Bactericidal Activity Of Vancomycin Research Articles

Antibacterial and Antibiofilm Potential of Bacterial Cellulose Hydrogel Containing Vancomycin against Multidrug-Resistant Staphylococcus aureus and Staphylococcus epidermidis.

The present study aimed to evaluate the in vitro antibacterial and antibiofilm activity of bacterial cellulose hydrogel produced by Zoogloea sp. (HYDROGEL) containing vancomycin (VAN) against bacterial strains that cause wound infections, such as multidrug-resistant (MDR) Staphylococcus aureus and Staphylococcus epidermidis. Initially, HYDROGEL was obtained from sugar cane molasses, and scanning electron microscopy (SEM) was performed to determine morphological characteristics. Then, VAN was incorporated into HYDROGEL (VAN-HYDROGEL). The antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was assessed using the broth microdilution method to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) against methicillin-sensitive S. aureus (MSSA) ATCC 25923, methicillin-resistant S. aureus (MRSA) ATCC 33591, S. epidermidis INCQS 00016 (ATCC 12228), five clinical isolates of MRSA, and nine clinical isolates of methicillin-resistant S. epidermidis, following the Clinical and Laboratory Standards Institute (CLSI) guidelines. Additionally, the antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was studied using the time-kill assay. Subsequently, the antibiofilm activity of VAN, HYDROGEL, and VAN-HYDROGEL was evaluated using crystal violet and Congo red methods, as well as SEM analysis. VAN and VAN-HYDROGEL showed bacteriostatic and bactericidal activity against MRSA and methicillin-resistant S. epidermidis strains. HYDROGEL did not show any antibacterial activity. Analysis of the time-kill assay indicated that HYDROGEL maintained the antibacterial efficacy of VAN, highlighting its efficiency as a promising carrier. Regarding antibiofilm activity, VAN and HYDROGEL inhibited biofilm formation but did not demonstrate biofilm eradication activity against methicillin-resistant S. aureus and S. epidermidis strains. However, it was observed that the biofilm eradication potential of VAN was enhanced after incorporation into HYDROGEL, a result also proven through images obtained by SEM. From the methods carried out in this study, it was possible to observe that HYDROGEL preserved the antibacterial activity of vancomycin, aside from exhibiting antibiofilm activity and enhancing the antibiofilm effect of VAN. In conclusion, this study demonstrated the potential of HYDROGEL as a candidate and/or vehicle for antibiotics against MDR bacteria that cause wound infections.

Estimation of the In-Vitro Synergistic Effect of Vancomycin with Bacteriophage and its Endolysin on Iraqi Local Isolates of Enterococcus faecalis

Enterococcus faecalis is known to cause many serious infections with an upsurge in the development of antibiotic resistant strains, especially vancomycin. Lytic bacteriophage and its endolysin have the potential to affect and lyse specific bacterial cells making them a possible alternative therapy to antibiotic resistant strains. The study aimed to investigate the synergistic effect of phage/ phage cocktail/ endolysin with vancomycin on E. faecalis isolated from urine samples. The antibioresistant profile 17 E. faecalis was done with an emphasis on the sensitivity to vancomycin. The lytic phages were isolated from the local environment. The infectivity and the coverage rate for the phage and phage cocktail were calculated. The enzyme of the lytic phage was isolated by chromatography. The synergistic effect was tested by turbidity reduction assay to evaluate the growth reduction level. It had been found that 6/17 E. faecalis isolates were resistant to vancomycin, 7/17 isolates were intermediate, and 4/17 were susceptible. Three lytic phages were identified with an infectivity rate of 100%, 76.4%, and 88.2%. The phage cocktail yielded 100% rate of infectivity and 91.6 % coverage rate. The reduction in the growth levels of the 17 E.faecalis after treatment with phage / phage cocktail/ vancomycin/ mixture of vancomycin and phage cocktail was effective. The synergistic effect of vancomcyin together with the phage cocktail significantly reduced the growth of 70.6% of the isolates. The antibacterial activity of vancomycin plus endolysin treatment was revealed in a time dependent manner. Thus, the synergistic effect of vancomycin with phage/ endoloysin illustrated an effective method to treat the antibiotic-resistant strains of E. faecalis to overcome this emerging clinical problem.

Antibiotic sensitivity analysis of clinical coagulase-negative staphylococci

Background. The increasing role of coagulase-negative staphylococci in the occurrence of staphylococcal infections leads to the need for close attention to them. Special control is required over the sensitivity of bacteria to antibiotics and the spread of methicillin resistance, as a sign of multiple resistance to antibacterial drugs. It is also important to identify the virulence factors of coagulase-negative staphylococci, which determine their behavior in the environment.The aim. To evaluate the sensitivity of strains of coagulase-negative staphylococci to clinically significant antibiotics daptomycin, vancomycin, linezolid and oxacillin and lantibiotic warnerin.Methods. Determination of the minimal inhibitory concentrations of antibacterial compounds for clinical coagulase-negative staphylococci by standard methods of serial dilutions and disc diffusion. Identification of the phenomenon of decreased susceptibility of bacteria to vancomycin by population analysis and concentration gradient. Lipid analysis by thin layer chromatography. Results. High antibacterial activity of vancomycin, daptomycin and linezolid against clinical strains of coagulase-negative staphylococci was shown. The upper limit of the minimum inhibitory concentrations of vancomycin within the sensitive phenotype and the expansion of the ranges of the minimum inhibitory concentrations of daptomycin and warnerin towards an increase in oxacillin-resistant isolates were revealed. The heterogeneous nature of sensitivity to vancomycin of the cultures of the studied strains and the possibility of their rapid enrichment with subpopulations with reduced sensitivity to this antibiotic have been established. The selection of resistance of coagulase-negative staphylococci to vancomycin was accompanied by an increase in the synthesis of lysylphosphatidylglycerol and a decrease in their sensitivity to cationic peptide compounds.Conclusion. The revealed prevalence of the methicillin-resistant phenotype of clinical strains of coagulase-negative staphylococci, along with the presence in the lipid spectrum of the universal factor of resistance to cationic antibacterial compounds, lysylphosphatidylglycerol, entails the need for new methodological solutions for diagnosing infections caused by coagulase-negative staphylococci.

Long-term antibacterial activity of vancomycin from calcium phosphate cement in vivo.

Periprosthetic joint infection is a major complication of total joint arthroplasty, with treatment requiring a two-stage exchange procedure and 6 weeks of systemic antibiotics. However, depending on the infection site, intravenous delivery of antibiotics like vancomycin (VCM) can have poor tissue transferability, thus reducing their therapeutic effect. This study demonstrates the 24-week invivo release profile and antibacterial activity of VCM from calcium phosphate cement impregnated with VCM (CPC/VCM) and compares them with those from polymethylmethacrylate impregnated with VCM (PMMA/VCM). Rats were implanted with the test specimens between the fascia and quadriceps. After implantation for 24 weeks, the test specimens were removed and residual VCM was extracted to calculate the concentration of VCM released into rat tissues. We also examined the antibacterial activity of releasable VCM from the removed test specimens by placing them directly onto the surface of agar. CPC/VCM released greater concentrations of VCM for a longer period of time within the 24 weeks than PMMA/VCM. Moreover, CPC/VCM released 1.4 to 26.1-fold more VCM than PMMA/VCM. Using Staphylococcus aureus, antibacterial activity was logarithmically correlated with VCM concentration across the entire concentration range tested (12.5-800μg/mL). While the area within which inhibition was observed-the inhibition zone-for both CPC/VCM and PMMA/VCM formed and gradually shrank with time after implantation, that for CPC/VCM was significantly larger than that for PMMA/VCM in each week after implantation. CPC/VCM releases greater amounts of VCM with antibacterial activity for longer periods of time than PMMA/VCM, suggesting that CPC is effective for facilitating the release of antibiotics for local action in patients with established postoperative infection.

Poly (ε-caprolactone)/Poly (lactic acid) fibers produced by rotary jet spinning for skin dressing with antimicrobial activity.

The rotary jet spinning technique permits the production of biomaterials that can be used as devices that come into contact with biological systems (including biological fluids) for diagnostic or surgical applications. These materials are composed of synthetic or natural compounds and allow the incorporation of drugs for therapeutic purposes. Two solutions containing 50% poly(lactic acid) (PLA) and 50% poly(ε-caprolactone) (PCL) diluted in three different solvents were prepared for rotary jet spinning (RJS) process. Vancomycin, an antibiotic indicated for the treatment of severe staphylococcal infections in patients with penicillin allergy, was added in the polymer solutions, to obtain drug-loaded fibrous mats. Morphological surface characterization by scanning electron microscopy revealed heterogeneous pores in the microfibers. Vancomycin loading interfered with the morphology of all samples in terms of fiber size, leading to smaller diameter fibers. Attenuated total reflectance/Fourier transform infrared spectroscopy was used for identification of the samples. The vibrational characteristics of PCL/PLA and vancomycin were consistent with expectations. Vero cell culture assays by the extract dilution and direct contact methods revealed the absence of cytotoxicity, except for the sample prepared with 50% of PCL and of a 9/2 (V/V) vancomycin content, with the growth of confluent and evenly spread cells on the fibrous mats surface. Microbiological analysis, performed on Staphylococcus aureus by the halo inhibition test and by the broth dilution method, showed that the antibacterial activity of vancomycin was maintained by the loading process in the polymer fibers. The results showed that rotary jet spinning produces satisfactory amounts of Vancomycin-loaded fibers, as potential web dressing for wound repair.

Supramolecular self-assembled drug delivery system (SADDs) of vancomycin and tocopherol succinate as an antibacterial agent: in vitro, in silico and in vivo evaluations

In this study self-assembled drug delivery system (SADDs) composed of a hydrophobic d-α-tocopherol succinate (TS) and a hydrophilic vancomycin (VCM) were formulated, and its potential for enhancing the antibacterial activity of VCM against Staphylococcus aureus (SA) and Methicillin-resistant Staphylococcus aureus (MRSA) were explored. The SADDs were synthesized via supramolecular complexation, then characterized for in silico, in vitro and in vivo studies. In silico studies confirmed the self-assembly of VCM/TS into NPs. The size, surface charge and drug loading of the SADDs was ˂100 nm, −27 mV and 68%, respectively. The SADDs were non-hemolytic and biosafe. A sustained release of VCM from SADDs was noted, with 52.2% release after 48 hr. The in vitro antibacterial test showed a twofold decrease in Minimum inhibitory concentration (MIC) against SA and MRSA, and a significantly higher reduction in MRSA biofilms compared to bare VCM. Further, in silico studies confirmed strong and stable binding of TS to MRSA efflux pumps. The in vivo study using mice skin infection models showed a 9.5-fold reduction in bacterial load after treatment with SADDs, in comparison with bare VCM. These findings affirmed that VCM/TS NPs as a promising novel nano-delivery for treating bacterial infections.

Constitutive expression of the cryptic vanGCd operon promotes vancomycin resistance in Clostridioides difficile clinical isolates.

To describe, for the first time (to the best of our knowledge), the genetic mechanisms of vancomycin resistance in clinical isolates of Clostridioides difficile ribotype 027. Clinical isolates and laboratory mutants were analysed: genomically to identify resistance mutations; by transcriptional analysis of vanGCd, the vancomycin resistance operon encoding lipid II d-alanine-d-serine that is less bound by vancomycin than native lipid II d-alanine-d-alanine; by imaging of vancomycin binding to cell walls; and for changes in vancomycin bactericidal activity and autolysis. Vancomycin-resistant laboratory mutants and clinical isolates acquired mutations to the vanSR two-component system that regulates vanGCd. The substitutions impaired VanSR's function, resulting in constitutive transcription of vanGCd. Resistance was reversed by silencing vanG, encoding d-alanine-d-serine ligase in the vanGCd operon. In resistant cells, vancomycin was less bound to the cell wall septum, the site where vancomycin interacts with lipid II. Vancomycin's bactericidal activity was reduced against clinical isolates and laboratory mutants (64 and ≥1024 mg/L, respectively) compared with WT strains (4 mg/L). Truncation of the potassium transporter TrkA occurred in laboratory mutants, which were refractory to autolysis, accounting for their survival in high drug concentrations. Ribotype 027 evolved first-step resistance to vancomycin by constitutively expressing vanGCd, which is otherwise silent. Experimental evolutions and bactericidal assays show that ribotype 027 can acquire mutations to drastically enhance its tolerance to vancomycin. Thus, further epidemiological studies are warranted to examine the extent to which vancomycin resistance impacts clinical outcomes and the potential for these strains to evolve higher-level resistance, which would be devastating.

AB2-type amphiphilic block copolymer containing a pH-cleavable hydrazone linkage for targeted antibiotic delivery.

A novel AB2-type amphiphilic block copolymer [OA-CN-NH-(PEG)2] with hydrazone linkage was synthesized and explored for pH-triggered antibiotic delivery. Vancomycin (VCM) loaded micelles of the polymer [OA-CN-NH-(PEG)2-VCM] were spherical in shape with size, polydispersity index, zeta potential and entrapment efficiency of 130.33±7.36nm, 0.163±0.009, -4.33±0.55mV and 39.61±4.01% respectively. The dilution stability study exhibited no significant change in the size distribution of OA-CN-NH-(PEG)2-VCM micelles up to 320-fold dilution. An in vitro drug release assay confirmed greater release of VCM from OA-CN-NH-(PEG)2-VCM at pH 6, compared to pH 7.4. An in vitro antibacterial activity evaluation of OA-CN-NH-(PEG)2-VCM showed 2-fold enhancement in antibacterial activity of VCM after 54h of incubation against Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA) at acidic pH compared to physiological pH. An in vivo antibacterial activity of OA-CN-NH-(PEG)2-VCM further proved the enhanced activity of OA-CN-NH-(PEG)2-VCM against MRSA. In conclusion, micelles from pH-responsive OA-CN-NH-(PEG)2 could be utilized for site-specific delivery of VCM at the infection site.

Synthesis of chitosan coated metal organic frameworks (MOFs) for increasing vancomycin bactericidal potentials against resistant S. aureus strain.

Multiple drug resistant (MDR) has become a major issue in developing countries. MDR bacterial infections lead to significant increase in morbidity, mortality and cost of prolonged treatments. Therefore, designing of strategies for improving the antimicrobial potential of the therapeutic agents are highly required. Metal organic frameworks (MOFs) are highly tunable hybrid material, consist of metal ions linked together by organic bridging ligands have been used as an efficient drug delivery carrier because of their biodegradability, low toxicity and structure integrity upon loading and functionalizing process. Current study was based on the synthesis of chitosan coated MOFs with enhanced contact with S. aureus cell surface. Chitosan is deacetylated derivative of chitin and capable for non-bonding interaction with negatively charged bacterial cell leading to enhanced contact of MOFs with S. aureus. Chitosan coated MOFs were characterized with various techniques such as atomic force microscopy, scanning electron microscopy, DLS, FT-IR, TGA, DSC and Powder X-ray diffraction. They were also studied for their efficacy on resistant S. aureus, results revealed that Vancomycin bactericidal activity significantly increased upon loading in chitosan coated MOFs and caused increased inhibition of resistant S. aureus. AFM analysis of S. aureus strains clearly revealed complete distortion of morphology by treating with chitosan modified drug loaded MOFs. Findings of the current study suggest the potential of chitosan coated MOFs for reversing bacterial resistance against Vancomycin and provide new perspectives for improved antibiotic therapy of infections associated with MDR.

Antibacterial effects of vancomycin in combination with methicillin against methicillin-resistant and methicillinsensitive Staphylococcus aureus

Background and aims: Staphylococcus aureus is considered as a frequent cause of infections. Therefore, antibacterial agents including β-lactam are normally used to treat these infections while the emergence of antibiotic resistance is one of the major clinical problems in this respect. Accordingly, combination antibacterial therapy is one way to alleviate this problem. As a result, the present study aimed to investigate the combined effects of vancomycin and methicillin on clinical isolates of methicillin-resistant S. aureus (MRSA) and methicillinsensitive S. aureus (MSSA). In addition, a series of follow-up studies were performed to evaluate the antibacterial activity. Methods: The current cross-sectional study was conducted on 40 hospitalized patients from various clinical samples such as pus/wound swabs, blood, urine and sputum during a 6-month period in 2017. To this end, the antibacterial activities of vancomycin and methicillin, alone and in combination were investigated against MRSA and MSSA. Eventually, the inhibitory effects of vancomycin and methicillin alone and in combination were studied on the growth profile of MRSA and MSSA, as well as the expression of mecA gene. Results: Based on the results, the significant synergistic and partial synergistic activity with fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) indexes ranged from 0.27-0.938 and 0.313-0.844, respectively, in the combination of vancomycin and methicillin in MRSA and MSSA isolates. Further, the obtained data indicated that the combination of vancomycin and methicillin had a synergistic effect against MRSA isolates (P<0.01). The expression levels of the mecA gene were down-regulated by 5.25- fold in the combination of vancomycin and methicillin in MRSA isolate (P<0.001). Conclusion: In general, these events may reflect the potential uses of vancomycin and methicillin combination against MRSA. However, a greater understanding of the underlying molecular mechanisms of vancomycin and methicillin in combination could contribute to the development of therapeutic strategies.

Time-kill determination of the bactericidal activity of telavancin and vancomycin against clinical methicillin-resistant Staphylococcus aureus isolates from cancer patients

The bactericidal activity of vancomycin and telavancin was compared against 4 clinical methicillin-resistant Staphylococcus aureus isolates recently recovered from cancer patients, using minimum bactericidal concentration (MBC):MIC ratios and time-kill studies. All 4 isolates were susceptible to both agents based on individual MIC values. The 2 methodologies for assessing bactericidal activity produced variable results. Telavancin appeared to have somewhat better bactericidal activity than vancomycin based on narrower MBC:MIC ratios. However, based on the results of the time-kill studies, neither agent demonstrated reliable bactericidal activity (defined as a ≥3 log10 reduction of the starting inoculum at the end of 24hours) against these organisms. These findings might be of some therapeutic importance in certain clinical settings and/or specific patient populations (such as febrile neutropenic patients) in whom potent bactericidal activity is either desired or preferred.

Ion pairing with linoleic acid simultaneously enhances encapsulation efficiency and antibacterial activity of vancomycin in solid lipid nanoparticles

Ion pairing of a fatty acid with an antibiotic may be an effective strategy for formulation optimization of a nanoantibiotic system. The aim of this study was therefore to explore the potential of linoleic acid (LA) as an ion pairing agent to simultaneously enhance encapsulation efficiency and antibacterial activity of triethylamine neutralized vancomycin (VCM) in solid lipid nanoparticles (SLNs). The prepared VCM-LA2 conjugate was characterized by Fourier transform-infrared (FT-IR) spectroscopy, logP and binding energy calculations. The shifts in the FT-IR frequencies of COOH, NH2 and CO functionalities, an increase in logP value (1.37) and a lower interaction energy between LA and VCM (−125.54kcal/mol) confirmed the formation of the conjugate. SLNs were prepared by a hot homogenization and ultrasonication method, and characterized for size, polydispersity index (PI), zeta potential (ZP), entrapment efficiency (%EE), surface morphology and physical stability. In vitro antibacterial activity studies against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) were conducted. Size, PI and ZP for VCM-LA2_SLNs were 102.7±1.01, 0.225±0.02 and −38.8±2.1 (mV) respectively. SLNs were also stable at 4°C for 3 months. %EE for VCM-HCl_SLNs and VCM-LA2_SLNs were 16.81±3.64 and 70.73±5.96 respectively, indicating a significant improvement in encapsulation of the drug through ion pairing with LA. Transmission electron microscopy images showed spherical nanoparticles with sizes in the range of 95–100nm. After 36h, VCM-HCl showed no activity against MRSA. However, the minimum inhibitory concentration for VCM-HCl_SLNs and VCM-LA2_SLNs were 250 and 31.25μg/ml respectively against S. aureus, while against MRSA it was 500 and 15.62μg/ml respectively. This confirms the enhanced antibacterial activity of VCM-LA2_SLNs over VCM-HCl_SLNs. These findings therefore suggest that VCM-LA2_SLNs is a promising nanoantibiotic system for effective treatment against both sensitive and resistant S. aureus infections.

In Vitro Efficacies and Resistance Profiles of Rifampin-Based Combination Regimens for Biofilm-Embedded Methicillin-Resistant Staphylococcus aureus

To compare the in vitro antibacterial efficacies and resistance profiles of rifampin-based combinations against methicillin-resistant Staphylococcus aureus (MRSA) in a biofilm model, the antibacterial activities of vancomycin, teicoplanin, daptomycin, minocycline, linezolid, fusidic acid, fosfomycin, and tigecycline alone or in combination with rifampin against biofilm-embedded MRSA were measured. The rifampin-resistant mutation frequencies were evaluated. Of the rifampin-based combinations, rifampin enhances the antibacterial activities of and even synergizes with fusidic acid, tigecycline, and, to a lesser extent, linezolid, fosfomycin, and minocycline against biofilm-embedded MRSA. Such combinations with weaker rifampin resistance induction activities may provide a therapeutic advantage in MRSA biofilm-related infections.

Vancomycin tolerance in Gram-positive cocci

Vancomycin, a glycopeptide antimicrobial agent, represents the last line of defence against a wide range of multi-resistant Gram-positive pathogens such as enterococci, staphylococci and streptococci. However, vancomycin-resistant enterococci and staphylococci, along with vancomycin-tolerant clinical isolates, are compromising the therapeutic efficacy of vancomycin. It is conceivable that tolerance may emerge during prolonged vancomycin use. It has not been until recently, however, that the molecular basis of this tolerance began to be understood. Superoxide anions might be involved in the bactericidal activity of vancomycin in enterococci, and recent evidence suggests that the stringent response is partly responsible for vancomycin tolerance in Enterococcus faecalis. The mechanism of vancomycin tolerance in Staphylococcus aureus and Streptococcus pneumoniae is sometimes associated with a reduction of autolysin activity. Vancomycin tolerance in S. aureus and S. pneumoniae also appears to be somehow related with the two-component regulatory systems linked to cell envelope stress, although the precise molecular regulatory pathways remain poorly defined.

Vancomycin Bactericidal Activity as a Predictor of 30-Day Mortality in Patients with Methicillin-Resistant Staphylococcus aureus Bacteremia

Vancomycin has been the drug of choice for the treatment of serious methicillin-resistant Staphylococcus aureus (MRSA) infections for over 5 decades. It demonstrates slower bactericidal activity in comparison to the results seen with antistaphylococcal beta-lactams against S. aureus (1). Moise et al. showed that 30-day mortality was related to the in vitro bactericidal activity of vancomycin (3). This study sought to determine whether the in vitro bactericidal activity of vancomycin, as well as other MRSA strain-specific characteristics, such as a polymorphism at accessory gene regulator (agr) locus (4, 5) and vancomycin MIC (2, 7), impacts the mortality associated with MRSA bacteremia. A total of 129 consecutive MRSA blood isolates recovered from patients with MRSA bacteremia admitted to the First Department of Internal Medicine (52 beds) and Emergency Medical Care Center (32 beds), Fukuoka University Hospital, from 1991 through 2004 were identified. This study focused on 66 isolates recovered from the 66 patients initially treated with glycopeptides (vancomycin [n = 42 patients] or teicoplanin [n = 24 patients]) after the onset of bacteremia. Bactericidal assays were performed over 72 h as reported by Sakoulas et al., using a concentration of 16 μg/ml against MRSA at an initial inoculum of approximately 108 CFU/ml (6). The clinical data were extracted from patients' medical records, and mortality that occurred within 30 days after the onset of bacteremia was examined. The in vitro bactericidal activity of vancomycin showed high heterogeneity among the isolates, with reduction in viable bacteria at 72 h ranging from 2.5 log10 to 7.2 log10 CFU/ml. The median (interquartile range) bactericidal activity was 4.4 (3.8 to 5.4) log10 CFU/ml. Overall, 26 (39.4%) of the 66 patients died during the first 30 days after the onset of MRSA bacteremia. There was no difference in the 30-day mortality between the patients treated with vancomycin and those treated with teicoplanin (42.9% versus 33.3%, P = 0.45). Univariate analysis indicated a statistically significant relationship between mortality and the in vitro bactericidal activity of vancomycin (P = 0.017), renal failure indicated by the necessity for dialysis (P = 0.025), the Acute Physiological and Chronic Health Evaluation II (APACHE II) score (P = 0.007), and the presence of shock (P = 0.005), while agr group (P = 0.36), agr function (P = 0.07), and vancomycin MIC (P = 0.13) were not significant. Multivariate logistic regression analysis with forward stepping on mortality using independent variables, with a P value of <0.2 in the univariate analysis, showed that decreased in vitro bactericidal activity of vancomycin (odds ratio [OR], 2.04; P = 0.021), APACHE II score (OR, 1.16; P = 0.018), and the presence of shock (OR, 6.56; P = 0.025) were predictors of mortality. In addition, a Hill-type mathematical model (Fig. ​(Fig.1)1) identified a very close relationship between vancomycin bactericidal activity and mortality in patients with MRSA bacteremia (R2 = 0.983), with a 3.8-log reduction in bacteria necessary to achieve a 50% probability of survival. FIG. 1. Vancomycin pharmacodynamics showing the relationship between the probability of survival and bactericidal activity, which was fit to a Hill-type mathematical model (R2 = 0.983). The probability of survival based on the 30-day mortality data for ... Although previous studies have examined the relationship of vancomycin killing activity and treatment failure (3, 6), this current study is the first to demonstrate a relationship with attenuated vancomycin bacterial killing and an increased probability of mortality in the multivariate analysis. In addition, the attenuated vancomycin bactericidal activity was more frequently observed in isolates from endovascular sources than in other sources (P = 0.043). This result demonstrates that reduced vancomycin killing in vitro could therefore be a surrogate marker of high-risk sources of bacteremia. Although performing vancomycin bactericidal assays over 72 h may be too labor-intensive to successfully implement in clinical microbiological analyses, this study highlights the potential problems associated with suboptimal vancomycin killing. These findings suggest that the evaluation of this characteristic may therefore be useful through other phenotypic markers of tolerance, such as those measured by minimal bactericidal concentration (MBC)/MIC and serum bactericidal assays, when considering antimicrobial therapies that can be used as alternatives to either vancomycin or teicoplanin for the treatment of MRSA bacteremia.

Impact of accessory gene regulator (agr) dysfunction on vancomycin pharmacodynamics among Canadian community and health-care associated methicillin-resistant Staphylococcus aureus

BackgroundThe accessory gene regulator (agr) is a quorum sensing cluster of genes which control colonization and virulence in Staphylococcus aureus. We evaluated agr function in community- (CA) and healthcare-associated (HA) MRSA, to compare the pharmacodynamics and bactericidal activity of vancomycin against agr functional and dysfunctional HA-MRSA and CA-MRSA.Methods40 clinical isolates of MRSA from the Canadian Nosocomial Infection Surveillance Program were evaluated for delta-haemolysin production, as a surrogate marker of agr function. Time kill experiments were performed for vancomycin at 0 to 64 times the MIC against an initial inoculum of 106 and 108 cfu/ml of agr functional and dysfunctional CA-MRSA and HA-MRSA and these data were fit to a hill-type pharmacodynamic model.Results15% isolates were agr dysfunctional, which was higher among HA-MRSA (26.3%) versus CA-MRSA (4.76%). Against a low initial inoculum of 106 cfu/ml of CA-MRSA, vancomycin pharmacodynamics were similar among agr functional and dysfunctional strains. However, against a high initial inoculum of 108 cfu/ml, killing activity was notably attenuated against agr dysfunctional CA-MRSA (USA400) and HA-MRSA (USA100). CA-MRSA displayed a 20.0 fold decrease in the maximal reduction in bacterial counts (Emax) which was 3.71 log10 CFU/ml for agr functional vs. 2.41 log10 CFU/ml for agr dysfunctional MRSA (p = 0.0007).ConclusionsDysfunction in agr was less common among CA-MRSA vs. HA-MRSA. agr dysfunction demonstrated an impact on vancomycin bactericidal activity and pharmacodynamics against a high initial inoculum of CA-MRSA and HA-MRSA, which may have implications for optimal antimicrobial therapy against persistent, difficult to treat MRSA infections.

In vitro comparison of elution characteristics of vancomycin from calcium phosphate cement and polymethylmethacrylate

BackgroundCalcium phosphate cement [CPC (Biopex®)] has been used as the drug delivery system of choice for treatment of infected joint replacement because of its good elution efficiency. The influence of CPC polymerization on the bactericidal activity of vancomycin (VCM) impregnated into CPC has not been investigated. We compared VCM concentration, bactericidal activity, and profile of eluates between CPC and polymethylmethacrylate (PMMA; Cemex RX®). MethodsTest specimens consisted of a powder composite of CPC or PMMA, VCM and solvent (10:0.25:3.3 g). Each test specimen was immersed in sterile phosphate-buffered saline. Eluates obtained on days 1, 3, 7, and 14 and weeks 4, 8, and 12 were evaluated by high performance liquid chromatography (HPLC) and by microbiological assay (MBA). ResultsThe elution level of VCM from CPC/VCM on day 1 was 8.1 fold greater than that from PMMA/VCM. The detection periods of VCM from CPC/VCM and PMMA/VCM were 8 weeks and 14 days, respectively. The values of eluates from CPC/VCM and PMMA/VCM obtained by HPLC were comparable to those obtained by MBA. HPLC chromatogram showed that the elution profiles of VCM from CPC/VCM and PMMA/VCM on day 1 were very close to those of standard solutions. ConclusionsCPC could release more VCM over a longer period than PMMA. The polymerization of CPC and PMMA did not alter the inhibitory activity of VCM and did not denature VCM.

Development of Reduced Vancomycin Susceptibility in Methicillin‐SusceptibleStaphylococcus aureus

Most cases of reduced vancomycin susceptibility in Staphylococcus aureus reported in the literature have been in methicillin-resistant strains. We report the development of reduced vancomycin susceptibility in a series of clonally related, methicillin-susceptible S. aureus (MSSA) clinical isolates. This isogenic series permitted us to determine whether the evolution of reduced vancomycin susceptibility in MSSA is similar to that seen in MRSA. Differences in vancomycin population analysis profiles; chemical autolysis; vancomycin, oxacillin, and daptomycin minimum inhibitory concentrations; and bactericidal activities were examined. Progressive vancomycin resistance correlated with increasing daptomycin nonsusceptibility. Chemical autolysis and the bactericidal activity of vancomycin, oxacillin, and daptomycin were reduced in the final, vancomycin-intermediate S. aureus isolate, compared with the vancomycin-susceptible MSSA progenitor. Clinicians should recognize that reduced vancomycin susceptibility can occur in S. aureus irrespective of background methicillin susceptibility and that development of intermediate vancomycin susceptibility in MSSA may result in increased tolerance to several classes of anti-staphylococcal antibiotics.

Occurrence of vancomycin-tolerant and heterogeneous vancomycin-intermediate strains (hVISA) among Staphylococcus aureus causing bloodstream infections in nine USA hospitals

The bactericidal activities of vancomycin and daptomycin were evaluated in a large collection of methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia strains from nine major USA medical centres. To evaluate the occurrence of heterogeneous vancomycin-intermediate S. aureus (hVISA) among MRSA strains tolerant to vancomycin and/or with increased vancomycin or daptomycin MIC values. The accuracy of the macro Etest method (MET) compared with population analysis profiling (PAP) for the detection of hVISA was also assessed. A total of 1800 MRSA strains were collected from bloodstream infections at the nine sites (40 strains per year, per medical centre during the 2002-06 study period). Vancomycin and daptomycin MIC testing was performed by reference broth microdilution (all strains) and MBC tests on 50% of strains (randomly selected). A subset of isolates (n = 268) having an increased vancomycin MBC (> or =16 mg/L), an increased vancomycin MIC (> or =1 mg/L) and/or an increased daptomycin MIC (>0.5 mg/L) were tested for susceptibility to vancomycin and teicoplanin by MET. Overall, 181 of 900 (20.1%) MRSA tested exhibited vancomycin tolerance, varying from 10% to 43% among the medical centres evaluated, and from 11.7% in 2004 to 27.8% in 2005. No resistance trend was observed in any medical centre or in the overall study data. Daptomycin showed bactericidal activity against all strains tested. The accuracy of MET for identifying hVISA strains varied significantly with the criteria applied for positivity. The most frequently used criteria to define hVISA, i.e. MET reading values > or =8 mg/L for both vancomycin and teicoplanin or > or =12 mg/L for teicoplanin only, detected 20 of 36 PAP-positive strains (55.6% sensitivity), indicating that the prevalence of hVISA could be higher than currently appreciated. Daptomycin was bactericidal against hVISA strains.

Loss of vancomycin bactericidal activity against accessory gene regulator (agr) dysfunctional Staphylococcus aureus under conditions of high bacterial density

The impact of accessory gene regulator ( agr) dysfunction and high bacterial density on vancomycin killing and resistance was evaluated among 10 clinical methicillin-resistant Staphylococcus aureus bloodstream isolates using time kill experiments. Under conditions of high inocula and agr dysfunction, vancomycin activity was markedly attenuated, amplifying resistant mutants by 72 h.