obtained in independent experiments can be problematic. We have found simple technical devices to improve the reproducibility of the RAPD procedure which is therefore a very useful tool in epidemiology for identification and characterization of Staphylococcus spp.