Recent advances in the treatment of infections due to resistant Staphylococcus aureus

Design, Synthesis, Evaluation of Antimicrobial Activity and Docking Studies of New Thiazole-based Chalcones

BACKGROUND

Thiazole derivates as well as chalcones, are very important scaffold for medicinal chemistry. Literature survey revealed that they possess wide spectrum of biological activities among which are anti-inflammatory and antimicrobial.

OBJECTIVES

The current studies describe the synthesis and evaluation of antimicrobial activity of twenty eight novel thiazole-based chalcones.

METHODS

The designed compounds were synthesized using classical methods of organic synthesis. The in vivo evaluation of antimicrobial activity was performed by microdilution method.

RESULTS

All compounds have shown antibacterial properties better than that of ampicillin and in many cases better than streptomycin. As far as the antifungal activity is concerned, all compounds possess much higher activity than reference drugs bifonazole and ketoconazole. The most sensitive bacterial species was B. cereus (MIC 6.5-28.4 µmol × 10-2/mL and MBC 14.2-105.0 µmol × 10-2/mL) while the most resistant ones were L. monocytogenes (MIC 21.4-113.6 µmol × 10-2/mL) and E. coli (MIC 10.7- 113.6 µmol × 10-2/mL) and MBC at 42.7-358.6 µmol × 10-2/mL and 21.4-247.2 µmol × 10-2/mL, respectively. All the compounds exhibited antibacterial activity against the three resistant strains, MRSA, P. aeruginosa and E.coli. with MIC and MBC in the range of 0.65-11.00 µmol/mL × 10-2 and 1.30-16.50 µmol/mL × 10-2. Docking studies were performed.

CONCLUSION

Twenty-eight novel thiazole-based chalcones were designed, synthesized and evaluated for antimicrobial activity. The results showed that these derivatives could be lead compounds in search of new potent antimicrobial agents. Docking studies indicated that DNA gyrase, GyrB and MurA inhibition may explain the antibacterial activity.

Infection in the Neuroischemic Foot

Infection in the neuroischemic foot can lead to cellulitis, which often progresses to necrosis as a result of septic vasculitis. Therefore, it is important to diagnose infection early. However, the signs and symptoms of infection are diminished in the neuroischemic foot. Microbiological investigation is essential. Severe infection needs intravenous antibiotic therapy and urgent assessment of the need for surgical drainage and debridement. Infected neuroischemic feet need vascular assessment and intervention where appropriate. It is important to maintain strict metabolic control and optimize cardiovascular function. Recent modern approaches based on multi-disciplinary clinics have resulted in improved results in the management of infection in the ischemic diabetic foot.

4-Thiazolidinone derivatives as potent antimicrobial agents: microwave-assisted synthesis, biological evaluation and docking studies

A series of ten thiazolidin-4-one derivatives was synthesized and evaluated for their antibacterial, antifungal and HIV-1 reverse transcriptase (RT) inhibitory activity.

Oritavancin: a new avenue for resistant Gram-positive bacteria

Oritavancin, a new semisynthetic glycopeptide has a spectrum of activity similar to vancomycin, although it exhibits potent antimicrobial activity against vancomycin-resistant staphylococci and enterococci species. It has a long-terminal half-life of 360 h, is highly protein bound and has been dosed once-daily in clinical trials. Oritavancin has been studied in complicated skin and skin structure infections where it was noninferior to the comparator group of vancomycin/cephalexin. Thus far, oritavancin has a favorable side-effect profile and appears promising in the treatment of multidrug resistant Gram-positive bacteria.

Thiazole-based aminopyrimidines and N-phenylpyrazolines as potent antimicrobial agents: synthesis and biological evaluation

A series of eight thiazole-based N-phenylpyrazolines and two aminopyrimidines having several chalcone derivatives as precursors have been synthesized and evaluated for their antimicrobial activity.

Multi-objective optimization of glycopeptide antibiotic production in batch and fed batch processes

Fermentation optimization involves potentially conflicting multiple objectives such as product concentration and production media cost. Simultaneous optimization of these objectives would result in a multiobjective optimization problem, which is characterized by a set of multiple solutions, knows as pareto optimal solutions. These solutions gives flexibility in evaluating the trade-offs and selecting the most suitable operating policy. Here, ε-constraint approach was used to generate the pareto solutions for two objectives: product concentration and product per unit cost of media, for batch and fed batch operations using process model for Amycolatopsis balhimycina, a glycopeptide antibiotic producer. This resulted in a set of several pareto optimal solutions with the two objectives ranging from (0.75 g l(-1), 3.97 g $(-1)) to (0.44 g l(-1), 5.19 g $(-1)) for batch and from (1.5 g l(-1), 5.46 g $(-1)) to (1.1 g l(-1), 6.34 g $(-1)) for fed batch operations. One pareto solution each for batch and for fed batch mode was experimentally validated.

Crystal structure of a phenol-coupling P450 monooxygenase involved in teicoplanin biosynthesis

The lipoglycopeptide antibiotic teicoplanin has proven efficacy against gram-positive pathogens. Teicoplanin is distinguished from the vancomycin-type glycopeptide antibiotics, by the presence of an additional cross-link between the aromatic amino acids 1 and 3 that is catalyzed by the cytochrome P450 monooxygenase Orf6* (CYP165D3). As a goal towards understanding the mechanism of this phenol-coupling reaction, we have characterized recombinant Orf6* and determined its crystal structure to 2.2-Å resolution. Although the structure of Orf6* reveals the core fold common to other P450 monooxygenases, there are subtle differences in the disposition of secondary structure elements near the active site cavity necessary to accommodate its complex heptapeptide substrate. Specifically, the orientation of the F and G helices in Orf6* results in a more closed active site than found in the vancomycin oxidative enzymes OxyB and OxyC. In addition, Met226 in the I helix replaces the more typical Gly/Ala residue that is positioned above the heme porphyrin ring, where it forms a hydrogen bond with a heme iron-bound water molecule. Sequence comparisons with other phenol-coupling P450 monooxygenases suggest that Met226 plays a role in determining the substrate regiospecificity of Orf6*. These features provide further insights into the mechanism of the cross-linking mechanisms that occur during glycopeptide antibiotics biosynthesis.

Thiazole-based chalcones as potent antimicrobial agents. Synthesis and biological evaluation

As part of ongoing studies in developing new antimicrobials, we report the synthesis of a new class of structurally novel derivatives, that incorporate two known bioactive structures a thiazole and chalcone, to yield a class of compounds with interesting antimicrobial properties. Evaluation of antibacterial activity showed that almost all the compounds exhibited greater activity than reference drugs and thus could be promising novel drug candidates.

Regioselective deacetylation based on teicoplanin-complexed Orf2* crystal structures

Lipoglycopeptide antibiotics are more effective than vancomycin against MRSA as they carry an extra aliphatic acyl side chain on glucosamine (Glm) at residue 4 (r4). The biosynthesis of the r4 N-acyl Glc moiety at teicoplanin (Tei) or A40926 has been elucidated, in which the primary amine nucleophile of Glm is freed from the r4 GlcNac pseudo-Tei precursor by Orf2* for the subsequent acylation reaction to occur. In this report, two Orf2* structures in complex with β-D-octyl glucoside or Tei were solved. Of the complexed structures, the substrate binding site and a previously unknown hydrophobic cavity were revealed, wherein r4 GlcNac acts as the key signature for molecular recognition and the cavity allows substrates carrying longer acyl side chains in addition to the acetyl group. On the basis of the complexed structures, a triple-mutation mutant S98A/V121A/F193Y is able to regioselectively deacetylate r6 GlcNac pseudo-Tei instead of that at r4. Thereby, novel analogs can be made at the r6 sugar moiety.

Antibiotic-loaded chitosan film for infection prevention: A preliminary in vitro characterization

The growing infection rate by methicillin-resistant Staphylococcus aureus, especially with bone fracture fixation implants, is a major concern in extremity musculoskeletal wound treatment. This preliminary investigation evaluates the ability of chitosan film to be loaded with daptomycin and vancomycin in the operating room, in situ loading, and applied to musculoskeletal fixation devices to lessen or prevent infection. Films with 61, 71, and 80% degrees of deacetylation (DDA) made using lactic or acetic acid solvents were analyzed for their antibiotic uptake, elution, and activity along with film swelling ratio, ultimate tensile strength, Young's modulus, adhesive strength, and degradation. Chitosan films after 1 min of rehydration were able in a simulated, clinical setting to maintain mechanical integrity and adhesive strength to be applied to bone fracture fixation devices or implant surfaces. The film percent degradation increased with DDA increasing from 61 to 80%, but film degradation rate decreased in the presence of antibiotics. Eighty percent DDA chitosan films were optimal for absorbing and eluting antibiotics. Antibiotics eluted by the films were active against Staphylococcus aureus. These findings indicate that an 80% DDA chitosan film is potentially advantageous as a clinically adjunctive treatment in musculoskeletal injuries to lessen or prevent infections.

Comparative effectiveness of antibiotics for the treatment of MRSA complicated skin and soft tissue infections

OBJECTIVE

With a growing number of studies and comparators in MRSA skin infections, a unified framework for comparing treatments is needed for health technology assessment (HTA). The objective was to systematically assess the success rates of common antimicrobial agents for the treatment of complicated skin and soft tissue infections (cSSTIs) caused by MRSA.

METHODS

MEDLINE, EMBASE, and Cochrane databases were searched to identify published clinical trials in which dalbavancin, daptomycin, linezolid, telavancin, teicoplanin, tigecycline, and vancomycin were used to treat cSSTIs. Pooled efficacy estimates were generated from clinical and microbiological determinations of success for the MRSA-subgroups in cSSTI clinical trials using a Bayesian meta-analytic approach. Success rates for each antibiotic were reported with 95% Bayesian confidence intervals (called credible intervals [CrI]). In sensitivity analyses the impact of different model parameters and article quality were investigated.

RESULTS

Out of 36 identified studies, 14 studies on six antibiotics with 28 treatment arms (n = 1840) were included in the analysis. No MRSA data in cSSTI were found for teicoplanin. The pooled success rate and CrI(95%) for each agent was: vancomycin (74.7%; CrI(95%): 64.1%-83.5%), dalbavancin (87.7%; CrI(95%): 74.6%-95.4%), linezolid (84.4%; CrI(95%): 76.6%-90.6%), telavancin (83.5%; CrI(95%): 73.6%-90.8%), daptomycin (78.1%; CrI(95%): 54.6%-93.2%) and tigecycline (70.4%; CrI(95%): 48.0%-87.6%). Comparisons between antibiotics suggested differences versus vancomycin for linezolid (+9.7%; CrI(95%): 4.4%-15.8%), dalbavancin (+13.1%; CrI(95%): 1.0%-23.8%), and telavancin (+8.8%; CrI(95%): 1.5-16.7%). The finding of lower vancomycin efficacy in MRSA cSSTI did not change in sensitivity analyses.

CONCLUSION

The results of this meta-analysis suggest higher success rates for linezolid and the new glycopeptides (dalbavancin and telavancin) in MRSA-confirmed cSSTIs. The uncertainty margins reflect the study limitations including number of cases and indirect nature of the comparisons. This example of Bayesian meta-analysis for MRSA cSSTI provides a potential framework for comparisons that is useful for HTA and formulary decision-making.

Future treatment options for Gram-positive infections--looking ahead

Multidrug-resistant Gram-positive infections remain a significant therapeutic problem, especially those due to Staphylococcus aureus. Antimicrobial choice is only one aspect of the management of these infections. New immunotherapies, exploitation of novel antibiotic targets, topical therapies and new drug delivery systems may have a future role in the management of S. aureus infection. At present, injectable antimicrobials are the main area of drug development and clinical interest. Since 1999, five anti-Gram-positive agents (moxifloxacin, quinupristin-dalfopristin, linezolid, daptomycin and tigecycline) have become available in the EU. At present, three other anti-Gram-positive agents are being considered by the European Medicines Agency (ceftobiprole, gemifloxacin and iclaprim), and a further four have completed phase III clinical trials (ceftaroline, dalbavancin, oritavancin and telavancin). The antibacterial spectra of these agents, their in vitro potencies, bactericidal activities and pharmacokinetics are well known. The safety profiles for those agents that have received regulatory approval and entered clinical practice are also firmly established. Most of the agents are pharmacodynamically promising and effective in clinical trials. As in the past, drug safety is likely to be a major determinant of which of the most recent drugs receive regulatory approval, and, in the long term, which agents will be successful in clinical practice.

Tigecycline: A review of a new glycylcycline antibiotic

Tigecycline derived from minocycline. It is part of a new class of antibiotics called glycylcyclines. Tigecycline is given intravenously and has activity against a variety of gram-positive and gram-negative bacterial pathogens, many of which are resistant to existing antibiotics. Tigecycline successfully completed phase III trials in which it was at least equal to intravenous vancomycin and aztreonam to treat complicated skin and skin structure infections (cSSSI), and to intravenous imipenem and cilastatin to treat complicated intra-abdominal infections (cIAI). Tigecycline side effects are primarily digestive upset. It should be a valuable addition to the armamentarium to treat even the most resistant pathogens.

Four cases of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections treated with tigecycline

We report 4 cases of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections who received treatment with tigecycline after unsuccessful treatment attempts with conventional drugs. All 4 patients were eventually cured although 1 experienced a relapse of her bacteremia while on treatment due to inadequate dosing.

Crystal structures of lipoglycopeptide antibiotic deacetylases: implications for the biosynthesis of A40926 and teicoplanin

The lipoglycopeptide antibiotics teicoplanin and A40926 have proven efficacy against Gram-positive pathogens. These drugs are distinguished from glycopeptide antibiotics by N-linked long chain acyl-D-glucosamine decorations that contribute to antibacterial efficacy. During the biosynthesis of lipoglycopeptides, tailoring glycosyltransferases attach an N-acetyl-D-glucosamine to the aglycone, and this N-acetyl-glucosaminyl pseudoaglycone is deacetylated prior to long chain hydrocarbon attachment. Here we present several high-resolution crystal structures of the pseudoaglycone deacetylases from the biosynthetic pathways of teicoplanin and A40926. The cocrystal structure of the teicoplanin pseudoaglycone deacetylase with a fatty acid product provides further insights into the roles of active-site residues, and suggests mechanistic similarities with structurally distinct zinc deacetylases, such as peptidoglycan deacetylase and LpxC. A unique, structurally mobile capping lid, located at the apex of these pseudoaglycone deacetylases, likely serves as a determinant of substrate specificity.

Treatment of hospital-acquired pneumonia caused by methicillin-resistant Staphylococcus aureus

Nosocomial pneumonia and ventilator-assisted pneumonia may be polymicrobial and can be caused by a wide spectrum of pathogens. Potentially multidrug-resistant microorganisms often represent the 'core' pathogens of the most severe infections. Among Gram-positive pathogens, methicillin-resistant Staphylococcus aureus (MRSA) plays a key role, mainly in mechanically ventilated patients or in patients with specific risk factors. The mainstay of treatment for MRSA pneumonia has been glycopeptide antibiotics, i.e. vancomycin and, to a lesser extent, teicoplanin. However, owing to its insufficient penetration into lung compartments, vancomycin may result in therapeutic failure or slow clinical responses. Moreover, vancomycin serum levels must be monitored in order to minimise nephrotoxicity and to maximise the concentration in the lung. Finally, the emergence of staphylococci isolates with reduced susceptibility to vancomycin suggests that glycopeptides should no longer be considered as first-line antibacterial agents for Gram-positive lung infections. Among new therapeutic options, linezolid may be an appropriate choice for MRSA pulmonary infections owing to its good pharmacokinetic profile in the lung and its acceptable tolerability, especially in patients with renal insufficiency or in those receiving other nephrotoxic agents. However, to contain the increasing emergence of drug resistance among hospitalised patients, these novel antimicrobial agents should be used judiciously, restricting their use to patients not responsive to, or intolerant of, glycopeptides. Other new drugs under development appear to be promising and deserve further evaluation.

Clinical impact of MRSA in a stem cell transplant unit: analysis before, during and after an MRSA outbreak

Meticillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen, with an increased incidence in the UK since 1993, causing serious morbidity and mortality in immunosuppressed patients. We analysed the frequency and outcome of MRSA infection in a single-centre transplant population over a 5-year period. The total number of patients infected was 41/776 (5%). The frequency in autologous, sibling and unrelated donor transplants was 3, 6 and 9%, respectively. Prior to 2004, the incidence was <4%/year; however, an outbreak in the day unit resulted in 22 patients becoming newly infected. Over 90% of infections were clinically relevant, half (49%) being bacteraemia. Three patterns were seen: known MRSA positive at any time before transplant (n=15), MRSA first detected during the neutropenia phase (n=5) and MRSA only post discharge (n=21). MRSA was implicated in a number of deaths, at all time points, in those infected. An intensive eradication policy resulted in new infections dropping to <2%. In conclusion, MRSA is likely to remain endemic in our unit, but robust early screening protocols and aggressive eradication strategies have effectively limited the spread of and morbidity due to this pathogen.

[Spontaneous bacterial peritonitis due to methicillin-resistant Staphylococcus aureus in patients with cirrhosis]

A substantial epidemiologic change in the etiology of spontaneous bacterial peritonitis (SBP) has been observed in recent years. Gram-positive, as well as multiresistant bacteria, have emerged as an important cause of SBP mainly among hospitalized patients. In this setting, SBP caused by methicillin-resistant Staphylococcus aureus (MRSA) could become a major clinical problem in the near future. We present two cases of SBP due to MRSA without clinical response to vancomycin, even though in vitro sensitivity was observed in both cases. We review the current literature on the incidence and clinical significance of SBP due to MRSA infection in cirrhotic patients, as well as its prevention and treatment.

Antimicrobial therapy of multidrug-resistant Streptococcus pneumoniae, vancomycin-resistant enterococci, and methicillin-resistant Staphylococcus aureus

Antibiotic resistance among pneumococci, enterococci, and staphylococci has become increasingly important in recent decades. Clinicians should be familiar with the nuances of antibiotic susceptibility testing and interpretation in selecting antibiotics for these infections. The clinical significance of penicillin-resistant Streptococcus pneumoniae, macrolide-resistant S pneumoniae, and multidrug-resistant S pneumoniae is discussed. The clinical spectrum and therapeutic approach to Enterococcus faecalis (i.e., vancomycin-sensitive enterococci) and E faecium (i.e., vancomycin-resistant enterococci) are discussed. Differences in therapeutic approach between methicillin-sensitive Staphylococcus aureus and methicillin-resistant S aureus (MRSA) infections are reviewed. Differences between in vitro susceptibility testing and in vivo effectiveness of antibiotics for hospital-acquired MRSA (HA-MRSA) are described. Finally, the clinical features of infection and therapy of HA-MRSA and community-acquired MRSA (CA-MRSA) infections are compared.

Synthesis and antimicrobial activity of novel 2-thiazolylimino-5-arylidene-4-thiazolidinones

New 2-thiazolylimino-5-arylidene-4-thiazolidinones (compounds 4a-j), unsubstituted or carrying hydroxy, methoxy, nitro and chloro groups on the benzene ring, were synthesized and assayed in vitro for their antimicrobial activity against Gram positive and Gram negative bacteria, yeasts and mould. The compounds were very potent towards all tested Gram positive microorganisms (MIC ranging from 0.03 to 6 microg/mL in most of the cases) and Gram negative Haemophilus influenzae (MIC 0.15-1.5 microg/mL), whereas no effectiveness was exhibited against Gram negative Escherichia coli and fungi up to the concentration of 100 microg/mL. The 5-arylidene derivatives showed an antibacterial efficacy considerably greater than that of the parent 2-(thiazol-2-ylimino)thiazolidin-4-one 3, suggesting that the substituted and unsubstituted 5-arylidene moiety plays an important role in enhancing the antimicrobial properties of this class of compounds. The remarkable inhibition of the growth of penicillin-resistant staphylococci makes these substances promising agents also for the treatment of infections caused by microorganisms resistant to currently available drugs.

Diagnostic PCR analysis of the occurrence of methicillin and tetracycline resistance genes among Staphylococcus aureus isolates from phase 3 clinical trials of tigecycline for complicated skin and skin structure infections

Diagnostic PCR assays were developed to track common genetic determinants of oxacillin resistance as well as resistance to classical tetracyclines in Staphylococcus aureus isolates from the recently completed worldwide phase 3 clinical trials of tigecycline. A total of 503 unique S. aureus strains isolated from complicated skin and skin structure infections were analyzed. The mecA gene was amplified from 120 strains (23.9%) determined to be resistant to oxacillin (MICs > or = 4 microg/ml). The prevalence of the mecA gene was found to vary regionally from 6.5% to 50.9% among isolates originating in Eastern Europe and North America, respectively. The presence of a tetracycline resistance determinant, tet(M) or tet(K), among methicillin-resistant S. aureus (MRSA) isolates also varied regionally, with a range of 11.9% to 46.2% among isolates tested from North America and Eastern Europe, respectively. The occurrence of a tetracycline resistance marker in methicillin-susceptible S. aureus (MSSA) strains varied from 2.5 to 16.1% among the isolates tested across the regions of study. The presence of tet(M) or tet(K) had no discernible effect on the tigecycline MICs for either MRSA or MSSA strains, which is consistent with the ability of the glycylcyclines to retain activity in the presence of both the ribosomal protection and efflux mechanisms of resistance to the tetracyclines.

New antibiotics for the treatment of severe staphylococcal infection in the critically ill patient

PURPOSE OF REVIEW

Infection by Staphylococcus aureus in critically ill patients is usually associated with antimicrobial resistance and high mortality. A more effective antibiotic treatment is needed to replace older drugs that have limited efficacy. Novel substances active on methicillin-resistant Staphylococcus aureus, which are already available on the market or are still in development, are discussed in this review, with emphasis on nosocomial infections.

RECENT FINDINGS

A number of new antibiotics are on the market (linezolid, quinupristin-dalfopristin, daptomycin) and there is good evidence regarding their efficacy, especially in methicillin-resistant Staphylococcus aureus infections. Linezolid is, to date, the best alternative in treating nosocomial pneumonia by methicillin-resistant Staphylococcus aureus. It is cost-effective; resistance levels are still very low but there are some concerns regarding its adverse events. Quinupristin-dalfopristin shows good activity in vitro but its efficacy in patients with pneumonia by methicillin-resistant Staphylococcus aureus is modest. Daptomycin is not recommended for pulmonary infections because of its reduced penetration in the lung tissue. Under current phase III trials in patients with nosocomial infections are tigecycline, ceftobiprole, and three new glycopeptides, all with particular activity against methicillin-resistant Staphylococcus aureus.

SUMMARY

For the moment, there are limited and rather expensive therapeutic options for the infections by Staphylococcus aureus in the critically ill. No dramatic superiority of the new drugs in comparison to the standard therapies was observed in most of the clinical trials. Better results on the efficacy of the drugs under investigation are expected.

Ceftobiprole: in-vivo profile of a bactericidal cephalosporin

Resistance to antimicrobials is a significant and growing problem, limiting treatment options, especially for serious Gram-positive infections. Ceftobiprole is a novel broad-spectrum cephalosporin that is active in vitro against streptococci and staphylococci, including penicillin-resistant strains of pneumococci and methicillin-resistant Staphylococcus aureus (MRSA). It maintains the activity of extended-spectrum cephalosporins against Gram-negative bacteria, including Enterobacteriaceae. The in-vivo activity of ceftobiprole has been demonstrated in mouse sepsis and subcutaneous abscess models of infection. Its activity also has been examined in several discriminative models of infection that mimic specific diseases in humans and permit testing of antimicrobial activity under a variety of defined pharmacokinetic conditions. These include experimental pneumonia in mice, a tissue cage model of foreign body infection in rats, and endocarditis models in rats and rabbits. In these models, ceftobiprole exhibits activity equivalent or superior to that of comparators against MRSA, including vancomycin-intermediate strains. These models also confirm the in-vivo activity of ceftobiprole against Gram-negative bacteria that are susceptible in vitro. The results from animal models support the evaluation of the clinical efficacy of ceftobiprole in humans and also predict clinical efficacy in the empirical treatment of severe infections. The broad spectrum of activity may allow ceftobiprole to be used as monotherapy for serious hospital-acquired infections where combination therapy would otherwise be required.

Can β-lactams be re-engineered to beat MRSA?

Methicillin-resistant Staphylococcus aureus (MRSA) strains are important nosocomial pathogens worldwide and now are also of growing importance in community-acquired infection. Their resistance depends upon a supplementary peptidoglycan transpeptidase, PBP2' (PBP-2a), which continues to function when normal PBPs have been inactivated by beta-lactams. PBP2' is encoded by the mecA gene, which is carried by the staphylococcal cassette chromosome, a large and somewhat variable DNA insert of uncertain origin. PBP2' does not wholly lack affinity for beta-lactams, but its affinity for available analogues is very weak. In principle, it should be possible to re-engineer beta-lactams to bind PBP2' strongly, and the desirability of this approach is self-evident: no other antibiotic class has a record equal to the beta-lactams for safety and efficacy. Moreover, there is consensus that beta-lactams are inherently more efficacious than vancomycin against infections due to susceptible staphylococci. In practice, finding viable PBP2'-active beta-lactams has proved difficult and the catalogue of near-misses extends back to the 1980s. At last, however, one cephalosporin with high affinity for PBP2'--ceftobiprole--is entering phase III trials. Ceftobiprole inhibits MRSA at 1-2 mg/L under standard conditions. Even when mecA/PBP2' was induced strongly, ceftobiprole MICs for MRSA only reached 4 mg/L, a clinically attainable concentration. A phase II trial in skin and skin structure infection recorded cures by ceftobiprole in 4/4 MRSA infections, and results of the phase III trials are awaited with great interest.

Cutaneous bacterial infections in the newborn

PURPOSE OF REVIEW

This review examines neonatal bacterial skin infections with respect to host immunity, bacterial pathogens, patterns of infection, and new therapeutic approaches.

RECENT FINDINGS

Advances have been made in our understanding of innate host defense and the emerging role of cutaneous antimicrobial peptides of the cathelicidin and defensin families. Toll-like receptors are being investigated with respect to their interactions with bacteria and other components of the innate immune defense, such as the antimicrobial peptides. The epidermal barrier remains an active area of research. Studies confirm that maintaining an intact epidermal barrier by minimizing exposure to soap and by not removing vernix caseosa are simple measures to improve skin barrier function. Active barrier-enhancing measures such as the application of topical emollients have shown mixed results in the prevention of nosocomial infection. A meta-analysis of studies performed in developed countries showed a trend of increasing risk for coagulase-negative staphylococcal infection. By contrast, a randomized controlled trial showed that infants treated with sunflower oil are less likely to experience nosocomial infections than are control infants. Infants with bacteremia and no known source of infection should be carefully examined because cutaneous abscesses have been shown to be an important nidus of infection. Methicillin-resistant Staphylococcus aureus is reaching epidemic proportions, making surface cultures an essential part of the evaluation of cutaneous bacterial infection.

SUMMARY

New insights have been gained regarding the basic science of neonatal host defense and these advances may produce new ways of approaching the prevention and treatment of bacterial skin infections in the newborn period.