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In this study the production of enterotoxin A-D and toxic shock syndrome toxin-1 (TSST-1) of 181 methicillin resistant (MRSA) and 100 methicillin sensitive (MSSA) Staphylococcus aureus first isolates from different patients was investigated. All the MRSA- and MSSA isolates in the study were collected in a period between 1993 and 1995 from specimens sent from 11 different acute care hospitals in the greater Düsseldorf area. As far as possible the isolates were matched according to ward and hospital. The isolates were collected in the same time period and matched for specimen from which isolated. Furthermore, only first isolates were analysed in both groups. No significant difference in the production of toxin of any type between MRSA and MSSA could be detected (51 and 40% respectively). When the individual toxins were analysed, again no significant difference between MRSA and MSSA was demonstrable (enterotoxin production by MRSA 40% and MSSA 36%, and TSST-1 16% and 8% respectively). Despite this, a slight tendency for MRSA to produce enterotoxin A and B and for MSSA to produce enterotoxin C was observed. In addition, generation of TSST-1 by both groups was independent of enterotoxin A-D production. Interestingly, no increase in the proportion of TSST-1- or enterotoxin-producing MRSA and MSSA isolates was observed in strains isolated from blood cultures from patients with a clinical diagnosis of sepsis. Genotypical pulsed-field-gel-electrophoresis (PFGE) and phenotypical (bacteriophage typing, lysotyping) characterization of the 181 MRSA isolates resulted in 28 different PFGE patterns (of which 19 were toxin producers) and 22 lysotyping groups (18 of which produced toxin). In summary, the investigated clinical S. aureus isolates showed no difference in their ability to produce toxin and this was independent of their sensitivity to methicillin.

Over a period of three years the incidence of methicillin resistant Staphylococcus aureus (MRSA) isolates in 11 hospitals in the greater Düsseldorf area was observed. From a total of 7,814 S. aureus isolates, 489 (6.3%) were methicillin resistant. From 198 different patients, MRSA first isolates and 291 second isolates could be cultured. Methicillin resistance among all S. aureus isolates from 11 hospitals in the greater Düsseldorf area, ranged from 0.5 to 7.8% dependant on the size of the hospital. The highest incidence (7.8%) was found in a 1,500 bed hospital and the lowest incidence in a smaller 200 bed hospital (0.5%). With respect to the distribution among clinical departments the highest incidence of MRSA isolates was found on intensive care units and surgical wards, 25.5% and 13.0% respectively. The commonest specimen from which the MRSA isolates were cultured were respiratory secretions (17.6%) followed by central venous catheter tips (12.8%). In terms of the drug resistance pattern: all isolates were resistant to the aminoglycosides and gyrase inhibitors, whereas between 80% and 90% were sensitive to fusidic acid, chloramphenicol and pyrimethamine-sulfamethoxazole. All the strains were sensitive to the glycopeptide antibiotics, vancomycin and teicoplanin. Strain typing of 181 available first isolates (from a total of 198 first isolates) by PFGE and phage lysotyping produced identical results in more than 90% of all cases. Twenty-eight different MRSA strain types were identified by PFGE and in total 23 lysotypes could be determined. During the period of investigation an increased incidence of MRSA on an intensive care unit was observed, in which a total of 204 MRSA (42% of the total number) were isolated. The strain typing using both methods showed that on that ICU eight different MRSA types were involved in this outbreak. A hygiene plan was implemented on the unit with considerable success in reducing the incidence and spread of MRSA.

Within the scope of the present study n = 183 MRSA isolates from the extended area of Düsseldorf and n = 93 international MRSA strains from seven different countries were typed by pulsed-field gel electrophoresis and two PCR methods (RAPD and 16S-23S-spacer amplification). The isolates could be subdivided into 30 different types by PFGE, into 21 by means of RAPD and 18 by 16S-23S-spacer amplification. PFGE had the highest discriminatory potential, however, a combined use of the three typing methods allows a more detailed differentiation even of those isolates with identical PFGE pattern. Both amplification procedures were rapid, easy in handling with reproductable results. For a temporary epidemiological analysis within 24 hours, both amplification methods could be combined. In case the investigated isolates were still suspected of showing a "clonal identity", they should be analysed by additional PFGE (lasting about four days). Although the international isolates were chosen by random selection, several MRSA strains with identical pattern could be found in different countries of the world. Some RAPD-, spacer- and PFGE pattern were constant over many years. This reflects a high genetic stability of single strains.

Over a period of three years, the frequency of the appearance of methicillin-resistant S. aureus strains (MRSA) was observed on a surgical intensive care unit. During this above-mentioned period of investigation it came to a heaped occurrence of nosocomial infections on this ICU with altogether 332 S. aureus-stems being isolated from different patient specimen. 204 (61.5%) of these were resistant against methicillin and could be divided into 48 first- and 156 follow-up-isolates. The thereupon accomplished differentiation of the 48 MRSA-first isolates by means of lysotyping and the pioneered GenePath Strain Typing System for a standardized pulsed-field-gel-electrophoresis (PFGE) gave the proof of 7 different MRSA-types. Around 7 different, in part parallel chains of infection on this ICU were observed, which could be led back to different strains. In reference to all analyzed S. aureus, an especially high rate (90%) of MRSA on this ICU could be isolated in taken wound-swabs, followed by 83.3% MRSA at catheter tips and 71,9% in tracheal and bronchial secretion. A consideration of the antibiotic susceptibility yielded, that also gentamicin and the quinolones showed an in-vitro resistance against MRSA, while fosfomycin, fusidic acid, chloramphenicol and trimethoprim/sulfamethoxazole reached positive responding rates between 80 and 100%. On the other hand, presently still 100% of the explored MRSA-strains are susceptible for glycopeptides such as vancomycin and teicoplanin. Because of intensive hospital hygienic measures the number of newly isolated MRSA could be reduced clearly on this ward.