Imipenem represses CRISPR-Cas interference of DNA acquisition through H-NS stimulation in Klebsiella pneumoniae

Association between the presence of CRISPR-Cas system genes and antibiotic resistance in Klebsiella pneumoniae isolated from patients admitted in Ahvaz teaching hospitals

BACKGROUND

This study aims to investigate the frequency of cas1 and cas3 and CRISPR1,2,3 genes in Klebsiella pneumoniae isolates, as well as their connection with antibiotic resistance.

MATERIALS AND METHODS

106 K. pneumoniae isolates were identified by biochemical assays and PCR. The susceptibility to antibiotics was determined by Kirby-Bauer disk diffusion method. Screening of ESBLs was undertaken by using double disk diffusion and standard disk diffusion methods. The E-test and mCIM techniques was used to confirm the disc diffusion-based carbapenem resistance profiles. CRISPR-Cas system genes were identified using PCR.

RESULTS

ESBL production was found in 19% of isolates. Carbapenemase production was found in 46% of the isolates. Furthermore, the bacteria were classified as multidrug (76%), extensively drug-resistant (4%), or pan-drug-resistant (2%). When CRISPR/Cas systems were present, antibiotic resistance was lower; conversely, when they were absent, resistance was higher.

CONCLUSIONS

If the CRISPR/Cas modules aren't present, the bacteria can still acquire foreign DNA, including antibiotic resistance genes. K. pneumoniae isolates with a CRISPR-Cas system were less likely to carry antibiotic-resistance genes than those lacking this defense system.

Carbapenem-resistant Klebsiella pneumoniae strains isolated from clinical specimens in Siirt, Türkiye; molecular characterization and antimicrobial resistance genes detection

This study aimed to molecularly identify carbapenem-resistant Klebsiella pneumoniae (CRKP) strains isolated from clinical samples and to determine antibiotic resistance genes. Only carbapenem-resistant strains were included in our study. Of the 35 CRKP strains, 18 (51.4%) were extensive drug, 11 (31.4%) were multi-drug, and 6 (17.1%) were pan-drug resistances. PCR amplification revealed that 25% of the strains carried the OXA-51, 20% the OXA-48, and %5 the OXA23 genes. Multilocus sequence typing (MLST) analysis based on seven house-keeping genes revealed sequence type 39. The capsule and O-antigen types were determined as KL103 and O2a, respectively. WGS analysis revealed the existence of β-lactamase, aminoglycoside, sulfonamide, Phenicol, and Fosfomycin-resistant genes. While the K. pneumoniae OmpK37 gene was detected in all 3 strains, the OmpK36 gene was detected only in the CRSU20 strain. This study is important as it is the first study to perform molecular analysis of CRKP strains from Siirt, Türkiye.

Geographic and environmental impacts on gut microbiome in Himalayan langurs (Semnopithecus schistaceus) and Xizang macaques (Macaca mulatta vestita)

Introduction

Gut microbiome plays a crucial role in the health of wild animals. Their structural and functional properties not only reflect the host's dietary habits and habitat conditions but also provide essential support for ecological adaptation in various environments.

Methods

This study investigated the gut microbiome of Himalayan langurs (Semnopithecus schistaceus) and Xizang macaques (Macaca mulatta vestita) across different geographic regions using 16S rRNA gene and metagenomic sequencing.

Results

Results showed distinct clustering patterns in gut microbiota based on geographic location. Soil had an insignificant impact on host gut microbiome. Himalayan langurs from mid-altitude regions exhibited higher levels of antibiotic resistance genes associated with multidrug resistance, while Xizang macaques from high-altitude regions showed a broader range of resistance genes. Variations in carbohydrate-active enzymes and KEGG pathways indicated unique metabolic adaptations to different environments.

Discussion

These findings provide valuable insights into the health and conservation of these primates and the broader implications of microbial ecology and functional adaptations in extreme conditions.

A new anti-CRISPR gene promotes the spread of drug-resistance plasmids in Klebsiella pneumoniae

The Klebsiella pneumoniae (K. pneumoniae, Kp) populations carrying both resistance-encoding and virulence-encoding mobile genetic elements (MGEs) significantly threaten global health. In this study, we identified a new anti-CRISPR gene (acrIE10) on a conjugative plasmid with self-target sequence in K. pneumoniae with type I-E* CRISPR-Cas system. AcrIE10 interacts with the Cas7* subunit of K. pneumoniae I-E* CRISPR-Cas system. The crystal structure of the AcrIE10-KpCas7* complex suggests that AcrIE10 suppresses the I-E* CRISPR-Cas by binding directly to Cas7 to prevent its hexamerization, thereby preventing the surveillance complex assembly and crRNA loading. Bioinformatic and functional analyses revealed that AcrIE10 is functionally widespread across diverse species. Our study reports a novel anti-CRISPR and highlights its potential role in spreading resistance and virulence among pathogens.

Molecular and bacteriological investigations for the co-existence CRISPR/Cas system and β-lactamases of types extended-spectrum and carbapenemases in Multidrug, extensive drug and Pandrug-Resistant Klebsiella pneumoniae

The recent approach towards combating the antimicrobial resistance has led to the use of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and associated sequence to overcome the challenges of antimicrobial resistance. Thus, this study aimed to detect the underlying resistance mechanisms such as ESBLs and carbapenemases and whether there is a correlation between multidrug, extensive drug and pan drug resistance and the occurrence of CRISPR loci. A total of one hundred study isolates were subjected to antimicrobial susceptibility testing using the AST card of the Vitek technique to detect resistance patterns involving ESBLs and carbapenemase (CRE). An investigation of the genes encoding CRISPR/Cas systems using PCR was achieved. Out of 81 (81.0%) resistant Klebsiella pneumoniae isolates, 71 (71%) and 21 (21.0%) produced ESBLs and carbapenemases, respectively. Also, 53 (53.0%), 19 (19.0%) and 9 (9.0%) were MDR, XDR, and PDR respectively. It was noted that Cas1, Cas3, CRISPR1, CRISPR2 and CRISPR3 were positive in 38 (38.0%) of the isolates, while CRISPR1 for incomplete CRISPR1-Cas systems alone was detected in 78 (78.0%). Further, the number of intact CRISPR1, intact CRISPR2 and intact CRISPR3 types were 7 (27.0%), 34 (34%) and 18 (18.0%) respectively. It is concluded that antibiotic resistance levels were inversely correlated with the existence of CRISPR/Cas systems. The absence of the CRISPR/Cas system increases the prevalence of MDR, XDR and PDR in ESBL and carbapenem-producing Klebsiella pneumoniae. With the increase in the degree of antibiotic resistance (MDR, XDR to PDR), the occurrence ratio of the (CRISPR)/CRISPR-associated sequence decreased.

Sub-MIC antibiotics increased the fitness cost of CRISPR-Cas in Acinetobacter baumannii

Introduction

The escalating prevalence of bacterial resistance, particularly multidrug-resistant bacteria like Acinetobacter baumannii, has become a significant global public health concern. The CRISPR-Cas system, a crucial defense mechanism in bacteria against foreign genetic elements, provides a competitive advantage. Type I-Fb and Type I-Fa are two subtypes of CRISPR-Cas systems that were found in A. baumannii, and the I-Fb CRISPR-Cas system regulates antibiotic resistance in A. baumannii. However, it is noteworthy that a majority of clinical isolates of A. baumannii lack or have incomplete CRISPR-Cas systems and most of them are multidrug-resistant. In light of this, our study aimed to examine the impact of antibiotic pressure on the fitness cost of the I-Fb CRISPR-Cas system in A. baumannii.

Methods and Results

In the study, we conducted in vitro competition experiments to investigate the influence of sub-minimum inhibitory concentration (sub-MIC) on the CRISPR-Cas systems' fitness cost in A. baumannii. We found that the fitness cost of the CRISPR-Cas system was increased under sub-MIC conditions. The expression of CRISPR-Cas-related genes was decreased, while the conjugation frequency was increased in AB43 under sub-MIC conditions. Through metabolomic analysis, we identified that sub-MIC conditions primarily affected energy metabolism pathways. In particular, we observed increased carbon metabolism, nitrogen metabolism, and intracellular ATP. Notably, the CRISPR-Cas system demonstrated resistance to the efflux pump-mediated resistance. Furthermore, the expression of efflux pump-related genes was increased under sub-MIC conditions.

Conclusion

Our findings suggest that the I-Fb CRISPR-Cas system confers a significant competitive advantage in A. baumanni. However, under sub-MIC conditions, its function and the ability to inhibit the energy required for efflux pumps are reduced, resulting in an increased fitness cost and loss of competitive advantage.

Prevalence of the CRISPR-cas system and its association with antibiotic resistance in clinical Klebsiella pneumoniae isolates

BACKGROUND AND OBJECTIVE(S)

CRISPR-Cas is a prokaryotic adaptive immune system that protects bacteria and archaea against mobile genetic elements (MGEs) such as bacteriophages plasmids, and transposons. In this study, we aimed to assess the prevalence of the CRISPR-Cas systems and their association with antibiotic resistance in one of the most challenging bacterial pathogens, Klebsiella pneumoniae.

MATERIALS AND METHODS

A total of 105 K. pneumoniae isolates were collected from various clinical infections. Extended-spectrum β-lactamases (ESBLs) phenotypically were detected and the presence of ESBL, aminoglycoside-modifying enzymes (AME), and CRISPR-Cas system subtype genes were identified using PCR. Moreover, the diversity of the isolates was determined by enterobacterial repetitive intergenic consensus (ERIC)-PCR.

RESULTS

Phenotypically, 41.9% (44/105) of the isolates were found to be ESBL producers. A significant inverse correlation existed between the subtype I-E CRISPR-Cas system's presence and ESBL production in K. pneumoniae isolates. Additionally, the frequency of the ESBL genes blaCTX-M1 (3%), blaCTX-M9 (12.1%), blaSHV (51.5%), and blaTEM (33.3%), as well as some AME genes such as aac(3)-Iva (21.2%) and ant(2'')-Ia (3%) was significantly lower in the isolates with the subtype I-E CRISPR-Cas system in comparison to CRISPR-negative isolates. There was a significant inverse correlation between the presence of ESBL and some AME genes with subtype I-E CRISPR-Cas system.

CONCLUSION

The presence of the subtype I-E CRISPR-Cas system was correlated with the antibiotic-resistant gene (ARGs). The isolates with subtype I-E CRISPR-Cas system had a lower frequency of ESBL genes and some AME genes than CRISPR-negative isolates.

Correlation of CRISPR/Cas and Antimicrobial Resistance in Klebsiella pneumoniae Clinical Isolates Recovered from Patients in Egypt Compared to Global Strains

The CRISPR/Cas system has been long known to interfere with the acquisition of foreign genetic elements and was recommended as a tool for fighting antimicrobial resistance. The current study aimed to explore the prevalence of the CRISPR/Cas system in Klebsiella pneumoniae isolates recovered from patients in Egypt in comparison to global strains and correlate the CRISPR/Cas to susceptibility to antimicrobial agents. A total of 181 clinical isolates were PCR-screened for cas and selected antimicrobial resistance genes (ARGs). In parallel, 888 complete genome sequences were retrieved from the NCBI database for in silico analysis. CRISPR/Cas was found in 46 (25.4%) isolates, comprising 18.8% type I-E and 6.6% type I-E*. Multidrug resistance (MDR) and extensive drug resistance (XDR) were found in 73.5% and 25.4% of the isolates, respectively. More than 95% of the CRISPR/Cas-bearing isolates were MDR (65.2%) or XDR (32.6%). No significant difference was found in the susceptibility to the tested antimicrobial agents among the CRISPR/Cas-positive and -negative isolates. The same finding was obtained for the majority of the screened ARGs. Among the published genomes, 23.2% carried CRISPR/Cas, with a higher share of I-E* (12.8%). They were confined to specific sequence types (STs), most commonly ST147, ST23, ST15, and ST14. More plasmids and ARGs were carried by the CRISPR/Cas-negative group than others, but their distribution in the two groups was not significantly different. The prevalence of some ARGs, such as blaKPC, blaTEM, and rmtB, was significantly higher among the genomes of the CRISPR/Cas-negative strains. A weak, nonsignificant positive correlation was found between the number of spacers and the number of resistance plasmids and ARGs. In conclusion, the correlation between CRISPR/Cas and susceptibility to antimicrobial agents or bearing resistance plasmids and ARGs was found to be nonsignificant. Plasmid-targeting spacers might not be naturally captured by CRISPR/Cas. Spacer match analysis is recommended to provide a clearer image of the exact behavior of CRISPR/Cas towards resistance plasmids.

Inverse Association between the Existence of CRISPR/Cas Systems with Antibiotic Resistance, Extended Spectrum β-Lactamase and Carbapenemase Production in Multidrug, Extensive Drug and Pandrug-Resistant Klebsiella pneumoniae

Antimicrobial resistance, with the production of extended-spectrum β-lactamases (ESBL) and carbapenemases, is common in the opportunistic pathogen, Klebsiella pneumoniae. This organism has a genome that can contain clustered regularly interspaced short palindromic repeats (CRISPRs), which operate as a defense mechanism against external invaders such as plasmids and viruses. This study aims to determine the association of the CRISPR/Cas systems with antibiotic resistance in K. pneumoniae isolates from Iraqi patients. A total of 100 K. pneumoniae isolates were collected and characterized according to their susceptibility to different antimicrobial agents. The CRISPR/Cas systems were detected via PCR. The phenotypic detection of ESBLs and carbapenemases was performed. The production of ESBL was detected in 71% of the isolates. Carbapenem-resistance was detected in 15% of the isolates, while only 14% were susceptible to all antimicrobial agents. Furthermore, the bacteria were classified into multidrug (77%), extensively drug-resistant (11.0%) and pandrug-resistant (4.0%). There was an inverse association between the presence of the CRISPR/Cas systems and antibiotic resistance, as resistance was higher in the absence of the CRISPR/Cas system. Multidrug resistance in ESBL-producing and carbapenem-resistant K. pneumoniae occurred more frequently in strains negative for the CRISPR/Cas system. Thus, we conclude that genes for exogenous antibiotic resistance can be acquired in the absence of the CRISPR/Cas modules that can protect the bacteria against acquiring foreign DNA.

Coexistence of blaKPC-IncFII plasmids and type I-E* CRISPR-Cas systems in ST15 Klebsiella pneumoniae

The CRISPR-Cas system in Klebsiella pneumoniae can prevent the entry of blaKPC-IncF plasmids. However, some clinical isolates bear the KPC-2 plasmids despite carrying the CRISPR-Cas system. The purpose of this study was to characterize the molecular features of these isolates. A total of 697 clinical K. pneumoniae isolates were collected from 11 hospitals in China, and tested for the presence of CRISPR-Cas systems using polymerase chain reaction. Overall, 164 (23.5%) of 697 K. pneumoniae isolates had type I-E* (15.9%) or type I-E (7.7%) CRISPR-Cas systems. The most prevalent sequence type among isolates carrying type I-E* CRISPR was ST23 (45.9%), followed by ST15 (18.9%). Isolates with CRISPR-Cas system were more susceptible to ten antimicrobials tested, including carbapenems, compared with the CRISPR-negative isolates. However, there were still 21 CRISPR-Cas-carrying isolates that showed resistance to carbapenems, and these isolates were subjected to whole-genome sequencing. Thirteen of these 21 isolates carried blaKPC-2-bearing plasmids, of which nine had a new plasmid type, IncFIIK34, and two had IncFII(PHN7A8) plasmids. In addition, 12 of these 13 isolates belonged to ST15, while only eight (5.6%, 8/143) isolates belonged to ST15 in carbapenem-susceptible K. pneumoniae carrying CRISPR-Cas systems. In conclusion, we found that blaKPC-2-bearing IncFII plasmids could co-exist with the type I-E* CRISPR-Cas systems in ST15 K. pneumoniae.

Characterization and comprehensive genome analysis of novel bacteriophage, vB_Kpn_ZCKp20p, with lytic and anti-biofilm potential against clinical multidrug-resistant Klebsiella pneumoniae

Introduction

The rise of infections by antibiotic-resistant bacterial pathogens is alarming. Among these, Klebsiella pneumoniae is a leading cause of death by hospital-acquired infections, and its multidrug-resistant strains are flagged as a global threat to human health, which necessitates finding novel antibiotics or alternative therapies. One promising therapeutic alternative is the use of virulent bacteriophages, which specifically target bacteria and coevolve with them to overcome potential resistance. Here, we aimed to discover specific bacteriophages with therapeutic potential against multiresistant K. pneumoniae clinical isolates.

Methods and Results

Out of six bacteriophages that we isolated from urban and medical sewage, phage vB_Kpn_ZCKp20p had the broadest host range and was thus characterized in detail. Transmission electron microscopy suggests vB_Kpn_ZCKp20p to be a tailed phage of the siphoviral morphotype. In vitro evaluation indicated a high lytic efficiency (30 min latent period and burst size of ∼100 PFU/cell), and extended stability at temperatures up to 70°C and a wide range of (2-12) pH. Additionally, phage vB_Kpn_ZCKp20p possesses antibiofilm activity that was evaluated by the crystal violet assay and was not cytotoxic to human skin fibroblasts. The whole genome was sequenced and annotated, uncovering one tRNA gene and 33 genes encoding proteins with assigned functions out of 85 predicted genes. Furthermore, comparative genomics and phylogenetic analysis suggest that vB_Kpn_ZCKp20p most likely represents a new species, but belongs to the same genus as Klebsiella phages ZCKP8 and 6691. Comprehensive genomic and bioinformatics analyses substantiate the safety of the phage and its strictly lytic lifestyle.

Conclusion

Phage vB_Kpn_ZCKp20p is a novel phage with potential to be used against biofilm-forming K. pneumoniae and could be a promising source for antibacterial and antibiofilm products, which will be individually studied experimentally in future studies.

Correlation between CRISPR Loci Diversity in Three Enterobacterial Taxa

CRISPR-Cas is an adaptive immunity system of prokaryotes, composed of CRISPR arrays and the associated proteins. The successive addition of spacer sequences in the CRISPR array has made the system a valuable molecular marker, with multiple applications. Due to the high degree of polymorphism of the CRISPR loci, their comparison in bacteria from various sources may provide insights into the evolution and spread of the CRISPR-Cas systems. The aim of this study was to establish a correlation between the enterobacterial CRISPR loci, the sequence of direct repeats (DR), and the number of spacer units, along with the geographical origin and collection source. For this purpose, 3474 genomes containing CRISPR loci from the CRISPRCasdb of Salmonella enterica, Escherichia coli, and Klebsiella pneumoniae were analyzed, and the information regarding the isolates was recorded from the NCBI database. The most prevalent was the I-E CRISPR-Cas system in all three studied taxa. E. coli also presents the I-F type, but in a much lesser percentage. The systems found in K. pneumoniae can be classified into I-E and I-E*. The I-E and I-F systems have two CRISPR loci, while I-E* has only one locus upstream of the Cas cluster. PCR primers have been developed in this study for each CRISPR locus. Distinct clustering was not evident, but statistically significant relationships occurred between the different CRISPR loci and the number of spacer units. For each of the queried taxa, the number of spacers was significantly different (p < 0.01) by origin (Africa, Asia, Australia and Oceania, Europe, North America, and South America) but was not linked to the isolation source type (human, animal, plant, food, or laboratory strains).

Clustered regularly interspaced short palindromic repeats-Cas system: diversity and regulation in Enterobacteriaceae

Insights into the arms race between bacteria and invading mobile genetic elements have revealed the intricacies of the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system and the counter-defenses of bacteriophages. Incredible spacer diversity but significant spacer conservation among species/subspecies dictates the specificity of the CRISPR-Cas system. Researchers have exploited this feature to type/subtype the bacterial strains, devise targeted antimicrobials and regulate gene expression. This review focuses on the nuances of the CRISPR-Cas systems in Enterobacteriaceae that predominantly harbor type I-E and I-F CRISPR systems. We discuss the systems' regulation by the global regulators, H-NS, LeuO, LRP, cAMP receptor protein and other regulators in response to environmental stress. We further discuss the regulation of noncanonical functions like DNA repair pathways, biofilm formation, quorum sensing and virulence by the CRISPR-Cas system. The review comprehends multiple facets of the CRISPR-Cas system in Enterobacteriaceae including its diverse attributes, association with genetic features, regulation and gene regulatory mechanisms.

CRISPR-Cas systems target endogenous genes to impact bacterial physiology and alter mammalian immune responses

CRISPR-Cas systems are an immune defense mechanism that is widespread in archaea and bacteria against invasive phages or foreign genetic elements. In the last decade, CRISPR-Cas systems have been a leading gene-editing tool for agriculture (plant engineering), biotechnology, and human health (e.g., diagnosis and treatment of cancers and genetic diseases), benefitted from unprecedented discoveries of basic bacterial research. However, the functional complexity of CRISPR systems is far beyond the original scope of immune defense. CRISPR-Cas systems are implicated in influencing the expression of physiology and virulence genes and subsequently altering the formation of bacterial biofilm, drug resistance, invasive potency as well as bacterial own physiological characteristics. Moreover, increasing evidence supports that bacterial CRISPR-Cas systems might intriguingly influence mammalian immune responses through targeting endogenous genes, especially those relating to virulence; however, unfortunately, their underlying mechanisms are largely unclear. Nevertheless, the interaction between bacterial CRISPR-Cas systems and eukaryotic cells is complex with numerous mysteries that necessitate further investigation efforts. Here, we summarize the non-canonical functions of CRISPR-Cas that potentially impact bacterial physiology, pathogenicity, antimicrobial resistance, and thereby altering the courses of mammalian immune responses.

Whole genome sequencing of Klebsiella pneumoniae clinical isolates sequence type 627 isolated from Egyptian patients

Klebsiella pneumoniae is considered a threat to public health especially due to multidrug resistance emergence. It is largely oligoclonal based on multi-locus sequence typing (MLST); in Egypt, ST 627 was recently detected. Despites the global dissemination of this ST, there is still paucity of information about it. Herein, we used 4 K. pneumoniae ST627 for whole genome sequencing utilizing an Illumina MiSeq platform. Genome sequences were examined for resistance and virulence determinants, capsular types, plasmids, insertion sequences, phage regions, and Clustered Regularly Interspaced Palindromic Repeats (CRISPR) regions using bioinformatic analysis. The molecular characterization revealed 15 and 65 antimicrobial resistance and virulence genes, respectively. Resistance genes such as tet(D), aph(3’’)-Ib, aph(6)-Id, blaTEM-234, fosA, and fosA6; were mainly responsible for tetracycline, aminoglycoside, and fosfomycin resistance; respectively. The capsular typing revealed that the four strains are KL-24 and O1v1. One plasmid was found in all samples known as pC17KP0052-1 and another plasmid with accession no. NZ_CP032191.1 was found only in K90. IncFIB(K) and IncFII(K) are two replicons found in all samples, while ColRNAI replicon was found only in K90. Entero P88, Salmon SEN5, and Klebsi phiKO2 intact phage regions were identified. All samples harbored CRISPR arrays including CRISPR1 and CRISPR2. Our results shed light on critical tasks of mobile genetic elements in ST 627 in antibiotic resistance spreading.

Molecular characterization of rectal isolates of carbapenemase-negative carbapenem-resistant enterobacterales obtained from ICU patients in Kuwait by whole-genome sequencing

Introduction. Carbapenem-resistant enterobacterales (CRE) are listed among the most urgent antibiotic resistance threats.Hypothesis. Previous studies on the mechanisms of CRE in Kuwait have focused on carbapenemases. There have been no studies on non-carbapenemase-producing CRE in Kuwait.Aim/Gap Statement. The aim of this study was to investigate the genetic characteristics of non-carbapenemase-producing carbapenem-resistant enterobacterales (NCPE) isolates using whole-genome sequencing (WGS).Methodology. Fourteen confirmed NCPE isolates that were negative for genes encoding carbapenemase production by polymerase chain reaction (PCR) assays using rectal swabs from intensive care unit patients were characterized using phenotypic, PCR and WGS methods. Susceptibility testing was performed via Etest and clonality via multi-locus sequence typing (MLST).Results. All of the isolates were resistant to ertapenem; 78.6 % were resistant to imipenem, meropenem and trimethoprim-sulfamethoxazole. Resistance to the other antibiotics was variable, ranging from 28.5 (colistin) through 50 (tigecycline) and 64.3 (amikacin) up to 85.7 % against both amoxicillin-clavulanic acid and ciprofloxacin. WGS detected several resistance genes mediating the production of β-lactamases, genes encoding an outer-membrane porin permeability mutation resulting in reduced susceptibility to β-lactams, including carbapenems, and genes for multidrug-resistant (MDR) efflux pumps. The isolates also possessed global activator protein MarA, which mediated reduced permeability to β-lactams. The existence of β-lactamase genes, overexpression of MDR efflux pumps and reduced permeability mediated by the porin genes were responsible for carbapenem resistance.Conclusions. This finding reflects the superior detection capabilities offered by WGS analysis, which can be used to complement traditional methods and overcome their limited resolution in clinical settings.

Involvement of the Histone-Like Nucleoid Structuring Protein (H-NS) in Acinetobacter baumannii's Natural Transformation

Most Acinetobacter baumannii strains are naturally competent. Although some information is available about factors that enhance or reduce the frequency of the transformation of this bacterium, the regulatory elements and mechanisms are barely understood. In this article, we describe studies on the role of the histone-like nucleoid structuring protein, H-NS, in the regulation of the expression of genes related to natural competency and the ability to uptake foreign DNA. The expression levels of the natural transformation-related genes pilA, pilT, pilQ, comEA, comEC, comF, and drpA significantly increased in a Δhns derivative of A. baumannii A118. The complementation of the mutant with a recombinant plasmid harboring hns restored the expression levels of six of these genes (pilT remained expressed at high levels) to those of the wild-type strain. The transformation frequency of the A. baumannii A118 Δhns strain was significantly higher than that of the wild-type. Similar, albeit not identical, there were consequences when hns was deleted from the hypervirulent A. baumannii AB5075 strain. In the AB5075 complemented strain, the reduction in gene expression in a few cases was not so pronounced that it reached wild-type levels, and the expression of comEA was enhanced further. In conclusion, the expression of all seven transformation-related genes was enhanced after deleting hns in A. baumannii A118 and AB5075, and these modifications were accompanied by an increase in the cells' transformability. The results highlight a role of H-NS in A. baumannii's natural competence.

Absence of the type I-E CRISPR-Cas system in Klebsiella pneumoniae clonal complex 258 is associated with dissemination of IncF epidemic resistance plasmids in this clonal complex

BACKGROUND

The pandemics caused by MDR Klebsiella pneumoniae are mostly due to the global dissemination of high-risk clonal complex 258 (CC258) and related IncF epidemic plasmids. However, the factors leading to the epidemiological advantages of CC258-IncF linkage remain obscure. The Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) and CRISPR-associated protein (CRISPR-Cas) systems, providing adaptive immunity against invading DNA, play an important role in the interactions between plasmids and hosts.

OBJECTIVES

To investigate the relationship between CRISPR-Cas systems and the high-risk linkage CC258-IncF.

METHODS

CRISPR-Cas loci were detected among 381 collected K. pneumoniae clinical isolates and 207 K. pneumoniae complete genomes available in GenBank. MLST was used to determine the genetic relatedness of these isolates. Nucleotide BLAST was used to search for protospacers on K. pneumoniae plasmids.

RESULTS

We observed an epidemic correlation between CRISPR-Cas loci, CC258 and IncF plasmids. Interestingly, most type I-E CRISPR-Cas systems identified carried spacers matching the backbone regions of IncF plasmids.

CONCLUSIONS

Our results suggest that the absence of type I-E CRISPR-Cas systems in K. pneumoniae CC258 is strongly associated with the dissemination of IncF epidemic plasmids, contributing to the global success of the international high-risk linkage CC258-IncF. Our findings provide new information regarding the dissemination and evolution of the high-risk linkage of K. pneumoniae CC258-IncF and pave the way for new strategies to address the problem of antibiotic resistance.

Bacteriophage therapy for challenging bacterial infections: achievements, limitations and prospects for future clinical use by veterinary dermatologists

BACKGROUND

Bacteriophages were discovered just over 100 years ago and have been used to treat bacterial infections in animals since the 1920s. The antimicrobial resistance crisis has led to a new surge of interest in the use of bacteriophage therapy as an alternative or supplement to antimicrobial therapy in humans and other animals.

OBJECTIVES

To describe the nature of bacteriophages and provide a critical review and update on the clinical use of bacteriophages in the treatment of challenging bacterial infections, with an emphasis on companion animal veterinary applications.

METHODS AND MATERIALS

The scientific literature on the subject was critically evaluated. Findings from the most pertinent papers have been presented in summary form and critiqued.

RESULTS

Over the last 20 years there has been a considerable increase in the volume and quality of publications dealing with bacteriophage therapy. Some recent papers build on excellent work published in the 1980s and describe promising veterinary applications. Challenges related particularly to the registration and approval of phage remedies will need to be overcome before phage therapy can become a mainstream tool for use in veterinary settings. Considerably more research, particularly controlled clinical trials, needs to be done.

CONCLUSIONS AND CLINICAL IMPORTANCE

Bacteriophage therapy is one of the most promising approaches to tackling the looming antimicrobial resistance crisis, yet substantial regulatory challenges will need to be overcome before it enters widespread use. Phage therapy also may, in the future, improve the management of challenging bacterial infections that are not necessarily multidrug-resistant.

CRISPR: A new paradigm of theranostics

Infectious and hereditary diseases are the primary cause of human mortality globally. Applications of conventional techniques require significant improvement in sensitivity and specificity in therapeutics. However, clustered regularly interspaced short palindromic repeats (CRISPRs) is an innovative genome editing technology which has provided a significant therapeutic tool exhibiting high sensitivity, fast and precise investigation of distinct pathogens in an epidemic. CRISPR technology has also facilitated the understanding of the biology and therapeutic mechanism of cancer and several other hereditary diseases. Researchers have used the CRISPR technology as a theranostic approach for a wide range of diseases causing pathogens including distinct bacteria, viruses, fungi and parasites and genetic mutations as well. In this review article, besides various therapeutic applications of infectious and hereditary diseases we have also explained the structure and mechanism of CRISPR tools and role of CRISPR integrated biosensing technology in provoking diagnostic applications.

The type I-E CRISPR-Cas system influences the acquisition of blaKPC-IncF plasmid in Klebsiella pneumonia

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) have disseminated worldwide and emerged as major threats to public health. Of epidemiological significance, the international pandemic of KPC-KP is primarily associated with CG258 isolates and bla_KPC-IncF plasmids. CRISPR-Cas system is an adaptive immune system that can hinder gene expansion driven by horizontal gene transfer. Because of bla_KPC-IncF plasmids are favored by CG258 K. pneumoniae, it was of interest to examine the co-distribution of CRISPR and bla_KPC-IncF plasmids in such isolates. We collected 459 clinical K. pneumoniae isolates in China and collected 203 global whole-genome sequences in GenBank to determine the prevalence of CRISPR-Cas systems. We observed that CRISPR-Cas system was significantly scarce in the CG258 lineage and bla_KPC-positive isolates. Furthermore, the results of conjugation and plasmid stability assay fully demonstrated the CRIPSR-Cas system in K. pneumoniae could effectively hindered bla_KPC-IncF plasmids invasion and existence. Notably, most bla_KPC-IncF plasmids were also proved to be good targets of CRISPR owing to carry matched and functional protospacers and PAMs. Overall, our work suggests that type I-E CRISPR-Cas systems could impact the spread of bla_KPC in K. pneumoniae populations, and the scarcity of CRISPR-Cas system was one of potential factors leading to the propagation of bla_KPC-IncF plasmids in CG258 K. pneumoniae.

Genomic analysis reveals high virulence and antibiotic resistance amongst phage susceptible Acinetobacter baumannii

In this study, we examined the association between antimicrobial resistance, CRISPR/Cas systems and virulence with phage susceptibility in Acinetobacter baumannii and investigated draft genomes of phage susceptible multidrug resistant A. baumannii strains from Thailand. We investigated 230 A. baumannii strains using 17 lytic A. baumannii phages and the phage susceptibility was 46.5% (107/230). Phage susceptibility was also associated with resistance to numerous antibiotics (p-value < 0.05). We also found association between biofilm formation and the presence of ompA gene among phage susceptible A. baumannii strains (p-value < 0.05). A. baumannii isolates carrying cas5 or combinations of two or three other cas genes, showed a significant increase in phage resistance. Whole-genome sequences of seven phage susceptible A. baumannii isolates revealed that six groups of antibiotic resistance genes were carried by all seven phage susceptible A. baumannii. All strains carried biofilm associated genes and two strains harbored complete prophages, acquired copper tolerance genes, and CRISPR-associated (cas) genes. In conclusion, our data exhibits an association between virulence determinants and biofilm formation among phage susceptible A. baumannii strains. These data help to understand the bacterial co-evolution with phages.

Histone-like Nucleoid-Structuring Protein (H-NS) Paralogue StpA Activates the Type I-E CRISPR-Cas System against Natural Transformation in Escherichia coli

Working mechanisms of CRISPR-Cas systems have been intensively studied. However, far less is known about how they are regulated. The histone-like nucleoid-structuring protein H-NS binds the promoter of cas genes (P _cas ) and suppresses the type I-E CRISPR-Cas system in Escherichia coli Although the H-NS paralogue StpA also binds P _cas , its role in regulating the CRISPR-Cas system remains unidentified. Our previous work established that E. coli is able to take up double-stranded DNA during natural transformation. Here, we investigated the function of StpA in regulating the type I-E CRISPR-Cas system against natural transformation of E. coli We first documented that although the activated type I-E CRISPR-Cas system, due to hns deletion, interfered with CRISPR-Cas-targeted plasmid transfer, stpA inactivation restored the level of natural transformation. Second, we showed that inactivating stpA reduced the transcriptional activity of P _cas Third, by comparing transcriptional activities of the intact P _cas and the P _cas with a disrupted H-NS binding site in the hns and hns stpA null deletion mutants, we demonstrated that StpA activated transcription of cas genes by binding to the same site as H-NS in P _cas Fourth, by expressing StpA with an arabinose-inducible promoter, we confirmed that StpA expressed at a low level stimulated the activity of P _cas Finally, by quantifying the level of mature CRISPR RNA (crRNA), we demonstrated that StpA was able to promote the amount of crRNA. Taken together, our work establishes that StpA serves as a transcriptional activator in regulating the type I-E CRISPR-Cas system against natural transformation of E. coli IMPORTANCE StpA is normally considered a molecular backup of the nucleoid-structuring protein H-NS, which was reported as a transcriptional repressor of the type I-E CRISPR-Cas system in Escherichia coli However, the role of StpA in regulating the type I-E CRISPR-Cas system remains elusive. Our previous work uncovered a new route for double-stranded DNA (dsDNA) entry during natural transformation of E. coli In this study, we show that StpA plays a role opposite to that of its paralogue H-NS in regulating the type I-E CRISPR-Cas system against natural transformation of E. coli Our work not only expands our knowledge on CRISPR-Cas-mediated adaptive immunity against extracellular nucleic acids but also sheds new light on understanding the complex regulation mechanism of the CRISPR-Cas system. Moreover, the finding that paralogues StpA and H-NS share a DNA binding site but play opposite roles in transcriptional regulation indicates that higher-order compaction of bacterial chromatin by histone-like proteins could switch prokaryotic transcriptional modes.

Association of CRISPR/Cas System with the Drug Resistance in Klebsiella pneumoniae

BACKGROUND

Klebsiella pneumoniae is a common opportunistic pathogen and its production of extended-spectrum β-lactamases (ESBL) and carbapenemases leads to drug resistance. Clustered regularly interspaced short palindromic repeats (CRISPRs) and their associated genes (Cas) are widespread in the genome of many bacteria and are a defense mechanism against foreign invaders such as plasmids and viruses.

PURPOSE

To investigate the prevalence of the CRISPR/Cas system in wild type strains of K. pneumoniae in the hospital and its association with drug resistance.

MATERIALS AND METHODS

A total of 136 strains were collected and characterized their susceptibility to antimicrobial agents. The prevalence of CRISPR/Cas system was detected by PCR and DNA sequencing was analyzed by CRISPRFinder. The statistical analysis of the results was performed by SPSS.

RESULTS

We found that 50/136 (37%) isolates produced ESBL and 30/136 (22%) isolates were resistant to carbapenems. These isolates were liable to be multidrug resistant against β-lactams, quinolones, and aminoglycosides. Among the carbapenem-resistant isolates, blaKPC was the main drug resistance-associated gene and different types of ESBL and AmpC genes were present. Resistance to β-lactams, quinolones, aminoglycosides, tetracyclines, and β-lactams/enzyme inhibitor were higher in absence of the CRISPR/Cas system. Eighteen spacers within the CRISPR arrays matched with the genomes of plasmids or phages, some of which carried drug resistance genes.

CONCLUSION

ESBL-producing and carbapenem-resistant K. pneumoniae are more likely to develop multidrug resistance and show an inverse correlation between drug resistance and CRISPR/Cas system. Absence of CRISPR/Cas modules allow for the acquisition of external drug resistance genes.

Klebsiella pneumoniae Type VI Secretion System Contributes to Bacterial Competition, Cell Invasion, Type-1 Fimbriae Expression, and In Vivo Colonization

Background

We previously isolated a Klebsiella pneumoniae strain, NTUH-K2044, from a community-acquired pyogenic liver abscess (PLA) patient. Analysis of the NTUH-K2044 genome revealed that this strain harbors 2 putative type VI secretion system (T6SS)-encoding gene clusters.

Methods

The distribution of T6SS genes in the PLA and intestinal-colonizing K pneumoniae clinical isolates was examined. icmF1-, icmF2-, icmF1/icmF2-, and hcp-deficient K pneumoniae strains were constructed using an unmarked deletion method. The roles of T6SSs in antibacterial activity, type-1 fimbriae expression, cell adhesion, and invasion and intestinal colonization were determined.

Results

The prevalence of T6SSs is higher in the PLA strains than in the intestinal-colonizing strains (37 of 42 vs 54 of 130). Deletion of icmF1/icmF2 and hcp genes significantly reduced interbacterial and intrabacterial killing. Strain deleted for icmF1 and icmF2 exhibited decreased transcriptional expression of type-1 fimbriae and reduced adherence to and invasion of human colorectal epithelial cells and was attenuated for in vivo competition to enable colonization of the host gut. Finally, Hcp expression in K pneumoniae was silenced by the histone-like nucleoid structuring protein via direct binding.

Conclusions

These results provide new insights into T6SS-mediated bacterial competition and attachment in K pneumoniae and could facilitate the prevention of K pneumoniae infection.

Whole Genome Sequencing of Extended Spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae Isolated from Hospitalized Patients in KwaZulu-Natal, South Africa

Extended spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae remain a critical clinical concern worldwide. The aim of this study was to characterize ESBL-producing K. pneumoniae detected within and between two hospitals in uMgungundlovu district, South Africa, using whole genome sequencing (WGS). An observational period prevalence study on antibiotic-resistant ESKAPE (i.e. Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) bacteria was carried out in hospitalized patients during a two-month period in 2017. Rectal swabs and clinical specimens were collected from patients hospitalized and were screened for ESBL-producing, Gram-negative ESKAPE bacteria using cefotaxime-containing MacConkey agar and ESBL combination disk tests. Nine confirmed ESBL-K. pneumoniae isolated from six patients and two hospitals were whole genome sequenced using an Illumina MiSeq platform. Genome sequences were screened for presence of integrons, insertion sequences, plasmid replicons, CRISPR regions, resistance genes and virulence genes using different software tools. Of the 159 resistant Gram-negative isolates collected, 31 (19.50%) were ESBL-producers, of which, nine (29.03%) were ESBL-K. pneumoniae. The nine K. pneumoniae isolates harboured several β-lactamase genes, including bla_CTX-M-15, bla_TEM-1b, bla_SHV-1, bla_OXA-1 concomitantly with many other resistance genes e.g. acc(6')-lb-cr, aadAI6, oqxA and oqxB that confer resistance to aminoglycosides and/or fluoroquinolones, respectively. Three replicon plasmid types were detected in both clinical and carriage isolates, namely ColRNAI, IncFIB(K), IncF(II). Sequence type ST152 was confirmed in two patients (one carriage isolate detected on admission and one isolate implicated in infection) in one hospital. In contrast, ST983 was confirmed in a clinical and a carriage isolate of two patients in two different hospitals. Our data indicate introduction of ESBL-producing K. pneumoniae isolates into hospitals from the community. We also found evidence of nosocomial transmission within a hospital and transmission between different hospitals. The Clustered Regularly Interspaced Palindromic Repeats (CRISPR)-associated cas3 genes were further detected in two of the nine ESBL-KP isolates. This study showed that both district and tertiary hospital in uMgungundlovu District were reservoirs for several resistance determinants and highlighted the necessity to efficiently and routinely screen patients, particularly those receiving extensive antibiotic treatment and long-term hospitalization stay. It also reinforced the importance of infection, prevention and control measures to reduce the dissemination of antibiotic resistance within the hospital referral system in this district.

CRISPR-Cas Biology and Its Application to Infectious Diseases

Infectious diseases remain a global threat contributing to excess morbidity and death annually, with the persistent potential for destabilizing pandemics. Improved understanding of the pathogenesis of bacteria, viruses, fungi, and parasites, along with rapid diagnosis and treatment of human infections, is essential for improving infectious disease outcomes worldwide. Genomic loci in bacteria and archaea, termed clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) proteins, function as an adaptive immune system for prokaryotes, protecting them against foreign invaders. CRISPR-Cas9 technology is now routinely applied for efficient gene editing, contributing to advances in biomedical science. In the past decade, improved understanding of other diverse CRISPR-Cas systems has expanded CRISPR applications, including in the field of infectious diseases. In this review, we summarize the biology of CRISPR-Cas systems and discuss existing and emerging applications to evaluate mechanisms of host-pathogen interactions, to develop accurate and portable diagnostic tests, and to advance the prevention and treatment of infectious diseases.

Strategies to combat antimicrobial resistance: anti-plasmid and plasmid curing

Antimicrobial resistance (AMR) is a global problem hindering treatment of bacterial infections, rendering many aspects of modern medicine less effective. AMR genes (ARGs) are frequently located on plasmids, which are self-replicating elements of DNA. They are often transmissible between bacteria, and some have spread globally. Novel strategies to combat AMR are needed, and plasmid curing and anti-plasmid approaches could reduce ARG prevalence, and sensitise bacteria to antibiotics. We discuss the use of curing agents as laboratory tools including chemicals (e.g. detergents and intercalating agents), drugs used in medicine including ascorbic acid, psychotropic drugs (e.g. chlorpromazine), antibiotics (e.g. aminocoumarins, quinolones and rifampicin) and plant-derived compounds. Novel strategies are examined; these include conjugation inhibitors (e.g. TraE inhibitors, linoleic, oleic, 2-hexadecynoic and tanzawaic acids), systems designed around plasmid incompatibility, phages and CRISPR/Cas-based approaches. Currently, there is a general lack of in vivo curing options. This review highlights this important shortfall, which if filled could provide a promising mechanism to reduce ARG prevalence in humans and animals. Plasmid curing mechanisms which are not suitable for in vivo use could still prove important for reducing the global burden of AMR, as high levels of ARGs exist in the environment.

The CRISPR-Cas system in Enterobacteriaceae

In nature, microorganisms are constantly exposed to multiple viral infections and thus have developed many strategies to survive phage attack and invasion by foreign DNA. One of such strategies is the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated proteins (Cas) bacterial immunological system. This defense mechanism is widespread in prokaryotes including several families such as Enterobacteriaceae. Much knowledge about the CRISPR-Cas system has been generated, including its biological functions, transcriptional regulation, distribution, utility as a molecular marker and as a tool for specific genome editing. This review focuses on these aspects and describes the state of the art of the CRISPR-Cas system in the Enterobacteriaceae bacterial family.

Whole-Genome-Sequencing characterization of bloodstream infection-causing hypervirulent Klebsiella pneumoniae of capsular serotype K2 and ST374

Hypervirulent K. pneumoniae variants (hvKP) have been increasingly reported worldwide, causing metastasis of severe infections such as liver abscesses and bacteremia. The capsular serotype K2 hvKP strains show diverse multi-locus sequence types (MLSTs), but with limited genetics and virulence information. In this study, we report a hypermucoviscous K. pneumoniae strain, RJF293, isolated from a human bloodstream sample in a Chinese hospital. It caused a metastatic infection and fatal septic shock in a critical patient. The microbiological features and genetic background were investigated with multiple approaches. The Strain RJF293 was determined to be multilocis sequence type (ST) 374 and serotype K2, displayed a median lethal dose (LD50) of 1.5 × 10² CFU in BALB/c mice and was as virulent as the ST23 K1 serotype hvKP strain NTUH-K2044 in a mouse lethality assay. Whole genome sequencing revealed that the RJF293 genome codes for 32 putative virulence factors and exhibits a unique presence/absence pattern in comparison to the other 105 completely sequenced K. pneumoniae genomes. Whole genome SNP-based phylogenetic analysis revealed that strain RJF293 formed a single clade, distant from those containing either ST66 or ST86 hvKP. Compared to the other sequenced hvKP chromosomes, RJF293 contains several strain-variable regions, including one prophage, one ICEKp1 family integrative and conjugative element and six large genomic islands. The sequencing of the first complete genome of an ST374 K2 hvKP clinical strain should reinforce our understanding of the epidemiology and virulence mechanisms of this bloodstream infection-causing hvKP with clinical significance.

Population genomics of hypervirulent Klebsiella pneumoniae clonal-group 23 reveals early emergence and rapid global dissemination

Severe liver abscess infections caused by hypervirulent clonal-group CG23 Klebsiella pneumoniae have been increasingly reported since the mid-1980s. Strains typically possess several virulence factors including an integrative, conjugative element ICEKp encoding the siderophore yersiniabactin and genotoxin colibactin. Here we investigate CG23's evolutionary history, showing several deep-branching sublineages associated with distinct ICEKp acquisitions. Over 80% of liver abscess isolates belong to sublineage CG23-I, which emerged in ~1928 following acquisition of ICEKp10 (encoding yersiniabactin and colibactin), and then disseminated globally within the human population. CG23-I's distinguishing feature is the colibactin synthesis locus, which reportedly promotes gut colonisation and metastatic infection in murine models. These data show circulation of CG23 K. pneumoniae decades before the liver abscess epidemic was first recognised, and provide a framework for future epidemiological and experimental studies of hypervirulent K. pneumoniae. To support such studies we present an open access, completely sequenced CG23-I human liver abscess isolate, SGH10.

Clinical Antibiotic-resistant Acinetobacter baumannii Strains with Higher Susceptibility to Environmental Phages than Antibiotic-sensitive Strains

Antibiotic-resistant Acinetobacter baumannii is associated with nosocomial infections worldwide. Here, we used clinically isolated A. baumannii strains as models to demonstrate whether antibiotic resistance is correlated with an increased susceptibility to bacteriophages. In this study, 24 active phages capable of infecting A. baumannii were isolated from various environments, and the susceptibilities of both antibiotic-sensitive and antibiotic-resistant strains of A. baumannii to different phages were compared. In our study, a total of 403 clinically isolated A. baumannii strains were identified. On average, the phage infection percentage of the antibiotic-resistant A. baumannii strains was 84% (from 81–86%), whereas the infection percentage in the antibiotic-sensitive A. baumannii strains was only 56.5% (from 49–64%). In addition, the risk of phage infection for A. baumannii was significantly increased in the strains that were resistant to at least four antibiotics and exhibited a dose-dependent response (p-trend < 0.0001). Among all of the A. baumannii isolates, 75.6% were phage typeable. The results of phage typing might also reveal the antibiotic-resistant profiles of clinical A. baumannii strains. In conclusion, phage susceptibility represents an evolutionary trade-off in A. baumannii strains that show adaptations for antibiotic resistance, particularly in medical environments that have high antibiotic use.

Two T7-like Bacteriophages, K5-2 and K5-4, Each Encodes Two Capsule Depolymerases: Isolation and Functional Characterization

Two Klebsiella bacteriophages K5-2 and K5-4, which are able to infect and grow on either capsular types K30/K69 and K5 or K8 and K5 of Klebsiella strains, were isolated and characterized. Each phage contained two open reading frames (ORFs), which encoded two putative capsule depolymerases, respectively. The first ORF encoded tail fiber proteins, which have K30/K69 depolymerase and K8 depolymerase activities. The second ORF encoded hypothetical proteins, which are almost identical in amino acid sequences, and have K5 depolymerase activity. Alcian blue staining of enzyme-treated capsular polysaccharides (CPS) showed that purified depolymerases can cleave purified Klebsiella CPS in vitro and liberate monosaccharaides. Capsule K5 deletion mutants were not lysed by either phage, suggesting that the capsule was essential for phage infection. Bacterial killing was observed when incubated Klebsiella strains with phages but not with purified depolymerases. Treatment with the K5-4 phage significantly increased the survival of mice infected with a K. pneumoniae K5 strain. In conclusion, two dual host-specific Klebsiella phages and their tailspikes exhibit capsule depolymerase activity were characterized. Each phage and phage-encoded depolymerase has specificity for capsular type K30/K69, K8 or K5, and could be used for the typing and treatment of K. pneumoniae infection.

[Why so rare if so essentiel: the determinants of the sparse distribution of CRISPR-Cas systems in bacterial genomes]

CRISPR-Cas (Cluster of Regularly Interspaced Short Palindromic Repeats) systems confer bacteria and archaea an adaptative immunity against phages and other invading genetic elements playing an important role in bacterial evolution. However, despite the protection they generate and high rate of horizontal transfer, less than 50% of bacterial genomes harbor a CRISPR-Cas system. As a comparison, 90% of archaea encode a CRISPR-Cas system and a bacterial genome codes for two restriction modification systems on average. This review describes CRISPR-Cas systems distribution in bacterial genomes and then details the different hypotheses put forward to explain the relative scarcity of CRISPR-Cas systems. More specifically, phage escape mechanisms, ecological factors such as phage diversity and abundance and intrinsic costs, such as maintenance or autoimmunity, are discussed. Overall, a better understanding of the downsides of encoding CRISPR-Cas systems is essential to explain their evolutionary dynamics and their relative success in different environments and clades.