Evaluation of a novel cocktail of six lytic bacteriophages against Shiga toxin-producing Escherichia coli in broth, milk and meat.

Phages are potentially useful as antimicrobial agents in food, especially cocktails of different phages which may prevent the development of bacterial resistance. Biocontrol assays with a six-phage cocktail, which is lytic against DH5α, an enteropathogenic (EPEC) and two Shiga-toxigenic (STEC) Escherichia coli strains, were performed in Hershey-Mg broth, milk and meat at refrigerated (4 °C), room (24 °C) and abusive (37 °C) temperatures. At 4 °C, cell counts were significantly lower (2.2-2.8 log10 CFU/mL) when E. coli strains (∼109 CFU/mL) were challenged against the phage cocktail (∼109 PFU/mL) in Hershey-Mg broth after 24 h. However, reductions were higher (3.2-3.4 log10 CFU/mL) after a 48 h exposure for all the strains tested. In addition, reduction values reached up to 3.4 log10 CFU/mL (24 °C) and 3.6 log10 CFU/mL (37 °C) in challenge tests after 24 h, though the reductions achieved were slightly lower after 48 h for the four E. coli strains tested. In milk, the cocktail was highly effective since bacterial counts were below the detection limit (<101 CFU/mL) at 4 °C, while the reductions ranged from 2 to 4 log10 CFU/mL at 24 °C after a 24 h exposure. At 37 °C, DH5α was eliminated within 2 h, and an average cell decrease of 4 log10 CFU/mL was observed for the three pathogenic strains tested. When the assays were performed in meat, biocontrol values ranged from 0.5 to 1.0 log10 CFU/mL after 48 h at 4 °C, while a higher cell inactivation was achieved at 24 °C (2.6-4.0 log10 CFU/mL) and 37 °C (3.0-3.8 log10 CFU/mL). Furthermore, higher inactivation values for O157:H7 STEC (1.55 ±â€¯0.35 log10 CFU/mL) at 4 °C were obtained in meat when incubation was extended up to 6 days. As a conclusion, our six-phage cocktail was highly effective at 24 °C and 37 °C, though less effective at 4 °C in both food matrices evaluated. Thus, it might be applied against pathogenic EPEC and STEC strains to prevent foodborne diseases especially when the cold chain is lost.

Action of Colloidal Bismuth Hydroxide Gel and its Commercial Cream on Enteropathogens and Colonizers of the Gastrointestinal Tract.

BACKGROUND: Acute diarrheal diseases constitute a world public health problem because they are the second cause of death in children under 5 years of age. Colloidal bismuth hydroxide gel (CBHG) is an active ingredient in low-cost, antidiarrhetic drugs for oral use; it does not inhibit intestinal motility, and it features very low intestinal absorption of <1%. MATERIALS AND METHODS: We analyzed the sensitivity by determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC); the effect on bacterial growth by studying the specific growth velocity and the generation time in growth curves; and bacterial attachment by counting viable plaques, of enteropathogenic Escherichia coli, shigatoxigenic E. coli O157:H7, Klebsiella pneumoniae, Salmonella spp., and Shigella flexneri in the commercial cream (Chobet® bismuth cream with pectin [CBCHP]), its active ingredient (CBHG), and its excipients (E) separately. RESULTS: CBCHP: MIC 6-10 mg/ml and MBC 7.5-15 mg/ml of bismuth; CBHG: MIC 6-10 mg/ml of bismuth. E: No inhibition was observed at the concentration studied in this study. At very low subinhibitory concentrations of CBCHP and CBHG, there was already evidence of a significant decrease in growth, which could not be recorded for E. CBCHP and CBHG presented an elevated capacity for bacterial displacement, significantly greater than E. CONCLUSIONS: We believed that the results obtained in this study are very promising from the treatment standpoint, as a possible treatment for cases of diagnosis or suspicion of bacterial gastroenteritis. The antimicrobial and attachment effects of CBCHP are exclusively due to its active ingredient CBHG; these effects are promoted in the presence of E.

Aryloxoalcanoic compounds induce resistance to antibiotic therapy in urinary tract infection caused by Escherichia coli.

Clofibric acid (CL) is a compound used to control hypertriglyceridemia, and ethacrynic acid (ET) is administered to enhance diuresis. These compounds are structurally analogous to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), as they have a chlorinated phenoxy moiety. As these agents are mainly excreted by the renal route, they could potentially coexist with Escherichia coli in the urinary tract of infected patients. Induction of the in vitro resistance of E. coli to hydrophilic antibiotics was determined by increasing the values of the minimum inhibitory concentration (2-40-fold). These results correlated with drastically inhibited expression of the hydrophilic bacterial channel OmpF. In vivo assays were performed in ascending urinary tract infection in female BALB/c mice. Treatment with the hydrophilic antibiotic cephalexin 25 mg kg(-1) day(-1) by the oral route diminished renal infection. The CFU mean values in the kidneys were between 75% and 89% lower than those in animals without treatment. Simultaneous exposure to CL (at a therapeutic dose, 28.6 mg kg(-1) day(-1)) did not change the effect of the treatment. In contrast, ET at 2.9 mg kg(-1) day(-1) or 2,4-D at 70 mg kg(-1) day(-1) inhibited the antibiotic therapeutic effect. Moreover, 2,4-D dramatically increased bacterial infection after 9 days of exposure.

Prevalence and Virulence Genes of Shigella spp. Isolated from Patients with Diarrhea in Rosario, Argentina.

The aim of this study was to determine the prevalence and virulence factors of Shigella species isolated from patients with diarrhea. Shigella species were isolated from 1,022 stool samples collected from different hospitals in Rosario, Argentina. The isolates were characterized using phenotypic tests, serotyping, and detection of virulence genes by PCR. One hundred strains (9.8% of samples collected) of Shigella were isolated. Shigella flexneri was the most frequently identified species (74%), followed by S. sonnei (26%). S. flexneri was also the predominant species isolated from children aged 6-14 years. These clinical strains of Shigella were then tested for the presence of ipaH, virA, ial, sen, and set using specific primers. virA was present in all strains, whereas ipaH was detected in 98% of strains and ial in 83%. sen was found in 71.6% of S. flexneri and 42.3% of S. sonnei isolates, and 41.9% of S. flexneri isolates were positive for set. Furthermore, 32.4% of S. flexneri isolates were positive for both set and sen. This study provides data on the prevalence and distribution of diverse Shigella strains.

Clofibric and ethacrynic acids prevent experimental pyelonephritis by Escherichia coli in mice.

Interfering Escherichia coli attachment to the urinary tract, using P-fimbriation inhibitors, can prevent pyelonephritis. Clofibric and ethacrynic acids are organic compounds structurally related, but with different pharmacological uses. These agents are potentially active in the urinary tract due to its elimination in an unaltered form by the renal route. This study described a pyelonephritogenic E. coli strain, grown in the presence of sub-inhibitory concentrations of clofibric or ethacrynic acids (0.1 and 1 mM, respectively), which exhibits inhibition of P1 erythrocytes agglutination and a drastic decrease in fimbriation, using electron microscopy and quantitative analyses of superficial proteins (decrease to a 17-25% in comparison with the control). In vivo assays were performed using ascending urinary tract infection in mice. The treatment with therapeutic doses of the drugs, administered 2 days before the bacterial challenge and daily until the end of the experiment (22 days), abolished renal infection after 7-10 days of drug exposure. Within this period clofibric acid did not produce adverse effects on the renal parenchyma. However, ethacrynic acid caused pyelitis and tubular cellular desquamation. These results suggested that clofibric acid might be useful in the short-term prophylaxis of urinary tract infection.

Effect of the herbicide 2,4-dichlorophenoxyacetic acid on uropathogenic Escherichia coli virulence factors.

The effects of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D)-widely used in the world and mainly excreted by the renal route in exposed humans-were studied on the virulence and surface characteristics of an uropathogenic Escherichia coli strain. When the urine was supplemented with 2,4-D in vitro, the compound significantly reduced the bacterial fimbriation assayed by hemagglutination and surface protein quantification. Protein values decreased from 0.24 mg/g dw to 0.05 or 0.12 mg/g dw by 1 or 0.1 mM 2,4-D treatment, respectively. The effects in vivo were studied in groups of mice challenged intra-urethra with E. coli and exposed by the oral route with three different 2,4-D doses (2.6, 25 or 70 mg/kg bw) during 22 days. Depending on the dose used, the herbicide significantly decreased or removed bacterial cells in mice bladder and kidneys; except in the group treated with the highest dose from the 9th day of treatment. The histological studies showed mononuclear cell infiltration at low doses, and toxic damage in the renal parenchyma at prolonged exposure with higher doses, up to tisular necrosis in the 70 mg/kg bw group after 9 days of treatment. Our investigations performed in an experimental model suggest that short time 2,4-D exposure at low doses could act in prevention of UTI stimulating leukocytic migration and decreasing bacterial fimbriation. On the contrary, high doses and long-term exposure enhanced renal damage resulting in infection recurrence.

The inhibitory effect of colloidal bismuth hydroxide gel on Escherichia coli O157:H7 and on the activity of Shiga toxins.

BACKGROUND: Shiga toxin-producing Escherichia coli (STEC) is the causative agent of hemolytic uremic syndrome (HUS). Colloidal bismuth hydroxide gel (CBHG) is an anti-diarrheal and antisecretory compound, which does not inhibit gastrointestinal motility and reaches an in vivo gut concentration of 10.8 mg/ml of bismuth. Its action on bacteria has not been studied. We analyzed its inhibitory effects on STEC, as well as the deactivation of the Shiga toxin (Stx) and its ability to block the spread of genes encoding Stx. We determined a minimum inhibitory concentration and bactericidal concentration for the STEC O157:H7 strain (EDL933), with CBHG and Chobet® bismuth cream with pectin (CBCHP). We analyzed its effect on Stx by means of cytotoxicity assay and ELISA, as well as its effect on the free 933 W Stx phage. RESULTS: Effect on the EDL933 strain: CBHG: MIC 10 mg/ml of bismuth. CBCHP: MIC 6 mg/ml and MBC 15 mg/ml of bismuth. Effect on EDL933 virulence factors: significant decrease in active Stx and 933 W Stx phage titer. ELISA did not find significant differences with treatment. CONCLUSIONS: The results obtained may be useful in the development of new therapeutic strategies based on the use of CBHG to prevent or improve the prognosis of HUS, as it can be used to control STEC infections.

Phage biocontrol of enteropathogenic and shiga toxin-producing Escherichia coli in meat products.

Ten bacteriophages were isolated from faeces and their lytic effects assayed on 103 pathogenic and non-pathogenic Enterobacteriaceae. Two phages (DT1 and DT6) were selected based on their host ranges, and their lytic effects on pathogenic E. coli strains inoculated on pieces of beef were determined. We evaluated the reductions of viable cells of Escherichia coli O157:H7 and non-O157 Shiga toxigenic E. coli strains on meat after exposure to DT6 at 5 and 24°C for 3, 6, and 24 h and the effect of both phages against an enteropathogenic E. coli strain. Significant viable cell reductions, compared to controls without phages, at both temperatures were observed, with the greatest decrease taking place within the first hours of the assays. Reductions were also influenced by phage concentration, being the highest concentrations, 1.7 × 10(10) plaque forming units per milliliter (PFU/mL) for DT1 and 1.4 × 10(10) PFU/mL for DT6, the most effective. When enteropathogenic E. coli and Shiga toxigenic E. coli (O157:H7) strains were tested, we obtained viable cell reductions of 0.67 log (p = 0.01) and 0.77 log (p = 0.01) after 3 h incubation and 0.80 log (p = 0.01) and 1.15 log (p = 0.001) after 6 h. In contrast, all nonpathogenic E. coli strains as well as other enterobacteria tested were resistant. In addition, phage cocktail was evaluated on two strains and further reductions were observed. However, E. coli bacteriophage insensitive mutants (BIMs) emerged in meat assays. BIMs isolated from meat along with those isolated by using the secondary culture method were tested to evaluate resistance phenotype stability and reversion. They presented low emergence frequencies (6.5 × 10(-7)-1.8 × 10(-6)) and variable stability and reversion. Results indicate that isolated phages were stable on storage, negative for all the virulence factors assayed, presented lytic activity for different E. coli virotypes and could be useful in reducing Shiga toxigenic E. coli and enteropathogenic E. coli viable cells in meat products.

Effect of preservatives on Shiga toxigenic phages and Shiga toxin of Escherichia coli O157:H7.

Toxin synthesis by Shiga toxin-producing Escherichia coli (STEC) appears to be coregulated through the induction of the integrated bacteriophages that encode the toxin genes. These phages might be the principal means for the dissemination and release of Shiga toxins. We evaluated the effect of three common food preservatives, potassium sorbate, sodium benzoate, and sodium propionate, on the propagation of the phages and Shiga toxins. We tested each preservative at four concentrations, 1, 1.25, 2.5, and 5 mg/ml, both on free phages and on lysogenic phages in bacteria. We also evaluated the expression of a lambdoid phage, which was exposed to increasing concentrations of preservatives, by measuring ß-galactosidase activity from SPC105, a transductant strain. Furthermore, we tested the effect of the preservatives on cytotoxigenic activity of Shiga toxin on Vero cells. We detected an increase of the inhibitory effect of the phage lytic activity, both in lysogenic and free phages, as the preservative concentration increased. However, the inhibition was higher on the lysogenic phages release than on free phages. Sodium benzoate and potassium sorbate were about equal at inhibiting phages; they were more effective than sodium propionate. A significant decrease of lacZ expression, encoded in a lambda phage, was observed. We also found a reduction in Shiga toxin titer caused by exposure of E. coli O157:H7 to 5 mg/ml sodium benzoate or potassium sorbate. These results imply that these three preservatives, used to inhibit microbial spoilage of foods, also act to inhibit lytic activity and dispersion of a phage carrying the gene encoding powerful Shiga cytotoxins. Also notable was the inactivation of Shiga toxin activity, although this effect was detected using concentrations of preservatives greater than those allowed by the Argentine Food Code.

Inhibition of the adhesion to catheters of uropathogenic Escherichia coli by sub-inhibitory concentrations of cefotaxime.

OBJECTIVE: To investigate the effect of sub-inhibitory concentrations of cefotaxime on adherence to siliconized latex urinary catheters of uropathogenic Escherichia coli strains from pregnant and non pregnant patients. STUDY DESIGN: Using random sampling, 30 E. coli strains were selected from hospitalized patients with catheter associated urinary tract infection, 12 from pregnant women and 18 from men and non-pregnant women. The strains were categorized on the basis of cefotaxime susceptibility, adhesion and biofilm production capacity, cell surface hydrophobicity and expression of adhesins and fimbriae in vitro. RESULTS: The overall results indicated that sub-inhibitory concentrations of cefotaxime could reduce the adhesiveness, the biofilm production and hence, potentially, the infection rate associated with indwelling urinary catheters. CONCLUSION: Based on our results, we propose that this reduction is due to decreasing exopolysaccharide production and increasing cell surface hydrophobicity of E.coli strains.

Diversidad de ß-lactamasas en aislamientos clínicos de enterobacterias / ß-lactamases diversity in clinical isolates of enterobacterias / Diversidade de ß-lactamases em isolamentos clinicos de enterobactérias

La rápida emergencia de resistencia a antimicrobianos debida a la presencia de b-lactamasas de espectro extendido (BLEE) tiene un impacto significativo en la salud pública. Las BLEEs son enzimas producidas por bacilos gramnegativos y confieren resistencia a las penicilinas, a todas las cefalosporinas y al aztreonam, pero no a los carbapenemes ni a las cefamicinas y la mayoría son inhibidas por el ácido clavulánico. El objetivo de este trabajo fue evaluar la resistencia a antibióticos b-lactámicos en aislamientos de Klebsiella pneumoniae, Escherichia coli y Proteus mirabilis y caracterizar las b-lactamasas responsables de dicha resistencia. Se analizaron 2.030 aislamientos (362 Klebsiella pneumoniae, 1.250 Escherichia coli y 175 Proteus mirabilis) provenientes de diferentes materiales clínicos de pacientes que concurrieron al Hospital Provincial del Centenario de la ciudad de Rosario (Santa Fe) durante el período 2008-2009. Los ensayos de sensibilidad antibiótica se realizaron de acuerdo con las recomendaciones del Clinical and Laboratory Standard Institute. Se confirmó la presencia de los genes codificantes de BLEE blaTEM, blaSHV, blaCTX-M y blaPER mediante la reacción en cadena de la polimerasa (PCR) utilizando cebadores específicos. Los aislados fueron caracterizados fenotípicamente como productores de BLEE y demostraron poseer varios genes bla. Se detectaron tres diferentes b-lactamasas BLEE derivadas de SHV, TEM y CTX-M y se demostró que pueden coexistir dos o más de estos genes en una misma bacteria.

The rapid emergence of antimicrobial resistance due to extended spectrum b-lactamases (ESBL) has a significant impact on public health. ESBL, produced by gram-negative bacilli, are enzymes that confer resistance to penicillins, cephalosporins and aztreonam, but not to carbapenems or cephamycins, and are usually inhibited by clavulanic acid. The aim of this study was to evaluate b-lactam resistance within isolates of Klebsiella pneumoniae, Escherichia coli, and Proteus mirabilis and to characterize the b-lactamases responsible for this resistance. A total of 2,030 strains (362 Klebsiella pneumoniae, 1,250 Escherichia coli, and 175 Proteus mirabilis) isolated from patients at Hospital Provincial del Centenario in Rosario-Santa Fe were analyzed from 2008 to 2009. Antibiotic sensitivity tests were performed according to Clinical and Laboratory Standard Institute recommendations. Molecular detection of ESBL-related bla genes, including blaTEM, blaSHV, blaCTX-M and blaPER was performed by polymerase chain reaction (PCR) using specific primers. The strains were phenotipically confirmed as ESBL producers and the isolates carried several bla genes. Three different b-lactamases were detected: SHV-related, TEM-related and CTX-M-related, showing that two or more genes may coexist in the same bacterium.

A rápida emergência de resistência a antimicrobianos devida à presença de b lactamases de espectro estendido (BLEE) tem um impacto significativo na saúde pública. As BLEEs são enzimas produzidas por bacilos gram-negativos e conferem resistência às penicilinas, a todas as cefalosporinas e ao aztreonam, mas não aos carbapenêmicos nem às cefamicinas e a maioria são inibidas pelo ácido clavulânico. O objetivo deste trabalho foi avaliar a resistência a antibióticos b-lactâmicos em isolamentos de Klebsiella pneumoniae, Escherichia coli e Proteus mirabilis e caracterizar as b-lactamases responsáveis por tal resistência. Foram analisados 2.030 isolamentos (362 Klebsiella pneumoniae, 1.250 Escherichia coli e 175 Proteus mirabilis) provenientes de diferentes materiais clínicos de pacientes que foram ao Hospital Provincial do Centenário da cidade de Rosario (Santa Fe) durante o período 2008-2009. Os ensaios de sensibilidade antibiótica foram realizados de acordo com as recomendações do Clinical and Laboratory Standard Institute. Confirmou-se a presença dos genes codificantes de BLEE blaTEM, blaSHV, blaCTX-M e blaPER mediante a reação em cadeia da polimerase (PCR) utilizando cevadores específicos. Os isolados foram caracterizados fenotipicamente como produtores de BLEE e demonstraram possuir vários genes bla. Foram detectadas três diferentes b-lactamases derivadas de SHV, TEM e CTX-M e se demonstrou que podem coexistir dois ou mais destes genes numa mesma bactéria.

Occurrence of non-O157 shiga toxin-producing Escherichia coli in ready-to-eat food from supermarkets in Argentina.

Between June 2000 and December 2001, 500 food samples were collected from supermarkets and shops selling ready-to-eat food in Rosario, Argentina, and examined for Escherichia coli. Forty-nine E. coli isolates from food samples were further characterized for virulence genes by multiplex polymerase chain reaction (PCR) targeting the stx1, stx2, stx2e, eaeA, CNF1, CNF2, Einv, LTI, STI, and STII genes in four groups. Out of 49 E. coli isolates screened by multiplex PCR, only 10 possessed Shiga toxin genes, stx1 and stx2 genes and none possessed the other genes. The Shiga toxin positive E. coli strains (STEC) were isolated from soft, cottage cheeses, chicken with sauce and vegetables mayonase. These E. coli isolates were serogrouped and belonged to O18 (two strains), O8, O57w, O79, O44, and O128; three strains were untypeable. Pulsed-field gel electrophoresis (PFGE) with XbaI generated a unique profile for each, having 10-15 bands ranging from 50 to 500 kb, except that strain ARG 20 generated small bands and was partly degraded. These strains are potential foodborne pathogens and their presence in ready-to-eat food illustrates the need to keep a careful watch for the source of pathogens and then develop methods to control them.

Effect of ciprofloxacin on adhesive properties of non-P mannose-resistant uropathogenic Escherichia coli isolates.

The influence of sub-MIC of ciprofloxacin on the surface properties of 25 non-P mannose-resistant uropathogenic Escherichia coli (UPEC) strains was studied. Thirteen isolates responded to antibiotic treatment with an increase in haemagglutination titre and/or surface hydrophobicity, which correlated with a higher expression of surface proteins. Only UPEC strains with ciprofloxacin-enhanced hydrophobicity increased their adhesiveness to urinary catheters that correlated, in one analysed case, with a dramatic increase in the number of fimbriae peripherally located. The overall results indicate that sub-MICs of ciprofloxacin could increase the adhesiveness, and hence the risk of colonization by UPEC strains expressing mannose-resistant adhesins different from type P.

Efecto del herbicida ácido 2, 4-Diclorofenoxiacético sobre la fimbriación de bacterias uropatógenas / Effect of the herbicide 2, 4-Dichlorophenoxyacetic acid on fimbriation of uropathogenic bacteria

Existen algunos datos epidemiológicos que demuestran que, en poblaciones rurales, la frecuencia de lesiones inflamatorias de origen infeccioso en el riñón es mayor en individuos expuestos a pesticidas. Estudios previos han demostrado que el herbicida 2,4-D altera las propiedades de adherencia bacteriana a riñón, mediada por fimbrias de Escherichia coli uropatógena, si bien aún no se ha estudiado el mecanismo que podría estar involucrado. El 2,4-D demostró capacidad de generar uniones covalentes a proteínas de bacilos gram negativos. Debido a este hallazgo, se hipotetizó que la unión del herbicida a proteínas involucradas en la síntesis, exportación o ensamble de las subunidades fimbriales podía alterar la expresión de las fimbrias. En este trabajo se demuestra una unión covalente del herbicida a proteínas de membrana externa de Escherichia coli uropatógena y paralelamenteuna disminución de la fimbriación, determinada por tres técnicas diferentes: hemoaglutinación, cuantificación de proteínas de superficie y microscopía electrónica. Una conclusión importante está referida a que la exposición accidental detrabajadores rurales al 2,4-D en muy bajas dosis y durante un corto período de tiempo tendría un efecto protector de la pielonefritis por disminución de la fimbriación; mientras que los altos niveles de exposición predispondrían a la recurrencia del proceso infeccioso en el modelo de la pielonefritis ascendente no obstructiva en ratón (Balagué et al 2002). Probablemente los estudios epidemiológicos que asocian exposición a los herbicidas e infección renal estén relacionados con este último tipo de exposiciones.

Epidemiological data demonstrate, on rural populations, that the frequency of inflammatory lesions in renal tissue is higher for individuals exposed to pesticides. Previous studies demonstrated that the herbicide 2,4-D altered the bacterial adherence properties to renal tissue, mediated by fimbriae in uropathogenic Escherichia coli, but the mechanism involved is still unknown. The acid 2,4-D has the ability to perform covalent bonds to proteins in gram-negative bacteria. Because of this fact, we hypothesized that the 2,4-D acid binds proteins involved in the synthesis, export or ensemble of fimbrial subunits, modifying fimbrial expression. In this work we demonstrated a covalent bond of the herbicide to outer membrane proteins in uropathogenic E. coli and a paralleldecrease of fimbriation, assayed by three different methods: hemmaglutination, surface protein quantification and electronmicroscopy. An important conclusion is that the accidental exposure of rural workers to 2,4-D may have a protective effect by a decrease in fimbriation, when it is used in low doses and during a short period of exposure. But, it must be considered that high doses and several days of exposure had adverse effects, like recurrence of infection, in the mouse model of ascendingpyelonephritis (Balagué et al, 2002). Probably, the epidemiological studies that associate the herbicide exposure with renal infection were due to the last kind of exposure described.

Efecto modulador de antibióticos sobre la adherencia bacteriana a biomateriales / Antibiotics modulation of bacterial adherence to medical biomaterials

La colonización de polímeros origina un foco de infección de difícil erradicación, debido a que las bacterias adheridas a materiales inertes presentaban propiedades fisiológicas especiales. Las infecciones urinarias complicadas debidas a sondas vesicales son las responsables del 40 por ciento de las infecciones urinarias hospitalarias. Se analizó el efecto modular de cefotaxima y ciprofloxacina en concentraciones subinhibitorias, sobre la adherencia a sondas vesicales de cepas uropatógenas de Escherichia coli. Este estudio se efectuó con cepas con bajo y elevado grado de hidrofobicidad determinados por agregación salina. Los experimentos de adherencia a sondas vesicales, en ausencia y presencia de ambos antibióticos, se realizaron a la hora y a las 24 h de contacto con los antibacterianos mencionados. El número de UFC/ml adheridas, se determinó por espectrofotometría y recuento de colonias. Se demostró que en la mayoría de las cepas con elevado grado de hidrofobicidad, aumentó el número de UFC/ml que se adhirieron a la sonda vesical, con alguno de los tratamientos. En forma inversa se comportaron las cepas con bajo grado de hidrofobicidad. El comportamiento diferente de las cepas, tratadas en las mismas condiciones, no permite generalizar el efecto de los antibióticos en concentraciones subinhibitorias, sobre la colonización bacteriana de sondas vesicales