Vancomycin-intermediate Strains Research Articles

Cladobotric Acids: Metabolites from Cultures of Cladobotryum sp., Semisynthetic Analogues and Antibacterial Activity.

Three new polyketide-derived natural products, cladobotric acids G–I (1–3), and six known metabolites (4, 5, 8–11) were isolated from fermentation of the fungus Cladobotryum sp. grown on rice. Their structures were elucidated by extensive spectroscopic methods. Two metabolites, cladobotric acid A (4) and pyrenulic acid A (10), were converted to a series of new products (12–20) by semisynthesis. The antibacterial activities of all these compounds were investigated against the Gram-positive pathogen Staphylococcus aureus including methicillin-susceptible (MSSA), methicillin-resistant and vancomycin-intermediate (MRSA/VISA), and heterogeneous vancomycin-intermediate (hVISA) strains. Results of these antibacterial assays revealed structural features of the unsaturated decalins important for biological activity.

Vancomycin intermediate resistant Staphylococcus aureus in the nasal cavity of asymptomatic individuals: a potential public health challenge.

The potential of transmitting multidrug resistant Staphylococcus aureus from asymptomatic individuals to healthy individuals could constitute a great challenge to antimicrobial therapy. The antibiograms of the S. aureus from asymptomatic individuals were determined by disk diffusion and agar dilution assay techniques with different antibiotics and vancomycin. Of the 152 S. aureus isolated, (59)38.8% isolates were multi-drug resistant strains. Streptomycin was the most effective and inhibited (135)88.82% of the isolates while ceftazidime inhibited (24)15.8% of the isolates. While (82)54.0% of the isolates inhibited by cefuroxime had resistant colonies within their inhibition zones (Rc) and ofloxacin inhibited (100)65.8% of the isolates without having resistant colonies within the inhibition zones, ceftazidime inhibited (7)4.6% of the isolates with resistant colonies within the inhibition zones. Subjecting the isolates to vancomycin showed that (27)17.8% were resistant to 2 µg/ml, (43)28.3% were resistant to 4 µg/ml and (27)17.8% of the isolates were simultaneously resistant to both concentrations of vancomycin. Although (100)65.8% of the isolates had MARindex ≥0.2, (52)34.2% of the isolates had MARindex ≤ 0.2 and (65)428% of the isolates were considered multidrug resistant strains. The isolation of multi-drug and vancomycin intermediate resistant strains of S. aureus in high percentage, in this study, presents a great threat to clinicians and general populace. The vancomycin intermediate resistant S. aureus (VISA) in asymptomatic individuals could be a critical concern to the therapeutic dilemma to be added to the presence of multi-drug resistance. A more sustainable therapy must be in place to prevent its dissemination or the outbreak of its infection.

Design and synthesis of novel desfluoroquinolone-aminopyrimidine hybrids as potent anti-MRSA agents with low hERG activity

Despite the fact that the introduction of a fluorine atom at the C-6 position has resulted in the evolution of fluoroquinolones, fluoroquinolone-induced cardiac toxicity has drawn considerable attention. In this context, desfluoroquinolone-based hybrids with involvement of C-7 aminopyrimidine functional group were designed and synthesized. The biological results showed majority of these hybrids still demonstrated potent anti-MRSA activity with MIC values between 0.38 and 1.5 μg/mL, despite the lack of the typical C-6 fluorine atom. Particularly, the most active B14 exhibited activities at submicromolar concentrations against a panel of MRSA strains including vancomycin-intermediate strains, levofloxacin-resistant isolates, and linezolid-resistant isolates, etc. As expected, it also displayed highly selective toxicity toward bacterial cells and low hERG inhibition. Further resistance development study indicated MRSA is unlikely to acquire resistance against B14. The docking study revealed that two hydrogen bonds were formed between the C-7 substituent and the surrounding DNA bases, which might contribute to overcome resistance by reducing the dependence on the magnesium-water bridge interactions with topoisomerase IV. These results indicate a promising strategy for developing new antibiotic quinolones to combat multidrug resistance and cardiotoxicity.

Delafloxacin activity against Staphylococcus aureus with reduced susceptibility or resistance to methicillin, vancomycin, daptomycin or linezolid.

Delafloxacin is a recently approved anionic fluoroquinolone antibiotic with broad-spectrum activity against Gram-positive and Gram-negative organisms. The drug has been approved for patients with acute bacterial skin and skin structure infections including those caused by MRSA. There are limited data available against MRSA blood isolates (MRSABIs), vancomycin-intermediate strains (VISA), vancomycin-resistant strains (VRSA), daptomycin-non-susceptible strains (DNSSA) and linezolid-resistant Staphylococcus aureus (LRSA). Antimicrobial activity of delafloxacin, levofloxacin, vancomycin, daptomycin and linezolid was determined against 110 MRSABIs, 15 VRSA, 35 VISA, 40 DNSSA and 6 LRSA. Microdilution testing using CAMHB was used to determine MIC according to CLSI guidelines. FDA breakpoints were used to determine delafloxacin susceptibility, and CLSI breakpoints were used for all other antibiotics. PCR testing for molecular markers was performed. Delafloxacin demonstrated activity against MRSABIs with an MIC90 of 1 mg/L and 68% susceptibility. Against the other groups the MIC90 and susceptibility were 1 mg/L and 40%, respectively, for VISA, 4 mg/L and 7% for VRSA and 1 mg/L and 38% for DNSSA. None of the LRSA isolates was susceptible to delafloxacin. Delafloxacin was active against 94% of MRSA blood isolates that were genotype SCC IVa. For MRSABIs with a levofloxacin MIC ≥8 mg/L (55/110), suggesting multiple mutations in the QRDR, delafloxacin MIC90 was 1 mg/L with a 36.4% susceptibility rate. Delafloxacin demonstrates superior activity to levofloxacin against recent MRSA blood isolates, VISA, VRSA and DNSSA, and demonstrates good activity against blood isolates most commonly found in the community.

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.

1588. Delafloxacin Activity Against Staphylococcus aureus with Reduced Susceptibility or Resistance to Methicillin, Vancomycin, Daptomycin, or Linezolid

BackgroundDelafloxacin is a recently approved anionic fluoroquinolone antibiotic with broad-spectrum activity against Gram-positive and Gram-negative organisms. The drug has been approved for patients with acute bacterial skin and skin structure infections including those caused by methicillin-resistant S. aureus. There is limited data available against methicillin-resistant S. aureus blood isolates (MRSABI), vancomycin intermediate strains (VISA), vancomycin-resistant strains (VRSA), daptomycin non-susceptible strains (DNSSA) and linezolid-resistant S. aureus (LRSA).MethodsAntimicrobial activity of delafloxacin, levofloxacin, vancomycin, daptomycin, ceftaroline, and linezolid was determined against recent (2016–2018) MRSABI (110), VRSA (15), VISA (35), DNSSA (40), and LRSA (6). Broth microdilution testing using Mueller–Hinton broth was used to determine minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) according to CLSI guidelines. FDA breakpoints were used to determine delafloxacin susceptibility, and CLSI breakpoints were used for all other antibiotics.ResultsAntimicrobial MIC90 expressed in mg/L and (% susceptible) MRSABI VISA VRSA DNSSA Delafloxacin1 (68)1 (40)4 (7)1 (38)Levofloxacin>16 (38)>16 (9)> 16 (0)>16 (15)Vancomycin1 (99)8 (0)>64 (0)8 (35)Daptomycin1 (96)4 (26)1 (100)4 (0)Ceftaroline1 (99)1 (100)1 (100)1 (100)Linezolid2 (100)2 (100)2 (100)2 (100)None of the LRSA were susceptible to delafloxacin or levofloxacin. All strains that were susceptible to the antimicrobial agents above had an MBC that was the same as the MIC or one dilution greater except for linezolid which demonstrated an MBC that was more than eight-fold greater than the MIC. For MRSABI isolates with a levofloxacin MIC ≥ 8 mg/L (55/110) suggesting multiple mutations in the quinolone-resistant determining region, the delafloxacin MIC90 was 1 mg/L with a 36.4% susceptibility rate.ConclusionDelafloxacin demonstrates superior activity to levofloxacin against recent MRSA blood isolates, VISA, VRSA, and DNSSA.Disclosures All authors: No reported disclosures.

Evaluation of apramycin activity against methicillin-resistant, methicillin-sensitive, and vancomycin-intermediate Staphylococcus aureus clinical isolates

We evaluated the in vitro activity of apramycin against clinical strains of vancomycin-intermediate and methicillin-resistant and -susceptible Staphylococcus aureus. Apramycin demonstrated an MIC50/MIC90 of 8/16 μg/mL. No strains had an MIC above the epidemiological cutoff value of 32 μg/mL, suggesting apramycin resistance mechanisms are rare in this strain population. The mounting evidence for broad-spectrum in vitro activity of apramycin against S. aureus and other bacterial species suggests that further exploration of apramycin or derivatives as repurposed human therapeutics is warranted.

Cymantrenyl-Nucleobases: Synthesis, Anticancer, Antitrypanosomal and Antimicrobial Activity Studies.

The synthesis of four cymantrene-5-fluorouracil derivatives (1–4) and two cymantrene-adenine derivatives (5 and 6) is reported. All of the compounds were characterized by spectroscopic methods and the crystal structure of two derivatives (1 and 6), together with the previously described cymantrene-adenine compound C was determined by X-ray crystallography. While the compounds 1 and 6 crystallized in the triclinic P-1 space group, compound C crystallized in the monoclinic P21/m space group. The newly synthesized compounds 1–6 were tested together with the two previously described cymantrene derivatives B and C for their in vitro antiproliferative activity against seven cancer cell lines (MCF-7, MCF-7/DX, MDA-MB-231, SKOV-3, A549, HepG2m and U-87-MG), five bacterial strains Staphylococcus aureus (methicillin-sensitive, methicillin-resistant and vancomycin-intermediate strains), Staphylococcus epidermidis, and Escherichia coli, including clinical isolates of S. aureus and S. epidermidis, as well as against the protozoan parasite Trypanosoma brucei. The most cytotoxic compounds were derivatives 2 and C for A549 and SKOV-3 cancer cell lines, respectively, with 50% growth inhibition (IC50) values of about 7 µM. The anticancer activity of the cymantrene compounds was determined to be due to their ability to induce oxidative stress and to trigger apoptosis and autophagy in cancer cells. Three derivatives (1, 4 and 5) displayed promising antitrypanosomal activity, with GI50 values in the low micromolar range (3–4 µM). The introduction of the 5-fluorouracil moiety in 1 enhanced the trypanocidal activity when compared to the activity previously reported for the corresponding uracil derivative. The antibacterial activity of cymantrene compounds 1 and C was within the range of 8–64 µg/mL and seemed to be the result of induced cell shrinking.

Safety assessment of Staphylococcus phages of the family Myoviridae based on complete genome sequences

Staphylococcus phages of the Myoviridae family have a wide host range and potential applications in phage therapy. In this report, safety assessments of these phages were conducted based on their complete genome sequences. The complete genomes of Staphylococcus phages of the Myoviridae family were analyzed, and the Open Reading Frame (ORFs) were compared with a pool of virulence and antibiotic resistance genes using the BLAST algorithm. In addition, the lifestyle of the phages (virulent or temperate) was also confirmed using PHACTS. The results showed that all phages were lytic and did not contain resistance or virulence genes based on bioinformatic analyses, excluding the possibility that they could be vectors for the dissemination of these undesirable genes. These findings suggest that the phages are safe at the genome level. The SceD-like transglycosylase, which is a biomarker for vancomycin-intermediate strains, was widely distributed in the phage genomes. Approximately 70% of the ORFs encoded in the phage genomes have unknown functions; therefore, their roles in the antibiotic resistance and virulence of Staphylococcus aureus are still unknown and require consideration before use in phage therapy.

Nationwide surveillance of resistance rates of Staphylococcus aureus clinical isolates from Greek hospitals, 2012–2013

Purpose To evaluate the in vitro efficacy of several anti-staphylococcal agents against a nationwide collection of contemporary Staphylococcus aureus clinical isolates from several healthcare centres in Greece. Methods Thirty hospitals throughout Greece (18 in Attica) provided all clinical isolates of S.aureus from April 2012 to May 2013 to a central lab to be re-submitted to susceptibility testing. The MICs were evaluated by Vitek® 2 with the exception of ceftaroline (OXOID M.I.C. Evaluator™). Vancomycin and daptomycin MICs were also evaluated by Etest®. Heterogeneously vancomycin-intermediate strains (hVISA) were detected by the Etest® GRD. VISA phenotype was confirmed by PAP-AUC. Results A total of 1005 isolates (39% MRSA) were studied. Susceptibility rates were: erythromycin 66.5%, clindamycin 79.2%, SXT 98.9%, rifampicin 97.3%, fusidic acid 67%, moxifloxacin 78.8%, vancomycin 99.9%, ceftaroline 92.9% and linezolid, tigecycline and daptomycin 100%. For mupirocin, high level resistance could be excluded for 98.9% of isolates. Vancomycin Etest® MIC50/90 were 1.5/1.5 mg/L, 58.5% of isolates exhibited a MIC > 1 and 8.7% a MIC of 2 mg/L, while Vitek® MIC50/90 were 1/1 and 3.1% showed MIC > 1 mg/L. One VISA strain was detected. Among the selected 175 isolates that were screened for hVISA phenotype, six (3.4%) were positive. In 315 bloodstream isolates, 64.1% had a vancomycin Etest® MIC > 1 mg/L. Conclusions This multi-centre surveillance study revealed that a significant percentage of contemporary S.aureus isolates from Greek patients have a vancomycin MIC (> 1 mg/L) that may compromise the clinical efficacy of the drug for the treatment of serious infections. The in vitro activity of SXT, rifampicin, mupirocin, linezolid, tigecycline, daptomycin and ceftaroline remains excellent.

Vancomycin susceptibility trends of methicillin-resistant Staphylococcus aureus isolated from burn wounds: a time for action.

Methicillin-resistant Staphylococcus aureus (MRSA) with reduced susceptibility to vancomycin poses a threat for patients in burn units throughout the world. This study aimed to investigate the reduced susceptibility to vancomycin of MRSA isolated from wounds of patients admitted to the Burns and Plastic Surgery Centre in Tripoli, Libya. All isolates were initially identified by chromagen medium then confirmed by PCR. The minimum inhibition concentration (MIC) was determined by E-test glycopeptide resistance detection (GRD). During the study, 210 isolates were obtained from 560 patients representing 132 (62.9%) and 78 (37.1%) of total samples received during years 2009 and 2010, respectively. MIC levels for vancomycin ranged from 0.5 to 2 µg/ml during the study, 13% of isolates displayed MIC of 1.5 µg/ml and 9% of the isolates displayed 2 µg/ml. Although MRSA isolates decreased dramatically during 2010 (37.1%) compared to 2009 (62.9%), overall, there was a significant increase in the proportion of MRSA isolates exhibiting higher vancomycin MICs during 2010 compared to 2009 (P = 0.0155). There was a significant increase of MICs at 1 µg/ml during 2010 compared with 2009 (P = 0.36). No vancomycin intermediate or resistant strains were found. There was a significant increase in the proportion of MRSA isolates exhibiting higher vancomycin MICs. We recommend that MRSA isolates should be monitored. Furthermore, implementation of infection control measures is urgently needed to prevent the spread of MRSA.

Impact of Glycopeptide Resistance in Staphylococcus aureus on the Dalbavancin In Vivo Pharmacodynamic Target.

Dalbavancin is a novel lipoglycopeptide with activity against Staphylococcus aureus, including glycopeptide-resistant isolates. The in vivo investigation reported here tested the effects of this antibiotic against seven S. aureus isolates with higher MICs, including several vancomycin-intermediate strains. Results of 1-log kill and 2-log kill were achieved against seven and six of the isolates, respectively. The mean free-drug area under the concentration-time curve (fAUC)/MIC values for net stasis, 1-log kill, and 2-log kill were 27.1, 53.3, and 111.1, respectively.

In-vitro activity of polyhexanide alone and in combination with antibiotics against Staphylococcus aureus

The resistance of Staphylococcus aureus is increasing, not only to antibiotics but also to antiseptics. To investigate the activity of the antiseptic polyhexanide and several antibiotics against clinical isolates of meticillin-susceptible and meticillin-resistant Staphylococcus aureus (MSSA and MRSA, respectively). Polyhexanide was tested alone and in combination with oxacillin, penicillin G, ampicillin, cefazolin, cefuroxime, imipenem, gentamicin, erythromycin, doxycycline, levoflocaxin, linezolid and vancomycin. Fifty MSSA and 50 MRSA strains, including one vancomycin-intermediate (VISA) strain, were tested. All strains were typed by pulsed-field gel electrophoresis (PFGE) to exclude testing of clonal isolates. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined using the serial broth microdilution technique according to DIN 58940. Combinations of polyhexanide and different antibiotics were investigated using the checkerboard technique. Polyhexanide MICs and MBCs in the range of 0.5-2mg/L were found for both MSSA and MRSA, and the VISA strain had MIC and MBC values of 2mg/L. All isolates were regarded as susceptible to polyhexanide, and no antagonism was observed between polyhexanide and the tested antibiotics. Synergism between polyhexanide and some bacteriostatic antibiotics (erythromycin, doxycycline and linezolid) was found for some strains. Polyhexanide appears to be suitable for the topical treatment of S.aureus alone and in combination with antibiotics.

Analysis of the Small RNA Transcriptional Response in Multidrug-Resistant Staphylococcus aureus after Antimicrobial Exposure

The critical role of noncoding small RNAs (sRNAs) in the bacterial response to changing conditions is increasingly recognized. However, a specific role for sRNAs during antibiotic exposure has not been investigated in Staphylococcus aureus. Here, we used Illumina RNA-Seq to examine the sRNA response of multiresistant sequence type 239 (ST239) S. aureus after exposure to four antibiotics (vancomycin, linezolid, ceftobiprole, and tigecycline) representing the major classes of antimicrobials used to treat methicillin-resistant S. aureus (MRSA) infections. We identified 409 potential sRNAs and then compared global sRNA and mRNA expression profiles at 2 and 6 h, without antibiotic exposure and after exposure to each antibiotic, for a vancomycin-susceptible strain (JKD6009) and a vancomycin-intermediate strain (JKD6008). Exploration of this data set by multivariate analysis using a novel implementation of nonnegative matrix factorization (NMF) revealed very different responses for mRNA and sRNA. Where mRNA responses clustered with strain or growth phase conditions, the sRNA responses were predominantly linked to antibiotic exposure, including sRNA responses that were specific for particular antibiotics. A remarkable feature of the antimicrobial response was the prominence of antisense sRNAs to genes encoding proteins involved in protein synthesis and ribosomal function. This study has defined a large sRNA repertoire in epidemic ST239 MRSA and shown for the first time that a subset of sRNAs are part of a coordinated transcriptional response to specific antimicrobial exposures in S. aureus. These data provide a framework for interrogating the role of staphylococcal sRNAs in antimicrobial resistance and exploring new avenues for sRNA-based antimicrobial therapies.

Surveillance of infection status of drug resistant Staphylococcus aureus in an Indian teaching hospital

ObjectiveTo access nosocomial and community accounts of multidrug resistant strains of Staphylococcus aureus (S. aureus) isolated by surveillance in a teaching hospital, over a period of 30 months. MethodsClinical samples from nosocomial sources, i.e., wards and cabins, intensive care unit (ICU) and neonatal intensive care unit (NICU) sources, as well as community or outpatient department (OPD) sources of a hospital were used for isolating strains of S. aureus resistant to methicillin/oxacillin and vancomycin, over a period, November 2009-April 2012. ResultsOf a total of 1 507 S. aureus isolates, 485 strains from community and 1 022 isolates were from nosocomial sources; Out of 485 (100%) OPD S. aureus isolates, 390 (80.41%) were MRSA strains. Similarly, from wards and cabins of 564 (100%) isolates, 461 (81.73%) strains were MRSA; whereas of 458 (100%) isolates obtained from ICU and NICU, 363 (79.25%) strains were MRSA. It was ascertained with χ2-tests of independence that MRSA strains were equally distributed in community or wards and cabins or ICU and NICU sources, alike rest other drug-resistant S. aureus strains. Antibiotic sensitivity patterns of isolated strains with 16 antibiotics were ascertained. Out of 390 (100%) MRSA strains isolated from OPD, 80 (20.51%) were vancomycin resistant (VRSA) and 173 (44.35%) strains were moderately sensitive to vancomycin or called, vancomycin intermediate strains (VISA). Similarly, from nosocomial sources, out of 461 (100%) MRSA isolates obtained from wards and cabins, 110 (23.86%) strains were VRSA and 208 (45.11%) were VISA strains, whereas out of 363 MRSA isolates obtained from ICU and NICU, 61 (16.8%) VRSA strains and 164 (45.17%) VISA strains were found. A progressive increase of percent values of drug resistance to 16 antibiotics used for antibiotic profiling revealed its subtle infection dynamics. ConclusionsThis study revealed the appalling state of occurrence of MRSA and VRSA in a resource-limited setting. A progressive increase of percent values of drug resistance to 16 antibiotics used revealed its subtle infection dynamics.

Promoter-Specific Transcription Inhibition in Staphylococcus aureus by a Phage Protein

Phage G1 gp67 is a 23 kDa protein that binds to the Staphylococcus aureus (Sau) RNA polymerase (RNAP) σ(A) subunit and blocks cell growth by inhibiting transcription. We show that gp67 has little to no effect on transcription from most promoters but is a potent inhibitor of ribosomal RNA transcription. A 2.0-Å-resolution crystal structure of the complex between gp67 and Sau σ(A) domain 4 (σ(A)(4)) explains how gp67 joins the RNAP promoter complex through σ(A)(4) without significantly affecting σ(A)(4) function. Our results indicate that gp67 forms a complex with RNAP at most, if not all, σ(A)-dependent promoters, but selectively inhibits promoters that depend on an interaction between upstream DNA and the RNAP α-subunit C-terminal domain (αCTD). Thus, we reveal a promoter-specific transcription inhibition mechanism by which gp67 interacts with the RNAP promoter complex through one subunit (σ(A)), and selectively affects the function of another subunit (αCTD) depending on promoter usage.

Current status of vancomycin susceptibility against methicillin resistant Staphylococcus aureus (MRSA) strains: A study at two tertiary care hospitals of Pakistan

Vancomycin has been considered mainstay treatment of infections caused by methicillin-resistant Staphylococcus aureus. The reports of the emergence of vancomycin intermediate and vancomycin resistant S. aureus from various parts of the world have been of great clinical concern. This study was performed to monitor the status of glycopeptide susceptibility against methicillin resistant S. aureus in our set up. All non-duplicate methicillin resistant Staphylococcus aureus (MRSA) isolates recovered during the period of study from various wards of Military Hospital Rawalpindi and PAEC General Hospital Islamabad, were subjected to the detection of minimum inhibitory concentrations of vancomycin using E-strips. Results were analyzed to evaluate the possible presence of vancomycin intermediate and resistant strains in the set up. A total of 276 methicillin-resistant S. aureus isolates were studied. The range of vancomycin minimum inhibitory concentrations (MIC) was 0.19 to 3 μg/mL. MIC 50 came out to be 0.75 μg/mL whereas the MIC 90 was 1.5 μg/ mL. 128 out of 276 (46%) isolates had vancomycin MIC equal to or greater than 1 μg/mL. Majority of the isolates (69%) were from pus samples. No vancomycin resistant or intermediate strain of MRSA was isolated during the study but there were a significant number of isolates having ≥ 1 µg/ml MIC of vancomycin. Key words: E- test, methicillin resistant Staphylococcus aureus, minimum inhibitory concentrations (MIC), susceptibility, vancomycin.

Autolytic activity and molecular characteristics of Staphylococcus haemolyticus strains with induced vancomycin resistance

The aim of this study was to investigate the molecular characteristics of induced vancomycin resistance in Staphylococcus haemolyticus. Autolytic properties and phenotypic characteristics of passage-selected vancomycin-resistant S. haemolyticus strains were examined. In addition, expression of autolysis-related genes (atl, lrgAB, sarA and lytS) was investigated using the RNase protection assay (RPA). The RPA results indicated that only the expression of the atl gene was significantly upregulated (2.5- to 6-fold increase) in vancomycin-intermediate and vancomycin-resistant strains. The vancomycin-resistant strains exhibited lower expression of murein hydrolase proteins and reduced autolytic activity compared with the parent strain. In addition, a reduced growth rate, cell wall thickening and higher survival rate in the presence of lysostaphin were observed in vancomycin-intermediate and vancomycin-resistant induced strains compared with the parent strain. In conclusion, altered autolytic properties, in particular upregulation of the atl gene, may contribute to vancomycin resistance in S. haemolyticus.

Vancomycin intermediate and high level vancomycin resistant Staphylococcus aureus clinical isolates in Osogbo, Nigeria

<p>The decreased vancomycin susceptibility and subsequent emergence of vancomycin resistant <em>Staphylococcus aureus </em>(VRSA) strains already multi-resistant to antibiotics is a major public health problem. In 2009, the Clinical and Laboratory Standards Institute (CLSI) altered its guidelines for vancomycin susceptibility testing in <em>S. aureus</em> and recent data suggests the possibility that VRSA may emerge more frequently than previously expected. Against this background, we conducted a study to ascertain the susceptibility status of clinical <em>S. aureus</em> isolates to vancomycin in our environment using vancomycin agar screen, disk diffusion and broth dilution methods. Of the total 49 <em>S. aureus </em>invasive strains isolated, 25 (51.0%) had vancomycin MIC of ≤2µg/ml by the CLSI standard broth dilution method and are classed as vancomycin susceptible; 18 (36.7%) had MIC of 4-8µg/ml (vancomycin intermediate resistant) and 6 (12.2%) had MIC of >256µg/ml (high level vancomycin resistant). Vancomycin agar screen with Mueller-Hinton agar containing 3µg/ml vancomycin (MHA-V3) correctly identified 20 of 25 (80%) vancomycin susceptible isolates; detected all 6 vancomycin resistant isolates and 16 of 18 (88.9%) vancomycin intermediate strains. Similarly, Mueller-Hinton agar containing 6µg/ml vancomycin (MHA-V6) correctly identified 23 of 25 (92%) vancomycin susceptible isolates and all 6 vancomycin resistant isolates but detected 14 (77.8%) of 18 vancomycin intermediate strains. Vancomycin disk diffusion test correctly identified all the 25 vancomycin susceptible <em>S. aureus</em> isolates giving 100% specificity but detected only 1 of 18 (5.6%) vancomycin intermediate and none (0%) of vancomycin resistant isolates. This result shows the occurrence of VISA and high level VRSA isolates in our environment, which contrary to current belief, may indicate widespread dissemination of VRSA. MHA-V3 agar is a useful alternative screening medium for vancomycin non-susceptibility detection in clinical <em>S. aureus</em> isolates but vancomycin disk diffusion is not useful in this regard.</p>

The role of non-β-lactam antimicrobials and screening for vancomycin resistance in methicillin resistant Staphylococcus aureus

The study was carried out to determine the prevalence of MRSA, VRSA and their current antimicrobial susceptibility pattern to various non-β-lactam antimicrobial agents to record the current status of MRSA response to commonly used antistaphylococcal antibiotics in Aligarh, India for a period of two years. A total of 430 Staphylococcus aureus strains were isolated from various clinical samples. Two hundred ninety (67.44%) of S. aureus were isolated from pus and most of these were from orthopaedics 124 (28.85%) and surgery wards 99 (23.02%). One hundred thirty eight (32.09%) strains were confirmed to be methicillin resistant by both phenotypic and genotypic methods. More than 80% of MRSA strains were multidrug resistant. However, all were uniformly sensitive to vancomycin and linezolid. Levofloxacin was the drug found to be resistant in just 16.47% MRSA strains. Vancomycin is the drug of choice for MRSA treatment. However, regular screening should be done for vancomycin intermediate and vancomycin resistant strains of Staphylococcus aureus .We suggest the use of levofloxacin for MRSA treatment since overuse of vancomycin can lead to the development of vancomycin resistance and more importantly it is beyond the scope of poor patients in developing countries like India.