Vancomycin-intermediate S. Aureus Research Articles

Antimicrobial Peptides with Antibacterial Activity against Vancomycin-Resistant Staphylococcus aureus Strains: Classification, Structures, and Mechanisms of Action

The emergence of bacteria resistant to conventional antibiotics is of great concern in modern medicine because it renders ineffectiveness of the current empirical antibiotic therapies. Infections caused by vancomycin-resistant Staphylococcus aureus (VRSA) and vancomycin-intermediate S. aureus (VISA) strains represent a serious threat to global health due to their considerable morbidity and mortality rates. Therefore, there is an urgent need of research and development of new antimicrobial alternatives against these bacteria. In this context, the use of antimicrobial peptides (AMPs) is considered a promising alternative therapeutic strategy to control resistant strains. Therefore, a wide number of natural, artificial, and synthetic AMPs have been evaluated against VRSA and VISA strains, with great potential for clinical application. In this regard, we aimed to present a comprehensive and systematic review of research findings on AMPs that have shown antibacterial activity against vancomycin-resistant and vancomycin-intermediate resistant strains and clinical isolates of S. aureus, discussing their classification and origin, physicochemical and structural characteristics, and possible action mechanisms. This is the first review that includes all peptides that have shown antibacterial activity against VRSA and VISA strains exclusively.

Effect of silver nanoparticles on vancomycin resistant Staphylococcus aureus infection in critically ill patients

ABSTRACT A prevalent increase in antimicrobial resistance represents a universal obstacle for the treatment of Staphylococcus aureus (S. aureus) infection, especially in critically ill patients. Silver nanoparticles are defined as broad spectrum bactericidal agents, which might be effective against vancomycin resistant S. aureus (VRSA). In this study, we examined the bactericidal efficacy of silver nanoparticles on VRSA in 150 blood and sputum samples isolated from intensive care patients. Methicillin resistant S. aureus (MRSA) isolates were identified in 83 samples, with an incidence of 55.3%. Meanwhile, VRSA isolates were found in 11 and 8 isolates (a total of 19 isolates out of 150) from sputum and blood samples, with an incidence of 14.67% and 10.67%, respectively, with a total incidence of 12.67%. Vancomycin intermediate S. aureus (VISA) isolates had an inhibitory zone ranging from 9 to 13 mm, which was found in 13 out of 19 isolates, whereas VRSA isolates had an inhibitory zone ranging from 0 to 6 mm, which was detected in 6 out of 19 isolates. The findings of this study confirm that silver nanoparticles are an effective treatment against VRSA.

Methicillin-Resistant Staphylococcus aureus (MRSA): Prevalence, Antimicrobial Susceptibility Pattern, and Detection of mecA Gene among Cardiac Patients from a Tertiary Care Heart Center in Kathmandu, Nepal.

Background:Methicillin Resistant Staphylococcus aureus (MRSA) is a significant human pathogen associated with nosocomial infections. mecA in the S. aureus is a marker of MRSA. The main objective of this study was to detect mecA and vanA genes conferring resistance in S. aureus among cardiac patients attending Sahid Gangalal National Heart Centre (SGNHC), Kathmandu, Nepal between May and November 2019.Methods:A total of 524 clinical samples (blood, urine, sputum) were collected and processed. Bacterial isolates were tested for antimicrobial susceptibility test (AST) and screening for MRSA was carried out by cefoxitin disc diffusion method. Minimum inhibitory concentration (MIC) of vancomycin for MRSA was established by agar dilution method and chromosomal DNA was extracted and used in polymerase chain reaction targeting the mecA and vanA genes.Results:Out of 524 specimens, 27.5% (144/524) showed bacterial growth. Among 144 culture positive isolates, S. aureus (27.1%; 39/144) was the predominant bacteria. Among 39 S. aureus isolates, all isolates were found resistant to penicillin followed by erythromycin (94.9%; 37/39), gentamicin (94.9%; 37/39) and cefoxitin (87.2%; 34/39). Out of 39 S. aureus, 87.2% (34/39) were MRSA. Among 34 MRSA, 8.8% (3/34) were vancomycin intermediate S. aureus (VISA). None of the MRSA was resistant to vancomycin. All of the 3 VISA isolates were obtained from inpatients. Of 39 S. aureus, 82.1% (32/39) harbored mecA gene. Similarly, the entire VISA isolates and 94.1% (32/34) of the MRSA isolates were tested positive for mecA gene.Conclusions:High prevalence of MRSA among the cardiac patients indicates the increasing burden of drug resistance among bacterial isolates. Since infection control is the crucial step in coping with the burgeoning antimicrobial resistance in the country, augmentation of diagnostic facilities with routine monitoring of drug resistance is recommended.

Vancomycin Resistance Among Clinical Isolates of Staphylococcus aureus Obtained from Selected Hospitals in Sokoto Metropolis

The decreased vancomycin susceptibility and subsequent emergence of vancomycin resistant Staphylococcus aureus (VRSA) strains is a major public health problem. This study was aimed at detecting the prevalence of vancomycin resistant Staphylococcus aureus among clinical isolates obtained from patients attending Specialist Hospital Sokoto and Maryam Abacha Women and Children Hospital Sokoto. A total of 80 S. aureus clinical isolates were obtained from the medical microbiology laboratories of the selected hospitals. Antibiotic sensitivity testing of the isolates was carried out using the agar dilution method and isolates were screened for vancomycin resistance using vancomycin agar screen method. Of the 80 S. aureus isolates studied, 69 (86.0%) were identified as vancomycin susceptible S. aureus (VSSA) with MIC value of ≤2 µg/ml, 11 (13.8%) were identified as vancomycin intermediate S. aureus (VISA) and had MIC value of 4-8 µg/mL (VISA) and none of the isolates was identified as vancomycin resistant aureus (VRSA). The study detects high prevalence rate of VISA in the study area and identifies the need for increased public awareness on the danger associated with the presence of drug resistant bacteria. Emphasis should be directed at discouraging practices such as the use of over the counter medications which increase the rate of development of drug resistant organisms.

Panton-Valentine Leukocidin-Positive Methicillin-Resistant Staphylococcus Aureus with Reduced Vancomycin Susceptibility: An Emerging Trend?

Abstract Methicillin-resistant Staphylococcus aureus (MRSA) is a major multidrug-resistant nosocomial pathogen. This class of MRSA, first reported in the early 1960s and now termed healthcare-associated MRSA (HA-MRSA), was followed by a newer class of MRSA, community-associated MRSA (CA-MRSA). The unique feature of the initial CAMRSA included Panton-Valentine leukocidin (PVL), an abscess-associated toxin and also S. aureus spread factor. CA-MRSA usually causes skin and soft-tissue infections, but occasionally causes invasive infections, including (necrotizing) pneumonia, sometimes preceded by respiratory virus infections. The most successful CA-MRSA USA300 (ST8/SCCmecIVa) caused an epidemic in the United States. In Russia, we first detected PVL-positive CAMRSA (ST30/SCCmecIVc) in Vladivostok in 2006, but with no more PVL-positive MRSA isolation. However, we recently isolated four lineages of PVL-positive MRSA in Krasnoyarsk. Regarding chemotherapy against invasive MRSA infections, vancomycin still remains a gold standard, in addition to some other anti-MRSA agents such as teicoplanin, linezolid, and daptomycin. For resistance, vancomycin-resistant MRSA (VRSA) with MICs of ≥16 μg/mL appeared in patients, but cases are still limited. However, clinically, infections from strains with MICs of ≥1.5 μg/mL, even albeit with susceptible MICs (≤2 μg/mL), respond poorly to vancomycin. Some of those bacteria have been bacteriologically characterized as vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA), generally with HA-MRSA genetic backgrounds. The features of the above PVL-positive Krasnoyarsk MRSA include reduced susceptibility to vancomycin, which meets the criteria of hVISA. In this review, we discuss a possible new trend of PVL-positive hVISA, which may spread and threaten human health in community settings.

Protein Biomarker Discovery for Methicillin-Sensitive, Heterogeneous Vancomycin-Intermediate and Vancomycin-Intermediate Staphylococcus aureus Strains Using Label-Free Data-Independent Acquisition Proteomics.

Rapid identification of methicillin-sensitive Staphylococcus aureus (MSSA), heterogeneous vancomycin-intermediate S. aureus (hVISA), and vancomycin-intermediate S. aureus (VISA) is important for accurate treatment, timely intervention, and prevention of outbreaks. Here, 90 S. aureus isolates were analyzed for protein biomarker discovery, including MSSA, vancomycin-susceptible S. aureus (VSSA), hVISA, and VISA strains. Label-free data-independent acquisition proteomics was used to identify protein biomarkers that allow for discrimination among MSSA, hVISA, and VISA strains. There were 8786 nonredundant peptides identified, corresponding to 418 different annotated nonredundant proteins. Two VISA protein biomarkers, two hVISA protein biomarkers, and one MSSA protein biomarker with high sensitivities and specificities were discovered and verified. Data are available via MassIVE with identifier MSV000085776.

Methicillin-resistant Staphylococcus aureus: epidemiology and antimicrobial susceptibility experiences from the University Hospital ‘Luigi Vanvitelli’ of Naples

ABSTRACT Methicillin-resistant Staphylococcus aureus (MRSA) is one of the important pathogens worldwide showing resistance to several widely used antibiotics. This has made the treatment of MRSA infections harder, especially due to their prevalence in the hospital setting. We evaluated the antibiotic susceptibility patterns of healthcare-associated MRSA infections with a focus on Vancomycin Intermediate S. Aureus (VISA) and macrolide-licosamide-streptogramin B (MLSB) phenotypes. A total of 417 Staphylococcus aureus (S. aureus) cases were isolated between January 2017 and December 2018, through several clinical specimens collected from the University Hospital ‘Luigi Vanvitelli’ of Naples. We identified bacterial strains using Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF) and antimicrobial susceptibility using Phoenix BD (Becton Dickinson, NJ, USA). Out of the total 417 S. aureus cases, 140 were MRSA (33.6%) and of these, 50% were soft tissue infections. All MRSA and Methicillin sensible S.aureus MSSA isolates were susceptible to linezolid and daptomycin. Two MRSA cases exhibited intermediate resistance to vancomycin and were of constitutive MLSB phenotype. Among the MRSA strains, 11.4% were constitutive and 43.6% were inducible MLSB phenotypes and 8.6% were macrolide-streptogramin B phenotype. This study characterized the epidemiological status, antibiotic resistance patterns, and current prevalent phenotypes of healthcare-associated MRSA. This knowledge can aid clinicians in improving the antimicrobial stewardship program by adapting appropriate guidelines for the proper use of MRSA antibacterial agents.

Bloodstream Infections Caused by S. aureus: Daptomycin Nonsusceptibility and Clinical Aspects

Background:Staphylococcus aureus is one of the leading pathogens isolated from bloodstream infections (BSIs), and vancomycin has been the main choice to treat MRSA (methicillin-resistant S. aureus) infections. Vancomycin-intermediate S. aureus (VISA) and heteroresistant-VISA (hVISA) have been described, limiting this antibiotic use. We evaluated aspects associated with the resistance and its clonality of the S. aureus isolated from BSIs, and we determined their association with clinical aspects of patients attended at Rio de Janeiro between 2016 and 2018. The detection of MRSA and trimethoprim-sulfamethoxazole resistant isolates was performed using the disk diffusion test, while the minimum inhibitory concentrations (MICs) were evaluated for 5 antimicrobials using the broth microdilution method. The MICs for ceftaroline and vancomycin of the MRSA isolates were determined using the E test. The presence of hVISA isolates was evaluated for isolates with vancomycin MICs of 1 and 2 μg/mL by screening on BHI agar added with vancomycin. The population profile was divided by the area under the curve (ie, PAP/AUC test). SCC mec was evaluated by PCR and the clonal profile by PFGE method. Among 123 S. aureus isolates from BSI, 31% were MRSA. MIC50 and MIC90 were daptomycin 2 and 2 μg/mL; linezolid, 1 and 1 μg/mL; oxacillin 1 and 256 μg mL; teicoplanin, 0.5 and 0.5 μg/mL and vancomycin 1 and 1 μg/ml. MIC values for ceftaroline and vancomycin were 0.75 and 2 μg/mL. The frequency of isolates not susceptible to daptomycin was 75%. The clonal lineages and SCCmec types found were USA100/ST5-II (50%), USA800/ST5-IV (22%), USA300/ST8-IV (15.8%), USA1100/ST30-IV (5.3%), BEC/ST239-III (5.3%), and 1 isolate carrying SCCmecV/ST1. We found 1 VISA isolate, and the PAP/AUC analysis detected 3 hVISA isolates that were associated with the USA100 and USA300 lineages. Overall, 85% of patients had a vascular catheter. More advanced age was associated with MRSA infection as was higher mortality. Patients with end-stage renal disease were more affected by MSSA infection. Daptomycin nonsusceptibility and VISA and hVISA phenotypes associated with prevalent clonal lineages were described. In addition, MRSA infections presented higher mortality, which emphasizes the importance of epidemiological studies.Funding: NoneDisclosures: None

Association of mprF mutations with cross-resistance to daptomycin and vancomycin in methicillin-resistant Staphylococcus aureus (MRSA)

We first reported a phenomenon of cross-resistance to vancomycin (VCM) and daptomycin (DAP) in methicillin-resistant Staphylococcus aureus (MRSA) in 2006, but mechanisms underlying the cross-resistance remain incompletely understood. Here, we present a follow-up study aimed to investigate genetic determinants associated with the cross-resistance. Using 12 sets of paired DAP susceptible (DAPS) and DAP non-susceptible (DAPR) MRSA isolates from 12 patients who had DAP therapy, we (i) assessed susceptibility to DAP and VCM, (ii) compared whole-genome sequences, (iii) identified mutations associated with cross-resistance to DAP and VCM, and (iv) investigated the impact of altered gene expression and metabolic pathway relevant to the cross-resistance. We found that all 12 DAPR strains exhibiting cross-resistance to DAP and VCM carried mutations in mprF, while one DAPR strain with reduced susceptibility to only DAP carried a lacF mutation. On the other hand, among the 32 vancomycin-intermediate S. aureus (VISA) strains isolated from patients treated with VCM, five out of the 18 strains showing cross-resistance to DAP and VCM carried a mprF mutation, while 14 strains resistant to only VCM had no mprF mutation. Moreover, substitution of mprF in a DAPS strain with mutated mprF resulted in cross-resistance and vice versa. The elevated lysyl-phosphatidylglycerol (L-PG) production, increased positive bacterial surface charges and activated cell wall (CW) synthetic pathways were commonly found in both clinical isolates and laboratory-developed mutants that carry mprF mutations. We conclude that mprF mutation is responsible for the cross-resistance of MRSA to DAP and VCM, and treatment with DAP is more likely to select for mprF-mediated cross-resistance than is with VCM.

Genomic and Long-Term Transcriptomic Imprints Related to the Daptomycin Mechanism of Action Occurring in Daptomycin- and Methicillin-Resistant Staphylococcus aureus Under Daptomycin Exposure.

Daptomycin (DAP) is one of the last-resort treatments for heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) and vancomycin-intermediate S. aureus (VISA) infections. DAP resistance (DAP-R) is multifactorial and mainly related to cell-envelope modifications caused by single-nucleotide polymorphisms and/or modulation mechanisms of transcription emerging as result of a self-defense process in response to DAP exposure. Nevertheless, the role of these adaptations remains unclear. We aim to investigate the comparative genomics and late post-exponential growth-phase transcriptomics of two DAP-resistant/DAP-susceptible (DAPR/S) methicillin-resistant S. aureus (MRSA) clinical strain pairs to focalize the genomic and long-term transcriptomic fingerprinting and adaptations related to the DAP mechanism of action acquired in vivo under DAP pressure using Illumina whole-genome sequencing (WGS), RNA-seq, bioinformatics, and real-time qPCR validation. Comparative genomics revealed that membrane protein and transcriptional regulator coding genes emerged as shared functional coding-gene clusters harboring mutational events related to the DAP-R onset in a strain-dependent manner. Pairwise transcriptomic enrichment analysis highlighted common and strain pair-dependent Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, whereas DAPR/S double-pair cross-filtering returned 53 differentially expressed genes (DEGs). A multifactorial long-term transcriptomic-network characterized DAPR MRSA includes alterations in (i) peptidoglycan biosynthesis, cell division, and cell-membrane (CM) organization genes, as well as a cidB/lytS autolysin genes; (ii) ldh2 involved in fermentative metabolism; (iii) CM-potential perturbation genes; and (iv) oxidative and heat/cold stress response-related genes. Moreover, a D-alanyl–D-alanine decrease in cell-wall muropeptide characterized DAP/glycopeptide cross-reduced susceptibility mechanisms in DAPR MRSA. Our data provide a snapshot of DAPR MRSA genomic and long-term transcriptome signatures related to the DAP mechanism of action (MOA) evidencing that a complex network of genomic changes and transcriptomic adaptations is required to acquire DAP-R.

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.

Prevalence of vanA Gene among Methicillin Resistant S. aureus Strains Isolated from Burn Wound Infections in Menoufia University Hospitals

Background: Staphylococcus aureus is a leading cause of burn wound infection. Vancomycin resistance among methicillin-resistant Staphylococcus aureus (MRSA) is becoming a worldwide growing threat. Objectives: to detect the prevalence of MRSA in burn patients and its antibiotic susceptibility patterns. In addition, the resistance patterns of MRSA to vancomycin and the prevalence of vanA gene among MRSA isolates were investigated. Methodology: A total 250 clinical samples were obtained from patients admitted to Burn Unit in Menoufia University Hospitals. Identification and antimicrobial susceptibility testing of S. aureus isolates were performed. Cefoxitin disk diffusion method was used to identify MRSA strains. Vancomycin resistance was determined by agar dilution method. Detection of mecA and vanA genes by multiplex PCR was done. Results: Staphylococcus aureus represented 43.3% of all isolates. By cefoxitin disc diffusion method, 94% (79/84) of isolated S. aureus were MRSA that showed a high resistance to most antimicrobials used with rates ranged from 40.5 % to 100%. Phenotypically among MRSA isolates, vancomycin sensitive S. aureus (VSSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) were 59.5%, 15.2%, 25.3% respectively. Among MRSA isolates, 17 (21.5%) isolates had vanA gene by PCR (16 isolates were VRSA and one isolate was VSSA).Conclusion: This study is considered as an alarm demonstrating that implementation of proper infection control measures is mandatory to control spread of such resistant strains in our hospital.

Vancomycin-loaded nanoparticles against vancomycin intermediate and methicillin resistant Staphylococcus aureus strains

Bacterial infections represent one of the leading causes of mortality in the world. Among causative pathogens, S. aureus is prominently known as the underlying cause of many multidrug resistant infections that are often treated with the first-line choice antibiotic vancomycin (VCM). Loading antibiotics into polymeric nanoparticles (Np) displays promise as an alternative method to deliver therapy due to the greater access and accumulation of the antibiotic at the site of the infection as well as reducing toxicity, irritation and degradation. The aim of this work was to prepare, characterize and evaluate VCM-loaded nanoparticles (VNp) for use against S. aureus strains. Moreover, conjugation of Nps with holo-transferrin (h-Tf) was investigated as an approach for improving targeted drug delivery. VNp were prepared by double emulsion solvent evaporation method using PLGA and PVA or DMAB as surfactants. The particles were characterized for size distribution, Zeta Potential, morphology by transmission electron microscopy, encapsulation yield and protein conjugation efficiency. Process yield and drug loading were also investigated along with an in vitro evaluation of VNp antimicrobial effects against S. aureus strains. Results showed that Np were spontaneously formed with a mean diameter lower than 300 nm in a narrow size distribution that presented a spherical shape. The bioconjugation with h-Tf did not appear to increase the antimicrobial effect of VNp. However, non-bioconjugated Np presented a minimal inhibitory concentration lower than free VCM against a MRSA (Methicillin-resistant S. aureus) strain, and slightly higher against a VISA (VCM intermediate S. aureus) strain. VNp without h-Tf showed potential to assist in the development of new therapies against S. aureus infections.

Vancomycin and nisin A are effective against biofilms of multi-drug resistant Staphylococcus aureus isolates from human milk.

Human milk provides complete nutrition for infants and at the same time promotes the growth of specific bacteria in the infant gastrointestinal tract. Breastfeeding can often be discontinued due to mastitis which is an inflammation of the breast tissue. We isolated 18 Staphylococcus aureus strains from milk donated by healthy (n = 6), subclinical (n = 6), and mastitic (n = 6) mothers, two strains of which were VISA (Vancomycin Intermediate S. aureus). All tested strains (n = 12) were able to form biofilms. We then examined the impact of nisin A and vancomycin alone and in combination on biofilm formation and eradication of selected strains (n = 8). We observed strain-specific responses, with the combinatorial treatment at 1/4X MIC (for both singularly) significantly inhibiting biofilm formation for seven out of eight strains when compared with nisin A or vancomycin alone. None of the selected treatments were able to eradicate pre-formed biofilms. Finally, we selected two strains, namely a VISA (APC3814H) and a strong biofilm former (APC3912CM) and used confocal microscopy to evaluate the effects of the antimicrobial agents at 1X MIC on biofilm inhibition and eradication. All treatments inhibited biofilm formation of APC3814H but were ineffective in eradicating a pre-formed biofilm. Single treatments at 1X MIC against APC3912CM cells did not prevent biofilm formation whereas combination treatment caused increased death of APC3912CM cells. Finally, the combination treatment reduced the thickness of the pre-formed APC3912CM biofilm as compared with the single treatments.

Identification and evaluation of Anisochilus carnosus (L. fil.) Wall. as a novel candidate with therapeutic potential against multi-drug resistant Staphylococcus aureus

BackgroundStaphylococcus aureus has been constantly emerging with newer drug resistance patterns; vancomycin intermediate S. aureus (VISA) and vancomycin resistant S. aureus (VRSA) being recent entries. Hence the growing quest for newer antibiotics has entered the realm of the plants as they are less explored and usually have negligible side effects. Although a number of medicinal plants are being used traditionally, their spectrum and mechanism of action are not completely deciphered. ObjectivesTo evaluate the aqueous (the traditionally administered extract) and acetone/ethanol (organic solvents with the highest capacity to extract phytoconstituents) extracts of ten medicinal plants traditionally used to treat respiratory infections in south India for antibacterial activity against S. aureus. MethodsThe antibacterial activity against S. aureus standard strain was evaluated by the broth dilution method. The extracts exhibiting antibacterial activity were further validated using 50 S. aureus isolates by the broth dilution and agar diffusion methods. ResultsOnly Anisochilus carnosus acetone extract (ACace; MIC-0.33 ± 0.14 mg/mL) exhibited significant antibacterial activity, and its zone diameter break points were determined. The sensitivity of the 50 S. aureus clinical isolates to ACace (72 %) was comparable to methicillin (68 %), linezolid (94 %) and clindamycin (82 %). Additionally, ACace, inhibited majority of the MRSA (87.5 %), VISA (70 %) and VRSA (83 %) isolates. ConclusionThis is the first study to report the antibacterial potential of a novel candidate, ACace against S. aureus, evaluate its inhibitory effect on clinical isolates including drug-resistant strains and highlight the importance of zone diameter break points for the evaluation of medicinal plant extracts.

Vancomycin intermediate strains of Staphylococcus aureus have dampened induction of type I interferon production

Abstract Studies by our group have shown that interferon (IFN) signaling contributes to pathogenesis of Staphylococcus aureus pneumonia and that different strains of S. aureus can activate type I IFN signaling via distinct receptors, such as TLR9 and NOD2, at various amplitudes. In this study we investigated the capacity of a wide range of S. aureus strains to induce both type I & III IFN. We screened 78 S. aureus strains from various clinical scenarios for their ability to induce IFN-β and IFN-λ in bone marrow-derived dendritic cells (BMDC) and found that both cytokines are differentially induced by various S. aureus strains independently of their isolation sites or methicillin resistance profiles. These induction patterns persisted over time and type I & III IFN differentially correlated with tumor necrosis factor α (TNF-α) production. Furthermore, vancomycin intermediate S. aureus (VISA) strains induced up to 45-fold less (P<0.001) IFN-β than the current epidemic methicillin-resistant S. aureus strain USA300 and displayed increased in vitro survival (up to 9-fold) after 4-hour exposure to BMDC. Further investigation of one VISA strain, HIP07930, showed decreased autolysis and increased resistance to lysostaphin compared to USA300, consistent with its reduction in IFN β induction. Interestingly, this strain also displayed decreased in vivo virulence compared to USA300 in a murine acute pneumonia model of infection (4.9-fold and 54.5-fold decrease in colony forming units in bronchoalveolar lavage fluid and lung homogenates, respectively, 24 hours post infection). Overall, this study demonstrates the heterogeneity of IFN induction by S. aureus and uncovered a unique property of VISA strains in their inability to induce type I IFN production.

Vancomycin Intermediate MRSA Isolates Obtained from Retail Chicken Meat and Eggs Collected at Pokhara, Nepal

Antimicrobial resistance among food animal isolates is increasing as a result of their uncontrolled uses. The monitoring of antibiotic resistance among these isolates is very necessary. S aureus was isolated from eggshells and chicken meat samples collected from different retail outlets of the Pokhara metropolitan. Samples were inoculated on Mannitol salt agar aseptically and inoculated overnight. Isolated yellow colonies were further examined by Gram-staining, catalase, and coagulase test to detect S aureus. Methicillin resistance was screened using cefoxitin disc. Vancomycin minimum inhibitory concentration (MIC) of Methicillin-resistant S aureus (MRSA) isolates were determined by the agar dilution method following CLSI guidelines. 139 S aureus were isolated from 205 samples. Among them, 89 were from egg samples (out of 125 samples) and 50 from chicken (out of 80 samples). The overall prevalence of MRSA was 12.94%. Antibiotic resistance was significantly higher in MRSA isolates compared to Methicillin sensitive S aureus (MSSA) isolates. The highest rate of resistance was noted for ampicillin, amoxicillin, and erythromycin while the least resistance was noted for gentamicin and amikacin. Vancomycin minimum inhibitory concentration (MIC) range of the MRSA isolates was 0.25-8μg/ml indicating the detection of both vancomycin-intermediate and sensitive isolates from the samples. This is the first study reporting vancomycin-intermediate S aureus (VISA) isolates from Nepal and indicates the increasing drug resistance among animal isolates. Further surveillance studies about the transmission of these pathogens to humans as well as detail molecular analyses are imminent.

Cinnamonitrile Adjuvants Restore Susceptibility to β-Lactams against Methicillin-Resistant Staphylococcus aureus

β-Lactams are used routinely to treat Staphylococcus aureus infections. However, the emergence of methicillin-resistant S. aureus (MRSA) renders them clinically precarious. We describe a class of cinnamonitrile adjuvants that restore the activity of oxacillin (a penicillin member of the β-lactams) against MRSA. The lead adjuvants were tested against six important strains of MRSA, one vancomycin-intermediate S. aureus (VISA) strain, and one linezolid-resistant S. aureus strain. Five compounds out of 84 total compounds showed broad potentiation. At 8 μM (E)-3-(5-(3,4-dichlorobenzyl)-2-(trifluoromethoxy)phenyl)-2-(methylsulfonyl)acrylonitrile (26) potentiated oxacillin with a >4000-fold reduction of its MIC (from 256 to 0.06 mg·L-1). This class of adjuvants holds promise for reversal of the resistance phenotype of MRSA.

Phenotypic Plasticity of Staphylococcus aureus in Liquid Medium Containing Vancomycin.

Phenotypic plasticity enables individuals to develop different phenotypes in a changing environment and promotes adaptive evolution. Genome-wide association study (GWAS) facilitates the study of the genetic basis of bacterial phenotypes, and provides a new opportunity for bacterial phenotypic plasticity research. To investigate the relationship between growth plasticity and genotype in bacteria, 41 Staphylococcus aureus strains, including 29 vancomycin-intermediate S. aureus (VISA) strains, were inoculated in the absence or presence of vancomycin for 48 h. Growth curves and maximum growth rates revealed that strains with the same minimum inhibitory concentration (MIC) showed different levels of plasticity in response to vancomycin. A bivariate GWAS was performed to map single-nucleotide polymorphisms (SNPs) associated with growth plasticity. In total, 227 SNPs were identified from 14 time points, while 15 high-frequency SNPs were mapped to different annotated genes. The P-values and growth variations between the two cultures suggest that non-coding region (SNP 738836), ebh (SNP 1394043), drug transporter (SNP 264897), and pepV (SNP 1775112) play important roles in the growth plasticity of S. aureus. Our study provides an alternative strategy for dissecting the adaptive growth of S. aureus in vancomycin and highlights the feasibility of bivariate GWAS in bacterial phenotypic plasticity research.

The study of reduced susceptibility of methicillin resistant Staphylococcus aureus to various antibiotics with special reference to glycopeptides in a tertiary care hospital in central India

Background: Staphylococcus aureus has emerged over the past several decades as a leading cause of hospital-associated and community acquired infections. Methicillin resistant S. aureus (MRSA), which are often resistant to several classes of antibiotics, is the most common cause of nosocomial infections and pose a great threat to the world. Vancomycin is regarded as the first-line drug for treatment of MRSA but resistance to this drug is being reported now a day.Methods: It was carried out for a period between January 2014 to June 2017 in the microbiology diagnostic laboratory. MRSA detection was performed by cefoxitin disk diffusion method. Screening for the vancomycin intermediate and the vancomycin resistant S. aureus (VISA and VRSA respectively) was carried out by using vancomycin screen. MIC (minimum inhibitory concentration) of vancomycin was tested by agar dilution method and E strip on all MRSA isolates.Results: A total of 287 S. aureus clinical isolates were included in the study. All MRSA were inoculated on vancomycin screen agar. Visible growth was present in 8 isolates. Five (3.73%) MRSA isolates with MIC of 4 were termed VISA (vancomycin intermediate S. aureus) by agar dilution method. Six isolates had the MIC of 4 and were termed as VISA.Conclusions: As disc diffusion method is not recommended by CLSI for S. aureus, vancomycin screen agar and MIC determination by either of the methods viz. agar dilution or E test can be used.