The accuracy of extended-spectrum beta-lactamase detection in Escherichia coli and Klebsiella pneumoniae in South African laboratories using the Vitek 2 Gram-negative susceptibility card AST-N255

Background: Phenotypic detection of extended-spectrum beta-lactamases (ESBLs) is based on the inhibition of ESBL enzymes by ß-lactamase inhibitors and on the comparison of cephalosporin activity with or without a ß-lactamase inhibitor. Many South African diagnostic laboratories rely on the Vitek 2 for automated susceptibility testing and for ESBL detection. However, the Gram-negative susceptibility card currently used locally (AST-N255) has been modified and its accuracy for ESBL detection is not known.Methods: We randomly selected 50 isolates of Klebsiella pneumoniae and Escherichia coli from a collection of clinical bloodstream isolates from Groote Schuur Hospital from 2015 to 2016, including ESBL-producing and non-ESBL-producing strains. We used standardised phenotypic (disc diffusion and broth microdilution) and genotypic (conventional polymerase chain reaction (PCR) for blaCTX-M, blaSHV and blaTEM) methods for detection of ESBLs. We compared ESBL detection by Vitek 2 to a composite reference standard comprising ESBL detection either by both phenotypic methods or by one phenotypic method together with genotypic detection.Results: The sensitivity of Vitek 2 system for detection of ESBLs was 33/36 or 92% (78% ­ 97%) for E. coli, and 40/40 or 100% (91% ­ 100%) for K.pneumoniae, whilst specificity was 10/10 or 100% (72% ­ 100%) and 9/10 or 90% (60% ­ 98%), respectively. This is comparable with previous studies.Conclusion: Using a composite reference standard of the phenotypic and genotypic methods employed in this study, no Vitek-categorised ESBL E. coli or K. pneumoniae was found to be a non-ESBL with the exception of possible misinterpretation with K. pneumoniae SHV-hyper-producing isolates

A mutation effecting gluconate catabolism in Escherichia coli: The locus for the main high affinity transport / Una mutación que afecta el catabolismo del gluconato en Escherichia coli: el locus para el transporte principal de alta afinidad

The bioH-malA region of the E.coli chromosome (min 75.5) includes the gntT gene which encodes a high affinity transport for gluconate. Other gnt loci have not been characterized in this region; nevertheless, because lesion in it affect severely the utilization of gluconate, it has been suggested as being more complex. This region was investigated with respect to gluconate catabolism through the characterization of suitable E.coli strains lysogenized with a specialized transducing phage carrying the bioH-malA region of the bacterial chromosome (cI857st68h80d2bioH-malA). It was found that the region transduced by this phage while includes the gntT gene lacks other gnt loci that might code additional activities for transport of gluconate or its phosphorylation. Moreover, the pleiotropic lesion gntM2, previously mapped into this region and suggested as altering gntT or a presumptive regulator gene that might be involved in this catabolism, resulted recessive in lysogens (partial diploids) containing the defective prophage. The results obtained supported the idea that gntM2 is an allele of gntT; consequently those results suggested the precise position of this gene on the cromosomic map and the central role that its product might have in the initial incorporation of gluconate in E.coli.

Tratamientos analíticos de muestras de IFN alfa 2b h-rec, para su cuantificación por ELISA / Analyticaltreatments of rec-h alpha 2b interferon samples for their quantitation by ELISA

La obtención de interferón 2b humanos recombinante (IFN alfa 2b hr) en E. coli, en forma insoluble, hace necesario el estudio del ratamiento de las muestras para su cuantificación mediante un sistema inmunoenzimático tipo ELISA. De los sistemas analíticos ensayados para la extracción de proteina insoluble, el óptimo resultó una modificación del tapón L aemmli con un 1 % de SDS y 2,5 % de 2-merceptoetanol. Las proteinas de la cepa productora y la mayoría de los sistemas tampones empleados no influyeron sobre el reconocimiento inmunológico del interferón a diluciones mayores de 1/500

Diagnóstico presuntivo de Escherichia coli enterotoxigênica através de provas de hemoaglutinaçäo / Presumptive diagnosis of enterotoxigenic Escherichia coli by hemagglutination tests

Foram realizadas provas de hemoaglutinaçäo empregando-se hemácias bovinas e humanas, com o objetivo de se comparar os padröes de hemoaglutinaçäo apresentados por amostras de Escherichia coli enterotoxigênicas e enteropatogênicas clássicas e näo enteropatogênicas e averiguar se este procedimento poderia ser empregado para uma demonstraçäo presuntiva de amostras enterotoxigênicas. A análise estatística, através do teste do X2 (p <0,01), evidenciou diferenças significativas entre os padröes de hemoaglutinaçäo exibidos pelas amostras enterotoxigênicas e amostras näo produtoras de enterotoxinas. Este resultado, acrescido do fato de que o método é simples, rápido e barato recomenda o seu emprego no diagnóstico presuntivo de Escherichia coli enterotoxigênica, pois, a pesquisa de enterotoxinas é um procedimento praticamente impossível de ser realizado, rotineiramente, por laboratórios de diagnóstico