Molecular epidemiology of a multiresistant Pseudomonas aeruginosa outbreak in a paediatric intensive care unit.

After isolation of multiresistant (MR) Pseudomonas aeruginosa from 3 hospitalized patients in a paediatric intensive care unit (PICU), a prospective surveillance programme was established to detect infected and/or colonized patients in the hospital. Isolates were examined by means of outer membrane protein (OMP) profiles, serotyping and DNA genomic analysis using pulsed-field gel electrophoresis (PFGE). Fifty-five P. aeruginosa strains were isolated from 23 hospitalized patients during September and October 1997. The median hospital stay before isolation of P. aeruginosa was 8 d. PFGE demonstrated that the same clone infected 14 patients, 4 of whom were not hospitalized in the PICU. Susceptibility patterns and OMP profiles correlated with PFGE results in 37.8% and 36.4% of cases, respectively. Serotype O11 correlated with pattern A in 77% of cases and serotype O4 correlated with unrelated strains in 75% of cases but did not discriminate between outbreak and unrelated isolates. Extensive investigation of cultures failed to identify a reservoir of P. aeruginosa. PFGE was superior to OMP analysis and serotyping for discriminating between strains. The possible mode of acquisition for most of the patients infected with the same clone was cross-contamination.

Outbreak of infection with extended-spectrum beta-lactamase-producing Klebsiella pneumoniae in a Mexican hospital.

Thirty-one strains of Klebsiella pneumoniae (including 10 duplicates) from 21 septicemic pediatric patients (age, <2 months) were studied during a 4-month period (June to October 1996) in which the fatality rate was 62% (13 of 21). These isolates identified by the API 20E system yielded the same biotype. Pulsed-field gel electrophoresis experiments revealed the same clone in 31 strains. The isolates were multidrug-resistant but were still susceptible to ciprofloxacin, imipenem, and cefoxitin. A 135-kb plasmid was harbored in all of the isolates. No transconjugants were obtained that were resistant to ampicillin, cefotaxime, tetracycline, or gentamicin. Isoelectric focusing for beta-lactamases was performed on all strains, and three bands with pIs of 5.4, 7.6, and 8.2 were obtained. Of these, the pI 8.2 beta-lactamase had an extended-spectrum beta-lactamase phenotype. PCR amplification of both TEM- and SHV-type genes was obtained. The sequence analysis of the SHV PCR product indicated a mutation corresponding to the SHV-5 beta-lactamase.

Antimicrobial resistance from enterococci in a pediatric hospital. Plasmids in Enterococcus faecalis isolates with high-level gentamicin and streptomycin resistance.

BACKGROUND: Enterococcus spp. is an important nosocomial and community-acquired pathogen. Recent studies have documented the increasing importance of this pathogen in children, particularly in the hospital setting. Our objective in this study was to report the frequency of antimicrobial resistance in enterococci and to determine the characteristics of high-level gentamicin resistance (HLGR) plasmids in Enterococcus faecalis clinical isolates. METHODS: Two hundred eighty-nine enterococcal isolates were collected during an 18-month period from a tertiary-care pediatric hospital in Mexico City. Isolates were screened for antibiotic resistance, including HLGR. High-level, gentamicin-resistant E. faecalis strains were selected for pulsed-field electrophoresis (PFGE) typing and plasmid analysis. Transferability of resistance markers was carried out using filter matings. RESULTS: Seventy-six percent of isolates were E. faecalis, 10% were E. avium, 5.2% E. faecium, 5.2% E. raffinossus, 1.38% E. malodoratus, 0.6% E. hirae, and 0.6% E. casseliflavus. Antimicrobial resistance was ampicillin and penicillin 29%, imipenem 17%, and vancomycin 3%, HLGR 5%. The following 15 high-level, gentamicin-resistant isolates were identified: six E. faecalis; four E. avium; three E. faecium, and two E. casseliflavus. Five of the six E. faecalis isolates were different by PFGE and transferred gentamicin and streptomycin resistance on filter membranes. Transfer frequencies ranged from 8.2 x 10(-4) to 6.92 x 10(-5) transconjugants/recipient cell. The plasmid content of donors and transconjugants were homogeneous (one plasmid of 47 kb). CONCLUSIONS: In this pediatric hospital, antimicrobial resistance in Enterococcus spp. is common. Frequency of high-level, gentamicin-resistant strains is low. Mechanism of HLGR appears to be due to a single plasmid dissemination.

Staphylococcal peritonitis in continuous ambulatory peritoneal dialysis: colonization with identical strains at exit site, nose, and hands.

To evaluate the relationship of nasal or skin Staphylococcus carrier status with identical strains and the development of staphylococcal peritonitis, 59 consecutive peritonitis episodes in patients using a twin-bag system for continuous ambulatory peritoneal dialysis from a single dialysis center were prospectively studied. Dialysate samples and exit-site, nose, and nail swabs from patients and their dialysis partners were obtained on the same day for culture. When bacteria belonging to the same species of the Staphylococcus genus were isolated from dialysate and at least one extraperitoneal anatomic site, pulsed-field gel electrophoresis typing was performed. The bacterial strains isolated from catheter exit site, nose, or nails of each patient and his or her dialysis partner were classified as identical or different. Twenty-seven of the 59 peritonitis episodes (46%) were caused by staphylococci. Nineteen of these 27 patients carried the same Staphylococcus species causing the peritonitis episode at the exit site, nose, or nails, but only 17 patients (63%) carried an identical strain. Four of 5 dialysis partners carried the same Staphylococcus species causing the peritonitis episode at nose or nails, but the strain was identical for only 3 dialysis partners (60%). Four patients and 1 dialysis partner carried unrelated strains of the Staphylococcus species causing the peritonitis episode. The most frequently colonized site with strains identical to that causing the peritonitis episode was the catheter exit site, followed by nose and nails. This finding may be clinically relevant because eradication of Staphylococcus aureus colonizing the catheter exit site may be more important and have a greater likelihood of success than maneuvers directed to more distant locations.

Use of pulsed-field gel electrophoresis typing to study an outbreak of infection due to Serratia marcescens in a neonatal intensive care unit.

Serratia marcescens is a well-known cause of nosocomial infections and outbreaks, particularly in critically ill neonates and immunocompromised patients. Numerous methods have been proposed for typing. We used pulsed-field gel electrophoresis (PFGE) typing to analyze an outbreak in a neonatal intensive care unit (NICU). We included 23 patient isolates from an outbreak (March to July 1995), and 10 patient isolates from different wards during the same time period. PFGE of whole-cell DNA digested by SpeI was used as a marker of strain identity. The most common presentation of the infection was sepsis in 18 of 23 (78%) neonates. Only four different biotypes were identified; biotype A8d accounted for 84% of the strains. PFGE typing revealed two clones responsible for two different clonal strain dissemination outbreaks from March to July, with 24 patient isolates being pattern A and 4 patient isolates being pattern E. PFGE typing suggests cross transmission between patients in the NICU and other wards. The isolates from 5 other patients showed distinct PFGE patterns. Extensive investigation and cultures failed to identify any environmental or staff reservoir of S. marcescens. This is one of the first reports applying PFGE to the study of S. marcescens, and this method was a useful marker of strain identity. PFGE typing distinguished strains which appeared to be the same by biotyping.

[Infections by anaerobes in children: frequency of isolation and antimicrobial resistance]. / Infecciones por anaerobios en niños: frecuencia de aislamiento y resistencia antimicrobiana.

We studied the frequency of isolation and antimicrobial susceptibility of strict anaerobic bacteria isolated in a paediatric hospital. A total of 1,753 samples from purulent material and hemocultures were processed. One hundred and thirty strains were isolated from 95 children: 44 from 48 cases of peritonitis (91.7%), 2 from 8 brain abscesses (25%), 23 from 124 soft tissue abscesses (18.5%), 4 from 64 empyemas or lung abscesses (6.3%) and 22 from 1,509 hemocultures (1.5%). Mixed infection (anaerobic and aerobic bacteria) was detected in 38.5% of the cases; however, in peritonitis 81.3% of the cases showed mixed infection. The more frequently isolated bacteria were: Bacteroides (44.6%), Clostridium (19.2%), Fusobacterium (7.7%) and gram positive cocci (7.7%). Propionibacterium acnes was isolated in 15 specimens; however, most of them were considered as contamination. Bacteroides was isolated more frequently from patients with peritonitis (51.6%). The susceptibility to five antibiotics was tested in 124 strains using the method of serial dilutions in agar plates. The genus Bacteroides showed a high resistance to penicillin (73.1%), moderate to clindamycin (11.5%) and low to cefoxitin, chloramphenicol and metronidazole (6.8%, 2% and 5.8%). The rest of the anaerobic strains tested (other gram negatives and grampositives) were highly sensitive to all the antimicrobials tested, except for clindamycin (26.7% and 36.9% resistance, respectively). Cefoxitin, chloramphenicol and metronidazole had the lower CMI50 and CMI90 for the genus Bacteroides; and for the rest of the bacteria, penicillin had the highest activity (CMI90 less than 0.025). Since the frequency of isolation of anaerobic bacteria in children with severe infections, presumably originated from the digestive tract, paranasal sinus and middle ear is high, anaerobic cultures must be practiced in these patients. Empiric antimicrobial treatment should also be started. This treatment should be with penicillin when the probability of isolation of Bacteroides is low (infections in the face, neck, thorax and soft tissues) and with metronidazole in intraabdominal infections. Because of the severity and probable etiology of brain abscesses, treatment with penicillin and chloramphenicol or metronidazole is recommended in these cases.

[Resistance of enterobacteria and Pseudomonas to old and new antimicrobial agents]. / Resistencia de enterobacterias y Pseudomonas a viejos y nuevos antimicrobianos.

Antibiotic sensitivity to eight common use antibiotics for 9,538 enterobacteria and Pseudomonas strains isolated from hospitalized children was studied using the serial dilution plate technique. Minimum inhibitory concentration to seven new antibiotics for 310 strains was also determined. Enterobacteria showed high resistance (50-80%) to ampicillin, carbenicillin, sulbenicillin, chloramphenicol and trimethoprim/sulfamethoxazole; resistance to piperacillin, gentamicin, tobramycin, and netilmicin was moderate (15-45%), and resistance to amikacin, cefotaxime, moxalactam and aztreonam was low (2-10%). Pseudomonas strains showed less than 20% resistance to carbenicillin, piperacillin, amikacin and aztreonam. Enterobacteria isolated from urine samples showed low resistance to nitrofurantoin and nalidixic acid (15%). Therapeutic recommendation for most frequent infections caused by these etiologic agents based on the resistance values found were elaborated.