Profiling of Virulence Determinants in Cronobacter sakazakii Isolates from Different Plant and Environmental Commodities

Survival and Expression of rpoS and grxB of Cronobacter sakazakii in Powdered Infant Formula Under Simulated Gastric Conditions of Newborns

Cronobacter sakazakii can cause severe illnesses in infants, predominantly in preterm newborns, with consumption of contaminated powdered infant formula (PIF) being the major vehicle of infection. Using a dynamic human gastrointestinal simulator called the SHIME, this study examined the effects of gastric acidity and gastric digestion time of newborns on the survival and expression of stress genes of C. sakazakii. Individual strains, inoculated at 7 log CFU/mL into reconstituted PIF, were exposed to gastric pH values of 4.00, 5.00 and 6.00 for 4 h with gradual acidification. The survival results showed that C. sakazakii grew in the stomach portion of the SHIME during a 4-h exposure to pH 4.00, 5.00 and 6.00 by 0.96-1.05, 1.02-1.28 and 1.11-1.73 log CFU/mL, respectively. The expression of two stress genes, rpoS and grxB, throughout gastric digestion was evaluated using reverse transcription qPCR. The upregulation of rpoS and grxB during the 4-h exposure to simulated gastric fluid at pH 4.00 showed that C. sakazakii strains may be experiencing the most stress in the pH 4.00 treatment. The gene expression results also suggest that C. sakazakii strains appeared to develop an acid adaptation response during the 4-h exposure that may facilitate their survival. Altogether, this study highlights that a combination of low gastric acidity, long digestion time in the presence of reconstituted PIF, created a favorable environment for the adaptation and survival of C. sakazakii in the simulation of a newborn's stomach. This study gives directions for future research to further advance our understanding of the behavior of C. sakazakii in the GI tract of newborns.

Function Characterization of Endogenous Plasmids in Cronobacter sakazakii and Identification of p-Coumaric Acid as Plasmid-Curing Agent

Virulence traits and antibiotic resistance are frequently provided by genes located on plasmids. However, experimental verification of the functions of these genes is often lacking due to a lack of related experimental technology. In the present study, an integrated suicide vector was used to efficiently and specifically delete a bacterial endogenous plasmid in Cronobacter sakazakii. The pESA3 plasmid was removed from C. sakazakii BAA-894, and we confirmed that this plasmid contributes to the invasion and virulence of this strain. In addition, the pGW1 plasmid was expunged from C. sakazakii GZcsf-1, and we confirmed that this plasmid confers multidrug resistance. We further screened plasmid-curing agents and found that p-coumaric acid had a remarkable effect on the curing of pESA3 and pGW1 at sub-inhibitory concentrations. Our study investigated the contribution of endogenous plasmids pESA3 and pGW1 by constructing plasmid-cured strains using suicide vectors and suggested that p-coumaric acid can be a safe and effective plasmid-curing agent for C. sakazakii.

Isolation and Identification of Cronobacter spp. from Fish and Shellfish Sold in Retail Markets

In this study, we investigated the incidence of Cronobacter spp. in seafood collected from retail fish markets of Mumbai, India. A total of 50 samples comprising fresh finfish (n = 32), shellfish (n = 6), dried fish (n = 9) and water (n = 3) were analyzed for Cronobacter spp. by selective enrichment, isolation and biochemical tests. Of 145 isolates presumptively identified as Cronobacter spp. by biochemical tests, 37 were confirmed as Cronobacter spp. by Polymerase Chain Reaction (PCR) specific to the internal transcribed spacer (ITS) regions. Based on the partial ITS gene sequence analysis, 35 isolates were identified as Cronobacter malonaticus and two as Cronobacter sakazakii. The highest incidence of Cronobacter spp. was in dried fish (55.6%), followed by shellfish (33.3%). The virulence gene ompA was detected in two Cronobacter sakazakii isolates. This is the first report of the incidence of Cronobacter spp. in fresh and dried seafood from India, which highlights the need to focus on this emerging pathogen in tropical seafood.

Genomic Analysis of Putative Virulence Factors Affecting Cytotoxicity of Cronobacter

Cronobacter spp. can cause systemic infections, such as meningitis, sepsis, and necrotizing enterocolitis, in immunocompromised patients, especially neonates. Although some virulence factors have been reported previously, the pathogenesis of Cronobacter remains unclear. In this study, we compared genome sequences from different Cronobacter species, sequence types, and sources, with the virulence genes in the virulence factor database. The results showed that Cronobacter has species specificity for these virulence genes. Additionally, two gene clusters, including sfp encoding fimbriae and hly encoding hemolysin, were discovered. Through cell adhesion, cytotoxicity, and hemolysis assays, we found that the isolates possessing the two gene clusters had higher cytotoxicity and stronger hemolysis capacity than those of other isolates in this study. Moreover, analysis of type VI secretion system (T6SS) cluster and putative fimbria gene clusters of Cronobacter revealed that T6SS have species specificity and isolates with high cytotoxicity possessed more complete T6SS cluster construction than that of the rest. In conclusion, the two novel gene clusters and T6SS cluster were involved in the mechanism underlying the cytotoxicity of Cronobacter.

Evaluation of commercial probiotic lactic cultures against biofilm formation by Cronobacter sakazakii

BACKGROUND/AIMS

Cronobacter sakazakii, an emergent pathogen is considered as a major concern to infants and neonates fed on reconstituted powdered infant milk formula. In conjunction with many other factors, biofilm forming capacity adds to its pathogenic potential. In view of the facts that infants are at highest risk to C. sakazakii infections, and emerging antibiotic resistance among pathogens, it is imperative to evaluate probiotic cultures for their efficacy against C. sakazakii. Therefore, pure probiotic strains were isolated from commercial probiotic products and tested for their antimicrobial and anti-biofilm activities against C. sakazakii.

METHODS

A total of 6 probiotic strains were tested for their antibiotic susceptibility followed by antimicrobial activity using cell-free supernatant (CFS) against C. sakazakii. The inhibitory activity of CFS against biofilm formation by C. sakazakii was determined using standard crystal violet assay and microscopic observations.

RESULTS

All the probiotic strains were sensitive to ampicillin, tetracycline, vancomycin and carbenicillin whereas most of the strains were resistant to erythromycin and novobiocin. Four of the 6 probiotic derived CFS possessed antimicrobial activity against C. sakazakii at a level of 40 μL. A higher biofilm inhibitory activity (>80%) was observed at initial stages of biofilm formation with weaker activity during longer incubation upto 48 hours (50%-60%).

CONCLUSIONS

The study indicated the efficacy of isolated commercial probiotics strains as potential inhibitor of biofilm formation by C. sakazakii and could be further explored for novel bioactive molecules to limit the emerging infections of C. sakazakii.

Ketogenic diet poses a significant effect on imbalanced gut microbiota in infants with refractory epilepsy

AIM

To investigate whether patients with refractory epilepsy and healthy infants differ in gut microbiota (GM), and how ketogenic diet (KD) alters GM.

METHODS

A total of 14 epileptic and 30 healthy infants were recruited and seizure frequencies were recorded. Stool samples were collected for 16S rDNA sequencing using the Illumina Miseq platform. The composition of GM in each sample was analyzed with MOTHUR, and inter-group comparison was conducted by R software.

RESULTS

After being on KD treatment for a week, 64% of epileptic infants showed an obvious improvement, with a 50% decrease in seizure frequency. GM structure in epileptic infants (P1 group) differed dramatically from that in healthy infants (Health group). Proteobacteria, which had accumulated significantly in the P1 group, decreased dramatically after KD treatment (P2 group). Cronobacter predominated in the P1 group and remained at a low level both in the Health and P2 groups. Bacteroides increased significantly in the P2 group, in which Prevotella and Bifidobacterium also grew in numbers and kept increasing.

CONCLUSION

GM pattern in healthy infants differed dramatically from that of the epileptic group. KD could significantly modify symptoms of epilepsy and reshape the GM of epileptic infants.