Distribution of virulence genes in spa types of methicillin-resistant Staphylococcus aureus isolated from patients in intensive care units

Molecular Epidemiology of Staphylococcus aureus in a Tertiary Hospital in Anhui, China: ST59 Remains a Serious Threat

Purpose

This study aimed to investigate the molecular characteristics, antimicrobial resistance and hemolytic phenotype of Staphylococcus aureus isolated from Anhui, China.

Results

From August 2021 to January 2022, 214 S. aureus isolates were collected from the Anhui Provincial Hospital. This study identified 117 methicillin-resistant S. aureus and 97 methicillin-sensitive S. aureus isolates, and the detection rate of methicillin-resistant isolates was 1.8-fold higher than the average isolates reported in China (53.9% vs 30.5%). S. aureus isolates share identity at five or more of the seven MLST-based housekeeping loci, referred to as the clonal complex (CC). Forty ST types were found in 214 clinical S. aureus isolates, with the most extensive distribution of ST59 and ST6697 typing numbers and higher CC5 detection rates than any other clonal group. (The ST typing is the result of the MLST typing website query.) To detect the virulence of ST types of S. aureus, hemolysis experiments were performed on 214 clinical isolates, and it was concluded that ST59 had a relatively robust hemolytic capacity.

Conclusion

Anhui S. aureus isolates have unique molecular and antibiotic resistance profiles. The antibiotic resistance profile may be related to the random use of antibiotics.

Molecular characterization and virulence gene profiling of methicillin-resistant Staphylococcus aureus associated with bloodstream infections in southern China

Methicillin-resistant Staphylococcus aureus (MRSA) causes an enormous illness burden, including skin and soft tissue infections (SSTIs), pneumonia, bloodstream infections (BSI), and sepsis. BSI are associated with significant patient morbidity and mortality worldwide. However, limited information is available on MRSA-related BSI in China. This study aimed to investigate the molecular characterization of 77 MRSA isolates recovered from hospitalized patients with BSI between 2012 and 2020 at three first-class tertiary hospitals in southern China based on multilocus sequence typing (MLST), spa typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Overall, 13 clonal complexes (CCs) were identified, with CC59 and CC5 being the largest clusters, indicating high genetic diversity among BSI-causing MRSA isolates. ST59 was the most prevalent MLST type (22.1%). ST5/ST764-MRSA SCCmec II was the predominant adult MRSA clone, whereas ST59-MRSA SCCmec IV was the most common pediatric MRSA clone. ST5-t2460, ST764-t1084, and ST59-t437 were the most common types of adult MRSA isolates, whereas ST59-t437 and ST59-t172 were the predominant types of children’s MRSA isolates. ST59-SCCmec IV/V represented the most common clone among community acquired-MRSA isolates. ST5/ST764-SCCmec II was the most common type of hospital-associated MRSA isolate. The most prevalent toxin-encoding genes detected were hla, hld, icaA, and clfA (96.1–100%). Forty-three (100%, 43/43) isolates harbored more than 18 of the tested virulence genes in adults and eight virulence genes (23.5%, 8/34) in children. Virulence gene analysis revealed diversity among different clones: the positivity rates for the Panton-Valentine leukocidin (PVL) gene were 55.8 and 35.3% in adult and pediatric MRSA isolates, respectively; the genes seb–sei were present in all adult strains; seb–seg–sei–seo were present in all ST5, ST59, ST15, ST45, and ST22 adult strains; and seg–sei–sem–sen–seo were present in different clones, including ST15, ST45, and ST22 adult MRSA isolates and ST25, ST30, ST546, and ST72 children’s MRSA isolates. Adult MRSA isolates had significantly higher antibiotic resistance rates and virulence gene prevalence than pediatric MRSA isolates. For 8 years, this study provided epidemiological data on the molecular characteristics and virulence genes in different groups of MRSA BSI in China. Our findings may provide critical information for a better understanding of MRSA BSI.

Methicillin-resistant Staphylococcus aureus of the clonal lineage ST5-SCCmecII-t2460 was associated with high mortality in a Wuhan hospital

Methicillin-resistant Staphylococcus aureus (MRSA) is an important human pathogen that can cause serious infectious diseases. An emerging MRSA strain, ST5-SCCmecII spa-type-t2460 (SMRSA), has spread rapidly since its recent emergence in China, but little information is available about this lineage. In this study, 91 MRSA isolates were collected from patients treated in the Zhongnan Hospital, Wuhan University, from 2018 to 2019, and investigated for their molecular characteristics, antibiotic resistance profiles, and clinical characteristics. The predominant lineage, SMRSA, accounted for 37.4% (34/91) of the isolates, followed by ST239-SCCmecIII-t030 (19.8%, 18/91) and ST59-SCCmecIV-t437 (8.8%, 8/91). In contrast to the latter two non-SMRSA (nSMRSA) lineages, which are among the main MRSA found in Chinese settings, SMRSA exhibited small colony variant (SCV) phenotype and had extremely high resistance rates to erythromycin (100.0%), clindamycin (100.0%), levofloxacin (100.0%), tetracycline (97.1%), moxifloxacin (97.1%), and ciprofloxacin (100%), but was more susceptible to rifampicin (resistance rate 3%). The levels of white blood cells (WBC) and procalcitonin (PCT) and the 30-day mortality in patients infected with SMRSA were (12.54 ± 6.61) × 10⁹/L, 0.66 ng/mL, and 52.9%, respectively, which were much higher than those in patients infected with nSMRSA. In addition, patients infected with SMRSA were more frequently admitted to the intensive care unit (ICU) and submitted to invasive procedures than those infected with nSMRSA. In conclusion, SMRSA showed SCV phenotype and exhibited multiple antibiotic-resistance profiles. In this study, SMRSA was associated with serious infections and poor prognosis. Compared with ST239, ST59, or other nSMRSA strains, patients infected with SMRSA strains have higher 30-day mortality, increased levels of inflammatory biomarkers, and more frequent ICU hospitalization and invasive procedures.

Spa typing of Staphylococcus aureus Isolated from Clinical Specimens from Outpatients in Iraq

Methicillin-resistant Staphylococcus aureus (MRSA) is notorious as a hospital superbug and a problematic pathogen among communities. The incidence of MRSA has substantially increased over time in Iraq. The aim of this study was to determine the prevalence and spa types of MRSA isolates from outpatients or patients upon admission into hospitals. Various biochemical tests identified S. aureus isolates, and then this identification was confirmed by PCR using species-specific 16S rRNA primer pairs. Antibiotic susceptibility was determined against methicillin, oxacillin, and vancomycin using the disk diffusion method. Vancomycin MIC was detected by VITEK 2 compact system. All the identified isolates were screened for the presence of mecA and lukS-PV-lukF-PV genes; 36 of them were subjected to spa typing-based PCR. Out of 290 clinical samples, 65 (22.4%) were S. aureus, of which 62 (95.4%) strains were resistant to oxacillin and methicillin. Except for two isolates, all MRSA isolates were mecA positive. One of the three MSSA isolates was mecA positive. Five strains were resistant to vancomycin. Fourteen (21.5%) isolates were positive for the presence of lukS-PV-lukF-PV genes. Spa typing of 36 S. aureus isolates revealed eleven different spa types, t304 (30.3%), t307 (19.4%), t346 (8.3%), t044 (8.3%), t15595 (8.3%), t386 (5.5%), t5475 (5.5%), t17928 (2.8%), t14870 (2.8%), t021 (2.8%), and t024 (2.8%). These findings could be useful for assessing the genetic relatedness of strains in the region for epidemiological and monitoring purposes, which would be essential to limiting the spread of MRSA.

Molecular epidemiology and virulence factors of methicillin-resistant Staphylococcus aureus isolated from patients with bacteremia

BACKGROUND

The various virulence factors of methicillin-resistant Staphylococcus aureus bacteremia (MRSAB) are associated with a high mortality rate worldwide. Further studies are warranted to confirm the significant relationship between the strains and virulence genes. Here, we prospectively investigated the molecular characteristics underlying the genotypes and virulence factors of MRSA isolated from patients with bacteremia.

METHODS

We collected 59 MRSA isolates from adult patients with bacteremia. Antimicrobial susceptibility results were obtained with the Vitek2 automated system. Genotypes were identified with multi-locus sequence typing (MLST) and pulse-field gel electrophoresis (PFGE), and 21 virulence genes were detected with polymerase chain reaction (PCR).

RESULTS

The 59 MRSA isolates mainly comprised ST5 (n = 31, 52.5%) and ST72 (n = 22, 37.2%). Most ST5 isolates and all ST72 isolates were clustered into one and two PFGE groups, respectively. The mean number of virulence genes was higher in ST5 than in ST72. Sel was more frequently detected in ST5 than in ST72, whereas sec and sed were found only in ST5. ST5 had significantly higher resistance against many antibiotics than ST72.

CONCLUSION

Most MRSA isolates causing bacteremia were ST5 (CC5) and ST72 (CC8), and those belonging to the same STs were divided into only a few PFGE groups. ST5 was associated with higher antibiotic resistance and staphylococcal superantigen toxin genes, than ST72, which may be related to its higher virulence.

Novel spa and Multi-Locus Sequence Types (MLST) of Staphylococcus Aureus Samples Isolated from Clinical Specimens in Korean

Staphylococcus aureus bacteremia is one of the most frequent and severe bacterial infections worldwide. The increased incidence of S. aureus infections with a diverse pattern of S. aureus protein A (spa) types across different geographic regions is a global challenge. This study investigated a novel spa type of methicillin-resistant S. aureus in a clinically isolated specimen. A total of 109 clinical S. aureus samples were subjected to 19 sets of antimicrobial susceptibility testing using the Kirby-Bauer disk diffusion method. Molecular typing was performed with S. aureus protein A (spa) and multi-locus sequence types (MLST) via polymerase chain reaction and sequencing. The methicillin-resistant S. aureus samples in our study accounted for 55.05% (60/109) of the total. A novel spa type was detected in five (5/60) strains. This gh22 isolate was identified in antimicrobial susceptibility tests of 15 kinds of antibiotics. Antibiotic resistance genes included mecA, TEM, aac(6')-aph(2"), ermA, and tetM. Eleven S. aureus samples were classified as t2460, t338, t324, t693, five unknown spa types (new spa types), and undefined MLST (novel MLST). We report a high prevalence rate of t2460 methicillin-resistant S. aureus samples in our country. Additionally, novel spa gh22, MLST ST4613, and clonal compact CC5-type strains (T1:M1:B1:B1:M1:E1:K1, r26:r17:r34:r34:r17:r13:r16, mlst;1:4:1:4:559:495:10) showing multidrug resistance were identified among S. aureus samples.

Multidrug-resistant Staphylococcus aureus Colonization in Healthy Adults Is more Common in Bhutanese Refugees in Nepal than Those Resettled in Ohio

Although studies have shown that human migration is one of the risk factors for the spread of drug-resistant organisms such as methicillin-resistant Staphylococcus aureus (MRSA), surveillance studies examining MRSA among refugee populations in the US are lacking. This study aimed to assess the prevalence and molecular characteristics of S. aureus among Bhutanese refugees living in Nepal and resettled in Northeast Ohio (NEO). One hundred adult Bhutanese refugees from each geographic location were enrolled between August 2015 and January 2016. The participants were interviewed to collect demographic information and potential risk factors for carriage. Nasal and throat swabs were collected for bacterial isolation. All S. aureus isolates were characterized by spa typing and tested for the presence of Panton-Valentine leukocidin (PVL) and mecA genes; selected isolates were tested by multilocus sequence typing (MLST). The overall prevalence of S. aureus was 66.0% and 44.0% in NEO and Nepal, respectively. In Nepal, 5.8% (3/52) of isolates were MRSA and 1.1% (1/88) in NEO. Twenty-one isolates in NEO (23.9%) were multidrug-resistant S. aureus (MDRSA), while 23 (44.2%) in Nepal were MDRSA. In NEO, 41 spa types were detected from 88 S. aureus isolates. In Nepal, 32 spa types were detected from 52 S. aureus isolates. spa types t1818 and t345 were most common in NEO and Nepal, respectively. The overall prevalence of PVL-positive isolates among S. aureus in Nepal and NEO was 25.0% and 10.2%. ST5 was the most common sequence type in both locations. Bhutanese refugees living in Nepal and resettled in NEO had high prevalence of S. aureus and MDRSA. The findings suggest a potential need for CA-MRSA surveillance among the immigrant population in the U S and among people living in Nepal, and a potential need to devise appropriate public health measures to mitigate the risk imposed by community-associated strains of S. aureus and MRSA.

Molecular characteristics and virulence gene profiles of Staphylococcus aureus causing bloodstream infection

Background

The rate of methicillin-resistant Staphylococcus aureus (MRSA) among the total of S. aureus isolates decreased to 35.3% in 2017 in China. It is unclear whether the molecular characteristics of S. aureus isolates have changed as the rate decreased.

Objective

This study aimed to investigate the molecular characteristics and virulence genes profile of S. aureus isolates causing bloodstream infection and analyze the correlation between the prevalence rates of the common sequence types and MRSA.

Methods

A total of 112 S. aureus strains from eight hospitals of four cities, including 32 MRSA isolates, were identified and evaluated through multilocus sequence typing, spa typing, and determination of virulence genes.

Results

Twenty-five STs were identified, of which ST5 (21.4%) was the most prevalent, whereas the prevalence of ST239 correlated with the rate of MRSA among all S. aureus isolates. Forty-six spa types were identified, of which t2460 (14.3%) was the most common. clfa, hla, seb, fnbA and hlb were the prevailing virulence genes. 81.3% MRSA and 45.0% methicillin-sensitive S. aureus (MSSA) isolates harbored six or more tested virulence genes. ST5-t2460, seldom noted in bloodborne S. aureus isolates in China, was the most common clone. The prevalence of harboring six or more virulence genes in ST5-t2460 and ST188-t189 were 93.8% and 8.3%, respectively.

Conclusion

ST5-t2460 was the most common clone in S. aureus causing bloodstream infection followed by ST188-t189, which had never been noted in China before. Moreover, ST5-t2460 harbored more virulence genes than ST188-t189, and the prevalence of ST239 clone decreased with the proportion of MRSA among all S. aureus isolates.

Prevalence, multidrug resistance and molecular typing of methicillin-resistant Staphylococcus aureus (MRSA) in retail meat from Punjab, India

OBJECTIVES

This study reports the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in retail meat from Punjab, India.

METHODS

Classical microbiological methods were applied to isolate and identify S. aureus isolates. Isolates also underwent Etest. PCR and sequencing were used to identify and characterise antimicrobial resistance genes. MLST, SCCmec and spa typing were performed.

RESULTS

A total of 408 meat and 101 swab samples were processed for S. aureus isolation. Phenotypic resistance was highest to penicillin (90.97%), followed by ciprofloxacin (61.80%), tetracycline (45.14%) and erythromycin (11.11%). Isolates from chicken samples showed significantly higher MICs for tetracycline than chevon and pork samples and significantly higher MICs for trimethoprim/sulfamethoxazole and gentamicin than chevon and swab samples (P<0.05). No isolates were phenotypically resistant to vancomycin (MICs of 0.5-2μg/mL). Most isolates (52.78%, 95% CI 44.63-60.93%) were multidrug-resistant and carried resistance genes to penicillin (blaZ), oxacillin (mecA), gentamicin (aacA-aphD), erythromycin (ermB, ermC) and tetracycline (tetK, tetL, tetM). MRSA was only found in chicken samples (2.72%; 4/147). Seven S. aureus (5.07%) were borderline oxacillin-resistant (MIC range 4-8μg/mL). All MRSA were SCCmecV-pvl⁺-t442, among which three isolates were ST5. Their genotype was mecA⁺, blaZ⁺, aacA-aphD⁺, tetK⁺, ermC^+/-. Among the erythromycin-resistant isolates, 25% were MRSA, of which 12.5% isolates expressed an inducible macrolide-lincosamide-streptogramin B (iMLS_B) phenotype.

CONCLUSION

These data confirm the presence of ST5-t442-MRSA-SCCmecV-pvl⁺ and iMLS_B MRSA in meat samples, indicating a potential role of meat in the dissemination of multidrug-resistant S. aureus strains and successful MRSA lineages in Punjab.

Molecular characterization of clonal lineage and staphylococcal toxin genes from S. aureus in Southern Nigeria

Background

Staphylococcus aureus is a human colonizer with high potential for virulence, and the spread of the virulent strains from the colonized hosts to non-carriers in the community is on the increase. However, there are few reports on comprehensive analysis of staphylococcal enterotoxin (SE) genes with clonal lineage in S. aureus in Africa. This is essential because of diversity of cultures and habits of the people. This study analyzed spa types and enterotoxin genes in S. aureus strains previously isolated from the human nostrils, poultry and clinical samples in Southern Nigeria.

Methods

Forty-seven S. aureus isolates were obtained from humans nostrils (n = 13), clinical strains (n = 21) and poultry (n = 13) from previous studies in Southern Nigeria. The strains were analyzed for mecA gene, selected toxins genes (sea, seb, sec, sed, see, seg, seh, sei, sej, sek, sel, sem, sen, seo, sep, seq, ser, seu) and Panton-Valentine leukocidin (PVL) gene (lukS-PV/lukF-PV) by PCR. Population structures of the strains were detected by Staphylococcal protein A (spa) typing.

Results

Twenty different spa types were obtained with the highest percentages, 17% observed in spa type t091 from clinical, nasal and poultry samples while t069 was the most prevalent spa type in poultry. Two MRSA were only detected in human strains. The poultry strains had the highest occurrence of SE genes (18%) followed by nasal strains (15%) and clinical strains (10%). Eighty-nine percent of all tested isolates harbored at least one SE gene; seo was the most prevalent (34%) followed by seg (30%) and sea (21%), while sec, see and sej were absent in all strains. Spa type t355 was associated with lukS-PV/lukF-PV gene and complete absence of all studied SE. Sea, seq, seb, sek were associated with spa type t069; sea was associated with t127 while sep was associated with spa type t091. There were coexistences of seo/seg and sei/seg.

Conclusions

The higher carriage of staphylococci enterotoxin genes by the nasal and poultry S. aureus strains suggests a high potential of spread of staphylococcal food poisoning through poultry and healthy carriers in the community. This is the first report of high occurrence of staphylococcal enterotoxins genes in poultry from Nigeria.

Distribution of the Most Prevalent Spa Types among Clinical Isolates of Methicillin-Resistant and -Susceptible Staphylococcus aureus around the World: A Review

Background:Staphylococcus aureus, a leading cause of community-acquired and nosocomial infections, remains a major health problem worldwide. Molecular typing methods, such as spa typing, are vital for the control and, when typing can be made more timely, prevention of S. aureus spread around healthcare settings. The current study aims to review the literature to report the most common clinical spa types around the world, which is important for epidemiological surveys and nosocomial infection control policies.

Methods: A search via PubMed, Google Scholar, Web of Science, Embase, the Cochrane library, and Scopus was conducted for original articles reporting the most prevalent spa types among S. aureus isolates. The search terms were “Staphylococcus aureus, spa typing.”

Results: The most prevalent spa types were t032, t008 and t002 in Europe; t037 and t002 in Asia; t008, t002, and t242 in America; t037, t084, and t064 in Africa; and t020 in Australia. In Europe, all the isolates related to spa type t032 were MRSA. In addition, spa type t037 in Africa and t037and t437 in Australia also consisted exclusively of MRSA isolates. Given the fact that more than 95% of the papers we studied originated in the past decade there was no option to study the dynamics of regional clone emergence.

Conclusion: This review documents the presence of the most prevalent spa types in countries, continents and worldwide and shows big local differences in clonal distribution.

Antimicrobial resistance and prevalence of CvfB, SEK and SEQ genes among Staphylococcus aureus isolates from paediatric patients with bloodstream infections

Staphylococcus aureus (S. aureus) is one of the most frequently isolated pathogens in neonatal cases of early and late-onset sepsis. Drug resistance profiles and carriage of toxin genes may affect the treatment and outcome of an infection. The present study aimed to determine the antimicrobial resistance patterns and frequencies of the toxin-associated genes conserved virulence factor B (CvfB), staphylococcal enterotoxin Q (SEQ) and staphylococcal enterotoxin K (SEK) among S. aureus isolates recovered from paediatric patients with bloodstream infections (BSIs) in Guangzhou (China). Of the 53 isolates, 43.4% were methicillin-resistant S. aureus (MRSA), and resistance rates to penicillin, erythromycin, clindamycin, trimethoprim/sulfamethoxazole, tetracycline, and ciprofloxacin of 92.5, 66.0, 62.3, 13.2, 20.8 and 1.9% were recorded, respectively. However, no resistance to nitrofurantoin, dalfopristin/quinupristin, rifampicin, gentamicin, linezolid or vancomycin was detected. Resistance to erythromycin, clindamycin and tetracycline in the MRSA group was significantly higher than that in the methicillin-susceptible S. aureus (MSSA) group. No significant differences in antimicrobial resistance patterns were noted between two age groups (≤1 year and >1 year). The proportion of S. aureus isolates positive for CvfB, SEQ and SEK was 100, 34.0 and 35.8%, respectively, with 24.5% (13/53) of strains carrying all three genes. Compared with those in MSSA isolates, the rates of SEK, SEQ and SEK + SEQ carriage among MRSA isolates were significantly higher. Correlations were identified between the carriage of SEQ, SEK and SEQ + SEK genes and MRSA (contingency coefficient 0.500, 0.416, 0.546, respectively; P<0.01). In conclusion, MRSA isolated from the blood of paediatric patients with BSIs not only exhibited higher rates of antimicrobial resistance than MSSA from the same source, but also more frequently harboured SEK and SEQ genes. The combination of the two aspects influenced the dissemination of MRSA among children. The present study clarified the characteristics of BSI-associated S. aureus and enhanced the current understanding of the pathogenicity and treatment of MRSA.

Effect of daily chlorhexidine bathing on the acquisition of methicillin-resistant Staphylococcus aureus in a medical intensive care unit with methicillin-resistant S aureus endemicity

BACKGROUND

Universal decolonization is recommended in intensive care units (ICUs) that have unacceptably high rates of methicillin-resistant Staphylococcus aureus (MRSA) despite implementation of basic prevention strategies.

METHODS

An interrupted time series study was performed to evaluate the effect of daily chlorhexidine bathing on the acquisition of MRSA in a medical ICU with MRSA endemicity. There was a 14-month control period and a 16-month chlorhexidine bathing period. Segmented Poisson regression analysis was performed to assess the impact of daily chlorhexidine bathing on the incidence density of MRSA. Also, chlorhexidine susceptibility testing with polymerase chain reaction for the qacA/B gene was performed on MRSA isolates collected during the chlorhexidine bathing period.

RESULTS

There was a significant reduction in trend (-0.056; 95% confidence interval, -0.095 to -0.017; P = .005) of incidence density of MRSA despite a significant increase in both level and trend of MRSA prevalence rates during the chlorhexidine bathing period. However, there was no significant reduction in level of incidence density of MRSA during the interventional period. Minimum inhibitory concentration of chlorhexidine and the detection rates of the qacA/B gene for a total of 174 MRSA isolates did not increase during the chlorhexidine bathing period.

CONCLUSIONS

Daily chlorhexidine bathing resulted in a significantly decreasing trend of MRSA acquisition rates irrespective of increased MRSA prevalence rates in the medical ICU. There was no shift of chlorhexidine-resistant MRSA strains.

Dissemination of fusidic acid resistance among Staphylococcus aureus clinical isolates

BACKGROUND

A significant trend towards increased fusidic acid (FA) resistance among Staphylococcus aureus with increased duration of use is of concern. The aim of the present study is to investigate the dissemination of fusidic acid resistance among Staphylococcus aureus clinical isolates.

METHODS

The susceptibility of S. aureus isolates to antimicrobial agents was determined by disc-diffusion method. The minimal inhibitory concertrations(MICs) of fusidic acid and vacomycin for fusidic acid-resisitant isolates were determined by ager dillution method. FA resistance determinants were determined by PCR and DNA sequencing. SCCmec typing, spa typing and multi-locus sequence typing were used for the determination of molecular characteristics for S. aureus isolates.

RESULTS

A total of 392 non-duplicate S. aureus isolates including 181 methicillin-resistant S. aureus (MRSA) isolates, which were isolated from the clinical specimens of patients at a Chinese tertiary hospital from January, 2012 to September, 2013, were collected for investigating FA resistance. Among 392 S. aureus clinical isolates tested, 56 (14.3%) with FA MIC values ranging from 2 μg/ml to ≥128 μg/ml were resistant to FA. The proportions of FA resistance among MRSA and MSSA isolates were 27.1% (49/181) and 3.3% (7/211). There was a trend of rapidly increased FA resistance among S. aureus and MRSA isolates from 5.2% and 8.9% in 2012 to 24.9% and 45.1% in 2013. Acquired FA resistance gene, fusB, was present in 73.2% (41/56) of FA-resistant S. aureus isolates. fusC and fusA mutation were not found in any of tested isolates. A total of 9 sequence types (STs) and 12 spa types were identified among the 56 FA-resistant S. aureus isolates. ST5 accounting for 66.1% (37/56) was the most prevalent ST. The majority (92.9%, 52/56) of the isolates tested belonged to clonal complex 5(CC5). t2460 was the most prevalent spa type, accounting for 67.9% (38/56) . ST5-MRSA- II-t2460 was predominant clone, accounting for 75.5% (37/49) of FA-resistant MRSA isolates and 66.1% (37/56) of FA-resistant S. aureus isolates. Five of 7 FA-resistant MSSA isolates belonged to ST630-MSSA.

CONCLUSION

Increased FA resistance among S. aureus isolates was found in China. fusB was predominant FA resistance determinant. The spread of CC5 clone, especially novel ST5-MRSA- II-t2460 clone with high-level resistance to FA, was responsible for the increase of FA resistance.

Antimicrobial susceptibility, virulence determinant carriage and molecular characteristics of Staphylococcus aureus isolates associated with skin and soft tissue infections

A better understanding of the antimicrobial susceptibility, carriage of virulence determinants and molecular characteristics of Staphylococcus aureus isolates associated with skin and soft tissue infections (SSTIs) may provide further insights related to clinical outcomes with these infections. From January 2012 to September 2013, a total of 128 non-duplicate S. aureus isolates were recovered from patients with SSTIs. All 128 S. aureus SSTI isolates carried at least five virulence genes tested. Virulence genes detected among at least 70% of all tested isolates included hld (100%), hla (95.3%), icaA (96.9%), clf (99.2%), sdrC (79.7%), sdrD (70.3%), and sdrE (72.7%). The prevalence of MRSA isolates with 10 virulence genes tested (54.4%, 31/56) was significantly higher than that among MSSA isolates (35.2%, 25/71) (p < 0.05). The positive rates of seb, sen, sem, sdrE and pvl among MRSA isolates were significantly higher than among MSSA isolates (p < 0.05). ST7 and ST630 accounting for 10.9% were found to be the predominant STs. The most prevalent spa type was t091 (8.6%). MRSA-ST59-SCCmec IV was the most common clone (12.3%) among MRSA isolates whereas among MSSA isolates the dominant clone was MSSA-ST7 (15.5%). Six main clonal complexes (CCs) were found, including CC5 (52.3%), CC7 (11.7%), CC59 (8.6%), CC88 (6.3%), CC398 (4.7%), and CC121 (3.1%). A higher carriage of seb and sec was found among CC59 isolates. In comparison to CC5 and CC7 isolates, those with the highest carriage rates (>80.0%) of sdrC and sdrD, CC59 isolates had lower prevalence of these two virulence genes. All CC59 isolates were susceptible to gentamicin and trimethoprim/sulfamethoxazole, while CC5 and CC7 isolates had resistance rates to these two antimicrobials of 25.4% and 20.9%, and 40.0% and 40.0%, respectively. The resistance rates for tetracycline, clindamycin, and erythromycin among CC5 isolates were lower than among CC7 and CC59 isolates. In conclusion, the molecular typing of S. aureus SSTI isolates in the present study showed considerable heterogeneity. ST7 and ST630 became prevailing clones. Different S. aureus clones causing SSTIs were associated with specific antimicrobial resistance and virulence gene profiles.

The carriage of the serine-aspartate repeat protein-encoding sdr genes among Staphylococcus aureus lineages

The serine-aspartate repeat proteins (Sdr) are members of a family of surface proteins and contribute to the pathogenicity of Staphylococcus aureus. Among 288 S. aureus isolates including 158 and 130 associated with skin and soft tissue infections and bloodstream infection, respectively; 275 (95.5%) were positive for at least one of three sdr genes tested. The positivity rates for sdrC, sdrD, and sdrE among S. aureus isolates were 87.8% (253/288), 63.9% (184/288), and 68.1% (196/288), respectively. 224 (77.8%) of 288 isolates were concomitantly positive for two or three sdr genes. There was an association between carriage of sdrE and methicillin-resistant S. aureus (MRSA) isolates, while the carriage rates of sdrC and sdrD in MRSA isolates were similar to those in methicillin-sensitive S. aureus (MSSA) isolates. The prevalence of co-existence of sdrC and sdrE among MRSA isolates was significantly higher than that among MSSA isolates (p < 0.05). All ST1, ST5, ST7, and ST25 isolates were positive for sdrD. While all ST121 and ST398 isolates were negative for sdrD. All ST59 and ST88 isolates were positive for sdrE. All ST1 isolates were concomitantly positive for sdrC and sdrD. Concomitant carriage of sdrC, sdrD, and sdrE was found among all ST5, 75.0% (9/12) of ST1, 69.2% (9/13) of ST6, 78.6% (11/14) of ST25, and 90.9% (20/22) of ST88 isolates. sdrD was linked to CC5, CC7 and CC88 isolates, especially CC88 isolates. There was a strong association between the presence of sdrE and CC59, CC88, and CC5 isolates. A significant correlation between concomitant carriage of sdrC, sdrD, and sdrE and CC88 isolates was found. sdrC-positive, sdrD-positive and sdrE-negative gene profile was significantly associated with CC7 clone. There was an association between sdrC-positive, sdrD-negative, and sdrE-positive gene profile and CC59 isolates. A correlation between sdrC-positive, sdrD-negative, and sdrE-negative gene profile and CC121 clone was found. More CC59 isolates carried sdrC-negative, sdrD-negative, and sdrE-positive gene profile relative to other four CCs isolates. All ST1 and ST5, 95.2% (20/21) of ST188 and 95.2% (20/21) of ST630 isolates were positive for sdrC. Taken together, our investigation indicated that different S. aureus lineages were associated with specific patterns of carriage of sdr genes.

Prevalence of Enterotoxin Genes and spa Genotypes of Methicillin-resistant Staphylococcus aureus from a Tertiary Care Hospital in China

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen that causes a variety of infections. MRSA has evolved resistance to multiple antibiotics. Genetic background and virulence differs in different geographic regions. The present study was aimed to investigate the prevalence of enterotoxin genes and spa genotypes of hospital-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) isolated from a tertiary care hospital of Jiangsu province, China.

MATERIALS AND METHODS

HA-MRSA isolates from August 2013 to April 2014 at a tertiary care hospital of China were collected. We investigated antimicrobial pattern, spa types, SCCmec types and the presence of 14 virulence genes.

RESULTS

Eighty HA-MRSA isolates were collected. Results from SCCmec typing revealed that 73.8% were type II; 13.8% were type III; 12.5% were type V. There were 19 different spa types. Spa type t2460 was the most common (35.0%), followed by t002 (11.3%). CC5 was the predominant MLST CCs type (50%). The most frequent toxin genes were sea, seb, sed, sel, sen and seo (100.0%). None of the investigated isolates carried the sec or tst.

CONCLUSION

Genotypic and virulence evaluation of the isolated HA-MRSA revealed that the isolates with CC5 and SCCmec II were the predominant type and highly homological. The virulence profiles mainly existed in the genes of sea, seb, sed, sel, sen, seo and ser. The prevalence of t2460 was an outbreak and the predominant spa type.

Molecular characteristics and virulence factors in methicillin-susceptible, resistant, and heterogeneous vancomycin-intermediate Staphylococcus aureus from central-southern China

BACKGROUND

Staphylococcus aureus is a leading cause of nosocomial infections. The purpose of this study was to evaluate the prevalence of methicillin-resistant S. aureus (MRSA) and heterogeneous vancomycin-intermediate S. aureus (hVISA), and compare the antimicrobial susceptibility, molecular characteristic, and virulence factors in methicillin-susceptible S. aureus (MSSA), MRSA, and hVISA from central-southern China.

METHODS

A total of 184 S. aureus were isolated from sterile body fluids. All isolates were subjected to population analysis profiling for the identification of hVISA phenotype and polymerase chain reaction analysis for genotyping and 31 virulence genes.

RESULTS

The prevalence of MRSA isolates was 41.8% in central-southern China. Of 77 MRSA isolates, 17 (22.1%) were identified as hVISA. The most common MRSA and MSSA clones were ST239-MRSA-SCCmecIII-t030-agr-I (55.8%) and ST188-MSSA-t189-agr-I (20.6%), respectively. The frequency of carriage of pvl, hemolysins, tst, and staphylococcal enterotoxin genes among MSSA isolates was significantly higher than that for MRSA isolates (p < 0.05); 98 MSSA isolates (53.3%) carried ≥ 10 tested virulence genes simultaneously, which was significantly higher than that of MRSA isolates (33.8%; p = 0.004). The 17 hVISA isolates carried a significantly small number of virulence genes; only two hVISA isolates carried ≥ 10 tested virulence genes simultaneously, and two hVISA isolates harbored only four virulence genes. Compared with other clonal complexes (CCs), CC1 and CC398 isolates harbored a higher frequency of exfoliatin genes, CC1 and CC59 harbored a higher frequency of pvl gene, and only CC1 isolates harbored lukED.

CONCLUSION

The prevalence of hVISA was considerably high in central-southern China. Simultaneous carriage of multiple virulence genes was common in S. aureus isolates; the virulence genes were more diverse and frequent among MSSA isolates than among MRSA isolates. Furthermore, the distribution of some virulence genes was correlated with the different S. aureus CCs.

Virulence Factors of Staphylococcus aureus Isolates in an Iranian Referral Children's Hospital

Objectives

The clinical importance of Staphylococcus aureus (S. aureus) is attributed to notable virulence factors, surface proteins, toxins, and enzymes as well as the rapid development of drug resistance. The aim of this study was to compare the occurrence of virulence factors produced by S. aureus strains isolated from children in an Iranian referral children's hospital.

Methods

The presence of genes encoding for the enterotoxins A (sea), B (seb), C (sec), D (sed), TSST-1 (tsst), exfoliative toxin A (eta), and exfoliative toxin B (etb) were detected by Multiplex polymerase chain reaction (PCR) using specific primers. In addition, the standardized Kirby-Bauer disc-diffusion method was performed on Mueller-Hinton agar.

Results

In total, 133 S. aureus isolates were obtained from different patients. Of these S. aureus isolates, 64 (48%) were methicillin-resistant S. aureus (MRSA), and all of these tested positive for the mecA gene. Regarding the classical enterotoxin genes, sea gene (40.6%) was the most prevalent followed by seb (19.6%), tsst (12.8%), eta (11.3%), etb (9%), sed (4.5%), and sec (3%). Among methicillin-susceptible S. aureus (MSSA) isolates, seb and tsst were the more prevalent toxins in comparison with MRSA isolates (p < 0.05), while the frequency of sea, sed, eta, and etb genes were higher among MRSA isolates (p > 0.05).

Conclusion

In our study enterotoxin A was produced by 40.6% of the isolates (48% from MRSA and 33% from MSSA isolates) which was higher than in previous reports. According to our results, strict hygiene and preventative measures during food processing are highly recommended.

Association of norB overexpression and fluoroquinolone resistance in clinical isolates of Staphylococcus aureus from Korea

OBJECTIVES

Although the prevalence of fluoroquinolone resistance among methicillin-resistant Staphylococcus aureus (MRSA) is known to be higher than in methicillin-susceptible S. aureus (MSSA), the reasons have never been identified.

METHODS

We randomly selected 115 isolates of S. aureus collected from 10 different hospitals in Korea between June 2009 and May 2011. To investigate the difference in fluoroquinolone resistance mechanisms between MRSA and MSSA, we evaluated gyrA and parC mutations and the relative expression of the multidrug efflux pump genes norA, norB and norC.

RESULTS

All 62 ciprofloxacin-resistant S. aureus had either gyrA or parC mutations. The S84L mutation of gyrA (59/62, 95.2%) and the S80F mutation of parC (61/62, 98.4%) were the most common. Fifty-eight (93.6%) strains had both the S84L mutation of gyrA and the S80F mutation of parC. Among the 115 isolates, norB overexpression was the most common, occurring in 49 (42.6%) strains. There were only two (1.7%) strains with norA overexpression and none with norC overexpression. Strains overexpressing norB were more common among ciprofloxacin-resistant S. aureus (33/62, 53.2%) than ciprofloxacin-susceptible S. aureus (16/53, 30.2%) (P = 0.013). When we analysed 62 ciprofloxacin-resistant S. aureus strains, those overexpressing norB were more common in ciprofloxacin-resistant MRSA (28/46, 60.9%) than in ciprofloxacin-resistant MSSA (5/16, 31.3%) (P = 0.041).

CONCLUSIONS

Increased expression of norB can be a factor that contributes to ciprofloxacin resistance in MRSA strains.

Current status of Staphylococcus aureus infection in a central teaching hospital in Shanghai, China

Background

To control the spread of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals, infection control measures such as hand hygiene practices were introduced into the teaching hospitals in Shanghai, China, in 2008. Currently, there is limited information characterizing the latest hospital-acquired S. aureus infections in this area. Therefore, we sought to determine the prevalence, molecular characteristics, and genotype-phenotype correlation of hospital-acquired S. aureus infections in Huashan Hospital, one of the largest teaching hospitals in Shanghai.

Results

Among 608 hospital-acquired S. aureus clinical isolates obtained from January to December of 2011 in Huashan Hospital, 68.1% were MRSA. The predominant MRSA clones were ST239-SCCmecIII and ST5-SCCmecII. ST239 was mainly recovered from respiratory specimens and sterile body fluids, ST5 was associated with respiratory specimens and blood, and ST1 was most prevalent in urine samples. In this study, 31 dispersed sequence types (STs) of methicillin-susceptible S. aureus (MSSA) were identified, most of which caused skin/soft tissue infection and bacteremia. The frequencies of pvl-, muPA-, and qacA/B-positive isolates were 1.6, 9.9, and 11.8% respectively. MuPA was more frequently identified in ST1 and ST5, and qacA/B was more prevalent in ST239 and ST5. Most of the pvl-positive isolates were MSSA, whereas the majority of muPA- and qacA/B-positive isolates were MRSA. ST239 and ST5 had higher resistance rates to multiple antibiotics. In Huashan Hospital, the infection rate in the intensive care unit (ICU) was 3.9 per 1000 hospitalized days, but only 1.2 per 1000 hospitalized days in the other wards. Each ward harbored its own dominant STs. Pulsed-field gel electrophoresis showed diversity within the same epidemic S. aureus clones originating from the same wards.

Conclusion

There is still a high prevalence of MRSA infections in the teaching hospital in Shanghai. There were also differences in the major infection types caused by MRSA and MSSA, and hospital-acquired S. aureus infections in the ICU of Huashan Hospital pose a greater threat to patient safety than in other wards. The high proportion of multiple antibiotic and chlorhexidine-based antiseptic-resistant clones in this hospital underscores the need for more effective infection control measures to help curtail dissemination of MRSA to hospitalized patients.

Molecular analysis and frequency of Staphylococcus aureus virulence genes isolated from bloodstream infections in a teaching hospital in Tianjin, China

Staphylococcus aureus is an important cause of bloodstream infections worldwide. We examined the prevalence of genes that encode erythromycin ribosome methylase and bacterial toxins in S. aureus collected from bloodstream infections. Sixty different S. aureus isolates were obtained from blood cultures of patients who were admitted to a Teaching Hospital in Tianjin from January 2006 to August 2011. The susceptibility of the isolates to 16 antibiotics was tested. Methicillin-resistant S. aureus (MRSA) was identified using the disk diffusion method with cefoxitin. PCR was used to detect genes that encode the staphylococcal enterotoxins, Panton-Valentine leukocidin, toxic shock syndrome toxin 1 and erythromycin ribosome methylase. Molecular analysis of the MRSA strains was done using pulsed-field gel electrophoresis (PFGE) and staphylococcal cassette chromosome mec (SCCmec) typing. The positivity rates of mecA, ermA, ermB, and ermC in the isolates were 13/60, 10/60, 18/60, and 18/60, respectively. Among the 60 isolates, 30 harbored enterotoxin genes, with sea as the most frequent toxin gene (33%), followed by sec (15%), sed (12%), and seb (5%). The see and tst genes were not found in any of the isolates. The pvl gene was detected in four strains. Eleven MRSA isolates were of the SCCmec type III; two MRSA isolates could not be determined through SCCmec typing. PFGE analysis of the 13 MRSA isolates produced 8 distinct pulsotypes. Virulence genes and erythromycin ribosome methylase genes were highly prevalent in these isolates. The PFGE results demonstrated that the MRSA spread through cloning, mainly involving SCCmec type III.

Clinical utility of the Xpert MRSA assay for early detection of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for many nosocomial and community-acquired infections, resulting in significant morbidity and mortality. A practical way to limit the spread of MRSA is early detection and proper treatment. However, screening culture for MRSA typically requires 2-3 days. The Xpert MRSA assay (Cepheid, Sunnyvale, CA, USA) is a real-time polymerase chain reaction-based assay developed for screening an MRSA-specific DNA sequence within the staphylococcal cassette chromosome in 2 h. Lower respiratory tract specimens, such as transtracheal aspirates (TTAs) and bronchoalveolar lavage fluid (BALF), are commonly obtained from intubated patients. Therefore, using the lower respiratory tract specimens with the Xpert MRSA assay may be a practical tool for patient care. We performed the Xpert MRSA assay on 108 TTA and 21 BALF specimens from 92 patients and compared the results to those obtained by culture. The two assays showed concordant results in 120 (93.0%) cases and discordant results in 9 (7.0%) cases, which were culture‑negative and Xpert MRSA-positive. Among the discordant cases, 5 patients developed culture-positive samples 2-15 days after the Xpert MRSA detected MRSA. We conclude that the Xpert MRSA assay is a rapid, sensitive and clinically useful test, particularly for the early detection of MRSA.

Virulence gene profiling and molecular characterization of hospital-acquired Staphylococcus aureus isolates associated with bloodstream infection

A better understanding of virulence gene profiling and molecular characterization of Staphylococcus aureus isolates associated with bloodstream infection (BSI) may provide further insights related to clinical outcomes with these infections. We analyzed 89 S. aureus isolates including 37 MRSA isolates (41.6%) recovered from 89 adult patients with BSI from 4 hospitals in Zhejiang province, eastern China. Thirty-five (94.6%) of MRSA isolates and 4 (7.7%) of methicillin-sensitive S. aureus (MSSA) isolates were resistant to multiple antimicrobials. All isolates harbored at least 2 of 22 possible virulence genes, including sdrC (92.1%), icaA (89.9%), hla (80.9%), clf (69.7%), sea (68.5%), sdrD (67.4%), hlb (67.4%), sdrE (65.2%), sei (51.7%), seg (50.6%), and cna (50.6%). Forty-four (49.4%) of all S. aureus BSI isolates, including 23 (62.2%) of MRSA isolates, harbored ≥10 of the virulence genes evaluated in this study. Sixteen (43.2%) MRSA isolates and 5 (9.6%) MSSA isolates harbored the gene encoding Panton-Valentine leukocidin (PVL). Collective genes for pvl, sdrE, sed, seg, and sei among MRSA isolates were significantly more frequent relative to MSSA isolates (P < 0.05). A total of 22 sequence types (STs), including novel ST2184, ST2199, and ST2200, and 33 spa types, including novel spa types t9530 and t9532, were identified among S. aureus BSI isolates, among which ST188 (15.7%) and ST7 (15.7%), and t091 (12.4%) and t189 (12.4%), seldom noted for Chinese isolates previously, were major STs and spa types, respectively. In contrast to previous reports, no predominant clones were found in the present study. Among the MRSA isolates, although ST239-MRSA-SCCmecIII, predominant clone in China, still represented the most common clone, it only accounted for 18.9%. However, ST188-MRSA- SCCmecIV seldom reported before accounted for 10.8%. Among the MSSA isolates, ST7-MSSA represented the most common clone (23.1%), followed by ST188-MSSA and ST630-MSSA (9.6% each). In conclusion, simultaneous carriage of multiple virulence genes and genetically considerable diversity were common among S. aureus BSI isolates. Furthermore, MRSA isolates exhibited more frequent carriage of superantigen genes and pvl relative to MSSA isolates. Taken together, there are distinctive virulence gene profiling and molecular characteristic among S. aureus isolates associated with bloodstream infection in China.