A fluoroquinolone induces a novel mitogen-encoding bacteriophage in Streptococcus canis

Evaluation of conjunctival graft procedures and factors that lead to graft complications in canine cases

PURPOSE

To describe the complications of conjunctival graft surgery occurring in cases at a referral ophthalmic service and evaluate factors that lead to occurrence of complications in canine cases.

METHODS

A retrospective case-control study was completed using data from the Veterinary Medical Center at the Western College of Veterinary Medicine, Saskatoon, Canada, between May 2015 and March 2020. Case records from dogs that underwent conjunctival pedicle graft surgery and subsequently either did or did not develop a conjunctival graft complication were reviewed.

RESULTS

One hundred and six dogs undergoing conjunctival graft surgeries were identified. Sixteen conjunctival graft complications occurred, of which, eight led to negative outcomes. Univariable analysis comparing canine eyes that developed complications to control eyes revealed potential (p ≤ .05) differences between the groups in post-operative fluoroquinolone use, Streptococcus canis isolation, intraoperative intravenous cefazolin use, corneal stromal white cell infiltrate, and mean ulcer diameter. The use of intraoperative cefazolin could not be effectively evaluated with available data; however, no dogs (n = 22) receiving intraoperative cefazolin developed complications. Multivariable analysis revealed that dogs that were treated with a second-generation fluoroquinolone and that had S. canis isolated had higher odds of experiencing complications than dogs that were not treated with a second-generation fluoroquinolone and that were S. canis negative (Odds ratio = 64.7 [95% CI 6.3-669], p < .0001).

CONCLUSIONS

Streptococcus species played a role in conjunctival graft complications in our study. Empiric selection of second-generation fluoroquinolone monotherapy may need reconsideration given the frequent isolation of Streptococcus spp. from canine ulcers. The use of intraoperative cefazolin may be associated with a lower complication rate.

Retrospective case series: Necrotising fasciitis in 23 dogs

BACKGROUND

Necrotising fasciitis (NF) is a rare, rapidly progressive subcutaneous bacterial infection. Few studies have characterised NF in dogs.

HYPOTHESIS/OBJECTIVES

To retrospectively describe clinical and laboratory findings, with treatments and outcomes, in dogs with NF.

ANIMALS

Twenty-three client-owned dogs treated at a veterinary teaching hospital between 1998 and 2021.

MATERIALS AND METHODS

Medical records and laboratory data from 23 dogs diagnosed with NF were reviewed.

RESULTS

Male dogs were significantly over-represented (p = 0.003). The most common presenting complaint was sudden lameness. Infection occurred in one or two limbs in 19 of 23 dogs, with right hindlimbs most often affected (13 of 23). Pitting oedema was evident in 14 of 23 dogs. Antibiotic and nonsteroidal anti-inflammatory drugs were administered before presentation in nine and 13 of 23 dogs, respectively. Common clinicopathological abnormalities included hypoalbuminemia, hyponatremia, elevated liver enzymes, elevated creatine kinase, increased bands and lymphopenia. Streptococcus canis was isolated from 18 of 23 dogs. Histopathological features included acute necrosis and severe neutrophilic inflammation. Fifteen dogs were euthanised or died, while surgical intervention led to survival in eight of 23 dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Dogs presenting for acute swelling of a limb with oedema should have the diagnosis of NF considered and early surgical intervention might increase survival.

Treatment of moderate grade dog bite wounds using amoxicillin-clavulanic acid with and without enrofloxacin: a randomised non-inferiority trial

BACKGROUND

Dog-to-dog bite wounds are a common veterinary emergency presentation: despite this, there is insufficient information to guide veterinarians on appropriate empirical antimicrobial management.

OBJECTIVES

Investigate the effectiveness of amoxicillin-clavulanic acid with and without enrofloxacin in the treatment of moderate grade dog bite wounds (DBW). To describe common pathogens and their antimicrobial susceptibility patterns.

MATERIALS AND METHODS

In a single-centre parallel group pragmatic trial, 50 dogs presenting with moderate grade DBW were prospectively randomised to receive amoxicillin-clavulanic acid (group A) or amoxicillin-clavulanic acid and enrofloxacin (group B). Swabs were taken for culture and susceptibility testing at admission. Stabilisation, wound care and surgical debridement were performed at the discretion of admitting clinicians. The primary outcome was complication due to infection at 10 days, with Bayesian inference used to estimate the difference in proportions between treatment groups.

RESULTS

Of the 24 dogs in treatment group A, 1 required the addition of enrofloxacin at re-examination. None of the 26 dogs in group B required alteration of antimicrobial coverage. The difference in complication rate due to infection between treatment groups was 4.2%. Twenty-one different organisms were identified: Staphylococcus pseudintermedius, Neisseria spp., Pasteurella multocida and P. canis were the most common. Over 90% of gram-negative and gram-positive isolates were susceptible to amoxicillin-clavulanic acid. Ninety-six percent of gram-negative and 86% of gram-positive isolates were susceptible to enrofloxacin.

CONCLUSION AND CLINICAL SIGNIFICANCE

Amoxicillin-clavulanic acid is an appropriate empirical antimicrobial choice for moderate DBW in South East Queensland. Reduced empirical enrofloxacin use will promote antimicrobial stewardship and potentially antimicrobial resistance.

Novel Models of Streptococcus canis Colonization and Disease Reveal Modest Contributions of M-Like (SCM) Protein

Streptococcus canis is a common colonizing bacterium of the urogenital tract of cats and dogs that can also cause invasive disease in these animal populations and in humans. Although the virulence mechanisms of S. canis are not well-characterized, an M-like protein, SCM, has recently identified been as a potential virulence factor. SCM is a surface-associated protein that binds to host plasminogen and IgGs suggesting its possible importance in host-pathogen interactions. In this study, we developed in vitro and ex vivo blood component models and murine models of S. canis vaginal colonization, systemic infection, and dermal infection to compare the virulence potential of the zoonotic S. canis vaginal isolate G361 and its isogenic SCM-deficient mutant (G361∆scm). We found that while S. canis establishes vaginal colonization and causes invasive disease in vivo, the contribution of the SCM protein to virulence phenotypes in these models is modest. We conclude that SCM is dispensable for invasive disease in murine models and for resistance to human blood components ex vivo, but may contribute to mucosal persistence, highlighting a potential contribution to the recently appreciated genetic diversity of SCM across strains and hosts.

Cryptic prophages within a Streptococcus pyogenes genotype emm4 lineage

The major human pathogen Streptococcus pyogenes shares an intimate evolutionary history with mobile genetic elements, which in many cases carry genes encoding bacterial virulence factors. During recent whole-genome sequencing of a longitudinal sample of S. pyogenes isolates in England, we identified a lineage within emm4 that clustered with the reference genome MEW427. Like MEW427, this lineage was characterized by substantial gene loss within all three prophage regions, compared to MGAS10750 and isolates outside of the MEW427-like lineage. Gene loss primarily affected lysogeny, replicative and regulatory modules, and to a lesser and more variable extent, structural genes. Importantly, prophage-encoded superantigen and DNase genes were retained in all isolates. In isolates where the prophage elements were complete, like MGAS10750, they could be induced experimentally, but not in MEW427-like isolates with degraded prophages. We also found gene loss within the chromosomal island SpyCIM4 of MEW427-like isolates, although surprisingly, the SpyCIM4 element could not be experimentally induced in either MGAS10750-like or MEW427-like isolates. This did not, however, appear to abolish expression of the mismatch repair operon, within which this element resides. The inclusion of further emm4 genomes in our analyses ratified our observations and revealed an international emm4 lineage characterized by prophage degradation. Intriguingly, the USA population of emm4 S. pyogenes appeared to constitute predominantly MEW427-like isolates, whereas the UK population comprised both MEW427-like and MGAS10750-like isolates. The degraded and cryptic nature of these elements may have important phenotypic and fitness ramifications for emm4 S. pyogenes, and the geographical distribution of this lineage raises interesting questions on the population dynamics of the genotype.

The disparate effects of bacteriophages on antibiotic-resistant bacteria

Faced with the crisis of multidrug-resistant bacteria, bacteriophages, viruses that infect and replicate within bacteria, have been reported to have both beneficial and detrimental effects with respect to disease management. Bacteriophages (phages) have important ecological and evolutionary impacts on their bacterial hosts and have been associated with therapeutic use to kill bacterial pathogens, but can lead to the transmission of antibiotic resistance. Although the process known as transduction has been reported for many bacterial species by classic and modern genetic approaches, its contribution to the spread of antibiotic resistance in nature remains unclear. In addition, detailed molecular studies have identified phages residing in bacterial genomes, revealing unexpected interactions between phages and their bacterial hosts. Importantly, antibiotics can induce the production of phages and phage-encoded products, disseminating these viruses and virulence-related genes, which have dangerous consequences for disease severity. These unwanted side-effects of antibiotics cast doubt on the suitability of some antimicrobial treatments and may require new strategies to prevent and limit the selection for virulence. Foremost among these treatments is phage therapy, which could be used to treat many bacterial infectious diseases and confront the pressing problem of antibiotic resistance in pathogenic bacteria. This review discusses the interactions between bacteriophages, antibiotics, and bacteria and provides an integrated perspective that aims to inspire the development of successful antibacterial therapies.

Induction of prophages by fluoroquinolones in Streptococcus pneumoniae: implications for emergence of resistance in genetically-related clones

Antibiotic resistance in Streptococcus pneumoniae has increased worldwide by the spread of a few clones. Fluoroquinolone resistance occurs mainly by alteration of their intracellular targets, the type II DNA topoisomerases, which is acquired either by point mutation or by recombination. Increase in fluoroquinolone-resistance may depend on the balance between antibiotic consumption and the cost that resistance imposes to bacterial fitness. In addition, pneumococcal prophages could play an important role. Prophage induction by fluoroquinolones was confirmed in 4 clinical isolates by using Southern blot hybridization. Clinical isolates (105 fluoroquinolone-resistant and 160 fluoroquinolone-susceptible) were tested for lysogeny by using a PCR assay and functional prophage carriage was studied by mitomycin C induction. Fluoroquinolone-resistant strains harbored fewer inducible prophages (17/43) than fluoroquinolone-susceptible strains (49/70) (P = 0.0018). In addition, isolates of clones associated with fluoroquinolone resistance [CC156 (3/25); CC63 (2/20), and CC81 (1/19)], had lower frequency of functional prophages than isolates of clones with low incidence of fluoroquinolone resistance [CC30 (4/21), CC230 (5/20), CC62 (9/21), and CC180 (21/30)]. Likewise, persistent strains from patients with chronic respiratory diseases subjected to fluoroquinolone treatment had a low frequency of inducible prophages (1/11). Development of ciprofloxacin resistance was tested with two isogenic strains, one lysogenic and the other non-lysogenic: emergence of resistance was only observed in the non-lysogenic strain. These results are compatible with the lysis of lysogenic isolates receiving fluoroquinolones before the development of resistance and explain the inverse relation between presence of inducible prophages and fluoroquinolone-resistance.

Importance of prophages to evolution and virulence of bacterial pathogens

Bacteriophages, or simply phages, are viruses infecting bacteria. With an estimated 10³¹ particles in the biosphere, phages outnumber bacteria by a factor of at least 10 and not surprisingly, they influence the evolution of most bacterial species, sometimes in unexpected ways. “Temperate” phages have the ability to integrate into the chromosome of their host upon infection, where they can reside as “quiescent” prophages until conditions favor their reactivation. Lysogenic conversion resulting from the integration of prophages encoding powerful toxins is probably the most determinant contribution of prophages to the evolution of pathogenic bacteria. We currently grasp only a small fraction of the total phage diversity. Phage biologists keep unraveling novel mechanisms developed by phages to parasitize their host. The purpose of this review is to give an overview of some of the various ways by which prophages change the lifestyle and boost virulence of some of the most dangerous bacterial pathogens.

Relevance in pathogenesis research

Research on pathogenesis of bacterial diseases involves exploration of the intricate and complex interactions among pathogen, host, and environment. Host-parasite-environment interactions that were relatively simple were the first to be understood. They include intoxications in which ingestion of a powerful bacterial toxin was sufficient to cause disease. In more complex cases bacteria occupy a variety of niches in the host and attack at an opportune time. Some bacterial pathogens have a brief encounter with the host; others are long-term guests. This variety of relationships involves a wide range of strategies for survival and transmission of bacterial pathogens. Molecular genetics, genomics and proteomics have facilitated understanding of the pathogens and hosts. Massive information often results from such studies and determining the relevance of the data is frequently a challenge. In vitro studies often attempt to simulate one or two critical aspects of the environment, such as temperature, pH, and iron concentration, that may provide clues as to what goes on in the host. These studies sometimes identify critical bacterial virulence factors but regulation of bacterial virulence and host response is complex and often not well understood. Pathogenesis is a process of continuous change in which timing and degree of gene expression are critical and are highly regulated by the environment. It is impossible to get the full picture without the use of natural or experimental infections, although experimental infections involve ethical and economic considerations which may act as a deterrent.

Successful treatment of necrotizing fasciitis in the hind limb of a great dane

A 5-month-old, intact female Great Dane was presented for an acute onset of rapidly progressive lameness, severe pain, and diffuse swelling of the right hind limb. Ultrasound evaluation revealed echogenic fluid pockets extending along fascial planes of the right hind limb, from the proximal femur to the hock. Necrotic soft tissues were debrided, and closed-suction drains were placed. No foreign material was identified at surgery. Fluid culture identified a beta-hemolytic Streptococcus sp., and affected fascial histopathology was consistent with necrotizing fasciitis. Postoperatively, the puppy was managed with intravenous broad-spectrum antibiotics, local infusions of amikacin, and daily physical rehabilitation. Oral pentoxifylline was administered to treat bronchopneumonia and streptococcal toxic shock syndrome that developed secondary to necrotizing fasciitis. To our knowledge, this is the first report of a successfully managed case of beta-hemolytic, streptococcal, necrotizing fasciitis successfully managed after a single surgical debridement in combination with systemic broad-spectrum antibiotics, local amikacin infusion, active closed-suction drainage, daily cytology, massage, and passive range-of-motion exercises to maintain limb function.

Comparative genomic analysis of ten Streptococcus pneumoniae temperate bacteriophages

Streptococcus pneumoniae is an important human pathogen that often carries temperate bacteriophages. As part of a program to characterize the genetic makeup of prophages associated with clinical strains and to assess the potential roles that they play in the biology and pathogenesis in their host, we performed comparative genomic analysis of 10 temperate pneumococcal phages. All of the genomes are organized into five major gene clusters: lysogeny, replication, packaging, morphogenesis, and lysis clusters. All of the phage particles observed showed a Siphoviridae morphology. The only genes that are well conserved in all the genomes studied are those involved in the integration and the lysis of the host in addition to two genes, of unknown function, within the replication module. We observed that a high percentage of the open reading frames contained no similarities to any sequences catalogued in public databases; however, genes that were homologous to known phage virulence genes, including the pblB gene of Streptococcus mitis and the vapE gene of Dichelobacter nodosus, were also identified. Interestingly, bioinformatic tools showed the presence of a toxin-antitoxin system in the phage phiSpn_6, and this represents the first time that an addition system in a pneumophage has been identified. Collectively, the temperate pneumophages contain a diverse set of genes with various levels of similarity among them.

Staphylococcus pseudintermedius necrotizing fasciitis in a dog

Staphylococcus pseudintermedius was implicated as the cause of rapidly progressive and fatal necrotizing fasciitis in a dog. The isolate was methicillin-susceptible and did not contain genes encoding the Panton-Valentine leukocidin. While Streptococcus canis is typically considered to be the main cause of necrotizing fasciitis in dogs, staphylococci should also be considered.

Antimicrobial resistance in companion animals

Antimicrobial resistance (AMR) is an emerging problem in companion animals, because of difficult-to-treat infections, possible pressure to use antimicrobials that are important in human medicine, and potential zoonotic transmission. The extent and importance of AMR in companion animals are poorly understood, in part because of limited surveillance; however, it is clear that resistance is problematic in many pathogens and commensals, including staphylococci, enterococci, Escherichia coli and Salmonella.

Group G streptococcal toxic shock-like syndrome in three cats

Three 8-week-old kittens were presented with a history of acute, generalized weakness and severe fever. One cat was dead upon presentation, and necropsy findings were supportive of a group G Streptococcus spp. septicemia. During their clinical courses, two of the three kittens developed a progressive, marked swelling of one or more limbs. One moribund and severely hypothermic cat was euthanized a few hours after presentation, and necropsy was also supportive of a group G Streptococcus spp. septicemia. One kitten recovered. Group G streptococcal toxic shock-like syndrome was suspected because of the fulminant progression of the septicemia.

Efficacy of orbifloxacin tablets for the treatment of superficial and deep pyoderma due to Staphylococcus intermedius infection in dogs

Orbifloxacin tablets were administered orally to 23 dogs with superficial and/or deep staphylococcal pyoderma. Response to therapy was excellent in 95.6% of the dogs. Duration of therapy varied from 21 to 40 days (average 29 days) for dogs having only superficial infections, and from 25 to 150 days (average 72 days) for dogs having deep infections. Relapses occurred in 18% of the dogs within a 3-month period. One dog developed a presumed adverse cutaneous drug reaction. Under the conditions of this study, orbifloxacin was an effective, safe, and convenient antibiotic for the treatment of superficial and deep staphylococcal pyoderma in dogs.

Principles of Antimicrobial Therapy

The most compelling reason for practicing judicious antimicrobial use is to facilitate therapeutic success. The definition of therapeutic success has changed in recent years, however; not only does success include eradication of infection, but it must now include avoidance of resistance. If the goal of antimicrobial therapy is to achieve sufficient concentrations at the site of infection such that the infecting organism is killed, therapy should be successful.

Phage Therapy - Everything Old is New Again

The study of bacterial viruses (bacteriophages or phages) proved pivotal in the nascence of the disciplines of molecular biology and microbial genetics, providing important information on the central processes of the bacterial cell (DNA replication, transcription and translation) and on how DNA can be transferred from one cell to another. As a result of the pioneering genetics studies and modern genomics, it is now known that phages have contributed to the evolution of the microbial cell and to its pathogenic potential. Because of their ability to transmit genes, phages have been exploited to develop cloning vector systems. They also provide a plethora of enzymes for the modern molecular biologist. Until the introduction of antibiotics, phages were used to treat bacterial infections (with variable success). Western science is now having to re-evaluate the application of phage therapy - a therapeutic modality that never went out of vogue in Eastern Europe - because of the emergence of an alarming number of antibiotic-resistant bacteria. The present article introduces the reader to phage biology, and the benefits and pitfalls of phage therapy in humans and animals.

Necrotizing Fasciitis: A Review

Necrotizing fasciitis is a rapidly spreading, bacterial, soft-tissue infection reported in both humans and dogs. A review of the pathophysiology, clinical findings, diagnosis, and treatment of necrotizing fasciitis is presented, with the goal of familiarizing veterinarians with this uncommon but potentially fatal condition. A case report highlighting the fulminant course of this disease is also included.

Recent trends on the molecular biology of pneumococcal capsules, lytic enzymes, and bacteriophage

Streptococcus pneumoniae has re-emerged as a major cause of morbidity and mortality throughout the world and its continuous increase in antimicrobial resistance is rapidly becoming a leading cause of concern for public health. This review is focussed on the analysis of recent insights on the study of capsular polysaccharide biosynthesis, and cell wall (murein) hydrolases, two fundamental pneumococcal virulence factors. Besides, we have also re-evaluated the molecular biology of the pneumococcal phage, their possible role in pathogenicity and in the shaping of natural populations of S. pneumoniae. Precise knowledge of the topics reviewed here should facilitate the rationale to move towards the design of alternative ways to combat pneumococcal disease.

Phages and the evolution of bacterial pathogens: from genomic rearrangements to lysogenic conversion

Comparative genomics demonstrated that the chromosomes from bacteria and their viruses (bacteriophages) are coevolving. This process is most evident for bacterial pathogens where the majority contain prophages or phage remnants integrated into the bacterial DNA. Many prophages from bacterial pathogens encode virulence factors. Two situations can be distinguished: Vibrio cholerae, Shiga toxin-producing Escherichia coli, Corynebacterium diphtheriae, and Clostridium botulinum depend on a specific prophage-encoded toxin for causing a specific disease, whereas Staphylococcus aureus, Streptococcus pyogenes, and Salmonella enterica serovar Typhimurium harbor a multitude of prophages and each phage-encoded virulence or fitness factor makes an incremental contribution to the fitness of the lysogen. These prophages behave like "swarms" of related prophages. Prophage diversification seems to be fueled by the frequent transfer of phage material by recombination with superinfecting phages, resident prophages, or occasional acquisition of other mobile DNA elements or bacterial chromosomal genes. Prophages also contribute to the diversification of the bacterial genome architecture. In many cases, they actually represent a large fraction of the strain-specific DNA sequences. In addition, they can serve as anchoring points for genome inversions. The current review presents the available genomics and biological data on prophages from bacterial pathogens in an evolutionary framework.

Genomic organization and molecular analysis of the inducible prophage EJ-1, a mosaic myovirus from an atypical pneumococcus

We report the complete genomic sequence of EJ-1, an inducible prophage isolated from an atypical Streptococcus pneumoniae strain that belongs to the Myoviridae morphology family. The phage and bacterial recombinational sites (attachment sites) have been also determined. The genome of the EJ-1 prophage (42935 bp) is organized in 73 open reading frames (ORFs) and in at least five major clusters. Bioinformatic and N-terminal amino acid sequence analyses enabled the assignment of possible functions to 52 ORFs. The predicted proteins coded for the EJ-1 genome revealed similarities in the lysogeny, DNA replication, regulation, packaging, and head morphogenesis protein clusters with those from several siphoviruses infecting lactic acid bacteria. However, the proteins encoded by genes orf53 to orf64, corresponding to putative tail proteins of the virion, were very similar to those of the defective Bacillus subtilis myovirus PBSX with the notable exception of the gene product of orf56 (the tape measure tail protein) that was similar to proteins from phages infecting Gram-negative bacteria. The first description of the genome of a myovirus infecting a low G + C content Gram-positive bacterium, a member of a group embracing important human pathogens and industrial relevant species, will contribute to expand our current knowledge on phage biology and evolution.

Prophage induction and expression of prophage-encoded virulence factors in group A Streptococcus serotype M3 strain MGAS315

The genome of the highly virulent group A Streptococcus (GAS) serotype M3 strain MGAS315 has six prophages that encode six proven or putative virulence factors. We examined prophage induction and expression of prophage-encoded virulence factors by this strain under in vitro conditions inferred to approximate in vivo conditions. Coculture of strain MGAS315 with Detroit 562 (D562) human epithelial pharyngeal cells induced the prophage encoding streptococcal pyrogenic exotoxin K (SpeK) and extracellular phospholipase A(2) (Sla) and the prophage encoding streptodornase (Sdn). Increased gene copy numbers after induction correlated with increased speK, sla, and sdn transcript levels. Although speK and sla are located contiguously in prophage Phi315.4, these genes were transcribed independently. Whereas production of immunoreactive SpeK was either absent or minimal during coculture of GAS with D562 cells, production of immunoreactive Sla increased substantially. In contrast, despite a lack of induction of the prophage encoding speA during coculture of GAS with D562 cells, the speA transcript level and production of immunoreactive streptococcal pyrogenic exotoxin A (SpeA) increased. Exposure of strain MGAS315 to hydrogen peroxide, an oxidative stressor, induced the prophage encoding mitogenic factor 4 (MF4), and there was a concomitant increase in the mf4 transcript. All prophages of strain MGAS315 that encode virulence factors were induced during culture with mitomycin C, a DNA-damaging agent. However, the virulence factor gene transcript levels and production of the encoded proteins decreased after mitomycin C treatment. Taken together, the results indicate that a complex relationship exists among environmental culture conditions, prophage induction, and production of prophage-encoded virulence factors.