RESUMEN
In the United States, serovar Kentucky has become one of the most frequently isolated Salmonella enterica serovars from chickens. The reasons for this prevalence are not well understood. Phenotypic comparisons of poultry Salmonella isolates belonging to various serovars demonstrated that serovar Kentucky isolates differed from those of most other serovars in their response to acid. Microarray and qPCR analyses were performed with aerated exponentially growing poultry isolates, Salmonella enterica serovar Kentucky 3795 and Enteritidis Nal(R), exposed for 10 min to tryptic soy broth (TSB) adjusted to pH 4.5 with HCl and to pH 5.5 with HCl or acetic acid. Data obtained by microarray analysis indicated that more genes were up- or down-regulated in strain Kentucky 3795 than in Enteritidis Nal(R) under acidic conditions. Acid exposure in general caused up-regulation of energy metabolism genes and down-regulation of protein synthesis genes, particularly of ribosomal protein genes. Both strains appear to similarly utilize the lysine-based pH homeostasis system, as up-regulation of cadB was observed under the acidic conditions. Expression of regulatory genes (rpoS, fur, phoPQ) known to be involved in the acid response showed similar trends in both isolates. Differences between Kentucky 3795 and Enteritidis Nal(R) were observed with respect to the expression of the hdeB-like locus SEN1493 (potentially encoding a chaperone important to acid response), and some differences in the expression of other genes such as those involved in citrate utilization and motility were noted. It appears that the early stages of the transcriptional response to acid by isolates Kentucky 3795 and Enteritidis Nal(R) are similar, but differences exist in the scope and in some facets of the response. Possibly, the quantitative differences observed might lead to differences in protein levels that could explain the observed differences in the acid phenotype of serovar Kentucky and other Salmonella serovars.
Asunto(s)
Ácido Acético/farmacología , Regulación Bacteriana de la Expresión Génica/genética , Ácido Clorhídrico/farmacología , Salmonella enterica/genética , Estrés Fisiológico/genética , Animales , Pollos , Medios de Cultivo/química , Regulación hacia Abajo/genética , Perfilación de la Expresión Génica/veterinaria , Regulación Bacteriana de la Expresión Génica/efectos de los fármacos , Genes Bacterianos/genética , Homeostasis , Concentración de Iones de Hidrógeno , Lisina/metabolismo , Análisis de Secuencia por Matrices de Oligonucleótidos/veterinaria , Enfermedades de las Aves de Corral/microbiología , Salmonelosis Animal/microbiología , Salmonella enterica/efectos de los fármacos , Salmonella enterica/crecimiento & desarrollo , Salmonella enteritidis/efectos de los fármacos , Salmonella enteritidis/genética , Salmonella enteritidis/crecimiento & desarrollo , Estrés Fisiológico/efectos de los fármacos , Regulación hacia Arriba/genéticaRESUMEN
For unknown reasons, Salmonella enterica Kentucky has become the serovar most frequently isolated from chickens and chicken carcasses in the United States. In an attempt to identify traits that may underlie this phenomenon, genetic and physiological features of 30 serovar Kentucky chicken isolates were compared with those of chicken isolates belonging to a range of other S. enterica serovars. Most of the well-known Salmonella virulence genes were detected in the serovar Kentucky isolates by PCR, but the cdtB, spvB, spvC, and pefA genes were not found. The serovar Kentucky isolates were as invasive as the non-Kentucky isolates in in vitro assays involving chicken embryo hepatocytes, but were less invasive than the Enteritidis, Mbandaki, and Typhimurium isolates when incubated with human HCT-8 cells. Statistical comparison of growth, biofilm formation, and stress survival data from the serovar Kentucky and those from the serovar Enteritidis, Hadar, Mbandaka, Senftenberg, Typhimurium, and Worthington isolates demonstrated either no differences or differences with only a few of the serovars; however, three data sets were different. These data sets included the OD(600) values of cultures grown in tryptic soy broth (TSB) adjusted to pH 5.5 with acetic acid and survival counts of cells grown in either TSB pH 7 or TSB adjusted to pH 5.5 with acetic acid and then transferred into TSB adjusted to pH 2.5 with HCl. Most notable was the log(10) reduction for acetic acid pre-exposed Kentucky isolates of 3.1 versus <1 log(10) for the other isolates upon transfer to pH 2.5. The connection, if any, between this acid response phenotype and the prevalence of the serovar Kentucky in poultry remains to be elucidated, but it is possible that slightly better growth in the presence of acetic acid in conjunction with not mounting a strong, energy-consuming acetic acid-induced adaptive acid response provides a small competitive advantage to this serovar in low acid environments such as the cecum where the pH is around 5.5.
