rRNA gene restriction patterns as an epidemiological marker in nosocomial outbreaks of Staphylococcus aureus infections

Identification of aminoglycoside-modifying enzymes by susceptibility testing: epidemiology of methicillin-resistant Staphylococcus aureus in Japan

A multiple-primer PCR was used to identify genes encoding aminoglycoside-modifying enzymes in 381 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). The technique used three sets of primers delineating specific DNA fragments of the aph(3')-III, ant(4')-I, and aac(6')-aph(2") genes, which influence the MICs of gentamicin, tobramycin, and lividomycin. Isolates with none of the three genes detected were susceptible to all three agents. Isolates with the aph(3')-III gene showed resistance to lividomycin (MIC > 1,024 microg/ml), and those with the ant(4')-I gene were resistant to tobramycin (MIC > or = 8 microg/ml). Isolates with only the aac(6')-aph(2") gene were resistant to gentamicin (MIC > or = 8 microg/ml) and tobramycin in decreasing order; those with both the ant(4')-I and aac(6')-aph(2") genes also were resistant to gentamicin and tobramycin, but in increasing order. Susceptibility testing, then, could detect specific genes. In 381 Japanese MRSA isolates, the ant(4')-I, aac(6')-aph(2"), and aph(3')-III genes were prevalent in 84.5, 61.7, and 8.9%, respectively. Isolates with only the ant(4')-I gene had coagulase type II or III, but isolates with both the ant(4')-I and aac(6')-aph(2") genes included all coagulase types. Most isolates with coagulase type IV or VII carried the aac(6')-aph(2") gene. Of the MRSA isolates with ant(4')-I and/or aac(6')-aph(2") genes, 97% were resistant to aminoglycosides in clinical use, but a new aminoglycoside, arbekacin, had excellent activity against these isolates.

Ribotyping and rapid identification of Staphylococcus xylosus by 16-23S spacer amplification

Ninety-five strains of Staphylococcus xylosus isolated from goat milk, French sausage or mice were analyzed together with 35 Staphylococcus type strains by 16-23S spacer amplification and ribotyping. The results obtained by PCR amplification of the 16-23S spacer region permitted the distinction of each type strain and additionally generated a DNA banding pattern characteristic for 93 of the 95 Staphylococcus xylosus strains. Ribotyping proved to be an efficient epidemiological tool for Staphylococcus xylosus species as it clustered the 95 strains into 23 distinct types.

Nasal carriage of Staphylococcus aureus and cross-contamination in a surgical intensive care unit: efficacy of mupirocin ointment

A six month prospective study was carried out in a surgical intensive care unit (SICU) of a university hospital to assess the incidence and routes of exogenous colonization by Staphylococcus aureus. A total of 157 patients were included in the study. One thousand one hundred and eleven specimens (nasal, surgical wound swabs, tracheal secretions obtained on admission and once a week thereafter, and all clinical specimens) were collected over a four month period from patients without nasal decontamination (A). They were compared with 729 specimens collected over a two month period from patients treated with nasal mupirocin ointment (B). All S. aureus strains were typed by restriction fragment length polymorphism (RFLP) pulsed-field gel electrophoresis after SmaI macrorestriction. The nasal colonization rates on admission were 25.5 and 32.7% in groups A and B, respectively. Thirty-one untreated patients (31.3%) and three patients (5.1%) treated with nasal ointment, acquired the nasal S. aureus in the SICU (P = 0.00027). Nasal carriers were more frequently colonized in the bronchopulmonary tract (Bp) and surgical wound (Sw) (62%) than patients who were not nasal carriers (14%) (P < 0.00001). The patterns were identical for nasal, Bp and Sw strains from the same patient. RFLP analysis characterized seven epidemic strains of methicillin-resistant S. aureus (MRSA) which colonized 60% of group A and 9% of group B patients (P < 0.00001). The bronchopulmonary tract infection rate was reduced in group B (P = 0.032). In conclusion, in an SICU, nasal carriage of S. aureus appeared to be the source of endogenous and cross-colonization. The use of nasal mupirocin ointment reduced the incidence of Bp and Sw colonization, as well as the MRSA infection rate.