Comparative analysis of genomic characteristics, virulence and fitness of community-associated Staphylococcus aureus ST121 clone causing fatal diseases in China and other CA-MRSA clones

The increasing rate of community-associated Staphylococcus aureus (CA-SA) worldwide has aroused global public concern for decades. Although ST121 clone is one of the prevalent CA-SA in China, there is still limited knowledge about it. In this study, we conducted a genomic analysis of 28 CA-SA ST121 isolates from severe bloodstream infection cases and 175 ST121 isolates from the public database. Phylogenetic analysis revealed the consistency and the complexity of global ST121 lineages, and suggested potential cross-country even cross-continental transmission of ST121 isolates. By investigating the virulence and fitness between ST121-CA-methicillin-resistant SA (CA-MRSA) and other CA-MRSA clones, we found that ST121-MRSA exhibits virulence comparable to the highly virulent USA300 clone, exceeding that of the predominant CA-MRSA lineage ST59 in China and the other American CA-MRSA clone MW2. Notably, based on analyses of virulence genes, eta, etb, edin-C and egc were only found in ST121, suggesting that the high virulence of ST121 may be attributed to the combination of these virulence factors encoded by mobile genetic elements. However, results of experiments in mice nasal and human alveolar epithelial cells showed that the colonization capacity of ST121 is much lower than that of other clones. Moreover, ST121-MRSA displayed much lower acid tolerance, suggesting that ST121-MRSA may not have such capacity to achieve the epidemiological success of other CA-MRSA clones and become the dominant lineage. Our findings expand current understanding of the epidemiology and pathogenicity of the hypervirulent ST121 clone, and highlight the importance of colonization capacity and environmental adaption in MRSA epidemiological success.

Closed genome sequences of two Listeria monocytogenes ST121 strains

We performed Oxford Nanopore and Illumina sequencing to generate accurate, closed genomes for the Listeria monocytogenes strains 6179 and L58-55. The new assemblies were generally similar to the previous Illumina-based assemblies, but additional rRNA operons and repeat regions were identified in the new assembly for strain 6179.

Predominance of community-associated, methicillin-susceptible Staphylococcus aureus infections among hospitalized children and adolescents

Introduction. Staphylococcus aureus infections cause significant morbidity and mortality in children and adolescents.Gap Statement. There is limited data on the characteristics of S. aureus infections requiring hospitalization in childhood.Aim.To investigate the molecular epidemiology and antibiotic resistance of S. aureus clinical isolates from children and adolescents.Methodology.All S. aureus isolates recovered from patients aged <18 years, admitted to a referral hospital, with culture-proven invasive or non-invasive infections during the 4 year period 2015 to 2018 were analysed for antimicrobial resistance, virulence genes, PFGE and multilocus sequence typing (MLST). Cases were assigned to community-associated, community-onset healthcare-associated or hospital-associated infections based on epidemiological case definitions.Results.Among 139 S. aureus infections, 88.5 % (123/139) were caused by methicillin-susceptible isolates (MSSA) and 73.4 % (102/139) were classified as community-associated infections. tst and lukS/lukF-PV genes were more common among MRSA as compared to MSSA isolates (tst, p 0.04; lukS/lukF-PV, p 0.007). Invasive disease was noted in 22/139 patients (15.8 %). Staphylococcal scalded skin syndrome caused by fusidic-resistant MSSA increased over time (22.8 % in 2017-2018 vs 8.3 % in 2015-2016, OR 3.24; 95 % CI 1.10-8.36; P 0.03). By PFGE genotyping, 22 pulsotypes were identified. A total of five sequence types (STs) were identified among 58 isolates analysed by MLST. More than one third of MSSA isolates (40/123, 32.5 %) and 13/23 (56.5 %) of SSSS isolates belonged to pulsotype 1, classified as sequence type 121 (ST121). MRSA isolates were equally distributed to pulsotypes A (ST30), B (ST239), C (ST80), H (ST225). ST121 isolates carried fnbA (40/40), eta/etb genes (29/40), exhibited high resistance to fusidic acid and were increasingly resistant to mupirocin.Conclusion.In our population, community-associated MSSA was the predominant cause of S. aureus infections characterized by polyclonality, increasing resistance to fusidic acid and mupirocin. PFGE type 1 ST121 clone, harboured exfoliative toxin genes and was associated with rising trends of SSSS.

Emergence of a mupirocin-resistant, methicillin-susceptible Staphylococcus aureus clone associated with skin and soft tissue infections in Greece

BACKGROUND

Staphylococcus aureus causes various infections, including skin and soft tissue infections (SSTIs). In this study, methicillin-susceptible S. aureus (MSSA) from SSTIs among patients in three tertiary-care hospitals in Greece were studied in terms of antimicrobial resistance, clonal distribution, toxin and adhesin genes carriage.

RESULTS

During a five-year period (2014-2018), 6145 S. aureus were recovered from 13,244 patients with SSTIs and tested for antimicrobial susceptibility. MSSA were 4806 (78.21 %) including 1484 isolates with mupirocin minimum inhibitory concentration (MIC) > 64 mg/L (30.88 %). Two hundred and sixty representative mupirocin-resistant MSSA were analyzed for genes encoding Panton-Valentine leukocidin (PVL, lukS/lukF-PV), exfoliative toxins (eta, etb), adhesin FnbA (fnbA) and resistance genes mupA (high-level resistance to mupirocin), fusB (fusidic acid), aminoglycosides' modifying enzymes, ermA, ermC and msrA (macrolides/lincosamides) by PCRs. Strains were classified into clones by PFGE and MLST. All mupirocin-resistant MSSA were penicillin-resistant; 92.7 % expressed resistance to fusidic acid and 88.9 % to tobramycin. All 260 molecularly analyzed isolates were mupA-positive; all fusidic acid-resistant (241/260) carried fusB whereas, the tobramycin-resistant ones (230), ant(4')-Ia. The majority carried eta (93.85 %), etb (98.08 %) and fnbA (88.85 %). PFGE typing revealed a mostly unvarying population; 260 MSSA were grouped into three types. One major eta/etb-positive clone comprising of 258/260 strains (99.2 %), PFGE type 1, was classified as ST121, including nine strains co-carrying PVL. Another PVL-positive strain was identified as ST1, and one toxins-negative as ST21.

CONCLUSIONS

A mupirocin-resistant MSSA clone, ST121, carrying resistance, exfoliative toxins and adhesin genes, was spread and predominated in SSTIs from patients in Greece during the five-year studied period.

First Report on the Finding of Listeria mnocytogenes ST121 Strain in a Dolphin Brain

Listeria monocytogenes (Lm) is a ubiquitous bacterium that causes the foodborne illness, listeriosis. Clonal complexes (CC), such as CC121, are overrepresented in the food production industry, and are rarely reported in animals and the environment. Working within a European-wide project, we investigated the routes by which strains are transmitted from environments and animals to food and the food production environment (FPE). In this context, we report, for the first time, the occurrence of a ST121 (CC121) strain isolated from a dolphin brain. The genome was compared with the genomes of 376 CC121 strains. Genomic comparisons showed that 16 strains isolated from food were the closest to the dolphin strain. Like most of the food strains analyzed here, the dolphin strain included genomic features (transposon Tn6188, plasmid pLM6179), both described as being associated with the strain’s adaptation to the FPE. Like all 376 strains, the dolphin strain contained a truncated actA gene and inlA gene, both described as being associated with attenuated virulence. Despite this fact, the strain was able to cross blood-brain barrier in immunosuppressed dolphin exposed polychlorinated biphenyl and invaded by parasites. Our data suggest that the dolphin was infected by a food-related strain released into the Mediterranean Sea.

Septic arthritis caused by an emerging ST121 methicillin-susceptible, PVL-negative Staphylococcus aureus harbouring a variant of bone sialoprotein-binding protein gene

ST121/agr-IV methicillin-susceptible Staphylococcus aureus was isolated from a patient of septic arthritis (synovial fluid, blood, skin and nasal cavity). Although the Panton-Valentine leukocidin (PVL) gene was negative, this isolate harboured a gene encoding a variant of bone sialoprotein-binding protein with a shortened SD-repeat region.

Drug resistance and genetic characteristics of clinical isolates of staphylococci in Myanmar: high prevalence of PVL among methicillin-susceptible Staphylococcus aureus belonging to various sequence types

Prevalence, drug resistance and genetic characteristics were analysed for a total of 128 clinical isolates of staphylococci obtained from a tertiary hospital in Myanmar. The dominant species were S. aureus (39%) and S. haemolyticus (35%), followed by S. epidermidis (6%) and S. saprophyticus (5%). The majority of S. haemolyticus isolates (71.1%) harboured mecA, showing high resistance rates to ampicillin, cephalosporins, erythromycin and levofloxacin, while methicillin-resistant S. aureus (MRSA) was only 8% (four isolates) among S. aureus with type IV SCCmec. Panton-Valentine leukocidin (PVL) genes were detected in 20 isolates of S. aureus (40%), among which only one isolate was MRSA belonging to sequence type (ST) 88/agr-III/coa-IIIa, and the other 19 methicillin-susceptible S. aureus (MSSA) isolates were classified into six STs (ST88, ST121, ST1153, ST1155, ST1930, ST3206). An ST1153 MSSA isolate with PVL was revealed to belong to a novel coa type, XIIIa. ST121 S. aureus was the most common in the PVL-positive MSSA (47%, 9/19), harbouring genes of bone sialoprotein and variant of elastin binding protein as a distinctive feature. Although PVL-positive MSSA was susceptible to most of the antimicrobial agents examined, ST1930 isolates were resistant to erythromycin and levofloxacin. ST59 PVL-negative MRSA and MSSA had more resistance genes than other MRSA and PVL-positive MSSA, showing resistance to more antimicrobial agents. This study indicated higher prevalence of mecA associated with multiple drug resistance in S. haemolyticus than in S. aureus, and dissemination of PVL genes to multiple clones of MSSA, with ST121 being dominant, among hospital isolates in Myanmar.

Patients with Panton-Valentine leukocidin positive Staphylococcus aureus infections run an increased risk of longer hospitalisation

Staphylococcus aureus is a major cause of purulent infections. The spectrum of staphylococcal infections varies from mild superficial to invasive life-threatening diseases due to S. aureus ability to produce a wide range of virulence factors, including toxins. A prospective observational study was conducted in the Children Clinical University Hospital in Riga, Latvia. During a period of sixteen months from November 2006 to March 2008 224 S. aureus isolates were collected. Our study revealed that Panton-Valentine leukocidine (PVL) genes are carried by a high number (75%) of S. aureus isolates recovered from children hospitalised in the Children Clinical University hospital. Most of these isolates were associated with abscesses and other skin and soft tissue infections. Patients with PVL positive invasive infections stayed significantly longer in hospital than patients with PVL negative invasive infections. Clonal distribution of PVL positive S. aureus isolates were closely related, which provides evidence for the wide spread of PVL producing spa type t435 and ST121 staphylococci in community.