Superantigens in Staphylococcus aureus isolated from prosthetic joint infection

In Vitro Activity of Nisin A Against Staphylococci Isolated from Periprosthetic Joint Infection

Background/Objectives: Staphylococci are the most common causes of periprosthetic joint infection (PJI); new antimicrobials are needed to manage these difficult infections. Nisin A is a lantibiotic peptide derived from Lactococcus lactis that has antimicrobial activity against Gram-positive bacteria, including staphylococci, and is an FDA-approved preservative used in the food and dairy industry. Here, the in vitro nisin A susceptibility of PJI-associated staphylococci was assessed. Methods: The minimum inhibitory concentrations (MICs), minimum biofilm inhibitory concentrations (MBICs), and minimum biofilm bactericidal concentrations (MBBCs) of nisin A were measured by broth microdilution against 106 staphylococcus isolates isolated from PJI. MICs were assessed using 5 × 105 CFU/mL plus nisin A. For MBICs, biofilms were grown on pegged lids for 6 h, followed by 20 h of treatment. For MBBCs, pegged lids were transferred to plates containing media only for 20 h. The results were determined as the lowest concentrations with no visual growth. Two-dimensional MICs with nisin A and vancomycin were assessed for 20 isolates. Fractional inhibitory concentrations (FICs) were calculated to determine synergistic, additive, antagonistic, or indifferent interactions. Results: The MIC that inhibited 90% of S. aureus and S. epidermidis was 4 µg/mL, apart from for the MRSA subset (8 µg/mL). The MBIC that inhibited 90% of isolates was 4 µg/mL. The MBBCs ranged from 4 to 256 µg/mL. When tested together, nisin A and vancomycin yielded an FIC between 1.25 and 1.5, indicative of indifference, except for one isolate each of MRSA and MSSA, for which an additive effect (FIC of 1) was observed. Conclusions: Nisin A showed inhibitory activity against staphylococci that cause PJI.

Prevalence, antimicrobial resistance, and staphylococcal toxin genes of blaTEM-1a -producing Staphylococcus aureus isolated from animals in Chongqing, China

BACKGROUND

Staphylococcus aureus infection of livestock animals and humans is a major public health issue. There are reports of antimicrobial resistance and multiple staphylococcal superantigen genes in many countries and several provinces of China, but the status in Chongqing, China is uncertain.

OBJECTIVES

The aim of this study was to determine the prevalence, antimicrobial susceptibility, and other molecular characteristics of S. aureus isolates from livestock animals in Chongqing.

METHODS

Staphylococcus aureus was isolated and identified by selective enrichment and amplification of the nuc gene from 1371 samples collected at farms in Chongqing. The agar dilution method was used to determine the resistant phenotype, and extended spectrum β-lactamase genes were amplified by PCR. Methicillin-resistant S. aureus was verified by the presence of the mecA gene, and the presence or absence of SE, SEl, and TSST-1 genes was detected in the isolates.

RESULTS

We cultured 89 S. aureus isolates from 1371 samples between March 2014 and December 2017. These isolates were from pigs, cattle, goats, rabbits, and chickens. There were four methicillin-resistant S. aureus strains (three from pigs and one from a chicken). The 89 isolates had high resistance to penicillin (93.3%) and ampicillin (92.1%), but most were susceptible to amikacin and ofloxacin, with resistance rates below 10%. A total of 62.9% of the isolates had varying degrees of multidrug resistance. Almost all strains, except for three isolates from chickens, were positive for bla_TEM-1a . There were 19 of 20 tested staphylococcal SE/SEl/TSST-1 genes present (all except for seq), and the predominant genes were sei (58.4%), tst-1 (56.2%), and seg (51.7%).

CONCLUSIONS

The high antimicrobial resistance and prevalence of bla_TEM-1a reinforce the need to reduce the usage of antimicrobials in livestock. The universal existence of staphylococcal toxin genes implies a potential threat to public health by animal-to-human transmission via the food chain.

Surveillance of osteoarticular infections caused by Staphylococcus aureus in a paediatric hospital in Mexico City

Staphylococcus aureus is the main aetiologic agent of osteoarticular infections (OAIs) in paediatric patients. The aim of this prospective unicenter study was to describe the phenotypic and genotypic characteristics of S. aureus isolates obtained from OAIs in paediatric patients admitted to tertiary care hospital. Through a surveillance program called OsteoCode, a multidisciplinary team was created and we identified 27 patients with OAIs caused by S. aureus from 2019 to 2021. The susceptibility profile, virulence factors, biofilm formation, pulsed-field gel electrophoresis (PFGE), clonal complex (CC) and sequence type (ST) were determined. In addition, the clinical characteristics and evolution of the patients presented six months after the diagnosis of OAIs were described. Ninety-two percent of the isolates were methicillin-sensitive S. aureus (MSSA). In methicillin-resistant S. aureus (MRSA), SCCmec-II and SCCmec-V were detected. The pvl gene was only observed in MSSA (18.5%) and was associated with highest fever (p=0.015), multiple localization (p=0.017), and soft tissue sites of infection beyond the bone (pyomyositis, pulmonary abscess) (p=0.017). Biofilm formation was detected in 55.6% of isolates. The most common CC were CC5 and CC30 which represent the most common linages for bone and joint infections worldwide. The isolates were distributed in different STs, and ST672 was predominant. MRSA were associated with a longer duration of intravenous treatment and a prolonged hospital stay (p=0.023). Recurrent infection occurred in five children and orthopaedic complications in 33.3% of patients. This is the first study that reflects the epidemiology of S. aureus in OAIs in paediatric patients in Mexico; a clear predominance of MSSA distributed in different STs was observed. Our findings highlight that a multidisciplinary team is required for the diagnosis and treatment of OAIs.

Arana D, Monereo A, Domingo D, Cordero J, Sánchez Romero MI, García Viejo MÁ, Lora-Tamayo J, Chaves F. Genotypic and Phenotypic Characteristics of Staphylococcus aureus Prosthetic Joint Infections: Insight on the Pathogenesis and Prognosis of a Multicenter Prospective Cohort

BACKGROUND

Staphylococcus aureus is the leading cause of prosthetic joint infection (PJI). Beyond the antibiogram, little attention has been paid to the influence of deep microbiological characteristics on patient prognosis. Our aim was to investigate whether microbiological genotypic and phenotypic features have a significant influence on infection pathogenesis and patient outcome.

METHODS

A prospective multicenter study was performed, including all S. aureus PJIs (2016-2017). Clinical data and phenotypic (agr functionality, β-hemolysis, biofilm formation) and genotypic characteristics of the strains were collected. Biofilm susceptibility to antimicrobials was investigated (minimal biofilm eradication concentration [MBEC] assay).

RESULTS

Eighty-eight patients (39.8% men, age 74.7 ± 14.1 years) were included. Forty-five had early postoperative infections (EPIs), 21 had chronic infections (CPIs), and 19 had hematogenous infections (HIs). Twenty (22.7%) were caused by methicillin-resistant S. aureus. High genotypic diversity was observed, including 16 clonal complexes (CCs), with CC5 being the most frequent (30.7%). agr activity was greater in EPI than CPI (55.6% vs 28.6%; P = .041). Strains causing EPI were phenotypically and genotypically similar, regardless of symptom duration. Treatment failure (36.5%) occurred less frequently among cases treated with implant removal. In cases treated with debridement and implant retention, there were fewer failures among those who received combination therapy with rifampin. No genotypic or phenotypic characteristics predicted failure, except vancomycin minimal inhibitory concentration ≥1.5 mg/L (23.1% failure vs 3.4%; P = .044). MBEC50 was >128 mg/L for all antibiotics tested and showed no association with prognosis.

CONCLUSIONS

S. aureus with different genotypic backgrounds is capable of causing PJI, showing slight differences in clinical presentation and pathogenesis. No major microbiological characteristics were observed to influence the outcome, including MBEC.

Influence of molecular characteristics in the prognosis of methicillin-resistant Staphylococcus aureus prosthetic joint infections: beyond the species and the antibiogram

We have explored the relationship of phenotypic (antibiogram, β-haemolysis, agr functionality, biofilm formation) and genotypic characteristics on the prognosis of 18 cases of methicillin-resistant S. aureus prosthetic joint infection (2005-2015). All isolates belonged to CC5, and had agr type II. This pilot study suggests that phage-borne genes belonging to the immune evasion cluster (chp, sak and scn) were more frequent among episodes with treatment failure (80.0 vs. 37.5%).

Prevalence and characteristics of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus nasal colonization among a community-based diabetes population in Foshan, China

Aims/Introduction

Evidence suggests that diabetes might cause an increase in colonization of Staphylococcus aureus (S. aureus) and methicillin‐resistant S. aureus (MRSA) in community settings. We carried out a cross‐sectional study to determine the prevalence and influencing factors of S. aureus and MRSA nasal colonization among a community‐based diabetes population, and to identify the characteristics of the isolated strains.

Materials and Methods

A total of 956 participants from 11 community settings were included in the study.

Results

Of the 529 diabetes participants, 46 were colonized with S. aureus and 22 were colonized with MRSA. Of the 427 non‐diabetes participants, 25 were colonized with S. aureus and 12 were colonized with MRSA. Men (odds ratio 0.45, 95% confidence interval 0.20–0.99, P = 0.047) were less likely to have S. aureus nasal colonization, and those with well‐controlled blood glucose (odds ratio 2.04, 95% confidence interval 1.01–4.13, P = 0.047) among the diabetes population were more likely to have S. aureus nasal colonization. The proportion of multidrug‐resistant S. aureus strains in the diabetes population (52.17%) was higher than that in the non‐diabetes population (28.00%; χ² = 3.848, P = 0.050). The most common clonal complex type and Staphylococcal chromosome cassette mec type of MRSA in diabetes population was clonal complex 5 (40.91%) and type IV (27.27%), respectively. The proportion of Panton–Valentine leukocidin gene in MRSA strains was 17.65%. There was great sequence type diversity in MRSA strains.

Conclusions

The prevalence of MRSA in the community‐based diabetes population was moderate, and the high proportions of multidrug‐resistant S. aureus strains and diverse molecular characteristics in the diabetes population should be noticed.

Antibiofilm Activity of Low-Amperage Continuous and Intermittent Direct Electrical Current

Bacterial biofilms are difficult to treat using available antimicrobial agents, so new antibiofilm strategies are needed. We previously showed that 20, 200, and 2,000 μA of electrical current reduced bacterial biofilms of Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. Here, we tested continuous direct current at lower amperages, intermittent direct current, and combinations of surface materials (Teflon or titanium) and electrode compositions (stainless steel, graphite, titanium, or platinum) against S. aureus, S. epidermidis, and P. aeruginosa biofilms. In addition, we tested 200 or 2,000 μA for 1 and 4 days against biofilms of 33 strains representing 13 species of microorganisms. The logarithmic reduction factor was used to measure treatment effects. Using continuous current delivery, the lowest active amperage was 2 μA for 1, 4, or 7 days against P. aeruginosa and 5 μA for 7 days against S. epidermidis and S. aureus biofilms. Delivery of 200 μA for 4 h a day over 4 days reduced P. aeruginosa, S. aureus, and S. epidermidis biofilms on Teflon or titanium discs. A reduction of P. aeruginosa, S. aureus, and S. epidermidis biofilms was measured for 23 of 24 combinations of surface materials and electrode compositions tested. Four days of direct current delivery reduced biofilms of 25 of 33 strains studied. In conclusion, low-amperage current or 4 h a day of intermittent current delivered using a variety of electrode compositions reduced P. aeruginosa, S. aureus, and S. epidermidis biofilms on a variety of surface materials. The electricidal effect was observed against a majority of bacterial species studied.