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 ␤-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 ␤-lactamase had an extended-spectrum ␤-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 ␤-lactamase.Klebsiella pneumoniae is an important hospital-acquired pathogen with the potential of causing severe morbidity and mortality in pediatric patients. Several outbreaks of infection caused by K. pneumoniae isolates that are simultaneously resistant to broad-spectrum cephalosporins and aminoglycosides have been widely reported (8,9,18,21). Some of these multidrug-resistant isolates produce extended-spectrum ␤-lactamases (ESBLs) that are able to hydrolyze expanded-spectrum cephalosporins (e.g., ceftriaxone, cefotaxime, and ceftazidime), aztreonam, and related oxyimino-␤-lactams. Most of these enzymes are TEM-or SHV-type ␤-lactamases in which the substitution of one or more amino acids has altered the configuration of the active site (7,14,19). Most of the plasmids determining ESBLs are large (Ն80 kb) and encode multiple resistances (10). Little is known about the ESBL-producing Enterobacteriaceae in Mexico (23). The present work is a characterization of 31 ESBL-producing K. pneumoniae isolates from a nosocomial outbreak occurring in a hospital in Cuernavaca, Mexico. MATERIALS AND METHODSPatients and bacterial strains. The General Hospital in the state of Morelos is a secondary-care facility with 100 beds. The neonatal intensive care unit has 8 beds. An outbreak was suspected in the neonatal intensive care unit due to an increased number of isolates of K. pneumoniae from blood cultures during a 4-month period. A retrospective epidemiological investigation included 74 children less than 2 months old hospitalized from June to October 1996.Twenty-one clinical isolates were from blood; another 10 duplicate strains were from sites other than blood (urine and catheter tip) corresponding to 10 patients. In total there were 31 clinical isolates identified as K. pneumoniae by the API 20E system (BioMerieux, Merck).Susceptibility testing. The antimicrobial susceptibility was initially determined with the MicroScan (Dade) system, using the Combo 14 panel. Subsequently, MICs of several ␤-lactams were determine...

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.