Clustered Regularly Interspaced Short Palindromic Repeats Spacers Research Articles

CRISPR-Cas system positively regulates virulence of Salmonella enterica serovar Typhimurium

BackgroundSalmonella, a foodborne pathogen, possesses a type I-E clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated (Cas) system. We investigated the system’s role in regulating Salmonella virulence by deleting the CRISPR arrays and Cas operon.ResultsOur study demonstrates invasion and proliferation defects of CRISPR-Cas knockout strains in intestinal epithelial cells and macrophages owing to the repression of invasion and virulence genes. However, proliferation defects were not observed in the Gp91phox−/− macrophages, suggesting the system’s role in the pathogens’ antioxidant defense. We deduced that the CRISPR-Cas system positively regulates H2O2 importer (OmpW), catalase (katG), peroxidase (ahpC), and superoxide dismutase (soda and sodCI), thereby protecting the cells from oxidative radicals. The knockout strains were attenuated in in-vivo infection models (Caenorhabditis elegans and BALB/c mice) due to hypersensitivity against antimicrobial peptides, complement proteins, and oxidative stress. The attenuation in virulence was attributed to the suppression of LPS modifying (pmr) genes, antioxidant genes, master regulators, and effectors of the SPI-1 (invasion) and SPI-2 (proliferation) islands in knockout strains. The regulation could be attributed to the partial complementarity of the CRISPR spacers with these genes.ConclusionsOverall, our study extends our understanding of the role of the CRISPR-Cas system in Salmonella pathogenesis and its virulence determinants.

Phage-mediated resolution of genetic conflict alters the evolutionary trajectory of Pseudomonas aeruginosa lysogens.

The opportunistic human pathogen Pseudomonas aeruginosa is naturally infected by a large class of temperate, transposable, Mu-like phages. We examined the genotypic and phenotypic diversity of P. aeruginosa PA14 lysogen populations as they resolve clustered regularly interspaced short palindromic repeat (CRISPR) autoimmunity, mediated by an imperfect CRISPR match to the Mu-like DMS3 prophage. After 12 days of evolution, we measured a decrease in spontaneous induction in both exponential and stationary phase growth. Co-existing variation in spontaneous induction rates in the exponential phase depended on the way the coexisting strains resolved genetic conflict. Multiple mutational modes to resolve genetic conflict between host and phage resulted in coexistence in evolved populations of single lysogens that maintained CRISPR immunity to other phages and polylysogens that lost immunity completely. This work highlights a new dimension of the role of lysogenic phages in the evolution of their hosts.IMPORTANCEThe chronic opportunistic multi-drug-resistant pathogen Pseudomonas aeruginosa is persistently infected by temperate phages. We assess the contribution of temperate phage infection to the evolution of the clinically relevant strain UCBPP-PA14. We found that a low level of clustered regularly interspaced short palindromic repeat (CRISPR)-mediated self-targeting resulted in polylysogeny evolution and large genome rearrangements in lysogens; we also found extensive diversification in CRISPR spacers and cas genes. These genomic modifications resulted in decreased spontaneous induction in both exponential and stationary phase growth, increasing lysogen fitness. This work shows the importance of considering latent phage infection in characterizing the evolution of bacterial populations.

CRISPR and CRISPR-MVLST reveal conserved spacer distribution and high similarity among Salmonella enterica serovar Infantis genomes from Brazil and other countries.

Salmonella enterica serovar Infantis (S. Infantis) is a globally distributed non-typhoid serovar infecting humans and food-producing animals. Considering the zoonotic potential and public health importance of this serovar, strategies to characterizing, monitor and control this pathogen are of great importance. This study aimed to determine the genetic relatedness of 80 Brazilian S. Infantis genomes in comparison to 40 non-Brazilian genomes from 14 countries using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-Multi-Locus Virulence Sequence Typing (CRISPR-MVLST). CRISPR spacers were searched using CRISPR-Cas++ and fimH and sseL alleles using BLAST and MEGA X. Results were analyzed using BioNumerics 7.6 in order to obtain similarity dendrograms. A total of 23 CRISPR1 and 11 CRISPR2 alleles formed by 37 and 26 types of spacers, respectively, were detected. MVLST revealed the presence of five fimH and three sseL alleles. CRISPR's similarity dendrogram showed 32 strain subtypes, with an overall similarity ≥ 78.6. The CRISPR-MVLST similarity dendrogram showed 37 subtypes, with an overall similarity ≥ 79.2. In conclusion, S. Infantis strains isolated from diverse sources in Brazil and other countries presented a high genetic similarity according to CRISPR and CRISPR-MVLST, regardless of their source, year, and/or place of isolation. These results suggest that both methods might be useful for molecular typing S. Infantis strains using WGS data.

Analysis of CRISPR-Cas loci distribution in Xanthomonas citri and its possible control by the quorum sensing system.

Xanthomonas is an important genus of plant-associated bacteria that causes significant yield losses of economically important crops worldwide. Different approaches have assessed genetic diversity and evolutionary interrelationships among the Xanthomonas species. However, information from clustered regularly interspaced short palindromic repeats (CRISPRs) has yet to be explored. In this work, we analyzed the architecture of CRISPR-Cas loci and presented a sequence similarity-based clustering of conserved Cas proteins in different species of Xanthomonas. Although absent in many investigated genomes, Xanthomonas harbors subtype I-C and I-F CRISPR-Cas systems. The most represented species, Xanthomonas citri, presents a great diversity of genome sequences with an uneven distribution of the CRISPR-Cas systems among the subspecies/pathovars. Only X. citri subsp. citri and X. citri pv. punicae have these systems, exclusively of subtype I-C system. Moreover, the most likely targets of the X. citri CRISPR spacers are viruses (phages). At the same time, few are plasmids, indicating that CRISPR/Cas system is possibly a mechanism to control the invasion of foreign DNA. We also showed in X. citri susbp. citri that the cas genes are regulated by the diffusible signal factor, the quorum sensing (QS) signal molecule, according to cell density increases, and under environmental stress like starvation. These results suggest that the regulation of CRISPR-Cas by QS occurs to activate the gene expression only during phage infection or due to environmental stresses, avoiding a possible reduction in fitness. Although more studies are needed, CRISPR-Cas systems may have been selected in the Xanthomonas genus throughout evolution, according to the cost-benefit of protecting against biological threats and fitness maintenance in challenging conditions.

Prevalence and Characterization of CRISPR Locus 2.1 Spacers in Escherichia coli Isolates Obtained from Feces of Animals and Humans.

The clustered regularly interspaced short palindromic repeat (CRISPR) has been studied as an immune system in prokaryotes for the survival of bacteriophages. The CRISPR system in prokaryotes records the invasion of bacteriophages or other genetic materials in CRISPR loci. Accordingly, CRISPR loci can reveal a history of infection records of bacteriophages and other genetic materials. Therefore, identification of the CRISPR array may help trace the events that bacteria have undergone. In this study, we characterized and identified the spacers of the CRISPR loci in Escherichia coli isolates obtained from the feces of animals and humans. Most CRISPR spacers were found to stem from phages. Although we did not find any patterns in CRISPR spacers according to sources, our results showed that phage-derived spacers mainly originated from the families Inoviridae, Myoviridae, Podoviridae, and Siphoviridae and the order Caudovirales, whereas plasmid-derived CRISPR spacers were mainly from the Enterobacteriaceae family. In addition, it is worth noting that the isolates from each animal and human source harbored source-specific spacers. Considering that some of these taxa are likely found in the gut of mammalian animals, CRISPR spacers identified in these E. coli isolates were likely derived from the bacteriophageome and microbiome in closed gut environments. Although the bacteriophageome database limits the characterization of CRISPR arrays, the present study showed that some spacers were specifically found in both animal and human sources. Thus, this finding may suggest the possible use of E. coli CRISPR spacers as a microbial source tracking tool. IMPORTANCE We characterized spacers of CRISPR locus 2.1 in E. coli isolates obtained from the feces of various sources. Phage-derived CRISPR spacers are mainly acquired from the order Caudovirales, and plasmid-derived CRISPR spacers are mostly from the Enterobacteriaceae family. This is thought to reflect the microbiome and phageome of the gut environment of the sources. Hence, spacers may help track the encounter of bacterial cells with bacterial cells, viruses, or other genetic materials. Interestingly, source-specific spacers are also observed. The identification of source-specific spacers is thought to help develop the methodology of microbial source tracking and understanding the interactions between viruses and bacteria. However, very few spacers have been uncovered to track where they originate. The accumulation of genome sequences can help identify the hosts of spacers and can be applied for microbial source tracking.

Novel configurations of type I-E CRISPR-Cas system in Corynebacterium striatum clinical isolates

Clustered regularly interspaced short palindromic repeats (CRISPR) are a prokaryotic adaptive immune system that, through Cas proteins, promote the degradation of foreign nucleic acids such as phages and plasmids. We analyzed 10 genomes of Corynebacterium striatum clinical isolates from a public hospital in Rio de Janeiro, Brazil, the most emergent multidrug-resistant Corynebacterium species. All isolates were submitted to antimicrobial susceptibility testing. The occurrence and diversity of the CRISPR system were investigated by bioinformatics tools. Our analysis revealed that the isolates exhibited type I-E gene arrangements, and 3 more multidrug-resistant isolates, alternative type I-E gene arrangements, showing a divergent gene arrangement within the cas operon. Phylogenetic analysis of the cas1 gene of this type I-E CRISPR-Cas system alternative arrangement, termed here type I-E’, showed a cluster in a distinct clade of the type I-E CRISPR-Cas system. The systems’ guanine-cytosine (GC) content is lower than the genomic DNA’s GC content, and mobile genetic elements were found in some isolates near the CRISPR-Cas system. Most CRISPR spacers are unknown indicating that there is a reservoir of unexplored corynebacteriophages and plasmids. Some spacers showed perfect homologies with phage and plasmid sequences. Intact phage regions were found in 3 of our isolates, ranging from 9.1 to 43.8 kb, with regions showing similarity to Rhodococcus and Corynebacterium phages. Our results may contribute to research about the CRISPR-Cas system diversity in C. striatum, where there are no published data to date.

Clustered Regularly Interspaced Short Palindromic Repeats in Xanthomonas citri-Witnesses to a Global Expansion of a Bacterial Pathogen over Time.

Xanthomonas citri pv. citri, a Gram-negative bacterium, is the causal agent of citrus canker, a significant threat to citrus production. Understanding of global expansion of the pathogen and monitoring introduction into new regions are of interest for integrated disease management at the local and global level. Genetic diversity can be assessed using genomic approaches or information from partial gene sequences, satellite markers or clustered regularly interspaced short palindromic repeats (CRISPR). Here, we compared CRISPR loci from 355 strains of X. citri pv. citri, including a sample from ancient DNA, and generated the genealogy of the spoligotypes, i.e., the absence/presence patterns of CRISPR spacers. We identified 26 novel spoligotypes and constructed their likely evolutionary trajectory based on the whole-genome information. Moreover, we analyzed ~30 additional pathovars of X. citri and found that the oldest part of the CRISPR array was present in the ancestor of several pathovars of X. citri. This work presents a framework for further analyses of CRISPR loci and allows drawing conclusions about the global spread of the citrus canker pathogen, as exemplified by two introductions in West Africa.

Evaluation of effect based on different typing methods in Escherichia coli

Objective: To evaluate the typing and clinical application effect based on clustered regularly interspaced short palindromic repeats (CRISPRs), serotype, and Multilocus Sequence Typing (MLST). Methods: The spacers, serotype and sequence type (ST) were obtained with CRISPRsFinder, SeroTypeFinder and MLST. PCR was used to amplify the CRISPRs, and the spacers were used to predict serotype and ST, then comparing with the serotype and ST. Results: We defined the I-E CRISPR/Cas as CT-Ⅰ, I-F CRISPR/Cas as CT-Ⅱ, and only CRISPR3-4 as CT-Ⅲ. We designated each unique arrangement spacer profile as a unique CRISPRs type. A total of 79 CT types, 76 serotypes, and 66 STs were identified. The CRISPRs typing was the most discriminating, with the Simpson index of 0.936, having the highest correlation with serology with the adjusted Rand index of 0.908. The CRISPRs type could divide the same serotype (ST) into two subtypes [O157∶H7(ST11), O104∶H4(ST678), and O26∶H11(ST21)]. The detection rates of CRISPR1, CRISPR2, CRISPR3, CRISPR4, and CRISPR3-4 were 81.1%, 94.5%, 1.4%, 1.4%, and 4.6%, with the accuracy rate of 95.0% and 100.0% according to the spacers to forecast O157∶H7 (ST11) and ST131. Conclusion: Based on the CRISPRs spacer, this method can be used as an essential molecular typing for E.coli, as it presents a good typing and clinical application effect.

Adaptation by Type V-A and V-B CRISPR-Cas Systems Demonstrates Conserved Protospacer Selection Mechanisms Between Diverse CRISPR-Cas Types.

Adaptation of clustered regularly interspaced short palindromic repeats (CRISPR) arrays is a crucial process responsible for the unique, adaptive nature of CRISPR-Cas immune systems. The acquisition of new CRISPR spacers from mobile genetic elements has previously been studied for several types of CRISPR-Cas systems. In this study, we used a high-throughput sequencing approach to characterize CRISPR adaptation of the type V-A system from Francisella novicida and the type V-B system from Alicyclobacillus acidoterrestris. In contrast to other class 2 CRISPR-Cas systems, we found that for the type V-A and V-B systems, the Cas12 nucleases are dispensable for spacer acquisition, with only Cas1 and Cas2 (type V-A) or Cas4/1 and Cas2 (type V-B) being necessary and sufficient. Whereas the catalytic activity of Cas4 is not essential for adaptation, Cas4 activity is required for correct protospacer adjacent motif selection in both systems and for prespacer trimming in type V-A. In addition, we provide evidence for acquisition of RecBCD-produced DNA fragments by both systems, but with spacers derived from foreign DNA being incorporated preferentially over those derived from the host chromosome. Our work shows that several spacer acquisition mechanisms are conserved between diverse CRISPR-Cas systems, but also highlights unexpected nuances between similar systems that generally contribute to a bias of gaining immunity against invading genetic elements.

Genome Mining Approach Reveals the Occurrence and Diversity Pattern of Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-Associated Systems in Lactobacillus brevis Strains.

Clustered regularly interspaced short palindromic repeats (CRISPR) together with their CRISPR-associated (Cas) genes are widely distributed in prokaryotes that provide an adaptive defense mechanism against foreign invasive DNA. There is relatively little knowledge about the CRISPR-Cas diversity and evolution in Lactobacillus brevis strains. Therefore, in this study, a genome-mining approach was employed to investigate the diversity and occurrence of the CRISPR-Cas system in 83 L. brevis strains. Moreover, trans-activating CRISPR RNA (tracrRNA) and protospacer adjacent motif (PAM) as pivotal elements for the successful targeting and inference of phages by the subtype II CRISPR-Cas systems were surveyed. Finally, evolutionary paths of L. brevis strains under selective pressure from foreign invasive DNA such as plasmids and phages of studied strains were surveyed using acquisition and deletion events analysis of spacers. A total of 127 confirmed CRISPRs were identified, which were distributed in 69 strains. Among strains with confirmed CRISPRs, 35 strains only contained one CRISPR locus, 23 strains contained two CRISPR loci, and 12 strains contained three to six CRISPR loci. L. brevis strains frequently harbor more than one CRISPR system. Analysis of confirmed CRISPR arrays showed that 31 out of 127 confirmed CRISPRs included Cas genes which were categorized as one of the II-A, II-C, and I-E subtypes. Analysis of subtype II-A spacers reflected divergent evolution for 18 strains into 16 unique groups. Additional analysis of spacer sequences also confirmed the implication of characterizing CRISPR-Cas systems in targeting of phages and plasmids. The current study highlighted the potential of utilizing CRISPR spacer polymorphism in genotyping lactobacillus strains. Moreover, it provides deep insights into the occurrence, diversity, and functional impacts of the CRISPR-Cas system in L. brevis strains.

Antimicrobial Resistance and CRISPR Typing Among Salmonella Isolates From Poultry Farms in China.

Although knowledge of the clustered regularly interspaced short palindromic repeat (CRISPR)-Cas system has been applied in many research areas, comprehensive studies of this system in Salmonella, particularly in analysis of antibiotic resistance, have not been reported. In this work, 75 Salmonella isolates obtained from broilers or broilers products were characterized to determine their antimicrobial susceptibilities, antibiotic resistance gene profiles, and CRISPR array diversities, and genotyping was explored. In total, 80.00% (60/75) of the strains were multidrug resistant, and the main pattern observed in the isolates was CN-AZM-AMP-AMC-CAZ-CIP-ATM-TE-SXT-FOS-C. The resistance genes of streptomycin (aadA), phenicol (floR-like and catB3-like), β-lactams (blaTEM, blaOXA, and blaCTX), tetracycline [tet(A)-like], and sulfonamides (sul1 and sul2) appeared at higher frequencies among the corresponding resistant isolates. Subsequently, we analyzed the CRISPR arrays and found 517 unique spacer sequences and 31 unique direct repeat sequences. Based on the CRISPR spacer sequences, we developed a novel typing method, CRISPR locus three spacer sequences typing (CLTSST), to help identify sources of Salmonella outbreaks especially correlated with epidemiological data. Compared with multi-locus sequence typing (MLST), conventional CRISPR typing (CCT), and CRISPR locus spacer pair typing (CLSPT), discrimination using CLTSST was weaker than that using CCT but stronger than that using MLST and CLSPT. In addition, we also found that there were no close correlations between CRISPR loci and antibiotics but had close correlations between CRISPR loci and antibiotic resistance genes in Salmonella isolates.

Detection of Campylobacter jejuni diversity by clustered regularly interspaced short palindromic repeats (CRISPR) from an animal farm

Background Campylobacter jejuni is the leading bacterial pathogen that causes foodborne illness worldwide. Because of genetic diversity and sophisticated growth requirements of C. jejuni, several genotyping methods have been investigated to classify this bacterium during the outbreaks. One of such method is to use clustered regularly interspaced short palindromic repeats (CRISPR).ObjectivesThe goal of this study was to explore the diversity of C. jejuni isolates with CRISPR from an animal farm.MethodsSeventy‐seven C. jejuni isolates from an animal farm were used in this study. The day‐old broilers were reared with other poultry and farm animals, including layer hens, guinea hens, dairy goats and sheep. A small swine herd was also present on an adjacent, but separate plot of land. Isolation and identification of C. jejuni were performed according to the standard procedures. The CRISPR type 1 was PCR amplified from genomic DNA, and the amplicons were sequenced by the Sanger dideoxy method. The direct repeats (DRs) and spacers of the CRISPR sequences were identified using the CRISPRFinder.ResultsThe CRISPR sequences were detected in all 77 isolates. One type of DRs was identified in these 77 isolates. The lengths of the CRISPR locus ranged from 100 to 560 nucleotides, whereas the number of spacers ranged from one to eight. The distributions of the numbers of CRISPR spacers from different sources seemed to be random. Overall, 17 out of 77 (22%) C. jejuni isolates had two and five spacers, whereas 14 out of 77 (18%) isolates had three spaces in their genomes. By further analysis of spacer sequences, a total of 266 spacer sequences were identified in 77 C. jejuni isolates. By comparison with known published spacer sequences, we observed that 49 sequences were unique in this study. The CRISPR sequence combination of Nos. 16, 19, 48 and 57 was found among a total of 15 C. jejuni isolates containing various multi‐locus sequence typing (MLST) types (ST‐50, ST‐607, ST‐2231 and ST‐5602). No. 57 spacer sequence was unique from this study, whereas the other three (Nos. 16, 19 and 48) sequences were found in previous reports. Combination of Nos. 5, 9, 15, 30 and 45 was associated with ST‐353. To compare the CRISPR genotyping with other methods, the MLST was selected due to its high discriminatory power to differentiate isolates. Based on calculation of the Simpson's index of diversity, a combination of both methods had higher Simpson's index value than those for CRISPR or MLST, respectively.ConclusionsOur results suggest that the MLST from C. jejuni isolates can be discriminated based on the CRISPR unique spacer sequences and the numbers of spacers. In the future, investigation on the CRISPR resolution for C. jejuni identification in outbreaks is needed. A database that integrates both MLST sequences and CRISPR sequences and is searchable is greatly in demand for tracking outbreaks and evolution of this bacterium.

Tracking the dissemination of Erwinia amylovora in the Eurasian continent using a PCR targeted on the duplication of a single CRISPR spacer

Fire blight is the most devastating disease affecting pome fruit production globally. The pathogen is native to North America and was imported to western Europe in the 1950s, progressively spreading over the continent in the ensuing decades. Previous phylogenetic studies have revealed the extreme genetic homogeneity of the pathogen outside its center of origin, which makes epidemiological studies difficult. These are generally only possible using hypervariable regions of the genome such as those represented by CRISPRs (Clustered Regularly Interspaced Short Palindromic Repeats), which are, however, not practical to sequence due to their size and variability. Here, we present a simple PCR assay targeting the duplication of a single CRISPR spacer in Erwinia amylovora that was found to be an important marker to discriminate between two main European populations of the pathogen. We implemented the assay on a total of 582 isolates to follow the spread of fire blight across the continent over several decades and, wherever possible, within single countries. The results obtained point to the occurrence of two major separate introduction events for E. amylovora in Europe that occurred approximately 20 years apart, and confirmed the existence of two principal distribution areas located in Northeastern Europe and the Eastern Mediterranean Basin from which the pathogen moved on to colonize the Eurasian continent.

Characterization and Analysis of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) in Pandemic and Non-Pandemic Vibrio parahaemolyticus Isolates from Seafood Sources.

Vibrio parahaemolyticus is one of the significant seafood-borne pathogens causing gastroenteritis in humans. Clustered regularly interspaced short palindromic repeats (CRISPR) are commonly detected in the genomes of V. parahaemolyticus and the polymorphism of CRISPR patterns has been applied as a genetic marker for tracking its evolution. In this work, a total of 15 pandemic and 36 non-pandemic V. parahaemolyticus isolates obtained from seafood between 2000 and 2012 were characterized based on hemolytic activity, antimicrobial susceptibility, and CRISPR elements. The results showed that 15/17 of the V. parahaemolyticus seafood isolates carrying the thermostable direct hemolysin gene (tdh+) were Kanagawa phenomenon (KP) positive. The Multiple Antibiotic Resistance (MAR) index ranged between 0.1 and 0.4, and 45% of the isolates have an MAR index ≥ 0.2. A total of 19 isolates were positive for CRISPR detection, including all tdh+ trh− isolates, two of tdh− trh+, and each of tdh+ trh+ and tdh− trh−. Four spacer types (Sp1 to Sp4) were identified, and CRISPR-positive isolates had at least one type of spacer homolog to the region of Vibrio alginolyticus megaplasmid. It is of interest that a specific CRISPR profile and spacer sequence type was observed with correlations to the hemolysin genotype (tdh/trh). Thus, these provide essential data on the exposure of foreign genetic elements and indicate shared ancestry within different genotypes of V. parahaemolyticus isolates.

CRISPR-Cas systems in Proteus mirabilis.

The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) is a bacterial defense mechanism against bacteriophages composed of two different parts: the CRISPR array and the Cas genes. The spacer acquisition is done by the adaptation module consisting of the hallmark Cas1 Cas2 proteins, which inserts new spacers into the CRISPR array. Here we aimed to describe the CRISPR-Cas system in Proteus mirabilis (P. mirabilis) isolates. CRISPR loci was observed in 30 genomic contents of 109 P. mirabilis isolates that each locus was consisted of two CRISPR arrays and each array had a different preserved leader sequences. Only the type I-E CRISPR-Cas system was common in these isolates. The source of the spacers was identified, including phages and prophages. CRISPR spacer origin analysis also identified a conserved PAM sequence of 5'-AAG-3' nucleotide stretch. Through collecting spacers, CRISPR arrays of P. mirabilis isolates were expanded mostly by integration of bacteriophageal source of spacers. This study shows novel findings in the area of the P-mirabilis CRISPR-Cas system. In this regard, among analyzed genome of P. mirabilis isolates, Class I CRISR-Cas systems were dominant, and all belonged to type I-E. In the flanks of the CRISPR, some other elements with regulatory role were also found. A motif of 11nt size was found to be preserved among the analyzed genome. We believe that it might has a CRISPR-Cas system transcription facilitator by targeting the Rho element.

Survival of Salmonella Under Heat Stress is Associated with the Presence/Absence of CRISPR Cas Genes and Iron Levels.

Clustered regularly interspaced short palindromic repeats (CRISPR) cas genes have been linked to stress response in Salmonella. Our aim was to identify the presence of CRISPR cas in Salmonella and its response to heat in the presence of iron. Whole genomes of Salmonella (n = 50) of seven serovars were compared to identify the presence of CRISPR cas genes, direct-repeats and spacers. All Salmonella genomes had all cas genes present except S. Newport 2393 which lacked these genes. Gene-specific primers were used to confirm the absence of these genes in S. Newport 2393. The presence/absence of CRISPR cas genes was further investigated among 469 S. Newport genomes from PATRIC with 283 genomes selected for pan-genome analysis. The response of eleven Salmonella strains of various serovars to gradual heat in ferrous and ferric forms of iron was investigated. A total of 32/283 S. Newport genomes that lacked all CRISPR cas genes clustered together. S. Newport 2393 was the most heat-sensitive strain at higher iron levels (200 and 220 pm) in ferrous and ferric forms of iron. The absence of CRISPR cas genes in S. Newport 2393 may contribute to its increase in heat sensitivity and iron may play a role in this. The high reduction in numbers of most Salmonella strains exposed to heat makes it unfeasible to extract RNA and conduct transcription studies. Further studies should be conducted to validate the survival of Salmonella when exposed to heat in the presence/absence of CRISPR cas genes and different iron levels.

Phenotypic Evaluation of Fire Blight Outbreak in the USDA Malus Collection

Fire blight, caused by pathogen Erwinia amylovora, is a major disease in Malus. Biological, chemical and cultural controls are efficient to manage fire blight, while rootstocks, and host resistance can limit damages. During the 2020 season a naturally occurring fire blight outbreak occurred in the United States Department of Agriculture (USDA) Malus collection, providing a unique opportunity to evaluate the diverse collection for fire blight susceptibility. The E. amylovora strain in the collection was identified as streptomycin resistant and characterized as CRISPR (clustered regularly interspaced short palindromic repeats) spacer array profile, 41:23:38. Fire blight severity was assessed using two approaches: (1) Average severity percentage, where the number of infected shoots was divided by the total number of shoots for the east and west facing sides of the tree; and (2) cut severity rating, where the trees were visually assessed after fire blight removal for amount of tree removed. Overall, 1142 trees of 41 Malus species were assessed for average severity and 2525 trees of 48 species were assessed for cut severity. A subset of 667 trees were for average severity in June and July to understand the disease progression. The species and trees presented here, can provide insight for future genetic fire blight resistance studies.

Utilization of Clustered Regularly Interspaced Short Palindromic Repeats to Genotype Escherichia coli Serogroup O80.

The hypervariable nature of clustered regularly interspaced short palindromic repeats (CRISPRs) makes them valuable biomarkers for subtyping and epidemiological investigation of Escherichia coli. Shiga toxin-producing E. coli (STEC) serogroup O80 is one hybrid pathotype that is emerging recently in Europe and is involved in hemolytic uremic syndrome with bacteremia. However, whether STEC O80 strains can be genotyped using CRISPR has not been evaluated. In this study, we aimed to characterize the genetic diversity of 81 E. coli serogroup O80 isolates deposited in the National Center for Biotechnology Information databases using CRISPR typing and to explore the association between virulence potential and CRISPR types (CTs). A total of 21 CTs were identified in 80 O80 strains. CRISRP typing provided discrimination with variants of a single serotype, which suggested a stronger discriminatory power. Based on CRISPR spacer profiles, 70 O80:H2 isolates were further divided into four lineages (lineage LI, LII, LIII, and LIV), which correlated well with whole-genome single nucleotide polymorphisms typing and virulence gene profiles. Moreover, the association between CRISPR lineages and virulence gene profiles hinted that STEC O80:H2 strains may originate from O80:H19 or O80:H26 and that lineage LI may have been evolved from lineage LII. CT2 and CT13 were shared by human and cattle isolates, suggesting that there might be the potential transmission between cattle and human. Collectively, CRISPR typing is one technology that can be used to monitor the transmission of STEC O80 strains and provide new insights into microevolution of serogroup O80.

Broadscale phage therapy is unlikely to select for widespread evolution of bacterial resistance to virus infection.

Multi-drug resistant bacterial pathogens are alarmingly on the rise, signaling that the golden age of antibiotics may be over. Phage therapy is a classic approach that often employs strictly lytic bacteriophages (bacteria-specific viruses that kill cells) to combat infections. Recent success in using phages in patient treatment stimulates greater interest in phage therapy among Western physicians. But there is concern that widespread use of phage therapy would eventually lead to global spread of phage-resistant bacteria and widespread failure of the approach. Here, we argue that various mechanisms of horizontal genetic transfer (HGT) have largely contributed to broad acquisition of antibiotic resistance in bacterial populations and species, whereas similar evolution of broad resistance to therapeutic phages is unlikely. The tendency for phages to infect only particular bacterial genotypes limits their broad use in therapy, in turn reducing the likelihood that bacteria could acquire beneficial resistance genes from distant relatives via HGT. We additionally consider whether HGT of clustered regularly interspaced short palindromic repeats (CRISPR) immunity would thwart generalized use of phages in therapy, and argue that phage-specific CRISPR spacer regions from one taxon are unlikely to provide adaptive value if horizontally-transferred to other taxa. For these reasons, we conclude that broadscale phage therapy efforts are unlikely to produce widespread selection for evolution of bacterial resistance.

Occurrence and Diversity of CRISPR Loci in Lactobacillus casei Group.

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) is an adaptive immune system that resists foreign genes through nuclease targeting in bacteria and archaea. In this study, we analyzed 68 strains of Lactobacillus casei group from the NCBI GenBank database, and bioinformatic tools were used to investigate the occurrence and diversity of CRISPR system. The results showed that a total of 30 CRISPR loci were identified from 27 strains. Apart from three strains which contained double loci with distinguishable distributed sites, most strains contained only one CRISPR locus. The analysis of direct repeat (DR) sequences showed that all DR could form stable RNA secondary structures. The CRISPR spacers showed diversity, and their origin and evolution were revealed through the investigation of their spacer sequences. In addition, a large number of CRISPR spacers showed perfect homologies to phage and plasmid sequences. Collectively, our results would contribute to researches of resistance in L. casei group, and also provide a new vision on the diversity and evolution of CRISPR/Cas system.