Corynebacterium pseudotuberculosis biovar ovis: evaluación de la sensibilidad antibiótica in vitro / Corynebacterium pseudotuberculosis biovar ovis: Evaluation of antibiotics susceptibility in vitro

Resumen Los objetivos de este trabajo fueron estudiar la sensibilidad antibiótica de aislamientos de Corynebacterium pseudotuberculosis procedentes de pequeños rumiantes e investigar la presencia de integrones que contienen genes de resistencia. Se estudiaron 15 aislamientos de diferentes fuentes por los métodos de difusión y dilución. Por el método de difusión, amoxicilina-clavulánico, ampicilina, cefotaxima, cefoxitina, ciprofloxacina, cloranfenicol, eritromicina, estreptomicina, gentamicina, imipenem, kanamicina, norfloxacina, penicilina, rifampicina, tetraciclina, trimetroprima-sulfametoxazol y vancomicina fueron activos frente al 100% de los aislamientos, mientras que amicacina presentó resultados variables. En los aislamientos que desarrollaron frente a amicacina se investigó la presencia de integrones de clase 1. El resultado fue negativo, sugiriendo la ausencia del integrón. Utilizando el método de dilución, los antibióticos más activos correspondieron a los grupos de cefalosporinas, gluco-péptidos, macrólidos, quinolonas y tetraciclinas. Se demostró menor actividad de p-lactámicos y aminoglucósidos. No se registró variabilidad en los perfiles antibióticos en los aislamientos procedentes de diferentes fuentes.

Abstract The aims of this work were to study the antibiotic susceptibility in Corynebacterium pseudotuberculosis isolated from small ruminants and to determine the presence of integrons that contain resistance genes. Fifteen isolates of different sources were analysed using the diffusion and the dilution methods. When the diffusion method was performed, amoxicillin-clavulanic, ampicillin, cefotaxime, cefoxitin, ciprofloxacin, chloramphenicol, erythromycin, streptomycin, gentamicin, imipenem, kanamycin, norfloxacin, penicillin, rifampicin, tetracycline, trimethoprim-sulfamethoxazole and vancomycin were effective against the 100% of isolates, while amikacin showed variable results. The isolates that were able to grow with amikacin, were studied in relation to the presence of integron class 1. The result was negative, suggesting the absence of integron. Using dilution method, the antibiotics belonging to the cephalosporin, glycopeptide, macrolide, quinolone, and tetracycline groups were the most active ones for the C. pseudotuberculosis biovar ovis isolates. Less activity of p-lactam and aminoglycosides were observed. There was no observation of variability in the antibiotic patterns in the strains coming from different sources.

Phenotypic and genotypic characterization of enterotoxigenic Escherichia coli isolated from diarrheic calves in Argentina.

Enterotoxigenic Escherichia coli (ETEC) is the most common and global cause of neonatal calf diarrhea, but there is a little information regarding calf ETEC strains in Argentina. In this study, five ETEC isolates from diarrheic dairy calves (2-10 d old) from Buenos Aires and Cordoba, Argentina were characterized on the basis of virulence gene (VG) pattern, O:H serotyping, hemolytic phenotype, phylogenetic group affiliation, antimicrobial (AM) resistance profile, and presence of integron class 1 and 2. The five isolates were examined by polymerase chain reaction (PCR) for the presence of 18 bovine VGs and showed the following genotypes: F5+/F41+/sta+ (D242), F5+/sta+ (D158), F5+/sta+ (D157), F5+ (D151-9), and F5+/iucD+ (D151-5). These VGs confer pathogenic potential and most of them are associated with the ETEC pathotype. The five isolates showed a non-hemolytic phenotype, belonged to five different serotypes: O101:H-, O141:H-, O60:H-, ONT:H10, and ONT:H-, and were assigned to the phylogenetic group A by the quadruplex Clermont PCR method. The AM resistance of the three isolates D242, D157, and D151-5 was determined by agar disk diffusion method for 24 AMs and they exhibited a multi-resistance phenotype (resistance to four different AM classes: Cephalosporins, Penicillins, Macrolides, and Ansamycins). In addition, class 1 integrons were found in the isolate D151-5 containing the dfrA17-aadA5 gene cassette and in the bovine ETEC reference strain FV10191 containing the dfrA1-aadA1 gene cassette. The present study revealed for the first time the occurrence of multi-resistant ETEC associated with neonatal diarrhea in dairy calves in Argentina. This finding may be used for diagnostic and therapeutic purposes.

Surveillance of antibiotic resistance evolution and detection of class 1 and 2 integrons in human isolates of multi-resistant Salmonella Typhimurium obtained in Uruguay between 1976 and 2000.

OBJECTIVES: To study the evolution of antibiotic resistance in isolates of Salmonella enterica subspecies enterica serovar Typhimurium (Salmonella Typhimurium) obtained in Uruguay between the years 1976 and 2000, and to determine the incidence of class 1 and 2 integrons in the multi-resistant isolates. METHODS: We studied 258 strains of Salmonella Typhimurium from various sources, isolated between 1976 and 2000. We determined the evolution of antibiotic resistance and the distribution of class 1 and 2 integrons in all isolates by means of disk diffusion assays and PCR. RESULTS: During the period 1989-2000 resistance to streptomycin was 56.8%, tetracycline 13.6%, sulfonamides 11.2%, and ampicillin 7.2%. Resistance to gentamicin, kanamycin, chloramphenicol, and nalidixic acid were lower than 5%; no resistance was detected to fluoroquinolones, oxyiminocephalosporins, and amikacin. These results show a dramatic decrease with respect to values found in the period 1976-1988. In this period, resistance to streptomycin was 63.2%, tetracycline 36.8%, sulfonamides 32.3%, and ampicillin 27.8%. Throughout the two periods, 29 multi-resistant Salmonella Typhimurium strains were isolated harboring some class of integron: 15 strains had only intI2, 11 strains presented both intI1 and intI2, and three isolates only intI1. CONCLUSIONS: Our results show a marked decrease in resistance throughout these years, along with a correlation between resistance to different antibiotics and the presence of integrons.

Emergence of dhfrXVb and blaCARB-4 gene cassettes in class 1 integrons from clinical Pseudomonas aeruginosa isolated in Amazon region.

Integrons play a role in horizontal acquisition and expression of genes, as well as gene reservoir, contributing for the resistance phenotype, particularly relevant to bacteria of clinical importance. We aimed to determine the composition and the organization of the class 1 integron variable region present in Pseudomonas aeruginosa clinical isolates from Brazil. Strains carrying class 1 integrons were resistant to the majority of antibiotics tested, except to imipenem and ceftazidime. Sequence analysis of the integron variable region revealed the presence of the blaCARB-4 gene into two distinct cassette arrays: aacA4-dhfrXVb-blaCARB-4 and aadB-aacA4-blaCARB-4. dhfrXVb gene cassette, which is rare in Brazil and in P. aeruginosa species, was found in one isolate. PFGE analysis showed the spread of blaCARB-4 among P. aeruginosa clones. The occurrence of blaCARB-4 and dhfrXVb in Brazil may contribute for developing resistance to clinically important antibiotics, and shows a diversified scenarium of these elements occurring in Amazon clinical settings, where no study about integron dynamics was performed to date.

Emergence of dhfrXVb and blaCARB-4 gene cassettes in class 1 integrons from clinical Pseudomonas aeruginosa isolated in Amazon region

Integrons play a role in horizontal acquisition and expression of genes, as well as gene reservoir, contributing for the resistance phenotype, particularly relevant to bacteria of clinical importance. We aimed to determine the composition and the organization of the class 1 integron variable region present in Pseudomonas aeruginosa clinical isolates from Brazil. Strains carrying class 1 integrons were resistant to the majority of antibiotics tested, except to imipenem and ceftazidime. Sequence analysis of the integron variable region revealed the presence of the blaCARB-4 gene into two distinct cassette arrays: aacA4-dhfrXVb-blaCARB-4 and aadB-aacA4-blaCARB-4 . dhfrXVb gene cassette, which is rare in Brazil and in P. aeruginosa species, was found in one isolate. PFGE analysis showed the spread of blaCARB-4 among P. aeruginosa clones. The occurrence of blaCARB-4 and dhfrXVb in Brazil may contribute for developing resistance to clinically important antibiotics, and shows a diversified scenarium of these elements occurring in Amazon clinical settings, where no study about integron dinamycs was performed to date.

[Integrons and resistance gene cassettes: structure and role against antimicrobials]. / Integrones y cassettes genéticos de resistencia: estructura y rol frente a los antibacterianos.

Bacteria have developed sophisticated and successful genetic mechanisms to evade the action of antimicrobials. Bacterial multiresistance has caused serious problems in the treatment of nosocomial infections. Integrons and gene cassettes are considered the main genetic elements in the evolution of plasmids and transposons that actively participate in the mobilization of genes, codifying different bacterial resistance mechanisms. This article reviews the historical and structural aspects of integrons and resistance gene cassettes and the presence of these structures in gram negative bacteria isolated from Chilean hospitals in the last ten years.