In vitro vancomycin susceptibility amongst methicillin resistant Staphylococcus aureus

Phenotypic and Molecular Detection of Biofilm Formation in Methicillin-Resistant Staphylococcus Aureus Isolated from Different Clinical Sources in Erbil City

Background

Staphylococcus aureus is an important causative pathogen. The production of biofilms is an important factor and makes these bacteria resistant to antimicrobial therapy.

Objectives

the current study aimed to assess the prevalence of resistance to antibacterial agents and to evaluate the phenotypic and genotypic characterization of biofilm formation among S. aureus strains.

Methods

This study included 50 isolates of Methicillin-resistant S. aureus (MRSA) and Methicillin-Susceptible S. aureus (MSSA). S. aureus was identified by molecular and conventional methods, and antimicrobial resistance was tested with a disc diffusion method. The biofilm formation was performed through the Microtiter plate method. Strains were subjected to PCR to determine the presence of nuc, mecA, icaA, icaB, icaC, and icaD genes.

Results

Of the 50 S. aureus isolates, 32(64%) and 18(36%) were MRSA and MSSA, respectively. A large number of MRSA and MSSA isolates showed resistance to Penicillin and Azithromycin, and a lower number of MRSA and MSSA isolates showed resistance to Amikacin Gentamicin. None of the isolates was resistant to Vancomycin. The MRSA strains had significantly higher resistance against antibiotics than MSSA strains (P = 0.0154). All isolates (MRSA and MSSA) were able to produce biofilm with levels ranging from strong (31.25 %), (16.6%) to moderate (53.12%), (50%) to weak (15.6%), (33.3%) respectively. The MRSA strains had a significantly higher biofilm formation ability than the MSSA strains (P = 0.0079). The biofilm-encoding genes were detected among isolates with different frequencies. The majority of S. aureus isolates, 42 (84%), were positive for the icaA. The prevalence rates of the icaB, icaC and icaD genes were found to be 37 (74%), 40 (80%) and 41 (82%), respectively.

Conclusions

The prevalence of biofilm encoding genes associated with multidrug resistance in S. aureus strains is high. Therefore, identifying epidemiology, molecular characteristics, and biofilm management of S. aureus infection would be helpful.

Association between high vancomycin minimum inhibitory concentration and clinical outcomes in patients with methicillin-resistant Staphylococcus aureus bacteraemia - A retrospective cohort study

The purpose of this study is to determine the role of high (≥ 1.5 mg/L) vancomycin minimum inhibitory concentration (VMIC) in predicting clinical outcomes in patients with methicillin-resistant Staphylococcus aureus bacteraemia (MRSAB). A retrospective study was conducted at Mayo Clinic, Minnesota. Patients ≥ 18 years with a 3-month follow-up were included. Outcomes were defined as 30-day all-cause in-hospital mortality, median duration of bacteraemia, metastatic infectious complications, and relapse of MRSAB. A total of 475 patients with MRSAB were identified, and 93 (19.6%) of them had high VMIC isolates. Sixty-four percent of patients were male with a mean age of 69.0 years. Active solid organ malignancy and skin and soft tissue infection as source of MRSAB were associated with high VMIC, while septic arthritis as a complication was significantly associated with low VMIC on multivariate analysis. Eighty-one (17.1%) patients died within 30 days of hospitalization, with no significant difference in mortality rates between the two groups. In-hospital mortality, median duration of bacteraemia, and metastatic infectious complications were not significantly associated with high VMIC MRSAB.

Characterization of methicillin-resistant Staphylococcus aureus through genomics approach

In the present study, a total of 35 S. aureus isolates collected from two different geographical locations viz., Germany and Hungary were tested for their methicillin-resistant phenotype which revealed a high incidence of methicillin-resistant S. aureus. The quantitative test for biofilm production revealed that 73.3% of isolates were biofilm producers. The isolates were further characterized using a set of biochemical and genotypic methods such as amplification and analysis of S. aureus species-specific sequence and mecA gene. The 33 mecA positive isolates were then characterized by the amplification of SCCmec and pvl toxin genes. Further, based on the biofilm-forming phenotype, 15 isolates were selected and characterized through PCR–RFLP of coa gene, polymorphism of spa gene and amplification of biofilm-associated genes. The dendrogram prepared from the results of both biochemical and genotypic analyses of the 15 isolates showed that except for the isolates SA G5 and SA H29, the rest of the isolates grouped themselves according to their locations. Thus, the two isolates were selected for further characterization through whole-genome sequencing. Comparative genome analysis revealed that SA G5 and SA H29 have 97.20% ANI values with 2344 gene clusters (core-genome) of which 16 genes were related to antibiotic resistance genes and 57 genes encode virulence factors. The highest numbers of singleton genes were found in SA H29 that encodes proteins for virulence, resistance, mobile elements, and lanthionine biosynthesis. The high-resolution phylogenetic trees generated based on shared proteins and SNPs revealed a clear difference between the two strains and can be useful in distinguishing closely related genomes. The present study demonstrated that the whole-genome sequence analysis technique is required to get a better insight into the MRSA strains which would be helpful in improving diagnostic investigations in real-time to improve patient care.

Isolation and Characterization of a New Endophytic Actinobacterium Streptomyces californicus Strain ADR1 as a Promising Source of Anti-Bacterial, Anti-Biofilm and Antioxidant Metabolites

In view of the fast depleting armamentarium of drugs against significant pathogens, like methicillin-resistant Staphylococcus aureus (MRSA) and others due to rapidly emerging drug-resistance, the discovery and development of new drugs need urgent action. In this endeavor, a new strain of endophytic actinobacterium was isolated from the plant Datura metel, which produced secondary metabolites with potent anti-infective activities. The isolate was identified as Streptomyces californicus strain ADR1 based on 16S rRNA gene sequence analysis. Metabolites produced by the isolate had been investigated for their antibacterial attributes against important pathogens: S. aureus, MRSA, S. epidermis, Enterococcus faecium and E. faecalis. Minimum inhibitory concentration (MIC₉₀) values against these pathogens varied from 0.23 ± 0.01 to 5.68 ± 0.20 μg/mL. The metabolites inhibited biofilm formation by the strains of S. aureus and MRSA (Biofilm inhibitory concentration [BIC₉₀] values: 0.74 ± 0.08–4.92 ± 0.49 μg/mL). The BIC₉₀ values increased in the case of pre-formed biofilms. Additionally, the metabolites possessed good antioxidant properties, with an inhibitory concentration (IC₉₀) value of 217.24 ± 6.77 µg/mL for 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging. An insight into different classes of compounds produced by the strain ADR1 was obtained by chemical profiling and GC-MS analysis, wherein several therapeutic classes, for example, alkaloids, phenolics, terpenes, terpenoids and glycosides, were discovered.

Fabrication of an Original Transparent PVA/Gelatin Hydrogel: In Vitro Antimicrobial Activity against Skin Pathogens

The design of actively efficient and low-toxicity formulations against virulent bacterial strains causing skin infections remains a challenging task. The aim of the present study was to develop and evaluate in vitro a hydrogel impregnated with a known plant extract for topical applications against major skin bacteria. A poly(vinyl alcohol) (PVA)/gelatin hydrogel, namely HG, was prepared by esterification following the solution casting method. The gelling process was realized by cross-linking the synthetic polymer PVA and the biopolymer gelatin in the presence of hydrochloric acid (HCl). A crude extract of Nigella sativa seeds was then encapsulated in HG, and the resulting HGE was characterized morphologically (by Scanning Electron Microscopy (SEM)), structurally (by X-ray powder diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy), behaviorally (by swelling behavior), and biologically (by the agar well diffusion method). The results of HGE were compared to HG and HG impregnated with 10% acetic acid (HGAA). SEM sections of HGE revealed a dense and porous surface, suggesting a good hydrophilicity. X-ray diffractograms indicated that HGE and HG had a similar degree of crystallinity. FTIR spectra confirmed that esterification occurred between PVA and gelatin suggesting that the amine group is involved in the intercalation of the plant extract components in HG. Further, HGE was found to be as wettable and swellable as HG, suggesting a good biocompatibility. Eventually, HGE exerted a pronounced inhibitory effect against two major skin pathogens, the Gram-negative Pseudomonas aeruginosa and the Gram-positive Staphylococcus aureus, suggesting a good extract release. Taken together, the experimental data indicated that HGE might be a promising wound dressing.

Different formulations of vancomycin: In vitro antimicrobial activity against clinical isolates of methicillin-resistant Staphylococcus aureus

We compared in vitro antimicrobial activity of four vancomycin formulations used clinically against clinical isolates of Staphylococcus aureus, including methicillin-resistant and -susceptible (MRSA and MSSA, respectively), using different susceptibility assays. The minimal inhibitory concentrations (MICs) against MRSA clinical isolates were significantly different for some vancomycin formulations by the broth microdilution and agar dilution methods. However, these variations would not compromise their clinical use, since the MICs were within the range recommended by the Clinical and Laboratory Standards Institute. Furthermore, 26.9% of MRSA clinical isolates showed a vancomycin MIC ≥1.5 μg/mL according to the Etest® method but none by broth microdilution. Regarding quality, all formulations were in accordance with United States Pharmacopeia criteria. Our results showed that all vancomycin formulations tested showed similar in vitro antimicrobial activity, making them suitable for clinical use, and that the evaluation method chosen to determine sensitivity to this antimicrobial should be carefully performed, particularly for MRSA.

Heterogeneous vancomycin-intermediate among methicillin resistant Staphylococcus aureus

BACKGROUND

Hetero-resistance vancomycin intermediate Staphylococcus aureus (hVISA) is phenotype, which on in-vitro susceptibility test is vancomycin susceptible (VSSA) but has a minority population of vancomycin intermediate (VISA). hVISA is responsible for vancomycin treatment failure. Population Analysis Profile- Area under Curve (PAP-AUC) is a test for detection of hVISA; however, this test is unsuitable for clinical microbiology laboratory. Tests, such as Brain Heart Infusion Agar with 6 μg/ml vancomycin (BHIA6V), E test and Macromethod E Test (MET) are available; however reported to have variable results.

METHODS

58 clinical isolates of Methicillin resistant S aureus (MRSA) having MIC of vancomycin more than 1 μg/ml by E test and agar dilution were analyzed by PAP-AUC, BHIA6V and MET.

RESULT

The prevalence of hVISA was 6.9%. hVISA isolates were having vancomycin E test MIC >2 μg/ml. Sensitivity of BHIA6V, MET and E test with MIC >2 μg/ml were 0.75, 0.67 and 1.0 respectively; however, positive predictive values (PPV) were 0.43, 0.4 and 0.27 respectively with PAP-AUC. PAP-AUC ratio correlated with MIC by E test and MET.

CONCLUSIONS

There is need for screening MRSA isolates showing in-vitro vancomycin susceptibility ≤2 μg/ml by agar dilution method for detection of hVISA. PAP-AUC test is unsuitable for routine laboratory testing. BHIA6V, MET and E test can be used for screening, however have low PPV.