Epidemiologic typing of Staphylococcus aureus by DNA restriction fragment length polymorphisms of rRNA genes: elucidation of the clonal nature of a group of bacteriophage-nontypeable, ciprofloxacin-resistant, methicillin-susceptible S. aureus isolates

Abstract

Analysis of DNA restriction fragment length polymorphisms of rRNA genes (ribotyping) was employed to assist in the epidemiologic investigation of the emergence and spread of ciprofloxacin-resistant Staphylococcus aureus at the Atlanta VA Medical Center because many isolates of interest were nontypeable by phages and harbored few plasmids useful as strain markers. Chromosomal DNAs of selected S. aureus isolates were digested initially with 20 different restriction enzymes. EcoRI appeared to give the best discrimination of hybridization banding patterns (ribotypes) and was used with all study isolates. Overall, 15 different ribotypes were seen among the 50 S. aureus isolates studied (7 ribotypes among 13 methiciUlin-susceptible S. aureus [MSSA] isolates and 9 ribotypes among 37 methicillin-resistant S. aureus [MRSA] isolates). Seven of eight ciprofloxacin-resistant MSSA (CR-MSSA) patient isolates had identical antibiograms, were nontypeable by phages, and had a single 22-MDa plasmid. Six of these seven CR-MSSA isolates had an identical ribotype pattern. Ribotyping distinguished this CR-MSSA strain or clone from MRSA and other MSSA isolates, including nontypeable isolates that contained a 22-MDa plasmid. Five ciprofloxacin-susceptible MSSA isolates studied had five ribotypes; one pattern was identical to the CR-MSSA clone. Twenty-three CR-MRSA isolates recovered from the Atlanta VA Medical Center had four different ribotypes. Ribotyping proved to be a useful molecular

Comparison of traditional and molecular methods of typing isolates of Staphylococcus aureus

“…In the present study, 4 of the 59 S. aureus isolates were nonreactive by phage typing, and 3 produced results during the study that differed from the original typing results. Approximately 20% of isolates submitted to CDC for typing are nonreactive by using the international phage typing set (16a); other studies suggest much higher percentages (5,17,20,30,37,42). Given our results and the time and labor required to maintain phage stocks and propagating strains, we concluded that bacteriophage typing is not a cost-effective method of typing S. aureus for most clinical laboratories, particularly since other available methods can be used to type a broader range of other microorganisms.…”

“…Bacteriophage typing has been used for typing S. aureus for many years, but its limitations are clearly recognized (5,20,30,37,42,45). In the present study, 4 of the 59 S. aureus isolates were nonreactive by phage typing, and 3 produced results during the study that differed from the original typing results.…”

“…Typing of methicillin-resistant strains of S. aureus has proven to be particularly difficult because most strains are derived from relatively few clones (5,6,10,22,37,40,46). The present study was organized to determine the strengths and weaknesses of 12 currently available typing systems, ranging from a simple antibiogram method to a more tech-nically demanding MLEE method, for discriminating among methicillin-susceptible and methicillin-resistant isolates.…”

Quantitative antibiogram typing using inhibition zone diameters compared with ribotyping for epidemiological typing of methicillin-resistant Staphylococcus aureus

“…However, one drawback of the method is that markers of antibiotic resistance are often carried by labile or movable genetic elements (e.g., plasmids or transposons) whose selection of expression may depend on environmental conditions. Moreover, since the advance of DNA-based typing methods, it has been repeatedly shown that MRSA isolates which were indistinguishable by antibiotic susceptibility tests could be discriminated on the basis of their genotypes (3,5,12,13,15,16). Thus, antibiogram typing is considered to have poor discriminatory power and is used by microbiologists only in the first instance for rapid screening of the similarities between different clinical isolates.…”

Coincidental outbreak of methicillin‐resistant Staphylococcus aureus in a hematopoietic stem cell transplantation unit

“…Outbreaks of infection caused by MRSA have timeconsuming and expensive consequences, and genetic analysis is useful, since it can be used to determine the route and origin of MRSA infection [3]. Currently available laboratory methods for determining DNA fragment sizes or sequences in MRSA isolates include Southern blotting [4], ribotyping [5], polymerase chain reaction (PCR) [6], and pulsed-field gel electrophoresis (PFGE) [4,7]. PFGE has become the most common tool for the rapid discrimination of MRSA strains due to its convenience, reliability, and cost-effectiveness [8,9].…”