Integrones y cassettes genéticos de resistencia a antimicrobianos en cepas de Shigella flexneri / Integrons and antimicrobial resistance gene cassettes in Shigella flexneri strains

BACKGROUND: The resistance of Shigella flexneri to antimicrobial agents can be associated to the presence of integrons that may contain and express antimicrobial resistance gene cassettes. AIM: To study antimicrobial resistance and the presence of integrons and antimicrobial gene cassettes in Shigella flexneri strains. MATERIAL AND METHODS: In vitro susceptibility to 27 antimicrobials was studied in twenty four Shigella flexneri strains isolated from stools. The presence of integrons class 1, 2 and 3 and antimicrobial resistance gene cassettes was investigated by polymerase chain reaction (PCR) using specific primers for each gene. RESULTS: Most strains were resistant to one of the following antimicrobials: ampicillin, sulphonamide, trimethoprim, tetracycline, streptomycin, sulfamethoxazole-trimethoprim or chloramphenicol. Twenty nine percent were simultaneously resistant to all these antimicrobials. Integrons class 1 and 2 were found in 19 strains (79 per cent). Class 3 integrons were not found. Gene cassettes dfrA1 and ant(3")I were associated to integrons class 2 in most strains (15/20, 75 per cent). Genes cat, tetB and blarTEM were detected in 18/24 (75 per cent), 7/24 (29 per cent) and 4/24 (17 per cent) of the strains, respectively and were not associated to any of the studied integrons. Genes that codify enzymes AAC(6')Ib and APH(3')VI were not detected in any strain. CONCLUSIONS: The high frequency of integrons found in the studied strains, could partly explain the increasing antimicrobial resistance of Shigella flexneri strains, isolated in Chile.

Prevalence and types of class 1 integrons in aminoglycoside-resistant Enterobacteriaceae from several Chilean hospitals.

Members of the family Enterobacteriaceae are responsible for a variety of nosocomial infections, treatment of which is limited due to their increasing resistance to antibiotics. Some bacterial genes encoding antibiotic resistance comprise the major part of gene cassettes, most of which are associated with integrons. In this work, the carriage of class 1, 2 and 3 integrons was investigated in 191 Enterobacteriaceae isolates from clinical specimens of hospitalized patients. Class 1 integrons were found to be the most common, whereas no class 3 integrons were detected. The variable regions of 13 class 1 integrons were characterized and four types were found. Type 1 harbours only ant(3")I, type 2 harbours ant(2")I and ant(3")I, type 3 harbours aac(6')Ib and ant(3")I and type 4 lacks inserted gene cassettes.

Activity of cefepime, cefotaxime, ceftazidime, and aztreonam against extended-spectrum-producing isolates of Klebsiella pneumoniae and Escherichia coli from Chilean hospitals.

Resistance of Gram-negative bacilli to third-generation cephalosporins has been increasing due to the production of extended-spectrum beta-lactamases. In this work, the activities of cefepime, cefotaxime, ceftazidime, and aztreonam, alone and in association with clavulanic acid, against isolates of Klebsiella pneumoniae and Escherichia coli are compared. These isolates produce extended-spectrum beta-lactamases as shown by the synergy tests and by the decrease in the MICs of cephalosporins in the presence of clavulanic acid. Cefepime was the most active compound against these microorganisms. In addition, the microorganisms exhibited lower frequencies of resistance to this cephalosporin.

Antibiotic resistant bacteria in fish from the Concepción Bay, Chile.

Antibiotic resistant bacteria from commercial demersal and pelagic fish captured in the Concepción Bay, Chile were investigated. Viable counts of antibiotic resistant bacteria isolated from gill and intestinal content samples showed high frequencies of resistance to ampicillin, streptomycin and tetracycline, while the proportion of chloramphenicol resistance was rather low. A high incidence of resistance to ampicillin, streptomycin, tetracycline and nitrofurantoin, as well as almost an absence of resistance to gentamicin, amikacin and cotrimoxazole was found among selected isolates which represented the resistant bacterial population. These strains mainly belonged to Vibrionaceae and Enterobacteriaceae and were predominantly resistant to 3 and 4 antibacterials. Isolates from demersal fish exhibited resistance to as many as 8-10 compounds, whereas those from pelagic fish were resistant to seven or fewer antibiotics. These results suggest that Chilean commercial fishes residing in waters near the disposals of urban sewage might play a role as carriers of antibiotic resistant bacteria prompting a health risk to public health for fish consumers.

Actividad de aminoglucósidos sobre cepas hospitalarias de Acinetobacter baumannii aisladas entre 1990 y 1998 / Antibacterial activity of aminoglycosides against nosocomial strains of Acinetobacter baumannii isolated between 1990 and 1999

Se investigó la actividad antibacteriana de aminoglucósidos frente a 487 cepas hospitalarias de Acinetobacter baumannii aisladas entre 1990 y 1998, y en algunas cepas se relaciona la resistencia con el contenido de DNA plasmídico. Para todos los aminoglucósidos probados se encontró una elevada frecuencia de cepas resistentes, con valores que variaron entre el 47 por ciento para amikacina (periodo 1990-1992) y el 94 por ciento para gentamicina (periodo 1993-1994). La curación de un plásmido de más de 30 kb se asoció con la pérdida de resistencia a amikacina, kanamicina y neomicina. Esto pudiera indicar que este plásmido contiene los genes que codifican para la combinación de enzimas modificantes de aminoglucósidos formada por AAC(6')I+APH(3')I. La resistencia a la gentamicina parece estar codificada principalmente en el cromosoma de las cepas de A. baumannii estudiadas o en transposones insertos en el cromosoma (AU)

Actividad de imipenem y meropenem sobre cepas de Acinetobacter baumannii aisladas en hospitales chilenos(1990-1998) / Activity of imipenem and meropenem against strains of Acinetobacter baumannii isolated from various Chilean hospitals (1990-1998)

Se estudió la actividad de imipenem y meropenem sobre 447 cepas de Acinetobacter baumannii aisladas entre los años 1990 y 1998 en diferentes hospitales de Chile. Se determinó el rango de CMI, la CMI50 y la CMI90 por el método de dilución en agar. La actividad antibacteriana fue similar para ambos antibióticos, aun cuando para las cepas aisladas en 1997 y 1998 se encontró un leve aumento de la CMI50 de imipenem y meropenem y de la CMI90 de meropenem. Aunque las cepas de A. baumannii permanecen sensibles a estos compuestos, es importante destacar que la CMI50 y la CMI90 han aumentado en los últimos años (AU)

[Presence of integrons and their relationships with the resistance to third generation cephalosporins among nosocomial isolates of Acinetobacter baumannii]. / Presencia de integrones y su relación con la resistencia a cefalosporinas de tercera generación en cepas de Acinetobacter baumannii de origen nosocomial.

BACKGROUND: Acinetobacter baumannii is an important etiological agent causing nosocomial infections. High level of resistance for different kind of antimicrobials has been observed, including beta-lactam antibiotics. This feature, chromosomal or plasmid encoded, has been associated to integrons harbouring antibiotic resistance gene cassettes. AIMS: To investigate the presence of integrons among clinical isolates resistant to third generation cephalosporins (3GC). MATERIAL AND METHODS: One hundred A. baumannii strains isolated from several Chilean hospitals were included in this study. Minimal inhibitory concentrations (MIC) of 3GC by an agar dilution method were carried out. Integrons class 1, 2 and 3 were investigated by colony blot hybridisation and confirmed by PCR. RESULTS: High level of resistance to all assayed 3GC was observed. On the other hand, integrón class 2 was the most prevalent (77% of isolates) followed by integron class 1 (52%). Forty six percent of isolates hybridised with probes for both of them. However, no positive hybridisation was detected for integron class 3. CONCLUSIONS: Nevertheless, most isolates harboured one or both class of integron; there was no direct relationship between the presence of these genetic structures and the resistance to this kind of beta-lactam antibiotics.

[Evaluation of Nugent and Amsel criteria for the diagnosis of bacterial vaginosis]. / Evaluación de los criterios de Nugent y Amsel para el diagnóstico de vaginosis bacteriana.

BACKGROUND: Bacterial vaginosis (BV) is a common disease in reproductive-age women and is associated to important gynecologic and obstetric complications. AIM: To study the occurrence of BV in apparently healthy women attending family planning clinics, using Amsel and Nugent diagnostic criteria. MATERIAL AND METHODS: Two hundred thirty nine women consulting for symptoms associated to cervicovaginitis, were studied. A sample from the lateral walls of the vagina was obtained with a sterile swab for microscopic analysis, Gram stain and amine test. RESULTS: According to Amsel and Nugent criteria a 31.1% and 31.8% BV prevalence was observed. The sensitivity and specificity of Nugent criteria, compared with Amsel criteria were 83.3% and 92.1%, respectively. CONCLUSIONS: The high prevalence of BV found in this study suggests that this vaginal infection should be diagnosed with standardized methods. Nugent criteria are economic easy to perform and sensitive and we propose that they should be used in local health centers.

[Activity of imipenem and meropenem against strains of Acinetobacter baumannii isolated from various Chilean hospitals]. / Actividad de imipenem y meropenem sobre cepas de Acinetobacter baumannii aisladas en hospitales chilenos(1990-1998).

The activity of two carbapenem compounds, imipenem and meropenem, against 447 strains of Acinetobacter baumannii isolated between 1990 and 1998 in different Chilean hospitals was determined. MIC ranges, MIC(50) and MIC(90), were determined by an agar dilution method. Similar antibacterial activities were observed for both antibacterials; however, a slight increase in the MIC(50) of imipenem and meropenem, and in the MIC(90) of meropenem was found among strains isolated from 1997-1998. Although A. baumannii remains susceptible to these antibiotics, the MIC(50) and MIC(90) have increased in recent years.

[Efficacy and tolerance of a five day course of ciprofloxacin in the treatment of urinary tract infection in women. Multicenter study]. / Eficacia y tolerancia de ciprofloxacina por 5 días en mujeres con infección urinaria. Estudio multicéntrico.

BACKGROUND: There is no consensus about the ideal antimicrobial agent and duration of treatment for urinary tract infection in women. AIM: To assess the efficacy of a five days course of ciprofloxacin for the treatment of urinary tract infection in women. PATIENTS AND METHODS: Women with urinary tract infection were treated with ciprofloxacin (Baycip, Bayer) 250 mg bid during 5 days. Patients were evaluated three to four days after treatment start, two to seven days and one month after treatment end. RESULTS: Of 101 eligible women, 96 aged 18 to 65 years old, coming from three major Chilean cities, participated in the study and 80 completed the follow up period. There was a 95% clinical success, 2.5% partial improvement and 2.5% treatment failure. The causal microorganism was erradicated in 90% of cases, in 1.2% treatment failed and in 8.7% a re-infection occurred. Adverse effects attributable to the drug were observed in 12 patients (headache in 3, gastrointestinal disturbances in 8, somnolence in 1 and irritability in 1). CONCLUSIONS: Ciprofloxacin is an useful antimicrobial for the treatment of lower urinary tract infection in women.

Presence of integrons in isolates of different biotypes of Acinetobacter baumannii from Chilean hospitals.

Class 1 and class 2 integrons were investigated by hybridisation in 100 isolates of multiresistant biotypes of Acinetobacter baumannii from Chilean hospitals. Most isolates of A. baumannii biotype 9, the prevalent biotype, harboured integrons of class 2 (Tn7-like) whereas no integrons were detected in infrequent biotypes. Integron-carrying isolates exhibited broader antibiotic resistance patterns as well as higher resistance levels to various antimicrobials.

[Adherence of Acinetobacter baumannii to rat tracheal tissue]. / Adherencia de Acinetobacter baumannii al tejido de tráquea de la rata.

BACKGROUND: Acinetobacter baumannii is an important nosocomial pathogen whose virulence factors have not been fully elucidated. AIM: To study the adherence and hemagglutinating capacity of several biotypes of Acinetobacter baumannii. MATERIAL AND METHODS: Thirty nine strains of Acinetobacter baumannii isolated from hospitalized patients were studied. The adherence of these strains to small pieces of rat tracheal tissue was studied. Additionally, their ability to hemagglutinate human erythrocytes and the effect of D-mannose and D-galactose on the adherence and hemagglutinating capacity was assessed. Transmission electron microscopy of strains was performed looking for the presence of fimbriae. RESULTS: All strains exhibited adherence to tissues. All strains had also D-mannose and D-galactose resistant hemagglutinating ability. Fimbriae were found in Acinetobacter baumannii and E coil cells. CONCLUSIONS: Adherence of Acinetobacter baumannii to rat tracheal tissue, apparently not related to the presence of fimbriae, may be a virulence mechanism of this bacterium.

[Surface characteristics and antimicrobial sensitivity of clinical strains of Acinetobacter spp]. / Características de superficie y sensibilidad antimicrobiana de cepas clínicas de Acinetobacter spp.

BACKGROUND: The treatment of nosocomial infections caused by Acinetobacter baumannii has been hindered by the easiness of this species to acquire antimicrobial resistance. AIM: To study surface hydrophobicity, the presence of capsule and antimicrobial susceptibility of nosocomial Acinetobacter spp strains. MATERIAL AND METHODS: Ninety four Acinetobacter spp strains isolated from a public hospital of Santiago, between July 1995 and April 1996, were studied. RESULTS: Compared to Acinetobacter genospecies 3 isolates, A baumannii isolates exhibited greater antimicrobial resistance, was uniformly susceptible to imipenem and highly resistant to other antimicrobials of clinical use. Most strains of biotypes 8 and 9 were hydrophilic and encapsulated, whereas those of infrequent biotypes and of Acinetobacter genospecies 3 were, with few exceptions, hydrophobic and not encapsulated. CONCLUSIONS: Capsule production might confer a greater virulence to Acinetobacter baumannii biotypes 8 and 9, and explain their higher prevalence in the studied hospital.

Adherence of Acinetobacter baumannii to rat bladder tissue.

Acinetobacter baumannii, an important nosocomial pathogen, causes severe infections in patients of intensive care units, but its pathogenic attributes are unknown. Previously, the adherence of A. baumannii to cell lines has been negative in the authors' laboratory. In this work, the adherence of strains of A. baumannii of various biotypes to small pieces of rat bladder tissue was investigated. Tissue pieces were submerged into cultures of A. baumannii and sessile cells were counted after removing planktonic bacteria. Fimbriae and sessile cells were examined by transmission and scanning electron microscopy, respectively. In contrast to a uropathogenic strain of Escherichia coli, all cultures exhibited a mannose- and galactose-resistant agglutination of human group O red blood cells as well as mannose- and galactose-resistant adherence to the bladder tissue. Inhibition of exopolysaccharide synthesis did not modify adherence. Indeed, adherence, apparently unrelated to these fimbriae or to the exopolysaccharide, may be a factor contributing to the pathogenicity of A. baumannii in the urinary tract or in other tissues.

Activity of selected beta-lactams, ciprofloxacin, and amikacin against different Acinetobacter baumannii biotypes from Chilean hospitals.

The activity of some third generation cephalosporins, aztreonam, imipenem, ciprofloxacin, and amikacin against isolates of Acinetobacter baumannii of various biotypes has been studied. The isolates, independently of the biotype, exhibited a broad multiresistance against cephalosporins. Ceftazidime was the most active and cefoperazone the least active compound. Aztreonam also showed low activity and no imipenem-resistant strains were found. Ciprofloxacin and amikacin were somewhat more active than cephalosporins, but resistant isolates were also frequent. Isolates of Biotypes 9 and 8 exhibited broader multiresistance than those of Biotype 6 and "other."

Effect of imipenem and sulbactam on sessile cells of Acinetobacter baumannii growing in biofilm.

The effect of the age of biofilms formed by Acinetobacter baumannii on the activity of sulbactam and imipenem on sessile cells was investigated. Against cells of young biofilms both antibiotics were rapidly bactericidal. As the biofilm aged, sulbactam lost most of its activity, but imipenem continued to be bactericidal to some extent. This fact probably reflects the ability of imipenem to exert bactericidal activity on slow-growing bacteria.

Biofilm formation by Acinetobacter baumannii.

Acinetobacter baumannii, an important nosocomial pathogen is usually found on various surfaces in the hospital environment. In this work, the ability to form biofilms on the surface of sterile coverslips by one clinical isolate of A. baumannii was studied. Sessile cells which adhered to coverslips after being immersed in a nutrient-deficient mineral medium were observed by epifluorescence and scanning electron microscopy at various times of incubation. A rapid increase in the number of sessile cells in young biofilms, followed by a slower increase of such cells was found. At 48 h biofilms were clearly visible and an amorphous material similar to the exopolysaccharide described in some other bacteria covered sessile cells was evident. Biofilm formation by A. baumannii probably favours its maintenance on solid surfaces in the hospital environment and protects the micro-organism against some antibacterial factors.