Identification of tigecycline- and vancomycin-resistant Staphylococcus aureus strains among patients with urinary tract infection in Iran

Staphylococcus aureus acquires resistance to glycopeptide antibiotic vancomycin via CXCL10

BACKGROUND

Glycopeptide antibiotic vancomycin is a bactericidal antibiotic available for the infection to Staphylococcus aureus (SA), however, SA has a strong adaptive capacity and thereby acquires resistance to vancomycin. This study aims to illuminate the possible molecular mechanism of vancomycin resistance of SA based on the 16S rRNA sequencing data and microarray profiling data.

METHODS

16S rRNA sequencing data of control samples and urinary tract infection samples were retrieved from the EMBL-EBI (European Molecular Biology Laboratory - European Bioinformatics Institute) database. Correlation of gut flora and clinical indicators was evaluated. The possible targets regulated by SA were predicted by microarray profiling and subjected to KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis. CXCL10 gene knockout and overexpression were introduced to evaluate the effect of CXCL10 on the virulence of SA and the resistance to vancomycin. SA strains were co-cultured with urethral epithelial cells in vitro. The presence of SA virulence factors was detected using PCR. Biofilm formation of SA strains was assessed using the microtiter plate method. Furthermore, the antibiotic sensitivity of SA strains was evaluated through vancomycin testing.

RESULTS

Gut flora and its species abundance had significant difference between urinary tract infection and control samples. SA was significantly differentially expressed in urinary tract infection samples. Resistance of SA to vancomycin mainly linked to the D-alanine metabolism pathway. SA may participate in the occurrence of urinary tract infection by upregulating CXCL10. In addition, CXCL10 mainly affected the SA resistance to vancomycin through the TLR signaling pathway. In vitro experimental results further confirmed that the overexpression of CXCL10 in SA increased SA virulence and decreased its susceptibility to vancomycin. In vitro experimental validation demonstrated that the knockout of CXCL10 in urethral epithelial cells enhanced the sensitivity of Staphylococcus aureus (SA) to vancomycin.

CONCLUSION

SA upregulates the expression of CXCL10 in urethral epithelial cells, thereby activating the TLR signaling pathway and promoting resistance to glycopeptide antibiotics in SA.

Multidrug-Resistant Commensal and Infection-Causing Staphylococcus spp. Isolated from Companion Animals in the Valencia Region

The emergence of antimicrobial resistance (AMR) and multidrug resistance (MDR) among microorganisms to commonly used antibiotics is a growing concern in both human and veterinary medicine. Companion animals play a significant role in the epidemiology of AMR, as their population is continuously increasing, posing a risk of disseminating AMR, particularly to strains of public health importance, such as methicillin-resistant Staphylococcus strains. Thus, this study aimed to investigate the prevalence of AMR and MDR in commensal and infection-causing Staphylococcus spp. in dogs and cats in Valencia region. For this purpose, 271 samples were taken from veterinary centers to assess antimicrobial susceptibility against 20 antibiotics, including some of the most important antibiotics for the treatment of Staphylococcus infections, including the five last resort antibiotics in this list. Of all the samples, 187 Staphylococcus spp. strains were recovered from asymptomatic and skin-diseased dogs and cats, of which S. pseudintermedius (≈60%) was more prevalent in dogs, while S. felis (≈50%) was more prevalent in cats. In the overall analysis of the isolates, AMR was observed for all antibiotics tested, including those crucial in human medicine. Furthermore, over 70% and 30% of the strains in dogs and cats, respectively, exhibited MDR. This study highlights the significance of monitoring the trends in AMR and MDR among companion animals. The potential contribution of these animals to the dissemination of AMR and its resistance genes to humans, other animals, and their shared environment underscores the necessity for adopting a One Health approach.

The Prevalence, Epidemiological, and Molecular Characterization of Methicillin-Resistant Staphylococcus aureus (MRSA) in Macau (2017-2022)

Macau, recognized as a global tourism hub and the world's most densely populated region, provides a unique environment conducive to methicillin-resistant Staphylococcus aureus (MRSA) transmission in healthcare and community settings, posing a significant public health concern both locally and globally. The epidemiology and molecular characteristics of MRSA in the distinct city of Macau remain largely unelucidated. This five-year longitudinal study (2017-2022) examined the local prevalence and molecular typing of MRSA in Macau, with future MRSA type distribution predicted through ARIMA modeling. We subsequently analyzed the epidemiological characteristics of MRSA, including specimen source, clinical department, collection year, season, patient age, sex, and the annual number of tourists. Comprehensive antibiotic resistance profiles of the strains were also assessed. Of 504 clinically isolated S. aureus strains, 183 (36.3%) were identified as MRSA by the cefoxitin disk diffusion method and validated through multi-locus sequence typing (MLST). The MRSA detection rate showed an upward trend, increasing from 30.1% in 2017 to 45.7% in 2022. SCCmec type IV was predominant (28.9%), followed by types II (25.4%), III (22.1%), and V (22.1%). The primary sources of MRSA isolates were sputum (39.2%) and secretions (25.6%). Older age emerged as a risk factor for MRSA infection, whereas no significant associations were found with seasonal variations, gender, or the annual number of tourists. Despite displaying universal resistance to cefoxitin, oxacillin, and benzylpenicillin, MRSA isolates in Macau remained fully sensitive to vancomycin, tigecycline, quinupristin, nitrofurantoin, and linezolid. Continuous surveillance and analysis of MRSA distribution in Macau could provide invaluable insights for the effective management of MRSA prevention and control measures within healthcare settings.

Tigecycline Resistance-Associated Mutations in the MepA Efflux Pump in Staphylococcus aureus

Tigecycline is an important antibacterial drug for treating infection by clinical multidrug-resistant bacteria, and tigecycline-resistant Staphylococcus aureus (TRSA) has been increasingly reported in recent years. Notably, only rpsJ and mepA are associated with the tigecycline resistance of S. aureus. The mepA gene encodes MepA efflux pumps, and the overexpression of mepA has been confirmed to be directly related to tigecycline resistance. Although the mutations of MepA widely occur, the associations between TRSA and mutations of MepA are still unclear. In this study, we explored mutations in the mepA genes from various sources. Then, tigecycline resistance-associated mutations T29I, E287G, and T29I+E287G in MepA were identified, and their effects were evaluated through mutant deletion and complementation, tigecycline accumulation assay, and molecular docking experiments. Results showed that the MICs of tigecycline, gentamicin, and amikacin increased in special complementary transformants and recovered after the addition of the efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). The tigecycline accumulation assay of the mepA-deleted mutant strain and its complementary transformants showed that T29I, E287G, and T29I+E287G mutations promoted tigecycline efflux, and molecular docking showed that mutations T29I, E287G, and T29I+E287G decreased the binding energy and contributed to ligand binding. Moreover, we inferred the evolutionary trajectory of S. aureus under the selective pressure of tigecycline in vitro. Overall, our study indicated that mutations in MepA play important roles in tigecycline resistance in S. aureus. IMPORTANCE Previous analysis has shown that overexpression of MepA is an exact mechanism involved in tigecycline resistance apart from the rpsJ mutation and is usually dependent on the mutant mepR. However, no research has evaluated the effects of diverse mutations discovered in TRSA in MepA. This study demonstrates that the mutations in MepA confer resistance to tigecycline without overexpression and provides genotypic references for identifying TRSA. Although tigecycline resistance-associated mutations in MepA identified in this study have not been observed in clinical isolates, the mechanism should be explored given that S. aureus strains are prevalent in the environment. Measures should be implemented to contain TRSA within the time window before tigecycline resistance-associated mutations in MepA are prevalent.

The combination of insulin and linezolid ameliorates Staphylococcus aureus pneumonia in individuals with diabetes via the TLR2/MAPKs/NLRP3 pathway

Diabetes mellitus (DM) complicated with Staphylococcus aureus (S. aureus) infection lacks effective treatment strategies. In this study, we found that insulin combined with linezolid has potential to deal with the thorny problem. In vitro, our drug sensitivity assay, bacterial growth curve and hemolytic tests showed that a combination of insulin and linezolid exerted good antibacterial and anti-α-hemolysin activity, CCK8 experiment, glucose content and glycogen content determination showed that the combination of insulin and linezolid increased murine macrophage survival rate and reduced the extracellular glucose level of high glucose-treated MH-S cells and intracellular glycogen level, and Western blot showed that the combination inhibited TLR2/MAPKs/NLRP3-related inflammatory pathways in MH-S cells. The results of in vivo experiments showed that the combination therapy stabilized glucose level, remained body weight, ameliorated lung injury including improving pulmonary edema and decreasing lung wet/dry weight ratio, reduced the CFUs and inflammation in the lung tissue in a mouse model of diabetes with S. aureus pneumonia, and inhibited the expression of TLR2, MAPKs and NLRP3 inflammatory pathway. Overall, the combination of insulin and linezolid as autolytic inhibitor exhibited the effects of significant antibacterial and improving glucose level in vitro and in vivo, and also has an anti-inflammation activity via the TLR2/MAPKs/NLRP3 pathway, this paves the way for new treatments for diabetes mellitus complicated with S. aureus infection.

Isolation of Staphylococcus aureus Urinary Tract Infections at a Community-Based Healthcare Center in Riyadh

Background The aim of this study was to assess the clinical presentation, risk factors, and comorbidities of the patients with Staphylococcus aureus bacteriuria, and to analyze the antimicrobial susceptibility data of S. aureus isolated from their urine samples. Methods A total of 90 isolates of S. aureus were collected from patients with urinary tract infections (UTIs). Urinalysis was performed manually, including macroscopic examination of color and appearance, and microscopic examination for the presence of urinary WBCs, RBCs, and bacteria. Full identification and susceptibility testing of S. aureus were performed by the VITEK 2 system (BioMérieux, Marcy-l'Étoile, France) using standard criteria. Results The majority of the patients were female (62%), with a mean age of 32.9 years. Most of the patients were outpatients (85%), and 52% were previously healthy with no underlying disease. Seventy positive urine cultures were associated with UTI symptoms, and the most common symptom was dysuria (40%). Out of 77 urinalyses performed, 58 were positive for UTI. Of the S. aureus isolated, 24% were methicillin-resistant S. aureus (MRSA). Susceptibility to vancomycin, teicoplanin, and linezolid was 100%, while susceptibility to erythromycin, clindamycin, gentamicin, trimethoprim-sulfamethoxazole, fusidic acid, and tetracycline, was 86%, 93%, 97%, 91%, 68%, and 87%, respectively. Conclusion Although S. aureus UTI is known to be associated with other risk factors such as urinary catheterization, long hospital stay, or complicated UTI, our results show the community-acquired presentation of UTI. Trimethoprim-sulfamethoxazole may be used as an effective treatment for UTI caused by S. aureus. S. aureus UTI could be an alarming sign of more invasive infections such as S. aureus bacteremia, though clinical evaluation and finding the source of S. aureus are crucial for effective treatment and prevention of further complications.

Molecular detection and occurrence of vancomycin resistance genes (van A, B, C1, C2/C3) among Enterococcus species isolated from farm ostriches

BACKGROUND

Evaluating the prevalence of vancomycin resistance genes (van genes) in enterococcal isolates from food-producing animals is an important public health issue because of the possibility of resistance genes spread to human.

OBJECTIVES

The present study aimed to determine the occurrence of vancomycin resistance genes among Enterococcus species obtained from ostrich faecal samples.

METHODS

One hundred and twenty-five faecal samples of apparently healthy ostriches from five different farms were investigated. Genes encoding vancomycin resistance were studied by multiplex-PCR, and susceptibility to six antibiotics was evaluated by disk-diffusion method.

RESULTS

In total, 107 Enterococcus spp. isolates were obtained and confirmed by biochemical and molecular tests. Enterococcus faecium was the prevailing species (56 isolates of 107; 52.3%), followed by E. hirae (24 isolates; 22.4%) and E. gallinarum (12 isolates; 11.2%). Of the 107 recovered isolates, 44% harboured at least a type of van genes. vanA, vanC2/3 and vanC1 were identified in 34 (31.7%), 13 isolates (12.1%) and 4 (3.7%) isolates respectively. Additionally, four isolates (E. gallinarum, E. rafinosus) co-harboured the the vanA and vanC1 or vanA and vanC2/3. Enterococcus faecium and Enterococcus hirae strains with the vanA genotype were the most frequent van-carrying enterococci from ostrich faecal samples. Among van-carrying enterococcal isolates, 23.4% were phenotypically resistant to vancomycin. This study revealed a relatively high prevalence (44%) of van-carrying enterococci in ostrich faecal samples.

CONCLUSIONS

Results of the present study suggest that ostrich faeces could be considered as a reservoir of vancomycin resistance genes, especially vanA containing enterococci that could be potentially transferred to human through the food chain.

Emergence of CC8/ST239- SCCmec III/t421 tigecycline resistant and CC/ST22-SCCmec IV/t790 vancomycin resistant Staphylococcus aureus strains isolated from wound: A two-year multi-center study in Tehran, Iran

Staphylococcus aureus as an opportunistic bacterial pathogen with intrinsic and acquired resistance to many antibiotics is a worldwide problem. The current study was undertaken to evaluate the resistance pattern, and determine the genetic types of multidrug-resistant S. aureus isolated from wound. This cross-sectional study was conducted over the period of two years (from December 2018 to November 2020) at the hospitals affiliated to Shahid Beheshti University of Medical Sciences, Tehran, Iran. In present study, 75 multidrug-resistant S. aureus isolates collected from wound infections were investigated. Phenotypic resistance was assessed by Kirby-Bauer disk diffusion method. Conventional PCR was performed for the detection of virulence encoding genes. Genotyping of strains was performed based on coa gene polymorphism using multiplex-PCR assay. SCCmec typing, spa typing and MLST were also used to characterize the genotype of the mupirocin, tigecycline and vancomycin resistant multidrug-resistant S. aureus isolates. All 75 multidrug-resistant S. aureus isolates in the study were confirmed as MRSA. Coagulase typing distinguished isolates into five genotypic patterns including III (40%), I (24%), IVb (16%), V (10.7%) and type X (9.3%). Resistance to tigecycline was detected in 4% of MDR-MRSA isolates and all belonged to CC8/ST239- SCCmec III/t421 lineage. According to our analysis, one VRSA strain was identified that belonged to coa type V and CC/ST22-SCCmec IV/t790 lineage. Resistance to mupirocin was detected in 9.3% of strains. All 7 mupirocin resistant MDR-MRSA isolates exhibited resistance to mupirocin in high level. Of these, 4 isolates belonged to CC/ST8-SCCmec IV/t008 (57.1%), 2 isolates belonged to CC/ST8-SCCmec IV/t064 (28.6%) and one isolate to CC/ST22-SCCmec IV/t790 (14.3%). Altogether, current survey provides a snapshot of the characteristics of S. aureus strains isolated from patients. Our observations highlighted type III as predominant coa type among multidrug-resistant MDR strains indicating low heterogeneity of these isolates. Our study also indicates the importance of continuous monitoring of the genotypes of MDR-MRSA isolates to prevent nosocomial outbreaks and the spread of MDR isolates.

A Strong Synergy Between the Thiopeptide Bacteriocin Micrococcin P1 and Rifampicin Against MRSA in a Murine Skin Infection Model

Antibiotic-resistant bacterial pathogens have become a serious threat worldwide. One of these pathogens is methicillin-resistant Staphylococcus aureus (MRSA), a major cause of skin and soft tissue infections. In this study we identified a strain of Staphylococcus equorum producing a substance with high antimicrobial activity against many Gram-positive bacteria, including MRSA. By mass spectrometry and whole genome sequencing the antimicrobial substance was identified as the thiopeptide bacteriocin micrococcin P1 (MP1). Based on its properties we developed a one-step purification protocol resulting in high yield (15 mg/L) and high purity (98%) of MP1. For shorter incubation times (5-7 h) MP1 was very potent against MRSA but the inhibitory effect was overshadowed by resistance development during longer incubation time (24h or more). To overcome this problem a synergy study was performed with a number of commercially available antibiotics. Among the antibiotics tested, the combination of MP1 and rifampicin gave the best synergistic effect, with MIC values 25 and 60 times lower than for the individual drugs, respectively. To assess the therapeutic potential of the MP1-rifampicin combination, we used a murine skin infection model based on the use of the multidrug-resistant luciferase-tagged MRSA strain Xen31. As expected, neither of the single antimicrobials (MP1 or rifampicin) could eradicate Xen31 from the wounds. By contrary, the MP1-rifampicin combination was efficient not only to eradicate but also to prevent the recurrence of Xen31 infection. Furthermore, compared to fucidin cream, which is commonly used in skin infection treatments, MP1-rifampicin combination was superior in terms of preventing resistance development. Our results show that combining MP1, and probably other thiopeptides, with antibiotics can be a promising strategy to treat SSTIs caused by MRSA and likely many other Gram-positive bacteria.

Systematic review and meta-analysis of the epidemiology of vancomycin-resistance Staphylococcus aureus isolates

BACKGROUND

Vancomycin‑resistant Staphylococcus aureus (VRSA) is a serious public health challenging concern worldwide.

OBJECTIVES

Therefore, the objective of present study of 62 published studies was to evaluate the prevalence of VRSA based on different years, areas, isolate source, antimicrobial susceptibility testing, and the genetic determinants.

METHODS

We searched the relevant articles that focused on the prevalence rates of VRSA in PubMed, Scopus, Embase, and Web of Science from 2000 to 2019. Statistical analyses were conducted using STATA software (version 14.0).

RESULTS

The prevalence of VRSA was 2% before 2006, 5% in 2006-2014, and 7% in 2015-2020 that showed a 3.5-fold increase in the frequency of VRSA between before 2006 and 2020 years. The prevalence of VRSA was 5% in Asia, 1% in Europe, 4% in America, 3% in South America, and 16% in Africa. The frequencies of VRSA isolated from clinical, non-clinical, and mixed samples were 6%, 7%, and 14%, respectively. The prevalence of VRSA was 12% using disk diffusion agar method, 7% using MIC-base methods, and 4% using mixed-methods. The prevalence of vanA, vanB, and vanC1 positive were 71%, 26%, and 4% among VRSA strains. The most prevalent genotype was staphylococcal cassette chromosomemec (SCCmec) II, which accounted for 57% of VRSA. The most prevalent staphylococcal protein A (spa) types were t002, t030, and t037.

CONCLUSION

The prevalence of VRSA has been increasing in recent years particularly in Africa/Asia than Europe/America. The most prevalent of genetic determinants associated with VRSA were vanA and SCCmec II. This study clarifies that the rigorous monitoring of definite antibiotic policy, regular surveillance/control of nosocomial-associated infections and intensive surveillance of vancomycin-resistance are required for preventing emergence and further spreading of VRSA.

Prevalence and Associated Factors of Methicillin Resistance Staphylococcus aureus (MRSA) Among Urinary Tract Infection Suspected Patients Attending at Arba Minch General Hospital, Southern Ethiopia

BACKGROUND

Urinary tract infection (UTI) is a very frequent infection both in the community and hospital patients, and the emergence of methicillin-resistant Staphylococcus aureus (MRSA) in the community setting and infections with this pathogen become a prevalent problem among UTI patients. Therefore, the aim of this study was to determine prevalence and associated factors of methicillin resistance staphylococcus aureus (MRSA) among urinary tract infection suspected patients attending at Arba Minch General Hospital.

METHODS

Facility-based cross-sectional study was done at Arba Minch General Hospital from July to October 2020. Midstream urine specimen was collected from outpatients, cultured and biochemical tests were performed to identify the intended pathogen, finally the antibiotic susceptibility pattern of MRSA was done and possible associated factors were determined. The cleaned data were entered and analyzed using SPSS version 21.

RESULTS

Four hundred and twenty two (422) adult outpatients were enrolled in this study, of which males accounted for 238 (56.4%) of the participants. The mean and standard deviation age of the participants was 27.4 (SD 27.4 ± 15.6) years. A total of 54 S. aureus isolates were recovered from urine specimen. The prevalence of MRSA among the isolated S. aureus was 23/54 (42.59% (95% CI (35.0, 47.0)). Participants who had previous exposure to UTI (p < 0.002), presence of chronic disease (p < 0.029), and hospitalization (p < 0.006) were statically associated with the prevalence of MRSA. From all the MRSA isolates, 53.7% were resistant against Nitrofurantoin.

CONCLUSION

This study revealed that MRSA could be prevalent in isolates from patients suspected of urinary tract infection and exhibiting different resistance pattern for antibiotics commonly used for treatment of staphylococcal infections.

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.

Mutations in the MepRAB efflux system contribute to the in vitro development of tigecycline resistance in Staphylococcus aureus

OBJECTIVE

To characterize the evolutionary pathways of tigecycline (TGC) resistance and alterations in the biological characteristics of hospital-derived Staphylococcus aureus isolates under selective pressure.

METHODS

Three clinical S. aureus strains and one standard S. aureus strain, ATCC 29213, were used for the in vitro selection of TGC-resistant S. aureus variants with gradient concentrations of TGC. Changes in drug resistance and genetic alterations in resistance-related genes (operon mepRAB and rpsJ) in mutant strains were determined. The efflux inhibitor assay for MepA and the fitness cost, determined by comparing the growth and virulence of parental and mutant strains, were also investigated.

RESULTS

Mutants induced in vitro showed a 64- to 128-fold increase in the minimum inhibitory concentration (MIC) of TGC. Substitution mutations were detected in the transcriptional repressor mepR and the efflux pump gene mepA. A K57M amino acid substitution occurred in the ribosomal S10 protein-encoding gene rpsJ. The MICs of TGC in the final mutants were significantly decreased in the presence of efflux pump inhibitors. It was worth noting that growth was unaffected by TGC resistance selection in vitro, with the exception of one strain, and the MICs of other antibiotics and virulence were also unaffected.

CONCLUSIONS

The evolution of TGC resistance in S. aureus in vitro is associated with a loss-of-function mutation in the efflux pump transcriptional repressor mepR and a missense mutation in the efflux pump-encoding gene mepA. Our work further validated the resistance mechanisms of S. aureus to TGC and reported previously undiscovered mutations.

Molecular Characterization, Drug Resistance and Virulence Analysis of Constitutive and Inducible Clindamycin Resistance Staphylococcus aureus Strains Recovered from Clinical Samples, Tehran - Iran

Background

Macrolide-lincosamide streptogramin B family is one of the important alternative antibiotics for treating staphylococcal infections. The aim of this study was to determine the characteristics and prevalence of antibiotic resistance genes in different coagulase types of clinical Staphylococcus aureus strains.

Methods

In the present study, 86 isolates with different phenotypes of MLS_B resistance were investigated. In vitro susceptibility was assessed by the disk diffusion and broth microdilution methods. PCR assays were used to detect resistance-related genes. Coagulase and SCCmec types were identified by multiplex PCR assay.

Results

The prevalences of constitutive MLS_B, inducible MLS_B, and MS phenotypes were found to be 23%, 14.2%, and 4.9%, respectively. The rates of resistance to mupirocin, fusidic acid, and tigecycline were found to be 9.3%, 4.6%, and 2.3%, respectively. The top three predominant resistance genes were mecA, tet(M), erm(C) representing 75.6, 50, and 40.7% of isolates. mupA (7%), fusB (3.5%), and fusC (1.2%) genes were also detected among tested isolates. Coagulase types were mainly type II (34.9%), followed by III (32.6%), V (20.9%), and I (11.6%).

Conclusion

These findings indicated high resistance rate and low genetic variability with the prominence of coa type II, highlighting the particular importance of diagnosis of these strains to avoid treatment failure.

The global prevalence of Daptomycin, Tigecycline, Quinupristin/Dalfopristin, and Linezolid-resistant Staphylococcus aureus and coagulase-negative staphylococci strains: a systematic review and meta-analysis

Objective

Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS) are among the main causes of nosocomial infections, which have caused major problems in recent years due to continuously increasing spread of various antibiotic resistance features. Apparently, vancomycin is still an effective antibiotic for treatment of infections caused by these bacteria but in recent years, additional resistance phenotypes have led to the accelerated introduction of newer agents such as linezolid, tigecycline, daptomycin, and quinupristin/dalfopristin (Q/D). Due to limited data availability on the global rate of resistance to these antibiotics, in the present study, the resistance rates of S. aureus, Methicillin-resistant S. aureus (MRSA), and CoNS to these antibiotics were collected.

Method

Several databases including web of science, EMBASE, and Medline (via PubMed), were searched (September 2018) to identify those studies that address MRSA, and CONS resistance to linezolid, tigecycline, daptomycin, and Q/D around the world.

Result

Most studies that reported resistant staphylococci were from the United States, Canada, and the European continent, while African and Asian countries reported the least resistance to these antibiotics. Our results showed that linezolid had the best inhibitory effect on S. aureus. Although resistances to this antibiotic have been reported from different countries, however, due to the high volume of the samples and the low number of resistance, in terms of statistical analyzes, the resistance to this antibiotic is zero. Moreover, linezolid, daptomycin and tigecycline effectively (99.9%) inhibit MRSA. Studies have shown that CoNS with 0.3% show the lowest resistance to linezolid and daptomycin, while analyzes introduced tigecycline with 1.6% resistance as the least effective antibiotic for these bacteria. Finally, MRSA and CoNS had a greater resistance to Q/D with 0.7 and 0.6%, respectively and due to its significant side effects and drug-drug interactions; it appears that its use is subject to limitations.

Conclusion

The present study shows that resistance to new agents is low in staphylococci and these antibiotics can still be used for treatment of staphylococcal infections in the world.

Vancomycin resistant Staphylococcus aureus infections: A review of case updating and clinical features

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MRSA infection is a global threat to public health.

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Vancomycin is one of the first-line drugs for the treatment of MRSA infections.

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MRSA with complete resistance to vancomycin have emerged in recent years.

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The total number of VRSA isolates is updated in this paper.

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Resistance mechanisms, characteristics of VRSA infections, as well as clinical treatments are reviewed.

The infection caused by methicillin-resistant Staphylococcus aureus (MRSA) is a global threat to public health. Vancomycin remains one of the first-line drugs for the treatment of MRSA infections. However, S. aureus isolates with complete resistance to vancomycin have emerged in recent years. Vancomycin-resistant S. aureus (VRSA) is mediated by a vanA gene cluster, which is transferred from vancomycin-resistant enterococcus. Since the first VRSA isolate was recovered from Michigan, USA in 2002, 52 VRSA strains have been isolated worldwide. In this paper, we review the latest progresses in VRSA, highlighting its resistance mechanism, characteristics of VRSA infections, as well as clinical treatments.

Detection of vancomycin nonsusceptible strains in clinical isolates of Staphylococcus aureus in northern Iran

Glycopeptides, particularly the cell wall-acting antibiotic vancomycin, are the safest cure for methicillin-resistant Staphylococcus aureus. The aim of this study was to evaluate nonsusceptibility of clinical isolates of S. aureus to vancomycin and investigate mutations in vraSR, a cell wall synthesis regulator gene, in vancomycin-resistant strains. Susceptibility of 110 clinical strains of S. aureus to methicillin and vancomycin were determined using disc diffusion method and determination of minimum inhibitory concentration, respectively. Presence of mecA and vanA genes was determined by PCR. Determination of spa types and mutations of the vraSR gene in vancomycin nonsusceptible isolates were assessed by PCR-sequencing analyses. In total, 47 isolates (42.73%) were recognized as MRSA, three (2.73%) strains were resistant to vancomycin, and eight (7.27%) strains were vancomycin intermediates. The MIC of vancomycin was 4-64 μg/ml in these isolates. All vancomycin nonsusceptible S. aureus strains were mecA positive and one isolate was positive for the vanA gene. Spa type t030 was found as the most common type. In vraSR sequence analysis, all 11 vancomycin nonsusceptible isolates had the D59E mutation in the vraR and E45G in vraS genes. R117H, R121S, and R121I are the other identified missense mutations in the vraR gene. The identification of a high percentage of MRSA and presence of VRSA and VISA isolates is a serious warning about the treatment of future MRSA infections and reveals the need for new and effective therapeutic agents.