[Serratia marcescens outbreak in Neonatal Intensive Care Unit: Guayaquil, Ecuador]. / Brote por Serratia marcescens en una Unidad de Cuidados Intensivos Neonatales: Guayaquil-Ecuador.

We report a Serratia marcescens outbreak occurred in the NICU of a pediatric hospital in Guayaquil, Ecuador. Nine cases of infection were detected, from which septicemia was developed in 55.5%. The index case was a newborn derived from another institution with septic arthritis caused by the outbreak strain. The infection rate was 17.6% and mortality rate was 33.3%. All isolates were resistant to aminoglycosides and susceptible to third generation cephalosporins and carbapenems. Clonality analysis by pulsed-field gel electrophoresis (PFGE) revealed the presence of two closely related clones confirming the horizontal spread. Measures were taken by the committee such as: strengthening the hand hygiene, patient hygiene and cohort studies of gastrointestinal colonization, which allowed the control of the outbreak.

DNA fragmentation in microorganisms assessed in situ.

Chromosomal DNA fragmentation may be a direct or indirect outcome of cell death. Unlike DNA fragmentation in higher eukaryotic cells, DNA fragmentation in microorganisms is rarely studied. We report an adaptation of a diffusion-based assay, developed as a kit, which allows for simple and rapid discrimination of bacteria with fragmented DNA. Intact cells were embedded in an agarose microgel on a slide, incubated in a lysis buffer to partially remove the cell walls, membranes, and proteins, and then stained with a DNA fluorochrome, SYBR Gold. Identifying cells with fragmented DNA uses peripheral diffusion of DNA fragments. Cells without DNA fragmentation show only limited spreading of DNA fiber loops. These results have been seen in several gram-negative and gram-positive bacteria, as well as in yeasts. Detection of DNA fragmentation was confirmed by fluoroquinolone treatment and by DNA breakage detection-fluorescence in situ hybridization. Proteus mirabilis with spontaneously fragmented DNA during exponential and stationary growth or Escherichia coli with DNA damaged after exposure to hydrogen peroxide or antibiotics, such as ciprofloxacin or ampicillin, was clearly detected. Similarly, fragmented DNA was detected in Saccharomyces cerevisiae after amphotericin B treatment. Our assay may be useful for the simple and rapid evaluation of DNA damage and repair as well as cell death, either spontaneous or induced by exogenous stimuli, including antimicrobial agents or environmental conditions.

Structure-function studies of arginine at position 276 in CTX-M beta-lactamases.

OBJECTIVES: In order to assess whether or not the Arg-276 of CTX-M-type enzymes is equivalent to the Arg-244 of IRT-TEM-derivative enzymes, we replaced the former with six different amino acids, some of them previously described as involved in resistance to beta-lactamase inhibitors in TEM-IRT derivatives. We also investigated the role of Arg276 in cefotaxime hydrolysis. METHODS: By site-directed mutagenesis and by use of the bla(CTX-M-1) gene as template, Arg-276 was replaced with six different amino acids (Trp, His, Cys, Asn, Gly and Ser). MICs of beta-lactams alone and in combination with beta-lactamase inhibitors were established. The seven enzymes (CTX-M-1 wild-type and six derived mutants) were purified by affinity chromatography, and kinetic parameters (k(cat), K(m), k(cat)/K(m)) towards cefalotin and cefotaxime were determined. Clavulanic acid IC(50) values were also assessed with all enzymes. RESULTS: No increase in MICs of beta-lactam/beta-lactamase inhibitor combination was detected with any of the six CTX-M-1-derived mutants, in agreement with the clavulanic acid IC(50) values. The MICs of cefotaxime were clearly lower for the Escherichia coli harbouring the Trp, Cys, Ser and Gly CTX-M-1 mutant enzymes than for CTX-M-1, and these enzymes showed a clearly reduced catalytic efficiency towards cefotaxime. As regards cefalotin, there was a moderate reduction in catalytic efficiency for Cys and His. CONCLUSIONS: Arg-276 in CTX-M-type beta-lactamases is not equivalent to Arg-244 in IRT-type enzymes. Position Arg-276 appears to be important for cefotaxime hydrolysis in CTX-M-type enzymes, although different effects were obtained regarding the replaced amino acid.

Interspecies spread of CTX-M-32 extended-spectrum beta-lactamase and the role of the insertion sequence IS1 in down-regulating bla CTX-M gene expression.

OBJECTIVES: To characterize the extended-spectrum beta-lactamases (ESBLs) as well as their genetic environment in different isolates of Enterobacteriaceae from a patient with repeated urinary tract infections. METHODS: Two isolates of Escherichia coli and one Proteus mirabilis, all with ESBL phenotypes, were studied. Conjugation experiments and restriction fragment length polymorphisms (RFLPs) were performed. Cloning of the bla genes was by plasmid restriction and fragments ligation. Antibiotic susceptibility testing was by Etest. The genetic environment was analysed by direct sequencing of the DNA surrounding the bla gene. RT-PCR was performed to study the differences in the bla(CTX-M) gene expression. RESULTS: The bla gene was transferred by conjugation from the three clinical isolates, which by RFLP showed the same plasmid. The bla gene and surrounding sequences were cloned, an approximately 9 kbp AccI fragment was sequenced and the bla(CTX-M-32) gene was identified. The MICs of ceftazidime for transconjugants and transformants bearing the bla(CTX-M-32) gene were lower than those previously reported. Analysis of the DNA surrounding the ESBL gene revealed a new genetic structure with two insertion sequences, IS5 and IS1, located immediately upstream of the bla(CTX-M-32) gene; IS1 was located between the bla gene and IS5, and within the -10 and -35 promoter boxes of the bla(CTX-M-32) gene. Microbiological and biochemical studies revealed lower bla(CTX-M-32) gene expression in bacterial isolates with IS1 between the promoter boxes. CONCLUSIONS: Data suggest putative in vivo horizontal bla(CTX-M-32) gene transfer between two different genera of Enterobacteriaceae. A new complex structure, IS5-IS1, was detected upstream of the bla gene and IS1 negatively modulated expression of the bla(CTX-M-32) gene because its location modified the bla promoter region.

[Prevalence of antiretroviral drug resistance among previously untreated Spanish patients infected with HIV]. / Prevalencia de resistencia a los fármacos antirretrovirales en pacientes españoles infectados por el VIH y sin tratamiento previo.

INTRODUCTION: Genotypic resistance was tested to investigate changes in the rates of resistance to antiretroviral drugs in non-treated patients in Spain. MATERIAL AND METHOD: A total of 209 HIV-infected patients from different autonomous communities in Spain without prior antiretroviral (AR) drug treatment were studied from 1997 to 2001. Regions of the HIV pol gene coding for protease (PR) and retrotranscriptase (RT) were sequenced in plasma samples by RT PCR amplification and automated PCR sequencing. RESULTS: At least one primary RT or PR mutation was detected in 14 patients (6.7%); 11 of them were associated with resistance to RT inhibitors (5.3%) and 3 to PR inhibitors (1.4%). The changes in the resistance rate between March 1997-February 1999 and March 1999-February 2001 were as follows: resistance mutations were detected in 3 of the 111 patients studied in the first period, and in 10 of 98 patients in the second period (2.7% versus 10.2%, P = 0.025). The infection time was less than three months in 1.5% of cases, less than 1 year in 13.4%, more than 1 year in 45.9% and unknown in 39.2%. CONCLUSION: The rate of primary resistance in naive patients is low in Spain, although there may be a trend toward an increase. The rising prevalence of resistance is a cause for concern.

Prevalencia de resistencia a los fármacos antirretrovirales en pacientes españoles infectados por el VIH y sin tratamiento previo / Prevalence of antiretroviral drug resistance among naive Spanish patients infected with HIV

Introducción. Para conocer la evolución de la tasa de resistencia a los antirretrovirales en España en pacientes no tratados previamente, estudiamos la resistencia genotípica. Material y método. Se estudiaron muestras plasmáticas de 209 pacientes infectados por el virus de la inmunodeficiencia humana (VIH), procedentes de diversas comunidades autónomas, que no habían recibido tratamiento antirretroviral desde 1997 a 2001. Analizamos la secuencia del gen pol que codifica la proteasa (PR) y la retrotranscriptasa (RT) del VIH usando un sistema de secuenciación automático. Resultados. En 14 pacientes (6,7%) se detectó al menos una mutación en la RT o mutación primaria en la PR. En 11 pacientes, las mutaciones se asociaron a resistencia a los inhibidores de la RT (5,3%) y en tres a los inhibidores de la PR (1,4%). La evolución de la tasa de resistencia entre marzo de 1997 a febrero de 1999 y de marzo de 1999 a febrero de 2001 fue la siguiente: se detectaron mutaciones codificadoras de resistencias en 3 de los 111 pacientes estudiados en el primer período mientras que se identificaron en 10 casos de 98 pacientes en el segundo período (2,7% frente a 10,2%; p = 0,025). En el 1,5% de los casos, el tiempo de la infección fue inferior a 3 meses, en el 13,4% 1 año y en el 39,2% de duración desconocida. Conclusión. El porcentaje de pacientes no tratados previamente con resistencia primaria en España es bajo pero preocupa la probable tendencia a su incremento (AU)

Introduction. Genotypic resistance was tested to investigate changes in the rates of resistance to antiretroviral drugs in non-treated patients in Spain. Material and method. A total of 209 HIV-infected patients from different autonomous communities in Spain without prior antiretroviral (AR) drug treatment were studied from 1997 to 2001. Regions of the HIV pol gene coding for protease (PR) and retrotranscriptase (RT) were sequenced in plasma samples by RT PCR amplification and automated PCR sequencing. Results. At least one primary RT or PR mutation was detected in 14 patients (6.7%); 11 of them were associated with resistance to RT inhibitors (5.3%) and 3 to PR inhibitors (1.4%). The changes in the resistance rate between March 1997-February 1999 and March 1999-February 2001 were as follows: resistance mutations were detected in 3 of the 111 patients studied in the first period, and in 10 of 98 patients in the second period (2.7% versus 10.2%, P = 0.025). The infection time was less than three months in 1.5% of cases, less than 1 year in 13.4%, more than 1 year in 45.9% and unknown in 39.2%. Conclusion. The rate of primary resistance in naive patients is low in Spain, although there may be a trend toward an increase. The rising prevalence of resistance is a cause for concern (AU)

Evaluation of different methods for detecting methicillin (oxacillin) resistance in Staphylococcus aureus.

OBJECTIVES: To evaluate the performance of oxacillin, cefazolin, cefoxitin, cefotaxime and imipenem discs; Etest for oxacillin; microdilution; agar screening plates with 2 and 6 mg/L of oxacillin; and PBP2' agglutination for detection of methicillin-resistant Staphylococcus aureus (MRSA). METHODS: A total of 102 clinical S. aureus isolates, including 51 MRSA isolates, tested by PCR for the presence or absence of the mecA gene (gold standard method), isolated from different patients and at different times, were tested with: oxacillin (1 microg), cefazolin, cefoxitin, cefotaxime and imipenem (all 30 microg) discs; Etest for oxacillin; microdilution with oxacillin; agar screening tests (ORSAB medium) with 2 mg/L or 6 mg/L of oxacillin; and PBP2' agglutination with two different kits for detection of MRSA strains. RESULTS: The cefoxitin disc, ORSAB medium and PBP2' detection all showed 100% sensitivity. The cefoxitin, cefazolin and imipenem discs, Etest for oxacillin, microdilution and agar screening method with 6 mg/L at 24 h showed the highest specificity (100%), although variable degrees of sensitivity. The cefoxitin disc, which showed negative and positive predictive values of 100% and 98%, respectively was the best method for detecting MRSA isolates. CONCLUSIONS: In the absence of availability of molecular biology techniques, the cefoxitin disc was the best predictor of methicillin resistance in S. aureus from among the techniques tested.

Risk factors for colonization and infection in a hospital outbreak caused by a strain of Klebsiella pneumoniae with reduced susceptibility to expanded-spectrum cephalosporins.

Between February 2001 and January 2002, an increase in the number of Klebsiella pneumoniae isolates with reduced susceptibility to expanded-spectrum cephalosporins (RSKp) was detected in the neonatal unit of the Juan Canalejo Hospital, and 21 patients were either colonized or infected by the bacterial isolates. The current "gold standard" method for typing K. pneumoniae isolates is pulsed-field gel electrophoresis. However, this technique is expensive and time-consuming. In a search for faster and accurate alternatives to this method, we investigated PCR-based fingerprinting techniques (enterobacterial repetitive intergenic consensus sequence PCR [ERIC-PCR], repetitive extragenic palindromic sequence-based PCR [REP-PCR], and RAPD [randomly amplified polymorphic DNA]) for their ability to characterize K. pneumoniae isolates. The causal agent of the nosocomial outbreak was characterized by these techniques and was found to be a single epidemic strain (RSKp). A multiple regression logistic model was developed to identify potential independent factors associated with colonization and/or infection by RSKp. Logistic regression analysis was applied to all significant variables (P < 0.05) in the univariate analysis, and it was revealed that intubation (odds ratio [OR], 27.0; 95% confidence interval [95%CI], 5.39 to 135.14) and prematurity (OR, 4.4; 95%CI, 0.89 to 21.89) were such independent factors. Moreover, oxime cephalosporins did not appear to be statistically significant. Overall, the results showed that PCR-based techniques are expeditious and useful methods for typing K. pneumoniae isolates. Of the techniques studied, ERIC-PCR showed the highest discriminatory index (D = 0.828), followed by RAPD (D = 0.826) and REP-PCR (D = 0.773)

Lack of correlation between phenotypic techniques and PCR-based genotypic methods for identification of Enterococcus spp.

A total of 123 genetically-unrelated strains of Enterococcus spp. strains (51 Enterococcus faecalis, 57 Enterococcus faecium, 10 Enterococcus gallinarum, and 5 Enterococcus casseliflavus) were phenotypically identified by biochemical profiles and by using an automated method. The strains were also analyzed by a PCR assay to assess the accuracy of the phenotypically-based methods for identification of Enterococcus spp. With this aim, a PCR assay using different cell targets, which allows simultaneous detection of glycopeptide-resistant genotypes as well as identification to the species level by means of different gene targets, was used as the gold standard method. All 51 strains of E. faecalis were correctly identified, whereas 48 of 57 strains (84.2%) of E. faecium, were correctly identified. All of the strains of E. gallinarum and 3 out of 5 strains of E. casseliflavus were also correctly identified. The overall results showed that it is possible to identify Enterococcus spp. at the molecular level in less than 30 hours, compared with the 48-96 hours required for the phenotypically-based methods. The excellent accuracy of the PCR assay in identifying these species, particularly E. faecium, must also be emphasized. These findings may have implications for the routine clinical identification of enterococci species.

High-level resistance to ceftazidime conferred by a novel enzyme, CTX-M-32, derived from CTX-M-1 through a single Asp240-Gly substitution.

A clinical strain of Escherichia coli isolated from pleural liquid with high levels of resistance to cefotaxime, ceftazidime, and aztreonam harbors a novel CTX-M gene (bla(CTX-M-32)) whose amino acid sequence differs from that of CTX-M-1 by a single Asp240-Gly substitution. Moreover, by site-directed mutagenesis we demonstrated that this replacement is a key event in ceftazidime hydrolysis