Emerging Phage Resistance in Pseudomonas aeruginosa PAO1 Is Accompanied by an Enhanced Heterogeneity and Reduced Virulence

Bacterial surface structures of a proteinic nature and glycoconjugates contribute to biofilm formation and provide shields to host defense mechanisms (e.g., the complement system and phagocytosis). A loss or alteration of these molecules, leading to phage resistance, could result in fewer virulent bacteria. In this study, we evaluate the biology and phenotype changes in Pseudomonas aeruginosa PAO1 phage-resistant clones, which emerge in phage-treated biofilms. We characterize these clones for phage-typing patterns, antibiotic resistance, biofilm formation, pathogenicity, and interactions with the innate immune system. Another important question that we address is whether phage-resistant mutants are also generated incidentally, despite the phage treatment-selective pressure, as the natural adaptation of the living biofilm population. It is found that the application of different phages targeting a particular receptor selects similar phage resistance patterns. Nevertheless, this results in a dramatic increase in the population heterogeneity, giving over a dozen phage-typing patterns, compared to one of the untreated PAO1 sessile forms. We also confirm the hypothesis that “phage-resistant bacteria are more susceptible to antibiotics and host-clearance mechanisms by the immune system”. These findings support phage application in therapy, although the overall statement that phage treatment selects the less virulent bacterial population should be further verified using a bigger collection of clinical strains.

Characterisation of Phage Susceptibility Variation in Salmonellaenterica Serovar Typhimurium DT104 and DT104b

The surge in mortality and morbidity rates caused by multidrug-resistant (MDR) bacteria prompted a renewal of interest in bacteriophages (phages) as clinical therapeutics and natural biocontrol agents. Nevertheless, bacteria and phages are continually under the pressure of the evolutionary phage–host arms race for survival, which is mediated by co-evolving resistance mechanisms. In Anderson phage typing scheme of Salmonella Typhimurium, the epidemiologically related definitive phage types, DT104 and DT104b, display significantly different phage susceptibility profiles. This study aimed to characterise phage resistance mechanisms and genomic differences that may be responsible for the divergent phage reaction patterns in S. Typhimurium DT104 and DT104b using whole genome sequencing (WGS). The analysis of intact prophages, restriction–modification systems (RMS), plasmids and clustered regularly interspaced short palindromic repeats (CRISPRs), as well as CRISPR-associated proteins, revealed no unique genetic determinants that might explain the variation in phage susceptibility among the two phage types. Moreover, analysis of genes coding for potential phage receptors revealed no differences among DT104 and DT104b strains. However, the findings propose the need for experimental assessment of phage-specific receptors on the bacterial cell surface and analysis of bacterial transcriptome using RNA sequencing which will explain the differences in bacterial susceptibility to phages. Using Anderson phage typing scheme of Salmonella Typhimurium for the study of bacteria-phage interaction will help improving our understanding of host–phage interactions which will ultimately lead to the development of phage-based technologies, enabling effective infection control.

Phenotypic Pattern of Vibrio choleraeIsolates from a Tertiary Care Hospital in Vadodara, Gujarat, India

Introduction: Cholera is an acute diarrhoeal disease caused by Vibrio cholerae (V.cholerae). Based on antigenic differences of O antigen, O1 serogroup can be divided into three serotypes. In addition, by performing various biochemical reactions, O1 Serogroup can be differentiated into two biotypes. Outbreaks of Cholera occur seasonally. It is associated with monsoon season, warm temperature, heavy rainfall and increased plankton population. Aim: The aim was to determine the trends in resistance pattern and phenotypic Pattern of Vibrio cholerae. Materials and Methods: A retrospective study was conducted during the period from June 2019-December 2019. Culture of Stool specimens were done on different agar media. Biotyping was done by conventional methods. Serotyping and phage typing was also done along with the Antibiotic susceptibility testing. Descriptive analysis was used and presented in terms of percentage. Results:V.cholerae was isolated in 72 patients and they belonged to serogroup O1 and biotype El Tor. The most common serotype was Ogawa. The predominant phage type were T2 by old scheme and T27 by new scheme of phage typing. The maximum number of V. cholerae isolates was seen in the month of November, 2019 followed by October, 2019. Conclusion: The phenotypic pattern and fluctuating seasonal trend of V. cholerae and antimicrobial resistance encourage the continued epidemiological and microbiological surveillance of the disease.

The forgotten typers: The rise and fall of Weimar bacteriophage-typing (1921–1935)

Using bacteriophages to type (identify) bacteria was one of the most important tools of twentieth-century epidemiology. Challenging existing accounts’ focus on Anglophone research, this paper shows that modern phage-typing arose in German-speaking continental laboratories from 1921 onwards. Several factors contributed to this rise: the limitations of existing phenotypic systems; demobilized German bacteriologists’ interwar engagement with phages as a means to explore bacterial type variation; the existence of well-stocked and well-defined microbial culture collections with a strong focus on typhoid and paratyphoid; the standardization, free provision and calibration of phage diagnostic systems by a centralized laboratory network; and phage-typers’ implicit agreement to black-box ontological controversies about phages' nature in favour of a mission-oriented focus on practical epidemiological applications. The result was an experimental system that simultaneously treated phages as technical objects and epistemic things. Although the human network supporting phage-typing collapsed after the Nazi rise to power, Weimar-era phage researchers laid the foundation for modern phage-based diagnostics and epidemiology.

Transposon Insertion Sequencing Elucidates Novel Gene Involvement in Susceptibility and Resistance to Phages T4 and T7 inEscherichia coliO157

ABSTRACTExperiments using bacteriophage (phage) to infect bacterial strains have helped define some basic genetic concepts in microbiology, but our understanding of the complexity of bacterium-phage interactions is still limited. As the global threat of antibiotic resistance continues to increase, phage therapy has reemerged as an attractive alternative or supplement to treating antibiotic-resistant bacterial infections. Further, the long-used method of phage typing to classify bacterial strains is being replaced by molecular genetic techniques. Thus, there is a growing need for a complete understanding of the precise molecular mechanisms underpinning phage-bacterium interactions to optimize phage therapy for the clinic as well as for retrospectively interpreting phage typing data on the molecular level. In this study, a genomics-based fitness assay (TraDIS) was used to identify all host genes involved in phage susceptibility and resistance for a T4 phage infecting Shiga-toxigenicEscherichia coliO157. The TraDIS results identified both established and previously unidentified genes involved in phage infection, and a subset were confirmed by site-directed mutagenesis and phenotypic testing of 14 T4 and 2 T7 phages. For the first time, the entiresapoperon was implicated in phage susceptibility and, conversely, the stringent starvation protein A gene (sspA) was shown to provide phage resistance. Identifying genes involved in phage infection and replication should facilitate the selection of bespoke phage combinations to target specific bacterial pathogens.IMPORTANCEAntibiotic resistance has diminished treatment options for many common bacterial infections. Phage therapy is an alternative option that was once popularly used across Europe to kill bacteria within humans. Phage therapy acts by using highly specific viruses (called phages) that infect and lyse certain bacterial species to treat the infection. Whole-genome sequencing has allowed modernization of the investigations into phage-bacterium interactions. Here, usingE. coliO157 and T4 bacteriophage as a model, we have exploited a genome-wide fitness assay to investigate all genes involved in defining phage resistance or susceptibility. This knowledge of the genetic determinants of phage resistance and susceptibility can be used to design bespoke phage combinations targeted to specific bacterial infections for successful infection eradication.