Methicillin-susceptible Staphylococcus aureus in skin and soft tissue infections, Northern Italy

A Sequalae of Lineage Divergence in Staphylococcus aureus from Community-Acquired Patterns in Youth to Hospital-Associated Profiles in Seniors Implied Age-Specific Host-Selection from a Common Ancestor

The rapidly changing epidemiology of Staphylococcus aureus and evolution of strains with enhanced virulence is a significant issue in global healthcare. Hospital-associated methicillin-resistant S. aureus (HA-MRSA) lineages are being completely replaced by community-associated S. aureus (CA-MRSA) in many regions. Surveillance programs tracing the reservoirs and sources of infections are needed. Using molecular diagnostics, antibiograms, and patient demographics, we have examined the distributions of S. aureus in Ha'il hospitals. Out of 274 S. aureus isolates recovered from clinical specimens, 181 (66%, n = 181) were MRSA, some with HA-MRSA patterns across 26 antimicrobials with almost full resistances to all beta-lactams, while the majority were highly susceptible to all non-beta-lactams, indicating the CA-MRSA type. The rest of isolates (34%, n = 93) were methicillin-susceptible, penicillin-resistant MSSA lineages (90%). The MRSA in men was over 56% among total MRSA (n = 181) isolates and 37% of overall isolates (n = 102 of 274) compared to MSSA in total isolates (17.5%, n = 48), respectively. However, these were 28.4% (n = 78) and 12.4% (n = 34) for MRSA and MSSA infections in women, respectively. MRSA rates per age groups of 0-20, 21-50, and >50 years of age were 15% (n = 42), 17% (n = 48), and 32% (n = 89), respectively. However, MSSA in the same age groups were 13% (n = 35), 9% (n = 25), and 8% (n = 22). Interestingly, MRSA increased proportional to age, while MSSA concomitantly decreased, implying dominance of the latter ancestors early in life and then gradual replacement by MRSA. The dominance and seriousness of MRSA despite enormous efforts in place is potentially for the increased use of beta-lactams known to enhance virulence. The Intriguing prevalence of the CA-MRSA patterns in young otherwise healthy individuals replaced by MRSA later in seniors and the dominance of penicillin-resistant MSSA phenotypes imply three types of host- and age-specific evolutionary lineages. Thus, the decreasing MSSA trend by age with concomitant increase and sub-clonal differentiation into HA-MRSA in seniors and CA-MRSA in young and otherwise healthy patients strongly support the notion of subclinal emergences from a resident penicillin-resistant MSSA ancestor. Future vertical studies should focus on the surveillance of invasive CA-MRSA rates and phenotypes.

Changes in molecular characteristics and antimicrobial resistance of invasive Staphylococcus aureus infection strains isolated from children in Kunming, China during the COVID-19 epidemic

Invasive Staphylococcus aureus (S. aureus) infection is associated with high rates of mortality in children. No studies have been reported on invasive S. aureus infection among children in Kunming, China, and it remains unknown whether the COVID-19 epidemic has affected S. aureus prevalence in this region. Thus, this study investigated the changes in molecular characteristics and antimicrobial resistance of invasive S. aureus strains isolated from children in Kunming during 2019–2021. In total, 66 invasive S. aureus strains isolated from children were typed by multilocus sequence typing (MLST), spa, and Staphylococcal cassette chromosome mec (SCCmec), and antimicrobial resistance and virulence genes were analyzed. A total of 19 ST types, 31 spa types and 3 SCCmec types were identified. Thirty nine (59.09%) strains were methicillin-sensitive S. aureus (MSSA) and 27 (40.91%) strains were methicillin-resistant S. aureus (MRSA). The most common molecular type was ST22-t309 (22.73%, 15/66), followed by ST59-t437 (13.64%, 9/66). In 2019 and 2021, the dominant molecular type was ST22-t309, while in 2020, it was ST59-t437. After 2019, the dominant molecular type of MRSA changed from ST338-t437 to ST59-t437. All strains were susceptible to tigecycline, ciprofloxacin, moxifloxacin, vancomycin, quinopudine-dafoputin, linezolid, levofloxacin, and rifampicin. From 2019 to 2021, the resistance to penicillin and sulfamethoxazole initially decreased and then increased, a trend that contrasted with the observed resistance to oxacillin, cefoxitin, erythromycin, clindamycin, and tetracycline. Sixteen antimicrobial resistance profiles were identified, with penicillin-tetracycline-erythromycin-clindamycin-oxacillin-cefoxitin being the most common, and the antimicrobial resistance profiles varied by year. The carrier rates of virulence genes, icaA, icaD, hla, fnbA, fnbB, clfA, clfB, and cna were 100.00%. Furthermore, sak, pvl, icaC, icaR, fib, lip, hlb, hysA, sea, seb, and tsst-1 had carrier rates of 96.97, 92.42, 87.88, 69.70, 84.85, 62.12, 56.06, 50, 37.87, 30.30, and 7.58%, respectively. Since COVID-19 epidemic, the annual number of invasive S. aureus strains isolated from children in Kunming remained stable, but the molecular characteristics and antimicrobial resistance profiles of prevalent S. aureus strains have changed significantly. Thus, COVID-19 prevention and control should be supplemented by surveillance of common clinical pathogens, particularly vigilance against the prevalence of multidrug-resistant and high-virulence strains.

Comparative Genomic Analysis of a Panton–Valentine Leukocidin-Positive ST22 Community-Acquired Methicillin-Resistant Staphylococcus aureus from Pakistan

Staphylococcus aureus (S. aureus) ST22 is considered a clinically important clone because an epidemic strain EMRSA-15 belongs to ST22, and several outbreaks of this clone have been documented worldwide. We performed genomic analysis of an S. aureus strain Lr2 ST22 from Pakistan and determined comparative analysis with other ST22 strains. The genomic data show that Lr2 belongs to spa-type t2986 and harbors staphylococcal cassette chromosome mec (SCCmec) type IVa(2B), one complete plasmid, and seven prophages or prophage-like elements. The strain harbors several prophage-associated virulence factors, including Panton–Valentine leukocidin (PVL) and toxic shock syndrome toxin (TSST). The single nucleotide polymorphism (SNPs)-based phylogenetic relationship inferred from whole genome and core genome revealed that strain Lr2 exhibits the nearest identities to a South African community-acquired methicillin-resistant S. aureus (CA-MRSA) ST22 strain and makes a separate clade with an Indian CA-MRSA ST22 strain. Although most ST22 strains carry blaZ, mecA, and mutations in gyrA, the Lr2 strain does not have the blaZ gene but, unlike other ST22 strains, carries the antibiotic resistance genes erm(C) and aac(6′)-Ie-aph(2″)-Ia. Among ST22 strains analyzed, only the strain Lr2 possesses both PVL and TSST genes. The functional annotation of genes unique to Lr2 revealed that mobilome is the third-largest Cluster of Orthologous Genes (COGs) category, which encodes genes associated with prophages and transposons. This possibly makes methicillin-resistant S. aureus (MRSA) Lr2 ST22 strain highly virulent, and this study would improve the knowledge of MRSA ST22 strains in Pakistan. However, further studies are needed on a large collection of MRSA to comprehend the genomic epidemiology and evolution of this clone in Pakistan.

Prevalence of Staphylococcus aureus in wild hedgehogs (Erinaceus europaeus) and first report of mecC-MRSA in Hungary

In 2011 mecC, a new mecA gene homologue, was described in a bovine isolate in the UK. Since then, mecC-positive methicillin-resistant Staphylococcus aureus (mecC-MRSA) has also been found in wild animals. An especially high prevalence of mecC-MRSA has been reported among hedgehogs in Sweden (64%) and Denmark (61%). Based on these findings we aimed to survey the hedgehog population for mecC-MRSA in Hungary. Altogether 200 hedgehogs were screened for Staphylococcus aureus using a culture-based method. The antibiotic susceptibility of the isolates to nine drugs was determined, their genetic relatedness was established by PFGE and spa-typing, and virulence genes were identified by PCR. Whole genome sequencing was performed for the single mecC-MRSA isolate found. Of the 200 animals, 13 were carriers of S. aureus (6.5%). Among these, one isolate was mecA positive and one was mecC positive. The isolates were susceptible to non-beta-lactam antibiotics. Toxin genes were not found, but the majority carried genes responsible for adhesion and biofilm production. The mecC-MRSA isolate was a single-locus variant of ST130, had a new spa type (t19701) and belonged to SCCmec type XI. It carried a recently described, novel exfoliative toxin (etE). This is the first report of mecC-MRSA in Hungary and the first survey of staphylococcus carriage among wild animals in the country. The mecC prevalence was much lower than in Northern European countries and rather similar to other countries in our region. MecC-MRSA could potentially emerge as a novel human pathogen, especially where close contact occurs between humans and animals.

Severe Staphylococcus aureus infections in children: Case reports and management of positive Panton-Valentine leucocidin cases

BACKGROUND

Staphylococcus aureus is a well-known bacterium associated with carriage and responsible for different types of infections. The Panton-Valentine leucocidin (PVL) is a key virulence factor causing tissue necrosis. PVL can, however, be present in both benign and life-threatening infections.

CASE REPORTS AND MANAGEMENT

We present three pediatric severe infections occurring over a period of only three weeks, in February 2021, and caused by genetically unrelated methicillin-sensitive Staphylococcus aureus producing PVL in a tertiary children's hospital in Belgium. The first one presented with necrotizing pneumonia, the second one with a neck abscess extended to the mediastinum, and the last one had sacral osteomyelitis complicated by endocarditis. The management of these infections is mostly based on expert opinions. The most appropriate treatment seems to be the combination of early surgical drainage of infected collections with an antibiotic regimen associating two antibiotics; beta-lactams and either clindamycin or linezolid. Human immunoglobulins also appear to be useful as adjunctive therapy.

CONCLUSION

PVL-producing Staphylococcus aureus is associated with life-threatening infections in children. Prompt management is needed including surgery and appropriate antibiotic regimens.

Clonal diversity and genomic characterization of Panton-valentine Leukocidin (PVL)-positive Staphylococcus aureus in Tehran, Iran

Background

Some Staphylococcus aureus strains produce Panton-Valentine leukocidin (PVL), a bi-component pore-forming toxin, which causes leukocyte lysis and tissue necrosis. Currently, there is very limited information on the molecular epidemiology of PVL-encoding S. aureus strains in Iran. This study aimed to determine the molecular epidemiology and genetic background of PVL-positive S. aureus clinical strains isolated from Iranian patients.

Methods

A total of 28 PVL-positive S. aureus strains were detected from 600 S. aureus isolates between February 2015 and March 2018 from different hospitals in Tehran, Iran. Antimicrobial susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Molecular genotyping was performed using SCCmec and accessory gene regulator (agr) typing, PVL haplotyping, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE).

Results

The highest antibiotic resistance rate was found to be against erythromycin (57.1%), followed by ciprofloxacin (42.8%) and clindamycin (35.7%). Moreover, 19 (67.9%) out of 28 S. aureus isolates were identified as MRSA, including CA-MRSA (14/19, 73.7%) and HA-MRSA (5/19, 26.3%). SCCmec type IVa was detected as the predominant type (10/19, 52.6%), followed by type III (5/19, 26.3%) and type V (4/19, 21.1%). The agr type I was identified as the most common type (14/28, 50%), and H and R haplotype groups were observed at frequencies of 67.9 and 32.1%, respectively. Among H variants, the predominant variant was H2 (78/9%). The isolates encompassed 21 different sequence types (STs), including 16 new STs (ST5147 to ST5162). Based on eBURST analysis, the isolates were clustered into five CCs, including CC30, CC22, CC1, CC8, and CC5 (ST5160), and nine singletons. PFGE typing showed that 24 isolates were clustered into A (4 pulsotypes), B (9 pulsotypes), and C (11 pulsotypes) clusters.

Conclusions

A high prevalence of PVL-positive CA-MRSA strains was detected in Iran. The majority of PVL-positive isolates were of H (mostly H2) variant, while R variant was harbored by 100% of PVL-positive MRSA strains. Also, CC8, CC22, and CC30 were identified as the dominant clones among PVL-encoding S. aureus strains. This study promotes a better understanding of the molecular epidemiology and evolution of PVL-positive S. aureus strains in Iran.

Prevalence of methicillin-resistant Staphylococcus aureus (MRSA) carriage and pattern of antibiotic resistance among sheep farmers from Southern Italy

PURPOSE

We conducted a cross-sectional study to measure the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization, with a particular focus on livestock associated (LA)-MRSA in farmers working in contact with livestock (sheep) in one Italian region. Furthermore, we have assessed the antimicrobial resistance pattern of isolates and the association of carriage with specific characteristic of farms and working tasks.

PATIENTS AND METHODS

Demographic data, occupational history, and contact with animals information was collected. Nasal and oropharyngeal swabs were collected and all samples were tested for the isolation and identification of S. aureus. Isolates were examined for antimicrobial susceptibility and all MRSA strains underwent molecular analyses through multiple-locus variable number of tandem repeat analysis (MLVA).

RESULTS

A total of 115 sheep farms and 275 sheep farmers were enrolled. MRSA colonized workers were found in three farms; S. aureus was isolated in 97 workers (35.5%), whereas MRSA was isolated in 3 (1.1%) workers. All MRSA isolates were classified as multidrug resistant. Two of the MRSA isolates were resistant to quinupristin/dalfopristin (QDA), mupirocin, erythromycin, and tetracycline. Among methicillin-susceptible S. aureus (MSSA), 32 (34%) were resistant to tetracycline, 31 (33%) to erythromycin, 26 (27.6%) to QDA, and 22 (23.4%) to linezolid and clindamycin. One MRSA belonged to MLVA complex (MC) 001, found to colonize both humans and animals.

CONCLUSION

The picture of MRSA transmission among sheep farmers does not seem to be critical, although there is the need to improve adequate control measures to prevent and minimize any biological risk in sheep farms for both animal and human health. Specific monitoring/surveillance programs would help in better understanding the epidemiology of resistant strains.

Community-associated Staphylococcus aureus PVL+ ST22 predominates in skin and soft tissue infections in Beijing, China

Purpose

Community-associated Staphylococcus aureus (CA S. aureus) is the most common causative pathogen of the skin and soft tissue infections (SSTIs). This study aims to determine clonal distribution, virulence factors of CA S. aureus clinical isolates from purulent SSTIs in Beijing, China.

Materials and methods

CA-S. aureus isolates were collected from 115 outpatients with purulent SSTIs from the department of dermatology from April 2015 to April 2017. Multilocus sequence typing and Staphylococcus cassette chromosome mec typing were performed to explore molecular characteristics. Phylogenetic analysis of 16S rRNA of dominant S. aureus isolates was performed using MEGA-X software. Virulence genes were detected by PCR, while biofilm formation was evaluated by a microtiter plate method. The antimicrobial susceptibility was tested by an automatic VITEK system.

Results

Forty-four CA-S. aureus isolates identified from SSTIs contain 9 methicillin-resistant S. aureus (MRSA) isolates (20.4%) and 35 methicillin-susceptible S. aureus isolates (MSSA) (79.6%). The dominant sequence types (STs) were ST22 (40.9%) and clonal complex 59 (CC59; 77.8%) in Community-associated methicillin resistant methicillin-resistant S. aureus. 27.8% of ST22 isolates were homologous to the epidemic ST22 EMRSA-15 in Europe. The prevalence of virulence genes lukS/lukF, tst-1, etA, edinA, icaA, and icaD was 50%, 93.2%, 4.5%, 4.5%, 100%, and 100%, respectively. All CC59 isolates exhibited stronger biofilm-forming capability than ST22 clones. Among the MSSA subgroup, the poor biofilm producers had significantly higher sensitivity to sulfamethoxazole/Trimethoprim.

Conclusion

The dominant epidemic clone PVL⁺ ST22 MSSA containing tst-1 occurs in Beijing, indicating that a PVL⁺ ST398 clone which was previously predominant in this district had been replaced by a new clone.

Prevalence of Staphylococcus aureus carriage and pattern of antibiotic resistance, including methicillin resistance, among contact sport athletes in Italy

Background and purpose: Athletes participating in contact or collision sports have a great chance of acquiring Staphylococcus aureus infections. The risk factors for colonization and infections include frequent antibiotic use, close contact situations, skin trauma, sharing of sports equipment, and poor hygiene. Therefore, our specific goals were to determine (1) prevalence of S. aureus among different types of contact sport athletes which were barely studied in the European region, (2) antimicrobial resistance of S. aureus isolates, and (3) association of carriage with particular risk factors of spor t practices.

Patients and methods: A cross-sectional study was conducted among contact or collision sport athletes in Italy. A questionnaire was used to gather information about sociodemographic characteristics, specific sport activities, and participants’ health conditions. Swabs were collected from the nares, oropharynx, and fingers and tested for S. aureus isolation and antimicrobial susceptibility.

Results:S. aureus was carried by 42% of 238 enrolled athletes. Colonization was associated with number of weekly training days, sharing of sports equipment, not taking a shower immediately after training, and a previous history of pharyngitis or sinusitis and skin manifestations. Isolates were resistant to clindamycin (24.8%) and erythromycin (15.8%). Of all athletes, 1.3% carried methicillin-resistant S. aureus (MRSA); MRSA were 3% of all S. aureus isolates. No strains were resistant to sulfamethoxazole/trimethoprim.

Conclusion: Our results have shown a high prevalence of S. aureus carriage and a relevant resistance to antimicrobials used for the treatment of S. aureus infections. Prevention efforts aimed at reducing S. aureus colonization, and thus potentially reducing infections, should be improved.

Outbreak report of investigation and control of an outbreak of Panton-Valentine Leukocidin-positive methicillin-sensitive Staphylococcus aureus (PVL-MSSA) infection in neonates and mothers

Background

In January 2011, there was an outbreak of Panton-Valentine Leukocidin-positive methicillin-sensitive Staphylococcus aureus (PVL-MSSA) infection in a neonatal unit (NNU).

We describe the investigation and control of an outbreak of PVL-MSSA infection in neonates. Setting: Neonatal unit in West London.

Methods

We performed descriptive and analytical (case-control study) epidemiological investigations. Microbiological investigations including screening of MSSA isolates by PCR for the presence of the luk-PV, mecA and mecC genes and comparison of isolate with Pulsed field gel electrophoresis (PFGE). Control measures were also introduced.

Results

Sixteen babies were infected/colonised with the outbreak strain. Of these, one baby developed blood stream infection, 12 developed skin pustules and four babies were colonised.

Four mothers developed breast abscesses. Eighty-seven babies in the unit were screened and 16 were found to have same PVL-MSSA strain (spa type t005, belonging to MLST clonal complex 22). Multivariate analysis showed gestational age was significantly lower in cases compared to controls (mean gestational age: 31.7 weeks v 35.6 weeks; P = 0.006). Length of stay was significantly greater for cases, with a median of 25 days, compared to only 6 days for controls (P = 0.01). Most (88%) cases were born through caesarean section, compared to less than half of controls. (P = 0.002).

No healthcare worker carriers and environmental source was identified. The outbreak was controlled by stopping new admissions to unit and reinforcing infection control precautions. The outbreak lasted for seven weeks. No further cases were reported in the following year.

Conclusions

Infection control teams have to be vigilant for rising prevalence of particular S. aureus clones in their local community as they may cause outbreaks in vulnerable populations in healthcare settings such as NNUs.

Whole-genome epidemiology, characterisation, and phylogenetic reconstruction of Staphylococcus aureus strains in a paediatric hospital

BACKGROUND

Staphylococcus aureus is an opportunistic pathogen and a leading cause of nosocomial infections. It can acquire resistance to all the antibiotics that entered the clinics to date, and the World Health Organization defined it as a high-priority pathogen for research and development of new antibiotics. A deeper understanding of the genetic variability of S. aureus in clinical settings would lead to a better comprehension of its pathogenic potential and improved strategies to contrast its virulence and resistance. However, the number of comprehensive studies addressing clinical cohorts of S. aureus infections by simultaneously looking at the epidemiology, phylogenetic reconstruction, genomic characterisation, and transmission pathways of infective clones is currently low, thus limiting global surveillance and epidemiological monitoring.

METHODS

We applied whole-genome shotgun sequencing (WGS) to 184 S. aureus isolates from 135 patients treated in different operative units of an Italian paediatric hospital over a timespan of 3 years, including both methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) from different infection types. We typed known and unknown clones from their genomes by multilocus sequence typing (MLST), Staphylococcal Cassette Chromosome mec (SCCmec), Staphylococcal protein A gene (spa), and Panton-Valentine Leukocidin (PVL), and we inferred their whole-genome phylogeny. We explored the prevalence of virulence and antibiotic resistance genes in our cohort, and the conservation of genes encoding vaccine candidates. We also performed a timed phylogenetic investigation for a potential outbreak of a newly emerging nosocomial clone.

RESULTS

The phylogeny of the 135 single-patient S. aureus isolates showed a high level of diversity, including 80 different lineages, and co-presence of local, global, livestock-associated, and hypervirulent clones. Five of these clones do not have representative genomes in public databases. Variability in the epidemiology is mirrored by variability in the SCCmec cassettes, with some novel variants of the type IV cassette carrying extra antibiotic resistances. Virulence and resistance genes were unevenly distributed across different clones and infection types, with highly resistant and lowly virulent clones showing strong association with chronic diseases, and highly virulent strains only reported in acute infections. Antigens included in vaccine formulations undergoing clinical trials were conserved at different levels in our cohort, with only a few highly prevalent genes fully conserved, potentially explaining the difficulty of developing a vaccine against S. aureus. We also found a recently diverged ST1-SCCmecIV-t127 PVL- clone suspected to be hospital-specific, but time-resolved integrative phylogenetic analysis refuted this hypothesis and suggested that this quickly emerging lineage was acquired independently by patients.

CONCLUSIONS

Whole genome sequencing allowed us to study the epidemiology and genomic repertoire of S. aureus in a clinical setting and provided evidence of its often underestimated complexity. Some virulence factors and clones are specific of disease types, but the variability and dispensability of many antigens considered for vaccine development together with the quickly changing epidemiology of S. aureus makes it very challenging to develop full-coverage therapies and vaccines. Expanding WGS-based surveillance of S. aureus to many more hospitals would allow the identification of specific strains representing the main burden of infection and therefore reassessing the efforts for the discovery of new treatments and clinical practices.

Activation of mast cells in skin abscess induced by Staphylococcus aureus (S. aureus) infection in mice

The skin abscess is a common inflammatory disease that occurs following the ubiquitous S. aureus infection. In our study, a skin abscess murine model was established and the dynamics of mast cells chemotaxing was evaluated. In the S. aureus-infected mice, severe infiltration of inflammatory cells in the dermis were observed, and mast cells were markedly accumulated in the skins. Besides, tryptase, the marker for mast cells activation, has a positive correlation with mast cell activity. The mast cells identified in the tissues were likely to be activated since they were associated with cell degranulation and the presence of tryptase. Our results suggested that mast cells and its mediator tryptase contribute to the inflammation of skin abscess induced by S. aureus infection.

An outbreak of skin infections in neonates due to a Staphylococcus aureus strain producing the exfoliative toxin A

PURPOSE

Staphylococcus aureus is an important cause of infections in hospitalized neonates. Preterm or low birthweight infants are especially at risk to develop a S. aureus infection due to the immaturity of the immune system, length of hospital stay and invasive procedures. Exfoliative toxin (ET)-producing S. aureus is often responsible for neonatal infections, causing clinical manifestations such as staphylococcal scalded skin syndrome, characterized by both localized blisters or generalized exfoliation of the skin.

METHODS

We describe an outbreak due to an S. aureus strain producing ETA occurring in a local hospital in Northern Italy. Molecular typing of the isolates included spa typing and multilocus sequence typing. DNA microarray hybridization was also performed on one representative strain.

RESULTS

In the period from July 2013 to February 2014, 12 neonates presented with skin infections, mainly bullae or pustules. Cultures of skin swabs yielded methicillin-susceptible S. aureus (MSSA). By molecular typing, an epidemic strain (t1393/ST5) was identified in nine neonates; microarray analysis and PCR revealed that it contained the ETA encoding gene. Screening of staff, mothers and healthy neonates and environmental cultures did not reveal the presence of the epidemic strain. However, the father of an infected neonate was found to be a carrier of MSSA t1393 five months after the outbreak started.

CONCLUSION

Implementation of hygiene procedures and sanitization of the ward twice terminated the outbreak. Timely surveillance of infections, supported by molecular typing, is fundamental to prevent similar episodes among neonates.

Diagnosis and management of skin and soft-tissue infections (SSTI). A literature review and consensus statement: an update

Skin and soft-tissue infections (SSTIs) are among the most common bacterial infections, posing considerable diagnostic and therapeutic challenges. Fourteen members of the Italian Society of Infectious Diseases, after a careful review of the most recent literature using Medline database and their own clinical experience, updated a previous paper published in 2011 by preparing a draught manuscript of the statements. The manuscript was successively reviewed by all members and ultimately re-formulated the present manuscript during a full day consensus meeting. The microbiological and clinical aspects together with diagnostic features were considered for necrotizing and not necrotizing SSTIs in the light of the most recent guidelines and evidences published in the last five years. The antimicrobial therapy was considered as well - both empirical and targeted to methicillin-resistant Staphylococcus aureus and/or other pathogens, also taking into account the epidemiological and bacterial resistance data and the availability of new antibacterial agents.

Current and future trends in antibiotic therapy of acute bacterial skin and skin-structure infections

In 2013 the US Food and Drug Administration (FDA) issued recommendations and guidance on developing drugs for treatment of skin infection using a new definition of acute bacterial skin and skin-structure infection (ABSSSI). The new classification includes cellulitis, erysipelas, major skin abscesses and wound infection with a considerable extension of skin involvement, clearly referring to a severe subset of skin infections. The main goal of the FDA was to better identify specific infections where the advantages of a new antibiotic could be precisely estimated through quantifiable parameters, such as improvement of the lesion size and of systemic signs of infection. Before the spread and diffusion of methicillin-resistant Staphylococcus aureus (MRSA) in skin infections, antibiotic therapy was relatively straightforward. Using an empiric approach, a β-lactam was the preferred therapy and cultures from patients were rarely obtained. With the emergence of MRSA in the community setting, initial ABSSSI management has been changed and readdressed. Dalbavancin, oritavancin and tedizolid are new drugs, approved or in development for ABSSSI treatment, that also proved to be efficient against MRSA. Dalbavancin and oritavancin have a long half-life and can be dosed less frequently. This in turn makes it possible to treat patients with ABSSSI in an outpatient setting, avoiding hospitalization or potentially allowing earlier discharge, without compromising efficacy. In conclusion, characteristics of long-acting antibiotics could represent an opportunity for the management of ABSSSI and could profoundly modify the management of these infections by reducing or in some cases eliminating both costs and risks of hospitalization.

Outbreak of Panton-Valentine Leukocidin-Associated Methicillin-Susceptible Staphylococcus aureus Infection in a Rugby Team, France, 2010-2011

Staphylococcus aureus strains that produce Panton-Valentine leukocidin are known to cause community infections. We describe an outbreak of skin abscesses caused by Panton-Valentine leukocidin-producing methicillin-susceptible S. aureus (clonal complex 121) in a professional rugby team in France during July 2010-February 2011. Eight team members were carriers; 7 had skin abscesses.

A point mutation in AgrC determines cytotoxic or colonizing properties associated with phenotypic variants of ST22 MRSA strains

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of skin and soft tissue infections. One of the highly successful and rapidly disseminating clones is MRSA ST22 commonly associated with skin tropism. Here we show that a naturally occurring single amino acid substitution (tyrosine to cysteine) at position 223 of AgrC determines starkly different ST22 S. aureus virulence phenotypes, e.g. cytotoxic or colonizing, as evident in both in vitro and in vivo skin infections. Y223C amino acid substitution destabilizes AgrC-AgrA interaction leading to a colonizing phenotype characterized by upregulation of bacterial surface proteins. The colonizing phenotype strains cause less severe skin tissue damage, show decreased susceptibility towards the antimicrobial LL-37 and induce autophagy. In contrast, cytotoxic strains with tyrosine at position 223 of AgrC cause infections characterized by inflammasome activation and severe skin tissue pathology. Taken together, the study demonstrates how a single amino acid substitution in the histidine kinase receptor AgrC of ST22 strains determines virulence properties and infection outcome.

Severe infections caused by Panton-Valentine leukocidin-positive Staphylococcus aureus in infants: report of three cases and review of literature

We report three cases of severe infections in infants caused by Panton-Valentine leukocidin positive Staphylococcus aureus and evolved with a positive outcome. The literature of Panton-Valentine leukocidin positive Staphylococcus aureus infections in infants is reviewed.

CONCLUSION

Our findings suggest that a prompt identification of Panton-Valentine leukocidin positive Staphylococcus aureus and an appropriate therapy can reduce mortality and long-term sequelae. Further research is needed to specify features of Panton-Valentine leukocidin positive Staphylococcus aureus infections in infants.

[Community-onset Staphylococcus aureus infection in neonates]

INTRODUCTION

Staphylococcus aureus is a major cause of neonatal community-onset infections. The emergence of methicillin-resistant S. aureus infections in this age group has been reported in USA in the last few years; however there are no studies in Spain. The aim of this study is to describe the epidemiological, clinical and microbiological characteristics of S. aureus community-onset infections in neonates.

METHODS

We prospectively reviewed the S. aureus infections in neonates over a three year period (2007-2009) in the Pediatric Emergency Department of Hospital 12 de Octubre in Madrid (Spain).

RESULTS

We recorded 30 cases of neonatal S. aureus community-onset infections. Only one isolated (3.3%) was resistant to methicillin, and two (6.7%) were PVL(+).

CONCLUSIONS

Despite the emergence of MRSA outside the hospital in pediatric population in Spain, CA-MRSA and SA PVL(+) infections are not frequent in neonates.

Outbreak of skin and soft tissue infections in a hospital newborn nursery in Italy due to community-acquired meticillin-resistant Staphylococcus aureus USA300 clone

BACKGROUND

Community-acquired meticillin-resistant Staphylococcus aureus (CA-MRSA) is responsible for severe infections in previously healthy people acquired in the community in different areas of the world.

AIM

To report an outbreak of CA-MRSA in a hospital newborn nursery in northern Italy in September-October 2010, its investigation and control measures.

METHODS

The epidemiology of the outbreak is reported. The investigation included screening neonates, parents and staff for MRSA carriage. Molecular strain typing was performed on MRSA isolates.

FINDINGS

The outbreak affected nine neonates with three severe infections. In addition, four mothers had postpartum mastitis, and three mothers and one father had skin infection. The outbreak strain belonged to the USA300 CA-MRSA clone. Asymptomatic carriage of the outbreak strain was found among neonates, parents and hospital staff. The implementation of appropriate infection control measures in the hospital terminated the outbreak.

CONCLUSIONS

To our knowledge, this is the first report of a hospital outbreak caused by the USA300 CA-MRSA clone in Europe. It is important to reinforce infection control measures, particularly in high-risk groups, such as neonates, to prevent USA300 from becoming endemic in European hospitals.

Panton-Valentine leukocidin is not the primary determinant of outcome for Staphylococcus aureus skin infections: evaluation from the CANVAS studies

The impact of Panton-Valentine leukocidin (PVL) on the severity of complicated skin and skin structure infections (cSSSI) caused by Staphylococcus aureus is controversial. We evaluated potential associations between clinical outcome and PVL presence in both methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates from patients enrolled in two large, multinational phase three clinical trials assessing ceftaroline fosamil for the treatment of cSSSI (the CANVAS 1 and 2 programs). Isolates from all microbiologically evaluable patients with monomicrobial MRSA or MSSA infections (n = 473) were genotyped by PCR for pvl and underwent pulsed-field gel electrophoresis (PFGE). Genes encoding pvl were present in 266/473 (56.2%) isolates. Infections caused by pvl-positive S. aureus were associated with younger patient age, North American acquisition, and presence of major abscesses (P<0.001 for each). Cure rates of patients infected with pvl-positive and pvl-negative S. aureus were similar overall (93.6% versus 92.8%; P = 0.72), and within MRSA-infected (94.5% vs. 93.1%; P = 0.67) and MSSA-infected patients (92.2% vs. 92.7%; P = 1.00). This finding persisted after adjustment for multiple patient characteristics. Outcomes were also similar when USA300 PVL+ and non-USA300 PVL+ infections were compared. The results of this contemporary, international study suggest that pvl presence was not the primary determinant of outcome in patients with cSSSI due to either MRSA or MSSA.

An outbreak of post-partum breast abscesses in Mumbai, India caused by ST22-MRSA-IV: genetic characteristics and epidemiological implications

A cluster of methicillin-resistant Staphylococcus aureus (MRSA) breast abscesses in women who had given birth at a hospital in Mumbai, India was investigated retrospectively. Nineteen of 20 cases were caused by a single clone: pvl-positive, spa type 648 (Ridom t852), ccrB:dru subtype 3:0, ST22-MRSA-IV. Despite the presence of pvl and SCCmec type IV, which are common genetic markers in community-associated MRSA, this outbreak was caused by a healthcare-associated, community-onset MRSA that was common in the hospital environment. Thus, infection control practices may have an important role in limiting the spread of this virulent clone.

Panton-Valentine leucocidin gene carriage among Staphylococcus aureus strains recovered from skin and soft tissue infections in Turkey

OBJECTIVES

Regardless of methicillin resistance, Panton-Valentine leucocidin (PVL)-positive Staphylococcus aureus isolates are associated with various types of infections and outbreaks. Limited data exist about the PVL content of S. aureus strains in Turkey. In this multicentre study, we aimed to assess the PVL positivity and antimicrobial susceptibilities of S. aureus isolates recovered from skin and soft tissue samples of both community and nosocomial origin in the study period, 2007-08.

METHODS

Two hundred and forty-two [92 community-acquired (CA) and 150 hospital-acquired (HA)] isolates were included in the study. Analysis of mecA and PVL was carried out using PCR. All isolates underwent susceptibility testing according to the CLSI.

RESULTS

Out of 242 isolates, 77 were mecA positive. PVL was not found among methicillin-resistant S. aureus (MRSA) isolates, but 8 (5.3%) HA methicillin-susceptible S. aureus (MSSA) and 14 (15.2%) CA-MSSA, mostly isolated from furuncles (71.4%), were positive for PVL. Among PVL-positive strains, the penicillin resistance rate was 90.9%. Low resistance rates, <10%, were detected for erythromycin, fusidic acid and co-trimoxazole. PVL-positive strains showed higher rates of susceptibility to erythromycin, gentamicin and rifampicin than negative isolates.

CONCLUSIONS

Based on the findings of this study, infection related to PVL-carrying CA-MRSA is not at an alarmingly high level, but population-based surveillance studies should be done to determine the real status.

Phase 2, randomized, double-blind, dose-ranging study evaluating the safety, tolerability, population pharmacokinetics, and efficacy of oral torezolid phosphate in patients with complicated skin and skin structure infections

Torezolid (TR-700) is the active moiety of the prodrug torezolid phosphate ([TP] TR-701), a second-generation oxazolidinone with 4- to 16-fold greater potency than linezolid against Gram-positive species including methicillin-resistant Staphylococcus aureus (MRSA). A double-blind phase 2 study evaluated three levels (200, 300, or 400 mg) of oral, once-daily TP over 5 to 7 days for complicated skin and skin structure infections (cSSSI). Patients 18 to 75 years old with cSSSI caused by suspected or confirmed Gram-positive pathogens were randomized 1:1:1. Of 188 treated patients, 76.6% had abscesses, 17.6% had extensive cellulitis, and 5.9% had wound infections. S. aureus, the most common pathogen, was isolated in 90.3% of patients (139/154) with a baseline pathogen; 80.6% were MRSA. Cure rates in clinically evaluable patients were 98.2% at 200 mg, 94.4% at 300 mg, and 94.4% at 400 mg. Cure rates were consistent across diagnoses, regardless of lesion size or the presence of systemic signs of infection. Clinical cure rates in patients with S. aureus isolated at baseline were 96.6% overall and 96.8% for MRSA. TP was safe and well tolerated at all dose levels. No patients discontinued treatment due to an adverse event. Three-stage hierarchical population pharmacokinetic modeling yielded a geometric mean clearance of 8.28 liters/h (between-patient variability, 32.3%), a volume of the central compartment of 71.4 liters (24.0%), and a volume of the peripheral compartment of 27.9 liters (35.7%). Results of this study show a high degree of efficacy at all three dose levels without significant differences in the safety profile and support the continued evaluation of TP for the treatment of cSSSI in phase 3 trials.

Neonatal staphylococcal scalded skin syndrome: clinical and outbreak containment review

Staphylococcal scalded skin syndrome (SSSS) is a toxin-mediated exfoliating skin condition predominated by desquamation and blistering. Neonatal outbreaks have already been reported; however, our outbreak highlights the potential for SSSS following neonatal health promotion measures such as intra-muscular vitamin K administration and metabolic screening (heel prick) as well as effective case containment measures and the value of staff screening. Between February and June 2007, five confirmed cases of neonatal SSSS were identified in full-term neonates born in an Irish regional maternity hospital. All infants were treated successfully. Analysis of contact and environmental screening was undertaken, including family members and healthcare workers. Molecular typing on isolates was carried out. An outbreak control team (OCT) was assembled and took successful prospective steps to prevent further cases. All five Staphylococcus aureus isolates tested positive for exfoliative toxin A, of which two distinct strains were identified on pulsed-field gel electrophoresis analysis. Two cases followed staphylococcal inoculation during preventive measures such as intra-muscular vitamin K administration and metabolic screening (heel prick). None of the neonatal isolates were methicillin resistant. Of 259 hospital staff (70% of staff) screened, 30% were colonised with S. aureus, and 6% were positive for MRSA carriage. This is the first reported outbreak of neonatal SSSS in Ireland. Effective case containment measures and clinical value of OCT is demonstrated. Results of staff screening underlines the need for vigilance and compliance in hand disinfection strategies in maternity hospitals especially during neonatal screening and preventive procedures.

Investigation of Panton-Valentine leukocidin expressing Staphylococcus aureus colonization among children in a child care center

The presence of Panton-Valentine leukocidin expressing Staphylococcus aureus colonization was investigated with a qualitative nucleic acid hybridization assay among 122 children and 19 staff in a child care center. Genotyping of 5 Panton-Valentine leukocidin-positive isolates by pulsed-field gel electrophoresis revealed that one child and a teacher from the same class were colonized with the clonally related strains. This finding allowed us to suggest that close contact with colonized people is a risk factor for being colonized.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.