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.

Serologic evidences suggesting the presence of Borrelia burgdorferi infection in Mexico.

BACKGROUND: Lyme disease is the most common vector-borne human disease in Europe and the United States. In Mexico, clinical cases suggestive of Lyme borreliosis have been reported; however, infection was not confirmed by serologic or microbiologic tests. METHODS: To study the prevalence of IgG antibodies against Borrelia burgdorferi among Mexican persons, a community-based sero-survey including all states of Mexico was done. A sample of 2,890 sera representing individuals of all ages and all socioeconomic levels was studied. Antibodies anti-B. burgdorferi were determined by enzyme-linked immunosorbent assay (ELISA) using a whole-cell sonicated extract of B. burgdorferi strain B31. Serum specimens positive for ELISA were further studied by Western blot (WB). A serum sample was considered positive by WB if at least three of the following protein bands were recognized: 18, 24, 28, 29, 31, 34, 39, 41, 45, 58, 62, 66, and 93 kDa. Some WB positive specimens were further confirmed with an immunodot-blot (IDB) test using recombinant and purified B. burgdorferi proteins. RESULTS: Of the 2,890 specimens, 34 were positive for ELISA; nine of these 34 were confirmed as positive by WB. Four of the nine WB positive sera were tested by IDB and all four were positive. The prevalence of WB confirmed cases in the sample studied was 0.3%. Positive specimens were from residents of the northeastern and central areas of Mexico. CONCLUSIONS: The serological evidences of this study suggest that Borrelia burgdorferi infection is present in the Mexican population. This finding should be confirmed by documenting the infection in clinical cases and in tick vectors.

Identification of the high-virulence clone of group B streptococci in Mexican isolates by growth characteristics at 40 degrees C.

Group B streptococci (GBS) colonizing the vagina and rectum of pregnant women cause invasive disease of the offspring in a small number of cases. The immune status of the host and differences in virulence among strains appear to be the main determinants for neonatal infection. A high-virulence clone (HVC) was proposed to cause much of the morbidity and mortality when a collection of GBS isolates was examined by multilocus enzyme electrophoresis. HVC isolates could be further distinguished by their inability to grow at 40 degrees C. This characteristic was used in the present study to examine a collection of 57 GBS isolates from Mexico City for the HVC. Three serotype III invasive strains were classified in the HVC. The other eleven invasive strains and all carrier isolates had growth curves unaffected at 40 degrees C. These results demonstrate the presence of the HVC in Mexico. Such a low prevalence could explain in part the low rate of GBS invasive neonatal disease in Mexico.

Decreased capacity for type-specific-antigen synthesis accounts for high prevalence of nontypeable strains of group B streptococci in Mexico.

The low incidence of group B streptococcal (GBS) invasive neonatal disease in Mexico has been attributed to the low prevalence of serotype III strains, a major serotype in developed countries. In addition, nontypeable strains account for 12% of the isolates in Mexico and < 1% of the isolates in the United States. In this study, 57 GBS isolates (28 nontypeable by the Lancefield procedure) from carrier and infected neonates and women from Mexico were also examined for the presence of type-specific antigen by an enzymatic procedure using N-acetylmuramidase digestion of the cell wall to release soluble type-specific antigen. Of the 28 nontypeable strains from Mexico, 23 were typeable by the enzyme extraction procedure, with serotype III being the predominant serotype in invasive disease. These results suggest that nontypeable isolates of GBS should be further examined by the enzymatic extraction procedure to determine the presence of type-specific antigen. Furthermore, these limited results suggest that serotype III is likely a major serotype in invasive disease also in Mexico.

Comparison of the response to the recombinant vaccine against hepatitis B virus in dialyzed and nondialyzed children with CRF using different doses and routes of administration.

In patients with chronic renal failure (CRF), parenteral transmission of the hepatitis B virus (HBV) is common. The response to the recombinant vaccine is 50%-80% of seroprotection. Therefore, to improve seroprotection, different strategies such as dose augmentation, vaccination at the predialysis stage, subcutaneous application, and using interleukin were tried, with unsatisfactory results. In children, there are no studies demonstrating the efficacy of the vaccine. The aim of this study was to evaluate the efficacy of the recombinant vaccine in children with CRF, in late as well as early phases, through the quantification of antibodies against the surface antigen in response to different doses of the vaccine against HBV. There were 103 patients who were assigned to three groups: (1) 25 patients with CRF in the early phase (undergoing pharmacological treatment only); (2) 67 patients with CRF in the late phase (treatment with peritoneal dialysis or hemodialysis); (3) 11 patients with CRF in the early phase (undergoing low-dose pharmacological treatment only). The antibodies against the serum antigen (HBsAg) were measured by the aEIA method. Urea, creatinine, and creatinine clearance were measured at 0, 2, and 12 months. In our seroprotection results we observed that group 1 and 3 developed earlier seroconversion (50% first month). In patients undergoing dialysis the seroconversion happened in 91% at month 13, but with lower concentration than group 1 and/or group 3 (p < 0.05). In conclusion, there is a better response in predialysis patients. The levels of antibodies are similar in groups 1 and 3 (with small doses), which are similar to the complete doses for an efficient immunity in children with chronic renal failure.

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.

[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.

Serogroup specificity and antimicrobial susceptibilities of Neisseria gonorrhoeae isolated in Mexico City.

The serogroup pattern of 87 clinical isolates of Neisseria gonorrhoeae was determined by monoclonal coagglutination and the in-vitro activity of seven antimicrobial agents against the same strains was tested by an agar dilution method. The frequency of resistance to spectinomycin, ampicillin, penicillin, erythromycin, chloramphenicol and tetracycline was 14.9%, 33.3%, 34.4%, 30%, 40.2% and 41.3%, respectively. All strains were susceptible to cefotaxime. Out of 87 strains tested, 29.8% produced beta-lactamases and 4.5% were chromosomally resistant to penicillin. In all instances resistance to a drug was associated with serogroup 1-B except for erythromycin. The results presented here correlate with observations made worldwide.

Haemophilus influenzae type b meningitis resistant to ampicillin and chloramphenicol.

We report two cases of meningitis due to Haemophilus influenzae type b resistant to ampicillin and chloramphenicol. In one child the meningitis was preceded by pneumonia and pleural effusion. Both children responded to treatment with cefotaxime.