National epidemiologic surveys of Enterobacter aerogenes in Belgian hospitals from 1996 to 1998.

Two national surveys were conducted to describe the incidence and prevalence of Enterobacter aerogenes in 21 Belgian hospitals in 1996 and 1997 and to characterize the genotypic diversity and the antimicrobial resistance profiles of clinical strains of E. aerogenes isolated from hospitalized patients in Belgium in 1997 and 1998. Twenty-nine hospitals collected 10 isolates of E. aerogenes, which were typed by arbitrarily primed PCR (AP-PCR) using two primers and pulsed-field gel electrophoresis. MICs of 10 antimicrobial agents were determined by the agar dilution method. Beta-lactamases were detected by the double-disk diffusion test and characterized by isoelectric point. The median incidence of E. aerogenes colonization or infection increased from 3.3 per 1,000 admissions in 1996 to 4.2 per 1000 admissions in the first half of 1997 (P < 0.01). E. aerogenes strains (n = 260) clustered in 25 AP-PCR types. Two major types, BE1 and BE2, included 36 and 38% of strains and were found in 21 and 25 hospitals, respectively. The BE1 type was indistinguishable from a previously described epidemic strain in France. Half of the strains produced an extended-spectrum beta-lactamase, either TEM-24 (in 86% of the strains) or TEM-3 (in 14% of the strains). Over 75% of the isolates were resistant to ceftazidime, piperacillin-tazobactam, and ciprofloxacin. Over 90% of the strains were susceptible to cefepime, carbapenems, and aminoglycosides. In conclusion, these data suggest a nationwide dissemination of two epidemic multiresistant E. aerogenes strains in Belgian hospitals. TEM-24 beta-lactamase was frequently harbored by one of these epidemic strains, which appeared to be genotypically related to a TEM-24-producing epidemic strain from France, suggesting international dissemination.

Epidemiological typing of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae isolates by pulsed-field gel electrophoresis and antibiotic susceptibility patterns.

Over a 16-month period, Klebsiella pneumoniae isolates from 102 patients admitted to a university hospital in Liege (Belgium) produced extended-spectrum beta-lactamases. Pulsed-field gel electrophoresis of genome macrorestriction patterns with XbaI and antibiotic susceptibility patterns subdivided 39 isolates into eight clonally related groups. Two of them were implicated in the course of this outbreak. They were responsible for successive waves of infection or colonization in different wards of the hospital while the others were encountered sporadically. A beta-lactamase with an isoelectric point of 7.6 and consistent with type SHV-2 characterized all nine isolates chosen among both major groups.

Typing of nosocomial strains of Serratia marcescens: comparison of pulsed-field gel electrophoresis of macrorestriction fragments with biotyping, esterase typing and ribotyping.

Fifty nosocomial isolates of Serratia marcescens, collected in six Belgian hospitals between 1986 and 1990, were characterized by using pulsed-field gel electrophoresis (PFGE) with XbaI. The results were compared with those previously obtained by three other methods: biotyping, esterase electrophoresis typing and ribotyping with EcoRI and HindIII. Macrorestriction analysis (42 PFGE groups) and esterase typing (42 zymotypes) proved to be the most discriminating, followed by ribotyping (28 ribotypes) and biotyping (10 biochemical profiles). Biotyping would serve as a screen to identify isolates, due to its accessibility. Esterase typing provided a reliable tool to make subdivisions within biotypes because of congruence between biochemical groups and esterase patterns. Additional discrimination was still achieved by ribotyping and PFGE. It is concluded that the combined results of these four markers were useful for distinguishing all epidemic and sporadic isolates.

Comparison of biotyping, ribotyping, and pulsed-field gel electrophoresis for investigation of a common-source outbreak of Burkholderia pickettii bacteremia.

Over a 3-month period, six immunocompromised patients developed one or more episodes of Burkholderia pickettii bacteremia and/or catheter infection. Vials of a commercially available, "sterile" saline for injection which had been used for flushing the patients' indwelling intravenous devices were implicated as the common source of the organisms. No further cases were diagnosed once the use of this saline was discontinued. Twenty-six isolates, including 9 outbreak-related strains from case patients and contaminated saline as well as 17 control strains, were tested comparatively by biotyping, ribotyping with EcoRI and HindIII, and pulsed-field gel electrophoresis (PFGE) with SpeI. Macrorestriction analysis revealed nine PFGE groups and was more discriminating than ribotyping (seven ribotypes) and biotyping (two biovars). Among the outbreak-related isolates, one B. pickettii type was found by the three typing methods. Furthermore, PFGE was useful for subdividing ribotypes and for distinguishing isolates involved in the outbreak from all epidemiologically unrelated strains.

Ribotyping for use in studying molecular epidemiology of Serratia marcescens: comparison with biotyping.

Ribotyping carried out with a nonradioactive probe (acetylaminofluorene ribosomal RNA kit I from Eurogentec, Seraing, Belgium) was performed for the characterization of 139 hospital strains of Serratia marcescens. These strains, which belonged to 11 biotypes and 1 nontypeable group, were isolated in seven hospitals in Belgium between 1986 and 1992. EcoRI and HindIII were used to obtain cleavage patterns. Analysis of the results produced 27 different patterns with EcoRI and 23 patterns with HindIII. Typeability reached 100%. Combination of the patterns obtained with each enzyme produced 38 distinct ribotypes. Percent similarity values, calculated by using the Dice coefficient and unweighted-pair group average linkage clustering, showed four main clusters and nine subclusters of ribopatterns at a similarity rate of approximately 80% or less. These groups did not coincide with those delimited by biotyping, although a rather good correlation was observed. The simultaneous use of the two methods has potential value in epidemiological studies.

Combination of biotyping and electrophoretic patterns of esterases for differentiation of nosocomial Serratia marcescens strains.

A total of 292 Serratia marcescens strains isolated in seven Belgian hospitals between 1986 and 1992 were submitted to both biotyping by carbon source utilization and esterase electrophoresis typing. The strains were assigned to 11 biotypes (290 isolates) or were auxotrophic (2 isolates), whereas the various electrophoretic patterns of their esterases produced 54 zymotypes. The two typing methods correlate well, since biotypes embraced more than one zymotype, while each zymotype was restricted to a single biotype. Esterase electrophoretic patterns represent a potent marker for delineating outbreaks of nosocomial infections, whereas biotyping appears to be an appropriate method for screening of strains.