Effect of erythromycin on Shigella infection of Caco-2 cells

Effect of Psidium guajava (guava) L. Leaf Decoction on Antibiotic-resistant Clinical Diarrhoeagenic Isolates of Shigella spp

Background: Although shigellosis is self-limiting, antibiotics are recommended to minimize the severity of symptoms and reduce mortality rates. However, due to the increasing reports of antibiotic resistance, alternative approaches are needed to combat shigellosis. Interest for research on medicinal plants has increased in recent years, and hence, they can be explored to treat this infectious diarrhoea. Objective: To study the effect of Psidium guajava L. (guava) leaf decoction (GLD) on the antibiotic-resistant clinical isolates of Shigella spp. Materials and Methods: A total of 43 isolated Shigella spp. from diarrhoeal patients were used in this study. The effect of GLD on the bacterial viability was initially assessed. The isolates were divided into two categories: sensitive and resistant to GLD. For sensitive isolates, antibacterial activity of GLD was evaluated while for resistant strains, the ability of GLD for reducing the bacterial invasion of the HEp-2 cell line underwent an investigation. Results: Among the 43 Shigella isolates, GLD affected the growth of 23 strains. The invasion of 9 strains from the 20 remaining resistant isolates was unaffected. Although the number of isolates was less, the data suggested that isolates belonging to S. flexneri serogroup were more sensitive to GLD in comparison with other spp (i.e., sonnei, boydii, and dysenteriae). Conclusion: The results of this study revealed the efficacy of GLD against drug-resistant Shigella spp. and thus could be considered for the treatment of diarrhoea. GLD can be a cost-effective alternative to antibiotics.

Type III Secretion-Dependent Sensitivity of Escherichia coli O157 to Specific Ketolides

A subset of Gram-negative bacterial pathogens uses a type III secretion system (T3SS) to open up a conduit into eukaryotic cells in order to inject effector proteins. These modulate pathways to enhance bacterial colonization. In this study, we screened established bioactive compounds for any that could repress T3SS expression in enterohemorrhagic Escherichia coli (EHEC) O157. The ketolides telithromycin and, subsequently, solithromycin both demonstrated repressive effects on expression of the bacterial T3SS at sub-MICs, leading to significant reductions in bacterial binding and actin-rich pedestal formation on epithelial cells. Preincubation of epithelial cells with solithromycin resulted in significantly less attachment of E. coli O157. Moreover, bacteria expressing the T3SS were more susceptible to solithromycin, and there was significant preferential killing of E. coli O157 bacteria when they were added to epithelial cells that had been preexposed to the ketolide. This killing was dependent on expression of the T3SS. Taken together, this research indicates that the ketolide that has accumulated in epithelial cells may traffic back into the bacteria via the T3SS. Considering that neither ketolide induces the SOS response, nontoxic members of this class of antibiotics, such as solithromycin, should be considered for future testing and trials evaluating their use for treatment of EHEC infections. These antibiotics may also have broader significance for treating infections caused by other pathogenic bacteria, including intracellular bacteria, that express a T3SS.

Identification of hyperinvasive Campylobacter jejuni strains isolated from poultry and human clinical sources

Campylobacter jejuni causes gastroenteritis with a variety of symptoms in humans. In the absence of a suitable animal model, in vitro models have been used to study virulence traits such as invasion and toxin production. In this study, 113 C. jejuni isolates from poultry and poultry-related (n=74) environments as well as isolates from human cases (n=39) of campylobacteriosis and bacteraemia were tested for invasiveness using INT 407 cells. The method was sufficiently reproducible to observe a spectrum of invasiveness amongst strains. As a result, strains were classified as low, high and hyper-invasive. The majority of strains (poultry and human) were low invaders (82 % and 88 %, respectively). High invasion was found for 5 % of human strains and 11 % of poultry-related isolates. However, only 1 % of poultry strains were classified as hyperinvasive compared to 13 % of human isolates (P=0.0182). Of those isolates derived from the blood of bacteraemic patients, 20 % were hyperinvasive, though this correlation was not statistically significant. An attempt was made to correlate invasiveness with the presence of seven genes previously reported to be associated with virulence. Most of these genes did not correlate with invasiveness, but gene cj0486 was weakly over-represented, and a negative correlation was observed for the gene ciaB. This trend was stronger when the two genes were analysed together, thus ciaB(-) cj0486(+) was over-represented in high and hyperinvasive strains, with low invaders more commonly found to lack these genes (P=0.0064).

Comparison of antimicrobial susceptibility between invasive and non-invasive Shigella organisms

Antimicrobial susceptibility was determined for ten strains of Shigella spp. comparing invasive (invasion plasmid containing) and non-invasive members of each strain. The activity of the antimicrobial agents could be classified into three types from the differences between the minimum inhibitory concentration (MIC) for the invasive and non-invasive shigellae. For type 1, there was no difference between the MIC (an MIC gap) for invasive and non-invasive organisms. For type 2, the MIC for the invasive organisms of a strain was higher than that of non-invasive organisms of the strain. In the third type, macrolides taken in by shigellae through the type III secretion apparatus, more effectively inhibited the growth of invasive than non-invasive organisms.

Enhanced anti-Shigella activity of erythromycin supplemented with sulfadiazine

Sulfadiazine enhanced the anti-Shigella activity of erythromycin. Erythromycin passes through the type III secretion apparatus and suppresses the growth of invasive Shigella organisms. Sulfadiazine enhanced this effect at the concentration under minimum inhibitory concentration and it came from not only the folate-inhibiting activity but also from a new function. It has proved that sulfadiazine stimulated type III secretion in Shigella as determined from the secretion of the pathogenic protein IpaB. As Congo red induced secretion of Ipa proteins and uptake of erythromycin through the type III secretion gate, sulfadiazine which is similar to Congo red in chemical structure may induce the uptake in the same way.