Outbreak of methicillin-resistant Staphylococcus aureus in a teaching hospital--epidemiological and microbiological surveillance

Molecular typing of Staphylococcus aureus based on PCR restriction fragment length polymorphism and DNA sequence analysis of the coagulase gene

A typing procedure for Staphylococcus aureus was developed based on improved PCR amplification of the coagulase gene and restriction fragment length polymorphism (RFLP) analysis of the product. All coagulase-positive staphylococci produced a single PCR amplification product of either 875, 660, 603, or 547 bp. Those strains of epidemic methicillin-resistant S. aureus 16 (EMRSA-16) studied all gave a product of 547 bp. PCR products were digested with AluI and CfoI, and the fragments were separated by gel electrophoresis. Ten distinct RFLP patterns were found among 85 isolates of methicillin-resistant S. aureus (MRSA) and 10 propagating strains (PS) of methicillin-sensitive S. aureus (MSSA) examined. RFLP patterns 1, 2, and 3 were specific to strains of EMRSA-3, -15, and -16, respectively. By contrast, RFLP patterns 4 and 5 were seen with a heterogeneous collection of strains, together with drug-resistant forms of S. aureus isolated in Europe and four propagating strains used for the international phage set. RFLP pattern 6 was given by the Airedale isolate and PS 95. RFLP pattern 7 encompassed EMRSA-2 (isolate 331), PS 94, and PS 96. An isolate from Germany gave RFLP pattern 8. Eight strains of MSSA gave patterns similar to those of methicillin-resistant strains (RFLP patterns 3, 4, 5, 6, and 7), but two, PS 42E and PS 71, gave unique RFLP patterns 9 and 10, respectively. The coagulase gene PCR products for 24 isolates of MRSA and two isolates of MSSA were sequenced for both strands. The sequences were aligned, and evolutionary lineages were inferred based on pairwise distances between isolates.

A four-year prospective study on microbial ecology of explanted prosthetic hips in 52 patients with "aseptic" prosthetic joint loosening

The bacteriology of explanted prosthetic hips and surrounding soft tissue was studied in 52 patients undergoing surgical revision for joint loosening. In a prospective four-year study, positive bacterial cultures were recorded in 34 (76%) patients. Coagulase-negative staphylococci were the predominant isolates, and 11 patients (33%) had more than three organisms isolated, 7 (20%) had two only, and 11 (33%) had one species. Among the 23 patients from whom specimens from all 11 predetermined anatomic sites were cultured, the highest frequency of positive cultures (52% and 47%) came from the shaft and capsular tissue, respectively. Organisms were less frequently recovered from the cement and acetabulum (13% and 4%, respectively). Using molecular typing in eight patients with paired isolates of the same species, clonal identity was found in four. An additional patient underwent a second revision for loosening 17 months after the first revision and the same clone of Staphylococcus epidermidis was isolated on both occasions.

Methicillin-resistant Staphylococcus haemolyticus on the hands of health care workers: a route of transmission or a source?

We undertook a cross-sectional study of hand carriage and environmental contamination of methicillin-resistant coagulase-negative staphylococci on three wards of a single subspeciality surgical service. Sixteen hand cultures from 15 health care workers and 32 environmental cultures were obtained. Of 49 isolates, 35 (72%) were Staphylococcus haemolyticus. This species comprised 14 of the 16 (87%) hand isolates and 21 of the 32 (66%) environmental isolates. Using restriction length polymorphism of total DNA, we identified a single clone of S. haemolyticus on the hands of four health care workers and in the environment at seven locations on two wards. The widespread dissemination of a single clone suggests transmission of S. haemolyticus on the wards and prompts further prospective studies.

Methicillin-resistant Staphylococcus aureus subtyping: interest of combined antibiotyping and esterase electrophoretic typing

Ninety-four methicillin-resistant Staphylococcus aureus isolates (MRSA) were characterized by means of two typing methods, antibiotyping and esterase electrophoretic typing. Antibiotyping, recorded on the basis of susceptibility testing of 13 antimicrobial agents, allowed the description of 18 antibiotypes, four of which comprised 30, 14, 14 and 12 strains respectively. Esterase electrophoretic typing, based on esterase activity against seven synthetic substrates after polyacrylamide-agarose gel electrophoresis, led to the description of 12 electrophoretic types, two of which were predominant with 60 and 20 strains respectively. The combined use of both typing methods yielded 32 combinations, three of which were predominant with 21, 12 and 11 strains respectively. A good differentiation of strains was achieved, particularly when the antibiotype was correlated to the electrophoretic type. Thus, the combination of antibiotyping with esterase electrophoretic typing may be proposed as a well-suited method for the characterization of MRSA strains.