Effects of vancomycin versus nafcillin in enhancing killing of methicillin-susceptible Staphylococcus aureus causing bacteremia by human cathelicidin LL-37

Recent studies have demonstrated that anti-staphylococcal beta-lactam antibiotics, like nafcillin, render methicillin-resistant Staphylococcus aureus (MRSA) more susceptible to killing by innate host defense peptides (HDPs), such as cathelicidin LL-37. We compared the effects of growth in 1/4 minimum inhibitory concentration (MIC) of nafcillin or vancomycin on the LL-37 killing of 92 methicillin-susceptible S. aureus (MSSA) isolates. For three randomly selected strains among these, we examined the effects of nafcillin, vancomycin, daptomycin, or linezolid on LL-37 killing and autolysis. Growth in the presence of subinhibitory nafcillin significantly enhanced LL-37 killing of MSSA compared to vancomycin and antibiotic-free controls. Nafcillin also reduced MSSA production of the golden staphylococcal pigment staphyloxanthin in 39 % of pigmented strains vs. 14 % for vancomycin. Among the antibiotics tested, only nafcillin resulted in significantly increased MSSA autolysis. These studies point to additional mechanisms of anti-staphylococcal activity of nafcillin beyond direct bactericidal activity, properties that vancomycin and other antibiotic classes do not exhibit. The ability of nafcillin to enhance sensitivity to innate HDPs may contribute to its superior effectiveness against MSSA, as suggested by studies comparing clinical outcomes to vancomycin treatment.

Bacterial Cytological Profiling (BCP) as a Rapid and Accurate Antimicrobial Susceptibility Testing Method for Staphylococcus aureus

Successful treatment of bacterial infections requires the timely administration of appropriate antimicrobial therapy. The failure to initiate the correct therapy in a timely fashion results in poor clinical outcomes, longer hospital stays, and higher medical costs. Current approaches to antibiotic susceptibility testing of cultured pathogens have key limitations ranging from long run times to dependence on prior knowledge of genetic mechanisms of resistance. We have developed a rapid antimicrobial susceptibility assay for Staphylococcus aureus based on bacterial cytological profiling (BCP), which uses quantitative fluorescence microscopy to measure antibiotic induced changes in cellular architecture. BCP discriminated between methicillin-susceptible (MSSA) and -resistant (MRSA) clinical isolates of S. aureus (n = 71) within 1–2 h with 100% accuracy. Similarly, BCP correctly distinguished daptomycin susceptible (DS) from daptomycin non-susceptible (DNS) S. aureus strains (n = 20) within 30 min. Among MRSA isolates, BCP further identified two classes of strains that differ in their susceptibility to specific combinations of beta-lactam antibiotics. BCP provides a rapid and flexible alternative to gene-based susceptibility testing methods for S. aureus, and should be readily adaptable to different antibiotics and bacterial species as new mechanisms of resistance or multidrug-resistant pathogens evolve and appear in mainstream clinical practice.

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Bacterial cytological profiling identifies antibiotic resistant S. aureus.

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BCP predicts best treatment options for multidrug resistant MRSA.

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Resistant strains are correctly identified within 1 h.

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BCP does not require prior knowledge of resistance mechanism.

There is a great need for rapid antimicrobial susceptibility testing (AST) as it can dramatically improve clinical outcome for bacterial infections. Most currently proposed ASTs are dependent on knowledge of known resistance genes or based solely on growth/lysis. We have developed a new diagnostic method for rapidly determining antibiotic susceptibility of Staphylococcus aureus using quantitative fluorescence microscopy to measure antibiotic induced changes in cellular architecture. Our test has the potential to change the way antibiotic susceptibility testing is done in the future and is readily adaptable to different antibiotics and bacterial species regardless of the mechanisms of resistance.

Ceftobiprole and ampicillin increase daptomycin susceptibility of daptomycin-susceptible and -resistant VRE

OBJECTIVES

The synergistic combination of daptomycin plus ampicillin has proven to be effective against VRE including daptomycin-non-susceptible strains. Ceftobiprole is a cephalosporin with broad binding affinity for enterococcal PBP subtypes including PBP5. Given the synergy between β-lactams and daptomycin against VRE, it was of interest to determine whether ceftobiprole offered any synergistic advantage with daptomycin compared with ampicillin.

METHODS

MICs were determined by broth microdilution in the presence and absence of ampicillin or ceftobiprole for 20 ampicillin-resistant VRE. Six strains, including two isogenic pairs of vancomycin-resistant Enterococcus faecium and two vancomycin-resistant Enterococcus faecalis, were evaluated for synergy using time-kill methods. Synergy was defined as a ≥2 log10 cfu/mL reduction of the combination over the most active single agent. Binding of daptomycin-bodipy in the presence and absence of ceftobiprole was quantified.

RESULTS

Daptomycin MICs ranged from 2 to 256 mg/L. The addition of ceftobiprole and ampicillin reduced daptomycin MICs by a median of 3 and 4 log2 dilutions, respectively. In time-kill studies, daptomycin plus either ceftobiprole or ampicillin was synergistic against four of six strains, but not the same strains. Both combinations were synergistic against the vancomycin-resistant E. faecalis strains. Ceftobiprole exposure increased daptomycin-bodipy binding by 2.8 times (P<0.0001).

CONCLUSIONS

Ceftobiprole appears to offer a similar degree of synergistic activity to ampicillin when combined with daptomycin against VRE. Further research should explore the genetic and phenotypic qualities of strains that respond preferentially to ceftobiprole as opposed to ampicillin.

Novel combinations of vancomycin plus ceftaroline or oxacillin against methicillin-resistant vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA

We demonstrated a significant inverse correlation between vancomycin and beta-lactam susceptibilities in vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA) isolates. Using time-kill assays, vancomycin plus oxacillin or ceftaroline was synergistic against 3 of 5 VISA and 1 of 5 hVISA isolates or 5 of 5 VISA and 4 of 5 hVISA isolates, respectively. Beta-lactam exposure reduced overall vancomycin-Bodipy (dipyrromethene boron difluoride [4,4-difluoro-4-bora-3a,4a-diaza-s-indacene] fluorescent dye) binding but may have improved vancomycin-cell wall interactions to improve vancomycin activity. Further research is warranted to elucidate the mechanism behind vancomycin and beta-lactam synergy.

Prevalence of the fsr locus in Enterococcus faecalis infections

The fsr locus of Enterococcus faecalis confers virulence in animal models. A retrospective analysis of fsr prevalence in diverse E. faecalis clinical isolates demonstrated fsr in all endocarditis isolates versus 53% of stool isolates (P = 0.005). This supports a role for fsr-mediated virulence in the pathogenesis of enterococcal infections in humans.

Methicillin-resistant Staphylococcus aureus: comparison of susceptibility testing methods and analysis of mecA-positive susceptible strains

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for an increasing number of serious nosocomial and community-acquired infections. Phenotypic heterogeneous drug resistance (heteroresistance) to antistaphylococcal beta-lactams affects the results of susceptibility testing. The present study compared the MRSA-Screen latex agglutination test (Denka Seiken Co., Ltd., Tokyo, Japan) for detection of PBP 2a with agar dilution, the VITEK-1 and VITEK-2 systems (bioMérieux, St. Louis, Mo.), and the oxacillin agar screen test for detection of MRSA, with PCR for the mecA gene used as the "gold standard" assay. Analysis of 107 methicillin-susceptible S. aureus (MSSA) isolates and 203 MRSA isolates revealed that the MRSA-Screen latex agglutination test is superior to any single phenotype-based susceptibility testing method, with a sensitivity of 100% and a specificity of 99.1%. Only one isolate that lacked mecA was weakly positive by the MRSA-Screen latex agglutination test. This isolate was phenotypically susceptible to oxacillin and did not contain the mecA gene by Southern blot hybridization. The oxacillin agar screen test, the VITEK-1 system, the VITEK-2 system, and agar dilution showed sensitivities of 99.0, 99.0, 99.5, and 99%, respectively, and specificities of 98.1, 100, 97.2, and 100%, respectively. The differences in sensitivity or specificity were not statistically significant. Oxacillin bactericidal assays showed that mecA- and PBP 2a-positive S. aureus isolates that are susceptible to antistaphylococcal beta-lactams by conventional methods are functionally resistant to oxacillin. We conclude that the accuracy of the MRSA-Screen latex agglutination method for detection of PBP 2a approaches the accuracy of PCR and is more accurate than any susceptibility testing method used alone for the detection of MRSA.

Linezolid resistance in a clinical isolate of Staphylococcus aureus

The new oxazolidinone antimicrobial, linezolid, has been approved for the treatment of infections caused by various gram-positive bacteria, including meticillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Although instances of linezolid resistance in VRE have been reported, resistance has not been encountered among clinical isolates of S aureus. We have characterised an MRSA isolate resistant to linezolid that was recovered from a patient treated with this agent for dialysis-associated peritonitis.

Brainstem and striatal encephalitis complicating Mycoplasma pneumoniae pneumonia: possible benefit of intravenous immunoglobulin

Encephalitides of the brainstem and the striatum associated with Mycoplasma pneumoniae infection are believed to be mediated by an autoimmune process triggered by the organism, a toxin or direct invasion by the organism itself. Inability to identify M. pneumoniae from cerebrospinal fluid by culture or polymerase chain reaction suggested a possible immunologic process. A trial of intravenous immunoglobulin in a critically ill patient with encephalitis that developed in parallel to M. pneumoniae pneumonia was associated with neurologic improvement within 48 h of treatment.

Corynebacterium jeikeium native valve endocarditis following femoral access for coronary angiography

We present a unique case of rapidly fatal native aortic-valve endocarditis due to Corynebacterium jeikeium, with inoculation as a complication of repeated femoral vascular access for coronary angiography.

Hypercalcemia in an AIDS patient treated with growth hormone

METHOD

Recombinant human growth hormone (rhGH) is a newly approved treatment for weight loss and wasting in patients with AIDS. We report a male patient with advanced AIDS who developed hypercalcemia 2 weeks after institution of rhGH therapy.

RESULTS

Parathyroid hormone, parathyroid hormone-related peptide and 1,25-dihydroxyvitamin D levels were suppressed, suggesting that hypercalcemia was mediated through alternative mechanisms. The hypercalcemia responded to discontinuation of rhGH and a single dose of intravenous pamidronate disodium and has not recurred in 8 months of follow-up.

CONCLUSION

We believe this to be the first reported case of rhGH-induced hypercalcemia in an HIV-infected patient.

[Role of endogenous basic fibroblast growth factor in experimental duodenal ulcer]

Authors investigated the role of endogenous bFGF in the development of experimental duodenal ulcer induced by cysteamine. The changes in endogenous bFGF in duodenum were examined by immunohistochemical method in the early stages of ulceration. A significant decrease was found in the immunoreactivity of bFGF in rat duodenal mucosa 12 and 24 hr after the administration of the duodenal ulcerogen cysteamine. Thus, in addition to being a novel potent pharmacologic agent, bFGF may play a pathophysiologic role in ulcer pathogenesis and healing.

Molecular and cellular basis of ulcer healing

BACKGROUND

The high ulcer recurrence rates after treatment with antacids or antisecretory drugs illustrate the need for direct treatment of GI ulcers by stimulating repair and healing mechanisms. The molecular regulators of ulcer healing include polyamines and growth factors such as EGF, TGF-beta, bFGF and PDGF.

METHODS AND RESULTS

Oral treatment of rats with bFGF or PDGF accelerated the healing of chronic cysteamine-induced duodenal ulcers without decreasing gastric secretion. We found that sucralfate binds bFGF in vitro and in vivo, and the elevated local concentration of this growth factor may contribute to the ulcer healing properties of sucralfate. Parallel treatment with bFGF + sucralfate resulted in synergistic healing of chronic duodenal ulcers and chronic gastritis.

CONCLUSIONS

Rapid changes in mucosal concentration of bFGF and EGF receptors during ulceration suggest that these peptides play a role in the natural history of GI ulcers. Thus, treatment based on molecular and cellular mechanisms of ulcer healing allows a direct and efficient ulcer therapy.

Genomic sequences capable of committing mouse and rat fibroblasts to adipogenesis

The mouse Swiss 3T3-F442A/3T3-C2 cell system is well suited for the isolation of genes involved in commitment to adipogenesis. 3T3-F442A cells convert to adipocytes with high efficiency in response to confluence and insulin. The sister clonal line 3T3-C2 does not respond to these signals, but can convert to adipocytes when transfected with DNA from 3T3-F442A preadipocytes or from human fat. Human fat-tissue biopsy FO46 DNA transfected into 3T3-C2 gave rise to fat foci after two rounds of transfection and selection. A cosmid library of a subclone of secondary transfectant 3T3-C2/FO46-1 was screened for the human repetitive Alu sequence. Five out of eight Alu+ recombinant clones committed 3T3-C2 cells to adipogenesis. The adipose commitment (AC) activity of one cosmid, p18A4, was found to reside in two small, non-identical, subcloned sequences 1.2kb and 2.0kb in length, each separately able to commit 3T3-C2, precrisis mouse and rat fibroblasts and the multipotential C3H10T1/2 cell line to adipogenesis. We conclude that commitment to adipogenesis can be effected in vitro with high efficiency by transfection of specific sequences into a variety of host cells.

Excess wild-type p53 blocks initiation and maintenance of simian virus 40 transformation

Wild-type (wt) murine p53 has been tested for its ability to block and reverse the transforming effects of simian virus 40 (SV40) large T antigen. Established and precrisis mouse cells overexpressing exogenously introduced wt p53 became resistant to SV40 transformation. The introduction of excess wt p53 into SV40-transformed precrisis cells reverted their transformed phenotype. However, the phenotype of SV40-transformed established cells was not reverted by excess wt p53. We conclude that an antioncogenic action of wt p53 is exerted during SV40 transformation and that in precrisis cells, the antitransforming action of wt p53 can be exerted both at initiation and during the maintenance of transformation.