Bacteriophages (phages) are selective viral predators of bacteria. Abundant and ubiquitous in nature, phages can be used to treat bacterial infections (phage therapy), including refractory infections and those resistant to antibiotics. However, despite an abundance of anecdotal evidence of efficacy, significant hurdles remain before routine implementation of phage therapy into medical practice, including a dearth of robust clinical trial data. Phage–bacterium interactions are complex and diverse, characterized by co‐evolution trajectories that are significantly influenced by the environments in which they occur (mammalian body sites, water, soil, etc.). An understanding of the molecular mechanisms underpinning these dynamics is essential for successful clinical translation. This review aims to cover key aspects of bacterium–phage interactions that affect bacterial killing by describing the most relevant published literature and detailing the current knowledge gaps most likely to influence therapeutic success.

Enterohemorrhagic Escherichia coli (EHEC) strains are zoonotic pathogens responsible for a range of severe human disease. The repertoire of virulence determinants promoting EHEC disease is encoded on both the main chromosome and virulence plasmid. We examined a multiply antibiotic‐resistant O26 EHEC strain for carriage of resistance genes on the virulence plasmid. The EHEC virulence plasmid containing a complex antibiotic‐resistance gene locus, designated as pO26‐CRL, was purified from EHEC O26:H ⁻ (patient with hemorrhagic colitis) and subjected to shotgun‐sequencing and bioinformatic analysis. Determination of the 111,481‐bp sequence of pO26‐CRL revealed genes encoding a functional enterohemolysin operon ( ehxCABD ), STEC‐specific extracellular serine protease ( espP ), putative EHEC adhesin ( tooxB) _ļ catalase/peroxidase ( katP ), and myristoyl transferase ( msbB ) involved in lipid A synthesis. A 22,609‐bp Tn21 derivative is inserted within the conjugal transfer gene traC and encodes resistance to trimethoprim, streptomycin, sulfathiozole, kanamycin, neomycin, β‐lactams, and mercuric chloride. Plasmid pO26‐CRL is nonconjugative but is mobilizable. This is the first report of an EHEC virulence plasmid containing a complex antibiotic resistance locus, and raises the concern that antibiotic use will coselect for virulence determinants, leading to increased disease potential in both commensal and pathogenic E. coli populations.—Venturini, C., Beatson, S. A., Djordjevic, S. P., Walker, M. J. Multiple antibiotic resistance gene recruitment onto the enterohemorrhagic Escherichia coli virulence plasmid. FASEB J. 24, 1160–1166 (2010). www.fasebj.org

Enterohemorrhagic Escherichia coli (EHEC) and atypical enteropathogenic E. coli (aEPEC) are important zoonotic pathogens that increasingly are becoming resistant to multiple antibiotics. Here we describe two plasmids, pO26-CRL₁₂₅ (125 kb) from a human O26:H- EHEC, and pO111-CRL₁₁₅ (115kb) from a bovine O111 aEPEC, that impart resistance to ampicillin, kanamycin, neomycin, streptomycin, sulfathiazole, trimethoprim and tetracycline and both contain atypical class 1 integrons with an identical IS26-mediated deletion in their 3´-conserved segment. Complete sequence analysis showed that pO26-CRL₁₂₅ and pO111-CRL₁₁₅ are essentially identical except for a 9.7 kb fragment, present in the backbone of pO26-CRL₁₂₅ but absent in pO111-CRL₁₁₅, and several indels. The 9.7 kb fragment encodes IncI-associated genes involved in plasmid stability during conjugation, a putative transposase gene and three imperfect repeats. Contiguous sequence identical to regions within these pO26-CRL₁₂₅ imperfect repeats was identified in pO111-CRL₁₁₅ precisely where the 9.7 kb fragment is missing, suggesting it may be mobile. Sequences shared between the plasmids include a complete IncZ replicon, a unique toxin/antitoxin system, IncI stability and maintenance genes, a novel putative serine protease autotransporter, and an IncI1 transfer system including a unique shufflon. Both plasmids carry a derivate Tn21 transposon with an atypical class 1 integron comprising a dfrA5 gene cassette encoding resistance to trimethoprim, and 24 bp of the 3´-conserved segment followed by Tn6026, which encodes resistance to ampicillin, kanymycin, neomycin, streptomycin and sulfathiazole. The Tn21-derivative transposon is linked to a truncated Tn1721, encoding resistance to tetracycline, via a region containing the IncP-1α oriV. Absence of the 5 bp direct repeats flanking Tn3-family transposons, indicates that homologous recombination events played a key role in the formation of this complex antibiotic resistance gene locus. Comparative sequence analysis of these closely related plasmids reveals aspects of plasmid evolution in pathogenic E. coli from different hosts.

The group A Streptococcus (GAS) M1T1 clone emerged in the 1980s as a leading cause of epidemic invasive infections worldwide, including necrotizing fasciitis and toxic shock syndrome^1,2,3. Horizontal transfer of mobile genetic elements has played a central role in the evolution of the M1T1 clone^4,5, with bacteriophage-encoded determinants DNase Sda1⁶ and superantigen SpeA2⁷ contributing to enhanced virulence and colonization respectively. Outbreaks of scarlet fever in Hong Kong and China in 2011, caused primarily by emm12 GAS^8,9,10, led to our investigation of the next most common cause of scarlet fever, emm1 GAS^8,9. Genomic analysis of 18 emm1 isolates from Hong Kong and 16 emm1 isolates from mainland China revealed the presence of mobile genetic elements associated with the expansion of emm12 scarlet fever clones^10,11 in the M1T1 genomic background. These mobile genetic elements confer expression of superantigens SSA and SpeC and resistance to tetracycline, erythromycin and clindamycin. Horizontal transfer of mobile DNA conferring multi-drug resistance and expression of a new superantigen repertoire in the M1T1 clone should trigger heightened public health awareness for the global dissemination of these genetic elements.

Between June and November 2010, a concerning rise in the number of cases of puerperal sepsis, a postpartum pelvic bacterial infection contracted by women after childbirth, was observed in the New South Wales, Australia, hospital system. Group A streptococcus (GAS; Streptococcus pyogenes ) isolates PS001 to PS011 were recovered from nine patients. Pulsed-field gel electrophoresis and emm sequence typing revealed that GAS of emm1.40 , emm75.0 , emm77.0 , emm89.0 , and emm89.9 were each recovered from a single patient, ruling out a single source of infection. However, emm28.8 GAS were recovered from four different patients. To investigate the relatedness of these emm28 isolates, whole-genome sequencing was undertaken and the genome sequences were compared to the genome sequence of the emm28.4 reference strain, MGAS6180. A total of 186 single nucleotide polymorphisms were identified, for which the phylogenetic reconstruction indicated an outbreak of a polyclonal nature. While two isolates collected from different hospitals were not closely related, isolates from two puerperal sepsis patients from the same hospital were indistinguishable, suggesting patient-to-patient transmission or infection from a common source. The results of this study indicate that traditional typing protocols, such as pulsed-field gel electrophoresis, may not be sensitive enough to allow fine epidemiological discrimination of closely related bacterial isolates. Whole-genome sequencing presents a valid alternative that allows accurate fine-scale epidemiological investigation of bacterial infectious disease.