Streptococcus suis, an Emerging Drug-Resistant Animal and Human Pathogen

Streptococcus suis, a major porcine pathogen, has been receiving growing attention not only for its role in severe and increasingly reported infections in humans, but also for its involvement in drug resistance. Recent studies and the analysis of sequenced genomes have been providing important insights into the S. suis resistome, and have resulted in the identification of resistance determinants for tetracyclines, macrolides, aminoglycosides, chloramphenicol, antifolate drugs, streptothricin, and cadmium salts. Resistance gene-carrying genetic elements described so far include integrative and conjugative elements, transposons, genomic islands, phages, and chimeric elements. Some of these elements are similar to those reported in major streptococcal pathogens such as Streptococcus pyogenes, Streptococcus pneumoniae, and Streptococcus agalactiae and share the same chromosomal insertion sites. The available information strongly suggests that S. suis is an important antibiotic resistance reservoir that can contribute to the spread of resistance genes to the above-mentioned streptococci. S. suis is thus a paradigmatic example of possible intersections between animal and human resistomes

VanA type enterococci from humans, animals and food: species distribution, population structure, Tn1546-typing and location, and virulence determinants

VanA-type human (n = 69), animal (n = 49), and food (n =36) glycopeptide-resistant enterococci (GRE) from different geographic areas were investigated to study their possible reservoirs and transmission routes. Pulsed-field gel electrophoresis (PFGE) revealed two small genetically related clusters, M39 (n = 4) and M49 (n = 13), representing Enterococcus faecium isolates from animal and human feces and from clinical and fecal human samples. Multilocus sequence typing showed that both belonged to the epidemic lineage of CC17. purK allele analysis of 28 selected isolates revealed that type 1 was prevalent in human strains (8/11) and types 6 and 3 (14/15) were prevalent in poultry (animals and meat). One hundred and five of the 154 VanA GRE isolates, encompassing different species, origins, and PFGE types, were examined for Tn1546 type and location (plasmid or chromosome) and the incidence of virulence determinants. Hybridization of S1- and I-CeuI-digested total DNA revealed a plasmid location in 98% of the isolates. Human intestinal and animal E. faecium isolates bore large (>150 kb) vanA plasmids. Results of PCR-restriction fragment length polymorphism and sequencing showed the presence of prototype Tn1546 in 80% of strains and the G-to-T mutation at position 8234 in three human intestinal and two pork E. faecium isolates. There were no significant associations (P > 0.5) between Tn1546 type and GRE source or enterococcal species. Virulence determinants were detected in all reservoirs but were significantly more frequent (P < 0.02) among clinical strains. Multiple determinants were found in clinical and meat Enterococcus faecalis isolates. The presence of indistinguishable vanA elements (mostly plasmid borne) and virulence determinants in different species and PFGE-diverse populations in the presence of host-specific purK housekeeping genes suggested that all GRE might be potential reservoirs of resistance determinants and virulence traits transferable to human-adapted clusters

Attenuation of Listeria monocytogenes Virulence by Cannabis sativa L. Essential Oil

Anti-virulence strategies are being explored as a novel approach to combat pathogens. Such strategies include inhibition of surface adhesion, tissue invasion, toxin production, and/or interference with the gene regulation of other virulence traits. Listeria monocytogenes, the causative agent of listeriosis, is a facultative intracellular food pathogen characterized by a wide distribution in the environment. Its ability to persist within biofilms and to develop resistance to sanitizers is the cause of significant problems in food processing plants and of steep costs for the food industry. In humans, the treatment of listeriosis is hampered by the intracellular location of listeriae and the poor intracellular penetration of some antibiotics. Eleven L. monocytogenes isolates from patients who were diagnosed with invasive listeriosis in Italy in 2014–2016 were studied. This in vitro and in vivo study explored the antibacterial and anti-virulence properties of a steam-distilled essential oil of Cannabis sativa L., which is being intensively investigated for its high content in powerful bioactive phytochemicals. Susceptibility experiments demonstrated a moderate bactericidal activity of the essential oil (Minimum Bactericidal Concentration &gt; 2048 μg/mL). Assessment of the effects of sublethal concentrations of the essential oil on L. monocytogenes virulence traits demonstrated a significant action on motility. Listeriae were non-motile after exposure to the essential oil. Light and scanning electron microscopy documented aggregates of listeriae with the flagella trapped inside the cluster. Real-time RT-PCR experiments showed downregulation of flagellar motility genes and of the regulatory gene prfA. The ability to form biofilm and to invade Caco-2 cells was also significantly reduced. Galleria mellonella larvae infected with L. monocytogenes grown in presence of sublethal concentrations of the essential oil showed much higher survival rates compared with controls, suggesting that the extract inhibited tissue invasion. Food contamination with L. monocytogenes is a major concern for the food industry, particularly for plants making ready-to-eat and processed food. The present work provides a baseline in the study of the anti-virulence properties of the C. sativa essential oil against L. monocytogenes. Further studies are needed to understand if it could be used as an alternative agent for the control of L. monocytogenes in food processing plants

Streptococcus suis Meningitis without History of Animal Contact, Italy

Streptococcus suis, a major swine pathogen worldwide, is emerging as a zoonotic agent capable of causing a variety of serious infections in swine as well as in persons exposed to pigs or to pork products. These infections include meningitis, septicemia, pneumonia, endocarditis, arthritis, and septic shock (1,2). Despite recent outbreaks among persons in China, S. suis disease in humans is a rare, probably underdiagnosed infection that usually occurs as sporadic cases (1,2). Persons in close occupational or accidental contact with pigs or pork products and those who eat uncooked or undercooked pork may be at higher risk than others. However, most infected persons are likely healthy carriers, and S. suis is believed to induce overt disease (especially meningitis) in only some circumstances (2). We describe a case of S. suis meningitis in a 68-year-old man from Sardinia, Italy, who had no reported contact with swine, other animals, or any animal products; the patient also had cancer, which was discovered incidentally during the workup

Streptococcus suis Meningitis without History of Animal Contact, Italy

Streptococcus suis, a major swine pathogen worldwide, is emerging as a zoonotic agent capable of causing a variety of serious infections in swine as well as in persons exposed to pigs or to pork products. These infections include meningitis, septicemia, pneumonia, endocarditis, arthritis, and septic shock (1,2). Despite recent outbreaks among persons in China, S. suis disease in humans is a rare, probably underdiagnosed infection that usually occurs as sporadic cases (1,2). Persons in close occupational or accidental contact with pigs or pork products and those who eat uncooked or undercooked pork may be at higher risk than others. However, most infected persons are likely healthy carriers, and S. suis is believed to induce overt disease (especially meningitis) in only some circumstances (2). We describe a case of S. suis meningitis in a 68-year-old man from Sardinia, Italy, who had no reported contact with swine, other animals, or any animal products; the patient also had cancer, which was discovered incidentally during the workup

Attenuation of Listeria monocytogenes virulence by Cannabis sativa L. essential oil

Introduction. In recent years, the use of plant products as alternative/adjunct antimicrobial agents to control pathogenic microorganisms has been attracting mounting interest. A major group of plant antimicrobial compounds is represented by essential oils (EOs), complex mixtures of volatile secondary metabolites belonging to different chemical families. Cannabis sativa L. has been grown for thousands of years for a multiplicity of purposes; in recent years, some genotypes containing low cannabinoid concentrations have been selected and used for research purposes. Listeria monocytogenes is a facultative intracellular food pathogen able to persist within biofilms and to develop resistance to sanitizers. In humans, the treatment of listeriosis is hampered by the intracellular location of listeriae and the poor intracellular penetration of some antibiotics. The purpose of this study was to investigate the in vitro and in vivo antibacterial and anti-virulence properties of an EO extracted from a legal C. sativa L. variety against L. monocytogenes isolates collected from patients with invasive listeriosis. Materials and Methods. Eleven L. monocytogenes strains isolated in Italy in 2014-2016 were studied. The antibacterial and anti-virulence activity of the EO, extracted from C. sativa Futura 75 by steam-distillation, was determined by susceptibility tests, biofilm formation assays, Caco-2 invasion assays, motility assays, optical and scanning electron microscopy, Real-time RT-PCR experiments, and Galleria mellonella survival assays. Results. A moderate bactericidal activity of the C. sativa EO was detected (Minimum Bactericidal Concentration >2048 mg/L). In presence of EO at sub-lethal concentrations, the ability to form biofilm and to invade Caco-2 cells was significantly reduced (up to 15% and 73%, respectively). Motility tests demonstrated that, listeriae became non-motile i.e. they didn’t show the typical umbrella-like growth. Real-time RT-PCR assay demonstrated a significant downregulation of motility genes (flaA, motA, and motB) in L. monocytogenes exposed to the EO. In survival experiments with Galleria mellonella, larvae infected with L. monocytogenes grown in presence of EO showed much higher (93%) survival rates compared with controls (50%). Discussion and Conclusions. Anti-virulence strategies are being explored among plant products as a novel approach to combat bacterial pathogens. The significant anti-virulence properties of C. sativa EO against L. monocytogenes suggests that it could be employed as an alternative agent to control L. monocytogenes infectio

Sinergia con antibiotici ed azione anti-virulenza di fitocomposti bioattivi

L’aumentata diffusione di patogeni antibiotico-resistenti e la mancanza di nuove molecole antibiotiche ha risvegliato l'interesse nei confronti di fitocomposti come possibili agenti antimicrobici. Vengono esposti i risultati di nostri studi recenti riguardanti l'azione sinergica con antibiotici e le proprietà anti-virulenza di alcuni fitocomposti nei confronti di ceppi clinici di patogeni umani multi-resistenti, produttori di biofilm e invasivi per cellule. Gli studi sull’attività antimicrobica di carvacrolo (monoterpene fenolico presente negli oli essenziali di Thymus vulgaris e Origanum vulgare) e di capsaicina (alcaloide presente in piante del genere Capsicum), nei confronti di Streptococcus pyogenes, eritromicino-resistenti ed invasivi per cellule respiratorie umane, hanno dimostrato che, a concentrazioni sub-MIC, il carvacrolo agiva in sinergia (FICI≤0.5) con eritromicina e che la capsaicina, riduceva l’espressione della streptolisina O e la capacità di invadere cellule respiratorie A549. Gli studi sull’attività antimicrobica di curcumina (composto polifenolico presente nel rizoma di Curcuma longa) nei confronti di Mycobacterium abscessus, multi-resistente e produttore di biofilm, hanno dimostrato che, a concentrazioni sub-MIC, la curcumina agiva in sinergia con amikacina, claritromicina, ciprofloxacina, e linezolid ed era in grado di disgregare il biofilm maturo. Studi più recenti sull’attività anti-virulenza di olio essenziale di Cannabis sativa L. [varietà di canapa a basso contenuto di THC (<0.2%), ad uso industriale] nei confronti di Listeria monocytogenes da casi di listeriosi umana invasiva, hanno dimostrato che, a concentrazioni sub-letali, l’olio essenziale era in grado di ridurre la produzione di biofilm, la motilità, la capacità di invadere cellule epiteliali intestinali umane Caco-2 e di aumentare la sopravvivenza di larve infettate di Galleria mellonella. In un momento storico in cui l’aumento dei patogeni multi-resistenti costituisce una vera e propria emergenza sanitaria, per combattere la quale gli antibiotici a disposizione sono sempre gli stessi, una strategia che sfrutti la sinergia con antibiotici tradizionali oppure l’azione anti-virulenza di fitocomposti offre nuove prospettive alla lotta contro l’antibiotico resistenza. In particolare, l’azione anti-virulenza presenta dei vantaggi rispetto agli antibiotici in quanto non esercita una pressione selettiva verso l’antibiotico-resistenza