Clinical, microbiological, and genetic characteristics of heteroresistant vancomycin-intermediate Staphylococcus aureus bacteremia in a teaching hospital

Reduced vancomycin susceptibility in Staphylococcus aureus clinical isolates: a spectrum of less investigated uncertainties

BACKGROUND

Staphylococcus aureus clinical isolates with vancomycin MICs of 2 µg/ml have been associated with vancomycin therapeutic failure and the heterogenous vancomycin-intermediate S. aureus (hVISA) phenotype. While carriage of van genes has usually been associated with higher level of MIC and frank vancomycin resistance, the unrecognized risk of hetero-resistance is frequently underestimated. Methods used for assessing vancomycin susceptibility have also shown different concordance and variable performance and accessibility in routine clinical diagnostics posing a challenge to inform treatment selection in hospital settings.

METHODS

A total of 195 clinical samples were obtained among which 100 S. aureus isolates were identified. Ninety-six MRSA isolates have been identified using cefoxitin disc and mecA gene detection. The vanA and vanB genes have been screened for in the studied isolates using conventional PCR amplification. Examination of reduced vancomycin susceptibility has been performed using vancomycin screen agar, Broth Micro Dilution method (BMD), and VITEK2. Blood isolates were screened for hVISA using PAP-AUC method.

RESULTS

Vancomycin screening agar applied to 96 MRSA isolates revealed 16 isolates with reduced vancomycin susceptibility. Further MIC testing revealed that 7 isolates were VISA and only 1 isolate was identified as VRSA using both BMD MIC method and VITEK2. Among 24 tested blood isolates, 4 isolates (16.7%) revealed the hVISA phenotype as identified using PAP-AUC method. Using PCR, vanA gene was identified in 5 S. aureus isolates (5%). Three of them were VSSA while the other two isolates were VISA.

CONCLUSION

In this study, we report the very low prevalence of VRSA among the tested S. aureus clinical isolates (1%) and the existence of hVISA phenotype among studied S. aureus blood isolates at the rate of 16.7% in our setting. Fifty percent (8/16) of isolates that demonstrated reduced vancomycin susceptibility using vancomycin agar screen tested susceptible using both broth dilution method and VITEK2. These finding together with the concerning silent carriage of vanA gene among VSSA and VISA (5%) may underly hidden and uninvestigated factors contributing to vancomycin treatment failure that warrant cautious vancomycin prescription.

Real-World Use and Treatment Outcomes of Ceftaroline Fosamil in Patients with Complicated Skin and Soft Tissue Infection: A Multinational Retrospective Study

Background

Ceftaroline fosamil is approved for the treatment of complicated skin and soft tissue infections (cSSTI) and community-acquired pneumonia (CAP); however, data on its real-world use and effectiveness in Europe and Latin America are currently limited. This retrospective observational study assessed ceftaroline fosamil use and treatment outcomes in adults hospitalized with cSSTI or CAP treated with ceftaroline fosamil in a usual care setting in Europe and Latin America. Results for patients with cSSTI are reported.

Methods

Data from patients with cSSTI who received ≥4 consecutive intravenous ceftaroline fosamil doses up to May 31, 2019, were collected from sites in Brazil, Colombia, France, Greece, Italy, and Spain. Patient characteristics, clinical management, hospitalization information, microbiological diagnosis, and clinical responses were summarized descriptively. Healthcare resource use variables were evaluated by clinical response to ceftaroline fosamil.

Results

Data for 132 patients were included (58.3% male; mean age 58.5 years). Most common lesions were cellulitis/fasciitis (62.1%), abscess (34.1%), and post-surgical wounds (19.7%). Pathogens most frequently identified were methicillin-resistant (18.2%) and methicillin-susceptible Staphylococcus aureus (17.4%). Median (range) ceftaroline fosamil treatment duration was 8 (2-60) days (daily doses of 1200 [400-2400] mg); 78 patients (59.1%) received monotherapy. In total, 75 (56.8%) patients had additional antibiotics after ceftaroline fosamil. Clinical response occurred in 118 (89.4%) patients. All-cause 30-day readmission occurred in 13 (9.8%) patients, and all-cause 30-day mortality in 7 (5.3%). Clinical response to ceftaroline was associated with >25% shorter length of hospital and intensive care stay, and with ~40% lower hospital costs, versus non-responders.

Conclusion

Ceftaroline fosamil was effective in treating adults with cSSTI and clinical response to ceftaroline fosamil was associated with reductions in healthcare resource use compared with non-responders, in Europe and Latin America.

Clinicaltrialsgov Identifier

NCT04198571.

Global distribution of heterogeneous vancomycin-intermediate Staphylococcus aureus strains (1997-2021): a systematic review and meta-analysis

BACKGROUND

Heterogeneous vancomycin-intermediate Staphylococcus aureus is considered one of the main causes in treatment failure of vancomycin, which leads to poor clinical outcomes. Herein, we comprehensively evaluated characteristics such as global prevalence, trend, and genetic backgrounds of these strains.

METHODS

In this study, we conducted a meta-analysis based on PRISMA checklist 2020. In the beginning, global databases were searched to achieve the studies related to the prevalence of hVISA in clinical isolates of methicillin-resistant Staphylococcus aureus. After retrieving the eligible English studies, the prevalence of hVISA isolates and their trend changes were assessed using event rate with 95% confidence intervals.

RESULTS

In the present study, the prevalence of 114 801 MRSA isolates (of 124 studies) was 64%. According to our results, although the frequency of infection with hVISA is increasing in recent years, there is not a significant difference between Asian countries and Europe/America (6.1% vs. 6.8%). In addition, infection with hVISA bacteria was higher in bacteraemic patients than other infections (9.4% vs. 5.5%), which increases hospitalization, treatment costs, and mortality in these patients. Isolates harbouring SCCmec types II and III are most common genotypes in hVISA strains.

CONCLUSIONS

The prevalence of hVISA is increasing, which will reduce the effectiveness of vancomycin treatment in the coming years. The presence of hVISA stains in blood samples was higher than the other samples, which is threatening for bacteraemic patients. The results of the current study indicate a universal program to identify and control the spread of such strains in nosocomial infections.

Diagnostic value of BHI-V4 for heterogeneous and vancomycin-intermediate Staphylococcus aureus isolates: a systematic review and meta-analysis

BACKGROUND

Brain-heart infusion agar supplemented with 4 µg/mL of vancomycin (BHI-V4) was commonly used for the detection of heterogeneous (hVISA) and vancomycin-intermediate Staphylococcus aureus (VISA). However, its diagnostic value remains unclear. This study aims to compare the diagnostic accuracy of BHI-V4 with population analysis profiling with area under the curve (PAP-AUC) in hVISA/VISA.

METHODS

The protocol of this study was registered in INPLASY (INPLASY2023120069). The PubMed and Cochrane Library databases were searched from inception to October 2023. Review Manager 5.4 was used for data visualization in the quality assessment, and STATA17.0 (MP) was used for statistical analysis.

RESULTS

In total, eight publications including 2153 strains were incorporated into the meta-analysis. Significant heterogeneity was evident although a threshold effect was not detected across the eight studies. The summary receiver operating characteristic (SROC) was 0.77 (95% confidence interval [CI], 0.74-0.81). The pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic score and diagnostic odds ratio were 0.59 (95% CI: 0.46-0.71), 0.96 (95%CI: 0.83-0.99), 14.0 (95% CI, 3.4-57.1), 0.43 (95%CI, 0.32-0.57), 3.48(95%CI, 2.12-4.85) and 32.62 (95%CI, 8.31-128.36), respectively.

CONCLUSION

Our study showed that BHI-V4 had moderate diagnostic accuracy for diagnosing hVISA/VISA. However, more high-quality studies are needed to assess the clinical utility of BHI-V4.

Detection of Vancomycin Resistance among Methicillin-Resistant Staphylococcus aureus Strains Recovered from Children with Invasive Diseases in a Reference Pediatric Hospital

Vancomycin is the cornerstone in treating methicillin-resistant Staphylococcus aureus (MRSA) infections. However, therapeutic failures can occur when MRSA strains with decreased susceptibility to glycopeptides (DSG) are involved. The aim of this study was to detect and characterize DSG in MRSA recovered from children with invasive diseases at a reference pediatric hospital between 2009 and 2019. Fifty-two MRSA strains were screened using agar plates with vancomycin 3 and 4 mg/L (BHI-3 and BHI-4); the VITEK2 system; and standard and macro E-tests. Suspicious hVISA were studied by population analysis profiling-area under the curve (PAP-AUC), and wall thickness was analyzed by transmission electron microscopy. Neither VRSA nor VISA were detected in this set. As only three strains met the hVISA criteria, the PAP-AUC study included 12 additional MRSA strains that grew one colony on BHI-4 plates or showed minimum inhibitory concentrations of vancomycin and/or teicoplanin ≥ 1.5 mg/L. One strain was confirmed as hVISA by PAP-AUC. The wall thickness was greater than the vancomycin-susceptible control strain; it belonged to ST30 and carried SCCmec IV. As expected, a low frequency of hVISA was found (1.9%). The only hVISA confirmed by PAP-AUC was not detected by the screening methods, highlighting the challenge that its detection represents for microbiology laboratories.

Resistance phenotype and genetic features of a heterogeneous vancomycin intermediate-resistant Staphylococcus aureus strain from an immunocompromised patient

Strain C1 was successfully isolated from an immunosuppressed patient with persistent bacteremia, who had not previously been exposed to glycopeptide antibiotics. This strain was found to be a heterogeneous vancomycin intermediate-resistant Staphylococcus aureus (hVISA). It is noteworthy that, following a brief period of vancomycin treatment, strains C6, C8, and C9, which were obtained from blood and other body parts, exhibited a significant reduction in heterogeneity as determined by population analysis profile-area under the curve (PAP-AUC) detection. Genotyping analysis revealed that these bacterial strains belonged to the same SCCmecIVa-ST59-t437-agrI genotype and shared the same virulome and resistome. In this study, a comparative genomics analysis was conducted between strain C1 and strain N315 to identify potential hVISA-associated mutations. Ultimately, a total of 205 mutation sites in 19 candidate genes, likely associated with the hVISA phenotype, were identified.

Prevalence and molecular characteristics of heterogeneous vancomycin intermediate Staphylococcus aureus in a tertiary care center of northern China

The use of glycopeptide medications may decline in line with the annual decline in methicillin-resistant Staphylococcus aureus (MRSA) detection rates in China. The rate of heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA)detection may be impacted by this. However, there is currently a dearth of information on the incidence of hVISA in China. This study aims to analyze the recent epidemiology and molecular characteristics of hVISA strains in Beijing, China. A total of 175 non-duplicate MRSA strains from various infection sites were collected from a medical center between January 2018 and May 2023 and underwent molecular typing and susceptibility testing (Vitek2). Vancomycin and teicoplanin MICs were also evaluated by standard broth microdilution method and agar dilution method, respectively. Isolates growing on screening agar (BHIV4 and BHIT5, brain heart infusion agar containing 4 μg/ml vancomycin and 5 μg/ml teicoplanin, respectively) were characterized further by analysis of macro-Etest (MET) and population analysis profiling with area under the curve (PAP-AUC). The proportion of hVISA among MRSA isolates was 8.6 %. BHIT5 could select all hVISA strains while BHIV4 and MET only selected two hVISA strains. Compared with vancomycin- susceptible Staphylococcus aureus (VSSA), hVISA isolates were less susceptible to erythromycin and clindamycin. In addition, hVISA frequency was MIC-independent despite using different detection methods. In total, 11 types of STs, 28 types of spa typing, four types of SCCmec typing, and two types of agr typing were identified and the predominant type in both MRSA and hVISA isolates was ST239-t030-SCCmecIII-agr I. The analysis of biofilm formation, growth, and virulence genes in hVISA strains revealed sparse information. The dataset presented in this study provided the prevalence and molecular characteristics of hVISA in hospital settings and the combination of BHIT5 and PAP-AUC may identify hVISA efficiently. The result of genotyping suggested the genotype of hVISA was mainly consistent with that of local MRSA. Additional studies on the characteristics of hVISA strains were necessary.

The Changing Epidemiology and Antimicrobial Susceptibility of Staphylococcus aureus Isolated from Blood Cultures in a University Hospital from Argentina

Staphylococcus aureus bacteremia (SAB) is one of the most common serious bacterial infections worldwide. In this study, we demonstrated changes in SAB epidemiology in an Argentinean University Hospital during an 8-year period (2009-2016). A total of 326 S. aureus clinical isolates were recovered in three periods: P1: 2009-2010, P2: 2012-2014, and P3: 2015-2016. Among these, 127 were methicillin-resistant S. aureus (MRSA) and were characterized by phenotypic and molecular methods. We hereby report a significant decline in multiple drug resistance among MRSA isolates associated with an increase in SCCmec IV between the three periods. A diversity of MRSA-IV clones (mainly ST30-MRSA-IV, ST5-MRSA-IV, and ST8-MRSA-IV) replaced between 2009 and 2016 the previous prevalent MRSA clone causing bloodstream infections at this hospital (ST5-MRSA-I). MRSA population structure continued to diversify between P2 and P3. Notably, ST8-MRSA-IV-t008 related to USA300 was first detected during P2, and ST8-MRSA-IV together with ST30-MRSA-IV related to the Southwest Pacific clone were the more prevalent MRSA genotypes circulating during P3.

Comparative Genomics Identifies Novel Genetic Changes Associated with Oxacillin, Vancomycin and Daptomycin Susceptibility in ST100 Methicillin-Resistant Staphylococcus aureus

Infections due to vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) represent a serious concern due to their association with vancomycin treatment failure. However, the underlying molecular mechanism responsible for the hVISA/VISA phenotype is complex and not yet fully understood. We have previously characterized two ST100-MRSA-hVISA clinical isolates recovered before and after 40 days of vancomycin treatment (D1 and D2, respectively) and two in vitro VISA derivatives (D23C9 and D2P11), selected independently from D2 in the presence of vancomycin. This follow-up study was aimed at further characterizing these isogenic strains and obtaining their whole genome sequences to unravel changes associated with antibiotic resistance. It is interesting to note that none of these isogenic strains carry SNPs in the regulatory operons vraUTSR, walKR and/or graXRS. Nonetheless, genetic changes including SNPs, INDELs and IS256 genomic insertions/rearrangements were found both in in vivo and in vitro vancomycin-selected strains. Some were found in the downstream target genes of the aforementioned regulatory operons, which are involved in cell wall and phosphate metabolism, staphylococcal growth and biofilm formation. Some of the genetic changes reported herein have not been previously associated with vancomycin, daptomycin and/or oxacillin resistance in S. aureus.

Multiomics characterization of methicillin-resistant Staphylococcus aureus (MRSA) isolates with heterogeneous intermediate resistance to vancomycin (hVISA) in Latin America

BACKGROUND

Heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) compromise the clinical efficacy of vancomycin. The hVISA isolates spontaneously produce vancomycin-intermediate Staphylococcus aureus (VISA) cells generated by diverse and intriguing mechanisms.

OBJECTIVE

To characterize the biomolecular profile of clinical hVISA applying genomic, transcriptomic and metabolomic approaches.

METHODS

39 hVISA and 305 VSSA and their genomes were included. Core genome-based Bayesian phylogenetic reconstructions were built and alterations in predicted proteins in VISA/hVISA were interrogated. Linear discriminant analysis and a Genome-Wide Association Study were performed. Differentially expressed genes were identified in hVISA-VSSA by RNA-sequencing. The undirected profiles of metabolites were determined by liquid chromatography and hydrophilic interaction in six CC5-MRSA.

RESULTS

Genomic relatedness of MRSA associated to hVISA phenotype was not detected. The change Try38 → His in Atl (autolysin) was identified in 92% of the hVISA. We identified SNPs and k-mers associated to hVISA in 11 coding regions with predicted functions in virulence, transport systems, carbohydrate metabolism and tRNA synthesis. Further, capABCDE, sdrD, esaA, esaD, essA and ssaA genes were overexpressed in hVISA, while lacABCDEFG genes were downregulated. Additionally, valine, threonine, leucine tyrosine, FAD and NADH were more abundant in VSSA, while arginine, glycine and betaine were more abundant in hVISA. Finally, we observed altered metabolic pathways in hVISA, including purine and pyrimidine pathway, CoA biosynthesis, amino acid metabolism and aminoacyl tRNA biosynthesis.

CONCLUSIONS

Our results show that the mechanism of hVISA involves major changes in regulatory systems, expression of virulence factors and reduction in glycolysis via TCA cycle. This work contributes to the understanding of the development of this complex resistance mechanism in regional strains.

Detection of heterogeneous vancomycin intermediate resistance in MRSA isolates from Latin America

BACKGROUND

Vancomycin is a common first-line option for MRSA infections. The heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) phenotype is associated with therapeutic failure. However, hVISA isolates are usually reported as vancomycin susceptible by routine susceptibility testing procedures.

OBJECTIVES

To detect and characterize the hVISA phenotype in MRSA isolates causing infections in nine Latin American countries.

METHODS

We evaluated a total of 1189 vancomycin-susceptible MRSA isolates recovered during 2006-08 and 2011-14. After an initial screening of hVISA using glycopeptide-supplemented agar strategies, the detection of hVISA was performed by Etest (GRD) and Macro-method (MET). Isolates deemed to be hVISA were subjected to population analysis profile/AUC (PAP/AUC) and WGS for further characterization. Finally, we interrogated alterations in predicted proteins associated with the development of the VISA phenotype in both hVISA and vancomycin-susceptible S. aureus (VSSA) genomes.

RESULTS

A total of 39 MRSA isolates (3.3%) were classified as hVISA (1.4% and 5.6% in MRSA recovered from 2006-08 and 2011-14, respectively). Most of the hVISA strains (95%) belonged to clonal complex (CC) 5. Only 6/39 hVISA isolates were categorized as hVISA by PAP/AUC, with 6 other isolates close (0.87-0.89) to the cut-off (0.9). The majority of the 39 hVISA isolates exhibited the Leu-14→Ile (90%) and VraT Glu-156→Gly (90%) amino acid substitutions in WalK. Additionally, we identified 10 substitutions present only in hVISA isolates, involving WalK, VraS, RpoB and RpoC proteins.

CONCLUSIONS

The hVISA phenotype exhibits low frequency in Latin America. Amino acid substitutions in proteins involved in cell envelope homeostasis and RNA synthesis were commonly identified. Our results suggest that Etest-based methods are an important alternative for the detection of hVISA clinical isolates.

Genomic Epidemiology of CC30 Methicillin-Resistant Staphylococcus aureus Strains from Argentina Reveals Four Major Clades with Distinctive Genetic Features

Staphylococcus aureus clonal complex 30 (CC30) has given rise to epidemics worldwide and is one of the most prevalent lineages in Argentina, represented by sequence type 30 methicillin-resistant S. aureus SCCmec type IV (ST30-MRSA-IV). ST30-MRSA-IV has displaced previous prevalent clones in the country and demonstrated increased virulence. Despite the burden of infections caused by ST30-MRSA-IV both in hospitals and in communities in Argentina, no detailed genome-based characterization of this clone is available to date. In this study, we used whole-genome sequencing (WGS) to evaluate the genetic diversity, population structure, and genomic characteristics of 190 CC30-MRSA strains circulating in Argentina between 2004 and 2015. Phylogenetic analysis revealed the existence of 4 major clades: ARG-1 (CC30-MRSA-IVc-spa t012), ARG-2 (ST30-MRSA-IVc-spa t021 related), ARG-3 (ST30-MRSA-IVh/j-spa t021 and related), and ARG-4 (CC30-MRSA-IVc-spa t019 and related). The clades were characterized by different distributions of antimicrobial resistance determinants, virulence genes, and mobile genetic elements (MGEs). While ARG-1 and ARG-4 were related to global epidemic MRSA-16 (EMRSA-16) and South West Pacific (SWP) clones, respectively, ARG-3 was phylogenetically distinct from previously defined CC30 epidemic clones. ARG-4, the most prevalent and geographically disseminated in the collection (N = 164), was characterized by specific MGEs and chromosomal mutations that might have contributed to its virulence and success. To our knowledge, this is the first genomic epidemiology study of CC30-MRSA in Argentina, which will serve as baseline genomic data going forward to inform public health measures for infection prevention and control.IMPORTANCE The rise in prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is of public health concern. In Argentina, several studies documented a shift in the epidemiology of CA-MRSA since 2009, with clonal complex 30 (CC30) and, in particular, sequence type 30 MRSA SCCmec type IV (ST30-MRSA-IV) replacing other clones both in communities and in hospitals and possibly displaying increased virulence. By sequencing the whole genomes of 190 CC30 MRSA isolates recovered from Argentina between 2005 and 2015, we showed that they represented a diverse population composed of 4 major clades. The predominant clade evolved from the South West Pacific clone but has acquired a distinct repertoire of mobile genetic elements, virulence genes, and chromosomal mutations that might play a role in its success. Our work is the first extensive genomic study of CC30 S. aureus in Argentina and will contribute not only to the development of genomic surveillance in the region but also to our understanding of the global epidemiology of this pathogen.

Global prevalence and distribution of vancomycin resistant, vancomycin intermediate and heterogeneously vancomycin intermediate Staphylococcus aureus clinical isolates: a systematic review and meta-analysis

Vancomycin-resistant Staphylococcus aureus (VRSA), Vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) are subject to vancomycin treatment failure. The aim of the present study was to determine their precise prevalence and investigate prevalence variability depending on different years and locations. Several international databases including Medline (PubMed), Embase and Web of Sciences were searched (data from 1997 to 2019) to identify studies that addressed the prevalence of VRSA, VISA and hVISA among human clinical isolates around the world. Subgroup analyses and meta-regression were conducted to indicate potential source of variation. Publication bias was assessed using Egger's test. Statistical analyses were conducted using STATA software (version 14.0). Data analysis showed that VRSA, VISA and hVISA isolates were reported in 23, 50 and 82 studies, with an overall prevalence of 1.5% among 5855 S. aureus isolates, 1.7% among 22,277 strains and 4.6% among 47,721 strains, respectively. The overall prevalence of VRSA, VISA, and hVISA before 2010 was 1.2%, 1.2%, and 4%, respectively, while their prevalence after this year has reached 2.4%, 4.3%, and 5.3%. The results of this study showed that the frequency of VRSA, VISA and hVISA after 2010 represent a 2.0, 3.6 and 1.3-fold increase over prior years. In a subgroup analysis of different strain origins, the highest frequency of VRSA (3.6%) and hVISA (5.2%) was encountered in the USA while VISA (2.1%) was more prevalent in Asia. Meta-regression analysis showed significant increasing of VISA prevalence in recent years (p value ≤ 0.05). Based on the results of case reports (which were not included in the calculations mentioned above), the numbers of VRSA, VISA and hVISA isolates were 12, 24 and 14, respectively, among different continents. Since the prevalence of VRSA, VISA and hVISA has been increasing in recent years (especially in the Asian and American continents), rigorous monitoring of vancomycin treatment, it's the therapeutic response and the definition of appropriate control guidelines depending on geographical regions is highly recommended and essential to prevent the further spread of vancomycin-resistant S. aureus.

Recent pattern of antibiotic resistance in Staphylococcus aureus clinical isolates in Eastern India and the emergence of reduced susceptibility to vancomycin

PURPOSE:

We aimed to determine the recent pattern of antibiotic resistance and assess the vancomycin susceptibility profile of clinical Staphylococcus aureus in view of emerging reports of vancomycin creep, reduced vancomycin susceptibility (RVS), including heterogeneous vancomycin-intermediate S. aureus (hVISA) and vancomycin-intermediate S. aureus, and vancomycin resistance in S. aureus isolates.

MATERIALS AND METHODS:

Consecutive, nonduplicate isolates of S. aureus between July 2015 and June 2016 were subjected to antimicrobial susceptibility testing using standard disk diffusion test or Etest as per the Clinical and Laboratory Standards Institute 2015. Detection of hVISA was done by glycopeptide resistance detection Etest according to the manufacturer's instructions in strains with vancomycin minimum inhibitory concentration of 1–2 μg/ml.

RESULTS:

A total of 284 S. aureus were obtained from pus (175, 61.6%), respiratory tract (31, 10.9%), urine (27, 9.5%), blood (25, 8.8%), body fluids (18, 6.3%), and catheter tips (8, 2.8%). 127 (44.7%) isolates were methicillin resistant, and 158 (55.6%) were multidrug resistant. High resistance was observed to penicillin (81.7%), erythromycin (62.3%), and ciprofloxacin (52.1%), whereas the resistance was low to gentamicin (5.3%), rifampicin (8.1%), and doxycycline (9.5%). Two hundred and fifty-one (88.3%) isolates were fully susceptible to vancomycin, whereas 33 (11.6%) demonstrated RVS. All were uniformly susceptible to linezolid, tigecycline, and daptomycin.

CONCLUSIONS:

A moderately high percentage of S. aureus isolates demonstrated RVS, which may limit its usefulness in methicillin-resistant isolates and may be associated with increased complications in methicillin-susceptible infections. In view of increasing glycopeptide resistance, the susceptibility status of vancomycin along with other antibiotics among clinical S. aureus isolates should be investigated periodically.

Analysis of Risk Factors for Multiantibiotic-Resistant Infections Among Surgical Patients at a Children's Hospital

BACKGROUND

To identify the potential risk factors for multiantibiotic-resistant infections and provide sufficient evidence for multiantibiotic resistance prevention and control.

MATERIALS AND METHODS

We conducted a retrospective study of all patients in pediatric orthopedics, pediatric heart surgery, and pediatric general surgery at a level 3, grade A children's hospital from January to December 2016. The clinical laboratory information monitoring system and the medical record system were used to collect patient information regarding age, surgery type, preoperative length of stay, admission season, incision type, preoperative infection, intraoperative blood loss, postoperative use of invasive equipment, duration of catheter drainage, and timepoint of intraoperative prophylactic antibiotics administration. We used logistic univariate and multivariate regression analysis to analyze the potential risk factors for multiantibiotic-resistant infections among pediatric surgical patients. SPSS 21.0 and Excel software packages were used for the statistical analysis.

RESULTS

In total, 2,973 patients met the inclusion criteria: 1,247 patients in pediatric orthopedics, 1,089 patients in pediatric heart surgery, and 637 patients in pediatric general surgery. At the end of the study, 113 patients were multiantibiotic-resistant infection cases; the rate of multiantibiotic-resistant infections was 3.80%, and the detection rate was 84.79%. Multivariate analysis indicated that the multiantibiotic-resistant infection cases were influenced by age, department, admission season, incision type, preoperative infection, and duration of catheter drainage.

CONCLUSIONS

Age, department, admission season, incision type, preoperative infection, and duration of catheter drainage may provide possible evidence for prevention and control strategies of multiantibiotic-resistant infections.

Vancomycin MIC Distribution among Methicillin-Resistant Staphylococcus Aureus. Is Reduced Vancomycin Susceptibility Related To MIC Creep?

AIM:

To determine the distribution of vancomycin MIC and the frequency of S. aureus strains with reduced vancomycin susceptibility among Methicillin-Resistant Staphylococcus aureus (MRSA) isolates.

METHODS:

MRSA isolates (n = 100) were tested for reduced susceptibility to vancomycin using MIC broth microdilution method (BMD), vancomycin screening agar with different vancomycin concentrations with and without casein, and Vitek 2 system.

RESULTS:

BMD detected (22%) vancomycin-intermediate S. aureus (VISA) and (78%) vancomycin-susceptible S. aureus (VSSA) but couldn’t detect nine (Heterogeneous VISA) (hVISA) isolates (9%) with MIC ≤ 2 µg/ml that grew on screening agar 4 µg/ml or 6 µg/ml. Adding casein to vancomycin screening agar increased detection rate of VISA by 4.5%. Screening agar with 6 µg/ml vancomycin overall detection rate for VISA was 95.45%. Probable ‘pre-hVISA’isolates (17%) showed growth on vancomycin screening agar 2 µg/ml with casein. Vitek 2 system failed to detect any VISA isolates.

CONCLUSION:

Vancomycin screening agar; 2 µg/ml and (4 and 6 µg/ml) were able to detect; probable “pre hVISA and (hVISA and VISA) isolates respectively based on their BMD MIC values. Decreased vancomycin susceptibility in MRSA isolates might be related to MIC creep. Analysis of vancomycin MIC values over longer periods is recommended to further study this phenomenon and its impact on vancomycin treatment failure.

Phenotypic and Molecular Characterisation of Staphylococcus Aureus with Reduced Vancomycin Susceptibility Derivated in Vitro

Vancomycin has been the primary agent used to treat serious Methicillin-resistant Staphylococcus aureus (MRSA) infection for many years. However, the rise of MRSA infection rates and the extensive use of vancomycin have led to the emergence of reduced vancomycin susceptibility. Therefore, four typical Staphylococcus aureus (S. aureus) strains from different clinical specimens were derivated by vancomycin in vitro to better clarify their phenotypic and molecular characteristics. Some experiments, such as stepwise selection of vancomycin-resistant strains, pulsed-field gel electrophoresis (PFGE), antimicrobial susceptibility test, population analysis profile-area under the curve (PAP-AUC), molecular typing, transmission electron microscopy, δ-hemolysin expression, autolysis assay, biofilm assay and quantitative real-time polymerase chain reaction (qPCR) for gene expression were carried out to compare the derivated bacteria with their parental strains. Results showed that the observed phenotypes of vancomycin-resistant strains such as hemolysin, autolysis and biofilm significantly reduced, which were associated with vancomycin resistance capability of the selected strain. The changes of phenotype and regulatory genes expression were inversely proportional to the vancomycin minimum inhibitory concentration (MICvan). Most heterogeneous vancomycin intermediate Staphylococcus aureus (hVISA) or VISA strains belonged to spa type t570 and agr group II. In summary, the clinical isolated vancomycin susceptible Staphylococcus aureus (VSSA), hVISA and VISA could be derivated into high vancomycin-resistant VISA in vitro, but it was difficult for them to develop into vancomycin resistant Staphylococcus aureus (VRSA). VISA and hVISA could gradually adapt to the environment with the vancomycin concentration that continuously elevates.

Staphylococcus aureus nasal carriage in health care workers: First report from a major public hospital in Argentina

Staphylococcus aureus causes numerous mild to severe infections in humans, both in health facilities and in the community. Patients and health care workers (HCWs) may disseminate strains during regular medical examinations or hospitalization. The aim of this study was to determine the nasal carriage rate of methicillin-susceptible and methicillin-resistant S. aureus among health care workers at Hospital Provincial del Centenario, a public general hospital in Rosario, Argentina. A transversal study was conducted on 320 health care workers. Nasal swabs were taken and presumptive S. aureus colonies were isolated. Bacterial identity and methicillin resistance status were confirmed by amplification of the nuc and mec genes. Chi square test and Fisher exact test were used for statistical analysis. Of 320 HCWs, 96 (30%) were nasal carriers of S. aureus, 20 of whom (6.3%) carried methicillin-resistant S. aureus (MRSA) and 76 (23.7%) methicillin-susceptible S. aureus (MSSA). Carriage was within thepublished values for physicians (30%) and higher for technicians (57%). Accompanying resistance (62/96, 64.6%) was detected, including resistance to fluoroquinolones (23/96, 24%), aminoglucosides (13/96, 13.5%) or to macrolides (33/96, 34.4%). All the strains were susceptible to vancomycin whereas only 3.1% (3/96), all of them on MSSA strains, were resistant to mupirocin. This study is the first one of its kind in Argentina and one of the few performed in South America, to highlight the relevance of nasal carriage of MRSA and MSSA in health care personnel and brings to light the need for consensus recommendations for regular S. aureus carriage screening as well as for decolonization strategies.

In vitro selection of Staphylococcus aureus mutants resistant to tigecycline with intermediate susceptibility to vancomycin

Background

Tigecycline (TIG) is an antibiotic belonging to the glycylcyclines class and appears to be a good choice to fight infections caused by Staphylococcus aureus. To date, TIG exhibits good activity against this microorganism. The aim of this work was to obtain in vitro mutants of S. aureus resistant to TIG and evaluate possible changes in their susceptibility patterns to other antibiotics.

Results

Two mutants of S. aureus resistant to TIG (MIC = 16 µg/mL) were selected in vitro from clinical isolates of methicillin-resistant S. aureus. In both mutants, corresponding to different lineage (ST5 and ST239), an increase of efflux activity against TIG was detected. One mutant also showed a reduced susceptibility to vancomycin, corresponding to the VISA phenotype (MIC = 4 µg/mL), with a loss of functionality of the agr locus. The emergence of the VISA phenotype was accompanied by an increase in oxacillin and cefoxitin MICs.

Conclusions

This study demonstrates that, under selective pressure, the increase of efflux activity in S. aureus is one of the mechanisms that may be involved in the emergence of tigecycline resistance. The emergence of this phenotype may eventually be associated to changes in susceptibility to other antibiotics such oxacillin and vancomycin.

Prevalence of vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA among methicillin-resistant S. aureus with high vancomycin minimal inhibitory concentrations in Taiwan: A multicenter surveillance study, 2012-2013

BACKGROUND/PURPOSE

Intermediate-resistance and heteroresistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) is reported worldwide. A surveillance study in 2003 showed that the prevalence rates of vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) in Taiwan were 0.2% and 0.7%, respectively. This study aimed to investigate the updated prevalence of VISA and hVISA in Taiwan.

METHODS

MRSA isolates from sterile sites with minimal inhibitory concentrations (MICs) of 1 μg/mL or more to vancomycin were collected from 15 participating hospitals in Taiwan. Enrolled MRSA isolates were submitted to antimicrobial susceptibility testing, staphylococcal cassette chromosome mec (SCCmec) element typing, and multilocus sequence typing. Isolates with vancomycin MIC of 1 μg/mL or 2 μg/mL were screened for vancomycin heterogeneous resistance by Etest glycopeptide-resistance detection (GRD). Those with positive GRD screening results were then analyzed by modified population analysis profiling-area under the curve method for confirmation of vancomycin heteroresistance.

RESULTS

Between 2012 and 2013, a total of 622 MRSA isolates from sterile sites with vancomycin MIC of 1 μg/mL or more were studied. The prevalence rates of hVISA and VISA among these isolates were 10.0% and 2.7%, respectively. The hVISA prevalence increased significantly compared to that in 2003. Compared with vancomycin-susceptible S. aureus, hVISA and VISA isolates were less susceptible to ciprofloxacin, clindamycin, daptomycin, gentamicin, rifampin, and trimethoprim/sulfamethoxazole, and are thus, more likely to have SCCmec II or III element. A twofold increase in either vancomycin or teicoplanin MIC doubled the probability of being hVISA.

CONCLUSION

Growing hVISA prevalence was highly suspected. Longitudinal surveillance of this phenomenon and monitoring of its clinical impact are necessary.

Staphylococcus aureus with reduced susceptibility to vancomycin in healthcare settings

Glycopeptide resistance in Staphylococcus aureus is a source of great concern because, especially in hospitals, this class of antibiotics, particularly vancomycin, is one of the main resources for combating infections caused by methicillin-resistant Staphylococcus aureus strains (MRSA). Reduced susceptibility to vancomycin (VISA) was first described in 1996 in Japan; since then, a phenotype with heterogeneous resistance to vancomycin (h-VISA) has emerged. H-VISA isolates are characterised by the presence of a resistant subpopulation, typically at a rate of 1 in 10(5) organisms, which constitutes the intermediate stage betweenfully vancomycin-susceptible S. aureus (VSSA) and VISA isolates. As VISA phenotypes are almost uniformly cross-resistant to teicoplanin, they are also called Glycopeptides-intermediate Staphylococcus aureus strains (GISA) and, in the case of heterogeneous resistance to glycopeptides, h-GISA. The overall prevalence of h-VISA is low, accounting for approximately 1.3% of all MRSA isolates tested. Mortality due to h-GISA infections is very high (about 70%), especially among patients hospitalised in high-risk departments, such as intensive care units (ICU). Given the great clinical relevance of strains that are heteroresistant to glycopeptides and the possible negative impact on treatment choices, it is important to draw up and implement infection control practices, including surveillance, the appropriate use of isolation precautions, staff training, hand hygiene, environmental cleansing and good antibiotic stewardship.