Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the SENTRY Antimicrobial Surveillance Program, 1997-1999

Prevalence of mecA gene among staphylococci from clinical samples of a tertiary hospital in Benin City, Nigeria

Background

The staphylococci have increasingly been associated with infections worldwide and anti-microbial resistance has made these versatile pathogens more recalcitrant in the hospital setting.

Objectives

This study sought to investigate the occurrence and distribution of Staphylococcus species as well as determine the prevalence of methicillin resistant Staphylococcus aureus (MRSA) and methicillin resistant coagulase negative staphylococci (MRCoNS) among clinical samples from University of Benin Teaching Hospital (UBTH) in Benin City.

Methods

Ninety one (91) clinical isolates comprising S. aureus and Coagulase Negative staphylococci (CoNS) were recovered from routine clinical specimens and anti-microbial susceptibility tests were carried out. Polymerase Chain Reaction (PCR) was thereafter carried out on these isolates to detect mecA gene.

Results

Staphylococcus species had its highest prevalence from infected wounds of patients (28.8%) while urine samples showed the least (5.4%). The highest level of resistance was to ceftazidime (S. aureus - 68%, CoNS - 75.6%) while the least resistance was observed for meropenem (S. aureus- 26%, CoNS- 46.3%). Using phenotypic method (with 1µg oxacillin antibiotic disc), the distribution of MRSA and MRCoNS was 44.0% and 46.3% respectively. PCR analysis showed that 38.0% of S. aureus and 41.5% of the CoNS had mecA gene respectively; wound swabs showed the highest prevalence with 30.5% of staphylococcal isolates being mecA gene positive. There was also no significant association between the Staphylococcal isolates and their isolation rate, isolation site and mecA gene distribution (p > 0.05).

Conclusion

This study draws attention on the increase in the prevalence of mecA gene (39.6%) and an increase in multidrug resistant staphylococci when compared to previous studies in our country; it recommends laboratory guidance and periodic review to stem the tide of resistance.

A Review of Staphylococcal Cassette Chromosome mec (SCCmec) Types in Coagulase-Negative Staphylococci (CoNS) Species

Coagulase-negative staphylococci (CoNS) are considered low pathogenic organisms. However, they are progressively causing more serious infections with time because they have adapted well to various antibiotics owing to their ability to form biofilms. Few studies have been conducted on CoNS in both, hospital and community-acquired settings, especially in Malaysia. Thus, it is important to study their species and gene distributions. A mobile genetic element, staphylococcal cassette chromosome mec (SCCmec), plays an important role in staphylococci pathogenesis. Among CoNS, SCCmec has been studied less frequently than Staphylococcus aureus (coagulase-positive staphylococci). A recent study (8) conducted in Malaysia successfully detected SCCmec type I to VIII as well as several new combination patterns in CoNS species, particularly Staphylococcus epidermidis. However, data are still limited, and further research is warranted. This paper provides a review on SCCmec types among CoNS species.

A facile, rapid and sensitive detection of MRSA using a CRISPR-mediated DNA FISH method, antibody-like dCas9/sgRNA complex

Rapid and reliable diagnosis of methicillin-resistant Staphylococcus aureus (MRSA) is crucial for guiding effective patient treatment and preventing the spread of MRSA infections. Nonetheless, further simplification of MRSA detection procedures to shorten detection time and reduce labor relative to that of conventional methods remains a challenge. Here, we have demonstrated a Clustered regularly interspaced palindromic repeats (CRISPR)-mediated DNA-FISH method for the simple, rapid and highly sensitive detection of MRSA; this method uses CRISPR associated protein 9/single-guide RNA (dCas9/sgRNA) complex as a targeting material and SYBR Green I (SG I) as a fluorescent probe. A dCas9/sgRNA-SG I based detection approach has advantages over monoclonal antibody in conventional immunoassay systems due to its ability to interact with the target gene in a sequence-specific manner. The detection limit of MRSA was as low as 10 cfu/ml and was found to be sufficient to effectively detect MRSA. Unlike conventional gene diagnosis methods in which PCR must be accompanied or genes are isolated and analyzed, the target gene can be detected within 30min with high sensitivity without performing a gene separation step by using cell lysates. We showed that the fluorescence signal of the MRSA cell lysate was more than 10-fold higher than that of methicillin-susceptible S. aureus (MSSA). Importantly, the present approach can be applied to any target other than MRSA by simply changing the single-guide RNA (sgRNA) sequence. Because dCas9/sgRNA-SG I based detection approach has proved to be easy, fast, sensitive, and cost-efficient, it can be applied directly at the point of care to detect various pathogens as well as MRSA in this study.

Pathogenic Mechanisms and Host Interactions in Staphylococcus epidermidis Device-Related Infection

Staphylococcus epidermidis is a permanent member of the normal human microbiota, commonly found on skin and mucous membranes. By adhering to tissue surface moieties of the host via specific adhesins, S. epidermidis is capable of establishing a lifelong commensal relationship with humans that begins early in life. In its role as a commensal organism, S. epidermidis is thought to provide benefits to human host, including out-competing more virulent pathogens. However, largely due to its capacity to form biofilm on implanted foreign bodies, S. epidermidis has emerged as an important opportunistic pathogen in patients receiving medical devices. S. epidermidis causes approximately 20% of all orthopedic device-related infections (ODRIs), increasing up to 50% in late-developing infections. Despite this prevalence, it remains underrepresented in the scientific literature, in particular lagging behind the study of the S. aureus. This review aims to provide an overview of the interactions of S. epidermidis with the human host, both as a commensal and as a pathogen. The mechanisms retained by S. epidermidis that enable colonization of human skin as well as invasive infection, will be described, with a particular focus upon biofilm formation. The host immune responses to these infections are also described, including how S. epidermidis seems to trigger low levels of pro-inflammatory cytokines and high levels of interleukin-10, which may contribute to the sub-acute and persistent nature often associated with these infections. The adaptive immune response to S. epidermidis remains poorly described, and represents an area which may provide significant new discoveries in the coming years.

Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

Gram-positive bacteria are a common cause of urinary-tract infection (UTI), particularly among individuals who are elderly, pregnant, or who have other risk factors for UTI. Here we review the epidemiology, virulence mechanisms, and host response to the most frequently isolated Gram-positive uropathogens: Staphylococcus saprophyticus, Enterococcus faecalis, and Streptococcus agalactiae. We also review several emerging, rare, misclassified, and otherwise underreported Gram-positive pathogens of the urinary tract including Aerococcus, Corynebacterium, Actinobaculum, and Gardnerella. The literature strongly suggests that urologic diseases involving Gram-positive bacteria may be easily overlooked due to limited culture-based assays typically utilized for urine in hospital microbiology laboratories. Some UTIs are polymicrobial in nature, often involving one or more Gram-positive bacteria. We herein review the risk factors and recent evidence for mechanisms of bacterial synergy in experimental models of polymicrobial UTI. Recent experimental data has demonstrated that, despite being cleared quickly from the bladder, some Gram-positive bacteria can impact pathogenic outcomes of co-infecting organisms. When taken together, the available evidence argues that Gram-positive bacteria are important uropathogens in their own right, but that some can be easily overlooked because they are missed by routine diagnostic methods. Finally, a growing body of evidence demonstrates that a surprising variety of fastidious Gram-positive bacteria may either reside in or be regularly exposed to the urinary tract and further suggests that their presence is widespread among women, as well as men. Experimental studies in this area are needed; however, there is a growing appreciation that the composition of bacteria found in the bladder could be a potentially important determinant in urologic disease, including susceptibility to UTI.

Distribution of SCCmec Elements and Presence of Panton-Valentine Leukocidin in Methicillin-Resistant Staphylococcusepidermidis Isolated from Clinical Samples in a University Hospital of Isfahan City, Iran

INTRODUCTION

Coagulase Negative Staphylococcus (CoNS) is considered as a major pathogen of nosocomial infections among immunosuppressed patients.

AIM

The aim of this study was to identify the types of Staphylococcal Cassette Chromosome mec (SCCmec) and Panton-Valentine Leukocidin (PVL) gene among clinical Methicillin-Resistant S. epidermidis (MRSE) isolates collected from Isfahan.

MATERIALS AND METHODS

This cross-sectional study was performed from March 2014 to January 2015 at a tertiary care hospital of Isfahan, Iran. Antimicrobial susceptibility tests of S. epidermidis isolates were performed by the disc diffusion method. All the strains were screened for methicillin resistance based on resistance to cefoxitin (30 μg) disc and presence of mecA gene. Determination of SCCmec typing and PVL toxin gene were performed by PCR method. For categorical variables different groups were compared using the Chi-square test or Fisher exact test. A p-value of <0.05 was considered significant for all statistical tests.

RESULTS

The frequency of MRSE was 53.8% according to the presence of mecA gene. The overall resistance rate was high with ciprofloxacin (81.4%). PCR analysis showed that 17% (12/70) of MRSE isolate carried the PVL gene and 43% (30/70) were SCCmec type I; 11.4% (8/70) were type II; and 34.2% (24/70) were type IV, whereas, 11.4% (8/70) of the MRSE isolates could not be typed.

CONCLUSION

SCCmec type I was the major type of SCCmec, which indicates an emergence of this SCCmec type in the studied medical centers. Increased prevalence of SCCmec types in community is cause of an increase in antibiotic resistance among microorganisms.

Galectin-3 Is a Target for Proteases Involved in the Virulence of Staphylococcus aureus

Staphylococcus aureus is a major cause of skin and soft tissue infection. The bacterium expresses four major proteases that are emerging as virulence factors: aureolysin (Aur), V8 protease (SspA), staphopain A (ScpA), and staphopain B (SspB). We hypothesized that human galectin-3, a β-galactoside-binding lectin involved in immune regulation and antimicrobial defense, is a target for these proteases and that proteolysis of galectin-3 is a novel immune evasion mechanism. Indeed, supernatants from laboratory strains and clinical isolates of S. aureus caused galectin-3 degradation. Similar proteolytic capacities were found in Staphylococcus epidermidis isolates but not in Staphylococcus saprophyticus Galectin-3-induced activation of the neutrophil NADPH oxidase was abrogated by bacterium-derived proteolysis of galectin-3, and SspB was identified as the major protease responsible. The impact of galectin-3 and protease expression on S. aureus virulence was studied in a murine skin infection model. In galectin-3^+/+ mice, SspB-expressing S. aureus caused larger lesions and resulted in higher bacterial loads than protease-lacking bacteria. No such difference in bacterial load or lesion size was detected in galectin-3^-/- mice, which overall showed smaller lesion sizes than the galectin-3^+/+ animals. In conclusion, the staphylococcal protease SspB inactivates galectin-3, abrogating its stimulation of oxygen radical production in human neutrophils and increasing tissue damage during skin infection.

Complete Genome Sequence of the Methicillin-Resistant Staphylococcus aureus Colonizing Strain M92

M92 is a methicillin-resistant Staphylococcus aureus (MRSA) colonizing strain belonging to ST239-MRSA-III. It frequently shows local nasal colonization in our hospital staff, but has never been associated with infection. We sequenced the complete genome of M92, in order to compare it to highly virulent MRSA strains to gain insight into MRSA virulence factors.

An Update on Clinical Burden, Diagnostic Tools, and Therapeutic Options of Staphylococcus aureus

Staphylococcus aureus is an important pathogen responsible for a variety of diseases ranging from mild skin and soft tissue infections, food poisoning to highly serious diseases such as osteomyelitis, endocarditis, and toxic shock syndrome. Proper diagnosis of pathogen and virulence factors is important for providing timely intervention in the therapy. Owing to the invasive nature of infections and the limited treatment options due to rampant spread of antibiotic-resistant strains, the trend for development of vaccines and antibody therapy is increasing at rapid rate than development of new antibiotics. In this article, we have discussed elaborately about the host-pathogen interactions, clinical burden due to S aureus infections, status of diagnostic tools, and treatment options in terms of prophylaxis and therapy.

Accessory gene regulator (Agr) functionality in Staphylococcus aureus derived from lower respiratory tract infections

Objective

Characterization of Staphylococcus aureus clinical isolates derived from lower respiratory tract infections (LRTIs), and correlation between the functionality of the accessory gene regulator (Agr) and genotypic and phenotypic characteristics, clinical variables and clinical outcome.

Methods

S aureus isolates derived from LRTIs and control groups (nasal carriage and bacteraemia) were genotyped using StaphyType DNA microarray. Agr activity was evaluated using the CAMP synergistic haemolysis assay and the Vesicle Lysis Test (VLT). Discordant strains were analysed by quantitative reverse-transcriptase real-time PCR (qRT-PCR).

Results

Agr was functional in 79.7% and 84.5% of strains according to the CAMP and VLT assays respectively. Higher concordance with RNAIII expression measured by qRT-PCR was observed with the VLT assay (76.2%) compared with the CAMP assay (23.8%). No statistically significant differences were observed in Agr functionality between the study groups, nor the phenotypical/genotypical bacterial characteristics. No association between increased mortality/respiratory complications and Agr function was observed.

Conclusions

Agr activity was high (82.2%) in isolates from LRTIs suggesting the importance of this global regulator in lower respiratory tract colonisation and infection. However, equally high Agr activity was observed in isolates derived from nasal carriage and bacteraemia, contradictory to previous observations. Agr functionality measured by the VLT assay was superior to CAMP assay.

New strategies for targeting and treatment of multi-drug resistant Staphylococcus aureus

Staphylococcus aureus is a major cause of bacterial infection in humans, and has been notoriously able to acquire resistance to a variety of antibiotics. An example is methicillin-resistant S. aureus (MRSA), which despite having been initially associated with clinical settings, now is one of the key causative agents of community-acquired infections. Antibiotic resistance in S. aureus involves mechanisms ranging from drug efflux to increased expression or mutation of target proteins, and this has required innovative approaches to develop novel treatment methodologies. This review provides an overview of the major mechanisms of antibiotic resistance developed by S. aureus, and describes the emerging alternatives being sought to circumvent infection and proliferation, including new generations of classic antibiotics, synergistic approaches, antibodies, and targeting of virulence factors.

A Standardized Regimen for the Treatment of Acute Postoperative Infections and Acute Hematogenous Infections Associated With Hip and Knee Arthroplasties

BACKGROUND

Papers concerning the treatment of periprosthetic infections and acute hematogenous infections often concern inhomogeneous treatment concepts or low numbers of patients; this results in inconsistent rates of treatment success.

METHODS

Thirty-nine patients with early periprosthetic infections and 28 patients with acute hematogenous infections were treated with a homogeneous concept and followed with a mean period of 41.8 (24-132) months in order to investigate the success rate and influencing factors. All patients were treated with open surgical debridement, a revision of all removable components and irrigation with an antiseptic solution (octinedine). All patients received a systemic vancomycin/rifampicin antibiotic therapy until the microorganism causing the infection could be identified; a specific antibiotic therapy then followed until the end of the sixth week.

RESULTS

This unified treatment regimen resulted in an overall success rate of 71.6%, an 82.1% success for early infections and 57.1% for acute hematogenous infections. Variables that influenced the recurrence of an infection were the timespan between revision and first appearance of symptoms (<2 days), the number of previous operations, the American Society of Anesthesiologists classification, and nicotine abuse.

CONCLUSION

It appears that, in cases of early postoperative infection, a reproducibly high rate of success in retaining an implant can be achieved with this specific therapy regime if surgical intervention can be carried out within 2 days of first symptoms.

Reactions with Antisera and Pathological Effects of Staphylococcus aureus Gamma-Toxin in the Cornea

PURPOSE

This study analyzed the toxicity of purified gamma-toxin from Staphylococcus aureus and the protectiveness of antisera to gamma-toxin in the rabbit cornea.

MATERIALS AND METHODS

Gamma-toxin was purified from cultures of alpha-toxin deficient S. aureus strain Newman Δhla. Antisera to native gamma-toxin (Hlg) were produced in rabbits. These antisera and a commercial polyclonal antibody to recombinant HlgB (rHlgB) were analyzed for specificity and toxin neutralization. Heat-inactivated gamma-toxin, active gamma-toxin either alone or with antisera or with commercial antibody to rHlgB, was injected into the rabbit cornea to observe the pathological effects using slit lamp examination scoring (SLE) and histological analyses.

RESULTS

Eyes with intrastromal injection of gamma-toxin developed SLE scores that were significantly higher than eyes injected with heat-inactivated gamma-toxin (p ≤ 0.003). Slit lamp and histological examination of eyes revealed that gamma-toxin injected into the cornea mediated conjunctival injection and chemosis, iritis, fibrin accumulation in the anterior chamber, and polymorphonuclear neutrophil infiltration of the cornea and iris. Also, eyes injected with gamma-toxin plus antisera to native whole gamma-toxin or HlgB, but not with commercial antibody to rHlgB, yielded significantly lower SLE scores than eyes injected with gamma-toxin alone (p ≤ 0.003).

CONCLUSIONS

This study illustrates that S. aureus gamma-toxin is capable of causing significant corneal pathology. Furthermore, the use of polyclonal antisera specific for native gamma-toxin was found to inhibit the damaging effects of the toxin in the rabbit cornea.

Killing of Staphylococcus aureus and Salmonella enteritidis and neutralization of lipopolysaccharide by 17-residue bovine lactoferricins: improved activity of Trp/Ala-containing molecules

Bovine lactoferricin (LfcinB) has potent antibacterial, antifungal and antiparasitic activities but is also hemolytic. Our objective was to identify LfcinB17-31 derivatives with reduced hemolysis and improved antimicrobial activity via substituting Cys3, Arg4, Gln7, Met10, and Gly14 with more hydrophobic residues. Two peptides, Lfcin4 and Lfcin5, showed higher activity against Staphylococcus aureus and Salmonella enteritidis and lower hemolytic activity than the parent peptide LfcinB17-31. These peptides permeabilized the outer and inner membranes of S. enteritidis; however, Lfcin5 did not permeabilize the inner membrane of S. aureus. Gel retardation and circular dichroism spectra showed that Lfcin4 and Lfcin5 bound to bacterial genomic DNA. Lfcin4 inhibited DNA, RNA and protein synthesis. Both peptides induced the peeling of membranes and the lysis of S. enteritidis. At doses of 10 and 15 mg/kg, Lfcin4 and Lfcin5 reduced the bacterial counts in infected thigh muscles by 0.03‒0.10 and 0.05‒0.63 log₁₀ CFU/g of tissue, respectively, within 10 h. Lfcin4 and Lfcin5 enhanced the survival rate of endotoxemic mice; reduced serum IL-6, IL-1β and TNF-α levels; and protected mice from lipopolysaccharide-induced lung injury. These data suggest that Lfcin4 and Lfcin5 may be antimicrobial and anti-endotoxin peptides that could serve as the basis for the development of dual-function agents.

Using Quantitative Spectrometry to Understand the Influence of Genetics and Nutritional Perturbations On the Virulence Potential of Staphylococcus aureus

Staphylococcus aureus (Sa) is the leading cause of a variety of bacterial infections ranging from superficial skin infections to invasive and life threatening diseases such as septic bacteremia, necrotizing pneumonia, and endocarditis. The success of Sa as a human pathogen is contributed to its ability to adapt to different environments by changing expression, production, or secretion of virulence factors. Although Sa immune evasion is well-studied, the regulation of virulence factors under different nutrient and growth conditions is still not well understood. Here, we used label-free quantitative mass spectrometry to quantify and compare the Sa exoproteins (i.e. exoproteomes) of master regulator mutants or established reference strains. Different environmental conditions were addressed by growing the bacteria in rich or minimal media at different phases of growth. We observed clear differences in the composition of the exoproteomes depending on the genetic background or growth conditions. The relative abundance of cytotoxins determined in our study correlated well with differences in cytotoxicity measured by lysis of human neutrophils. Our findings demonstrate that label-free quantitative mass spectrometry is a versatile tool for predicting the virulence of bacterial strains and highlights the importance of the experimental design for in vitro studies. Furthermore, the results indicate that label-free proteomics can be used to cluster isolates into groups with similar virulence properties, highlighting the power of label-free quantitative mass spectrometry to distinguish Sa strains.

Similar Clinical Severity and Outcomes for Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus Pediatric Musculoskeletal Infections

BACKGROUND

Prior studies of pediatric musculoskeletal infection have suggested that methicillin-resistant Staphylococcus aureus (MRSA) infections result in worse outcomes compared with infections with methicillin-susceptible S aureus (MSSA) strains. Based on these results, clinical prediction algorithms have been developed to differentiate between MRSA and MSSA early in a patient's clinical course. This study compares hospital outcomes for pediatric patients with MRSA and MSSA musculoskeletal infection presenting to the emergency department at a large tertiary care children's hospital.

METHODS

A retrospective study identified pediatric patients with S aureus musculoskeletal infection over a 5-year period (2008-2013) by sequential review of all pediatric orthopedic consults. Relevant demographic information, laboratory values, and clinical outcomes were obtained from the electronic medical record.

RESULTS

Of the 91 identified cases of S aureus pediatric musculoskeletal infection, there were 49 cases of MRSA infection (53%) and 42 cases of MSSA infection (47%). There were no significant differences between MRSA and MSSA infections in median hospital length of stay (4.8 vs 5.7 days, P = .50), febrile days (0.0 vs 1.5 days, P = .10), and antibiotic duration (28 vs 34 days, P = .18). Methicillin-resistant S aureus infections were more likely to require operative intervention than MSSA infection (85% vs 62%, P = .15). A logistic regression model based on C-reactive protein, temperature, white blood cell count, pulse, and respiratory rate at presentation demonstrated poor ability to differentiate between MRSA and MSSA infection.

CONCLUSIONS

The results demonstrated no significant differences between MSSA and MRSA musculoskeletal infections for most hospital outcomes measured. However, MRSA infections required more operative interventions than MSSA infections. In addition, a predictive model based on severity markers obtained at presentation was unable to effectively differentiate between MRSA and MSSA infection. The clinical utility and capacity for early differentiation of MRSA and MSSA depends on virulence patterns that may vary temporally and geographically.

Epidemiology, treatment, and economics of patients presenting to the emergency department for skin and soft tissue infections

OBJECTIVES

Skin and soft tissue infections (SSTIs) are among the most common bacterial diseases and represent a significant disease burden. The purpose of this study was to describe the real-world management of patients with SSTIs presenting to the emergency department (ED).

METHODS

This is a retrospective cohort study. Adult patients identified with a primary diagnosis of SSTI determined by ICD-9 codes were assessed from index presentation for up to 30 days. Records were reviewed 30 days prior to inclusion to ensure index hospitalization was captured. For recurrent visits, a similar strategy was implemented 30 days afterward.

RESULTS

Of 446 encounters screened, 357 were included; 106 (29.7%) were admitted to the hospital and 251 (70.3%) were treated outpatient. Of patients with a Charlson Comorbidity Index (CCI) score two or greater, 60.9% were treated as inpatients, whereas admission rates were 30.1% and 14.1% for patients with a CCI score of one and zero, respectively. Inpatients had an average length of stay (LOS) of 7.3 ± 7.1 days. No difference was detected in overall re-presentation to the facility 22.6% and 28.3% (p > 0.05) or in SSTI related re-presentation 10.4% and 15.1% (p > 0.05) between inpatient and outpatients. The most common gram-positive organisms identified on wound/abscess culture were MSSA (37.1% inpatients) and MRSA (66.7% outpatients). Mean total cost of care was $13,313 for inpatients and $413 for outpatients.

CONCLUSION

This analysis identifies opportunities to improve processes of care for SSTIs with the aim of decreasing LOS, reducing readmissions, and ultimately decreasing burden on the healthcare system.

Linezolid: a promising option in the treatment of Gram-positives

Linezolid, an oxazolidinone antimicrobial agent that acts by inhibiting protein synthesis in a unique fashion, is used in the treatment of community-acquired pneumonia, skin and soft-tissue infections and other infections caused by Gram-positive bacteria including VRE and methicillin-resistant staphylococci. Currently, linezolid resistance among these pathogens remains low, commonly <1.0%, although the prevalence of antibiotic resistance is increasing in many countries. Therefore, the development of resistance by clinical isolates should prompt increased attention of clinical laboratories to routinely perform linezolid susceptibility testing for this important agent and should be taken into account when considering its therapeutic use. Considering the importance of linezolid in the treatment of infections caused by Gram-positive bacteria, this review was undertaken to optimize the clinical use of this antibiotic.

Structure and Mechanism of Staphylococcus aureus TarS, the Wall Teichoic Acid β-glycosyltransferase Involved in Methicillin Resistance

In recent years, there has been a growing interest in teichoic acids as targets for antibiotic drug design against major clinical pathogens such as Staphylococcus aureus, reflecting the disquieting increase in antibiotic resistance and the historical success of bacterial cell wall components as drug targets. It is now becoming clear that β-O-GlcNAcylation of S. aureus wall teichoic acids plays a major role in both pathogenicity and antibiotic resistance. Here we present the first structure of S. aureus TarS, the enzyme responsible for polyribitol phosphate β-O-GlcNAcylation. Using a divide and conquer strategy, we obtained crystal structures of various TarS constructs, mapping high resolution overlapping N-terminal and C-terminal structures onto a lower resolution full-length structure that resulted in a high resolution view of the entire enzyme. Using the N-terminal structure that encapsulates the catalytic domain, we furthermore captured several snapshots of TarS, including the native structure, the UDP-GlcNAc donor complex, and the UDP product complex. These structures along with structure-guided mutants allowed us to elucidate various catalytic features and identify key active site residues and catalytic loop rearrangements that provide a valuable platform for anti-MRSA drug design. We furthermore observed for the first time the presence of a trimerization domain composed of stacked carbohydrate binding modules, commonly observed in starch active enzymes, but adapted here for a poly sugar-phosphate glycosyltransferase.

Historically, β-lactam class antibiotics such as methicillin have been very successful in the treatment of bacterial infections, effectively destroying bacteria by rupturing their cell walls while posing little harm to the human organism. In recent years, however, the alarming emergence of Methicillin Resistant S. aureus or MRSA has resulted in a world-wide health crisis, calling on new strategies to combat pathogenesis and antibiotic resistance. As such, understanding the pathways and players that orchestrate resistance is important for overcoming these mechanisms and restoring our powerful β-lactam antibiotic arsenal. In this article we describe the crystal structure of TarS, an enzyme responsible for the glycosylation of wall teichoic acid polymers of the S. aureus cell wall, a process that has been shown to be specifically responsible for methicillin resistance in MRSA. TarS is therefore a promising drug target whose inhibition in combinational therapies would result in MRSA re-sensitization to β-lactam antibiotics. Here we present the first structure of TarS together with several snap-shots of its substrate/product complexes, and elucidate important catalytic features that are valuable for rational drug design efforts to combat resistance in MRSA.

Coagulase negative staphylococcal sepsis in neonates: do we need to adapt vancomycin dose or target?

Background

Despite differences in types of infection and causative organisms, pharmacokinetic-pharmacodynamic (PKPD) targets of vancomycin therapy derived from adult studies are suggested for neonates. We aimed to identify doses needed for the attainment of AUC/MIC > 400 and AUC/MIC > 300 in neonates with sepsis and correlate these targets with recommended doses and treatment outcome.

Methods

Neonates who had Vancomycin therapeutic drug monitoring (TDM) performed between January 1, 2010 and December 31, 2012 were studied. Clinical characteristics, episodes of Gram-positive sepsis with outcomes and all neonatal blood culture isolates in hospital were collected from medical records. To estimate probability of target attainment of AUC/MIC >400 and AUC/MIC >300 a 1000-subject Monte Carlo simulation was performed by calculating AUC using Anderson’s (Anderson et al. 2006) and TDM trough concentrations (C_trough) based population PK models.

Results

Final dataset included 76 patients; 57 with confirmed Gram-positive sepsis. TDM was taken after the 1^st to 44^th dose. 84.1% of C_trough were within the range 5–15 mg/L. Currently recommended doses achieved probability of the targets (PTA) of AUC/MIC >400 and AUC/MIC >300 in less than 25% and 40% of cases, respectively. Doses required for 80% PTA of AUC/MIC > 400 for MIC ≥2 mg/L resulted in C_trough values ≥14 mg/L. Mean AUC/MIC values were similar in treatment failure and success groups.

Conclusion

With currently recommended vancomycin dosing the therapeutic target of AUC/MIC > 400 is achieved only by 25% of neonates. Appropriate PKPD targets and respective dosing regimens need to be defined in prospective clinical studies in this population.

A Phase III, randomized, controlled, non-inferiority trial of ceftaroline fosamil 600 mg every 8 h versus vancomycin plus aztreonam in patients with complicated skin and soft tissue infection with systemic inflammatory response or underlying comorbidities

OBJECTIVES

Increasing the ceftaroline fosamil dose beyond 600 mg every 12 h may provide additional benefit for patients with complicated skin and soft tissue infections (cSSTIs) with severe inflammation and/or reduced pathogen susceptibility. A Phase III multicentre, randomized trial evaluated the safety and efficacy of ceftaroline fosamil 600 mg every 8 h in this setting.

METHODS

Adult patients with cSSTI and systemic inflammation or comorbidities were randomized 2:1 to intravenous ceftaroline fosamil (600 mg every 8 h) or vancomycin (15 mg/kg every 12 h) plus aztreonam (1 g every 8 h) for 5-14 days. Clinical cure was assessed at the test of cure (TOC) visit (8-15 days after the final dose) in the modified ITT (MITT) and clinically evaluable (CE) populations. Non-inferiority was defined as a lower limit of the 95% CI around the treatment difference greater than -10%. An MRSA-focused expansion period was initiated after completion of the main study. Clinicaltrials.gov registration numbers NCT01499277 and NCT02202135.

RESULTS

Clinical cure rates at TOC demonstrated non-inferiority of ceftaroline fosamil 600 mg every 8 h versus vancomycin plus aztreonam in the MITT and CE populations: 396/506 (78.3%) versus 202/255 (79.2%) patients (difference -1.0%, 95% CI -6.9, 5.4) and 342/395 (86.6%) versus 180/211 (85.3%) patients (difference 1.3%, 95% CI -4.3, 7.5), respectively. In the expansion period, 3/4 (75%) patients treated with ceftaroline fosamil were cured at TOC. The frequency of adverse events was similar between groups.

CONCLUSIONS

Ceftaroline fosamil 600 mg every 8 h was effective for cSSTI patients with evidence of systemic inflammation and/or comorbidities. No new safety signals were identified.

Chronological changes in microbial profiles in external and middle ear diseases: a 20-year study in Korea

Microbial infection is one of the most significant causes of ear diseases, but microbial profiles are very diverse according to the diseases and change over time. The purpose of the study was to clarify differences and chronological changes in causative pathogens among infectious ear diseases over the last 20 years, and to identify antibiotic resistance. In total, 1191 isolates were included from patients diagnosed with chronic otitis media without cholesteatoma (COM), cholesteatomatous otitis media (Chole), middle ear effusion (MEE), including acute otitis media and otitis media with effusion, and external otitis (EO). Data were collected periodically for the years 1995, 2000, 2004, 2009, and 2013. Culture results and antibiotic resistance were assessed. The most common microorganism identified was S. aureus. The microbial profiles differed significant among the COM, Chole, and MEE groups (p < 0.001). In contrast, there was no distinct difference between COM and EO (p = 0.332). COM, Chole, and MEE also showed significant chronological changes in microbial profiles over time. The frequency of CNS increased markedly in COM and Chole (p = 0.029 and 0.028, respectively); however, S. pneumoniae infection decreased significantly in MEE (p = 0.016). Methicillin-resistant S. aureus (MRSA) demonstrated a constant trend (p = 0.564), whereas ciprofloxacin-resistant P. aeruginosa increased over time (p < 0.001). Microbial profiles have changed over a 20-year period. Increases in the frequency of coagulase-negative Staphylococcus (CNS) and bacterial resistance to ciprofloxacin, used widely in treating ear infections, are noteworthy.

Antisense locked nucleic acids targeting agrA inhibit quorum sensing and pathogenesis of community-associated methicillin-resistant Staphylococcus aureus

AIM

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is commonly associated with nonnosocomial skin and soft tissue infections due to its virulence, which is mainly controlled by the accessory gene regulator (agr) quorum sensing (QS) system. In this study (KFF)₃ K peptide-conjugated locked nucleic acids (PLNAs) targeting agrA mRNA were developed to inhibit agr activity and arrest the pathogenicity of CA-MRSA.

METHODS AND RESULTS

Two PLNAs were designed, and synthesized, after predicting the secondary structure of agrA mRNA. The influence on bacterial growth was tested using a growth curve assay. RT-qPCR, haemolysis assay, lactate dehydrogenase release assay and chemotaxis assay were used to evaluate the effects of the PLNAs on inhibiting agr QS. A mouse skin infection model was employed to test the protective effect of the PLNAs in vivo. None of the PLNAs were found to be bacteriostatic or bactericidal in vitro. However, one PLNA, PLNA34, showed strong ability to suppress expression of agrA and the effector molecule RNAIII in USA300 LAC strain. Furthermore, PLNA34 inhibited the expression of virulence genes that are upregulated by agr, including hla, psmα, psmβ and pvl. The haemolytic activity of the supernatants from PLNA34-treated bacteria was also dramatically reduced, as well as the capacity to lyse and recruit neutrophils. Moreover, PLNA34 showed high levels of protection in the CA-MRSA mouse skin infection model.

CONCLUSIONS

The anti-agrA PLNA34 can effectively inhibit the agr QS and suppress CA-MRSA pathogenicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

agrA is a promising target for the development of antisense oligonucleotides to block agr QS.

Pathogenic features of clinically significant coagulase-negative staphylococci in hospital and community infections in Benin

In West Africa, very little consideration has been given to coagulase negative Staphylococci (CNS). Herein, we describe the features contributing to the pathogenicity of 99 clinically-significant independent CNS isolates associated with infections encountered at the National Teaching Hospital Center of Cotonou (Benin). The pathogenic potentials of nosocomial strains were compared with community strains. S. haemolyticus (44%), S. epidermidis (22%) and S. hominis (7%) were the most frequently isolated while bacteremia (66.7%) and urinary tract infections (24.2%) were the most commonly encountered infections. Most strains were resistant to multiple antibiotics, including penicillin (92%), fosfomycin (81%), methicillin (74%) and trimethoprim-sulfamethoxazole (72%). The most frequently isolated species were also the most frequently resistant to methicillin: S. hominis (100%), S. haemolyticus (93%) and S. epidermidis (67%). Screening of toxic functions or toxin presence revealed hemolytic potential in 25% of strains in over 50% of human erythrocytes in 1h. Twenty-six percent of strains exhibited protease activity with low (5%), moderate (10%) and high activity (11%), while 25% of strains displayed esterase activity. Three percent of strain supernatants were able to lyse 100% of human polymorphonuclear cells after 30min. Polymerase chain reaction and latex agglutination methods revealed staphylococcal enterotoxin C gene expression in 9% of S. epidermidis. A majority of hospital-associated CNS strains (68%) had at least one important virulence feature, compared with only 32% for community-acquired strains. The present investigation confirms that these microorganisms can be virulent, at least in some individual cases, possibly through genetic transfer from S. aureus.

Epidemiology of patients with MSSA versus MRSA infections of orthopedic implants: Retrospective study of 115 patients

Factors that predict the occurrence of a surgical site infection due to methicillin-resistant Staphylococcus aureus (MRSA) are not well known; however this information could be used to modify the recommended antimicrobial prophylaxis. We carried out a retrospective study of S. aureus infections on orthopedic implants to determine: (1) whether epidemiological factors can be identified that predict a MRSA infection, (2) the impact of these factors as evidenced by the odds ratio (OR).

HYPOTHESIS

Risk factors for a MRSA infection can be identified from a cohort of patients with S. aureus infections.

MATERIALS AND METHODS

We identified 244 patients who experienced a S. aureus surgical site infection (SSI) in 2011-2012 documented by intraoperative sample collection. Of these 244 patients, those who had a previous SSI (n=44), those with a SSI but no orthopedic implant (n=80) or those who had the infection more than 1-year after the initial surgery (n=5) were excluded. This resulted in 115 patients (53 arthroplasty, 62 bone fixation) being analyzed for this study. There were 24 MRSA infections and 91 MSSA infections. The following factors were evaluated in bivariate and multifactorial analysis: age, sex, type of device (prosthesis/bone fixation), predisposition (diabetes, obesity, kidney failure), and environmental factors (hospitalization in intensive care unit within past 5 years, nursing home stay).

RESULTS

Two factors were correlated with the occurrence of MRSA infections. (1) Nursing home patients had a higher rate of MRSA infections (67% vs. 18%, P=0.017) with an OR of 8.42 (95% CI: 1.06-66.43). (2) Patients who had undergone bone fixation had a lower rate of MRSA infections than patients who had undergone arthroplasty (13% vs. 30%, P=0.023), OR 0.11 (95% CI: 0.02-0.56). Although the sample size was too small to be statistically significant, all of the patients with kidney failure (n=4) had a MRSA infection.

DISCUSSION

Since these MRSA infection risk factors are easy to identify, the antimicrobial prophylaxis could be adapted in these specific patient groups.

The single-species metagenome: subtyping Staphylococcus aureus core genome sequences from shotgun metagenomic data

In this study we developed a genome-based method for detecting Staphylococcus aureus subtypes from metagenome shotgun sequence data. We used a binomial mixture model and the coverage counts at >100,000 known S. aureus SNP (single nucleotide polymorphism) sites derived from prior comparative genomic analysis to estimate the proportion of 40 subtypes in metagenome samples. We were able to obtain >87% sensitivity and >94% specificity at 0.025X coverage for S. aureus. We found that 321 and 149 metagenome samples from the Human Microbiome Project and metaSUB analysis of the New York City subway, respectively, contained S. aureus at genome coverage >0.025. In both projects, CC8 and CC30 were the most common S. aureus clonal complexes encountered. We found evidence that the subtype composition at different body sites of the same individual were more similar than random sampling and more limited evidence that certain body sites were enriched for particular subtypes. One surprising finding was the apparent high frequency of CC398, a lineage often associated with livestock, in samples from the tongue dorsum. Epidemiologic analysis of the HMP subject population suggested that high BMI (body mass index) and health insurance are possibly associated with S. aureus carriage but there was limited power to identify factors linked to carriage of even the most common subtype. In the NYC subway data, we found a small signal of geographic distance affecting subtype clustering but other unknown factors influence taxonomic distribution of the species around the city.

Molecular characterization of Staphylococcus aureus isolates from various healthcare institutions in Nairobi, Kenya: a cross sectional study

Background

Staphylococcus aureus (S. aureus) has established itself over the years as a major cause of morbidity and mortality both within the community and in healthcare settings. Methicillin resistant S. aureus (MRSA) in particular has been a major cause of nosocomial infections resulting in significant increase in healthcare costs. In Africa, the MRSA prevalence has been shown to vary across different countries. In order to better understand the epidemiology of MRSA in a setting, it is important to define its population structure using molecular tools as different clones have been found to predominate in certain geographical locations.

Methods

We carried out PFGE, MLST, SCCmec and spa typing of selected S. aureus isolates from a private and public referral hospital in Nairobi, Kenya.

Results

A total of 93 S. aureus isolates were grouped into 19 PFGE clonal complexes (A–S) and 12 singletons. From these, 55 (32 MRSA and 23 MSSA) representative isolates from each PFGE clonal complex and all singletons were spa typed. There were 18 different MRSA spa types and 22 MSSA spa types. The predominant MRSA spa type was t037 comprising 40.6 % (13/32) of all MRSA. In contrast, the MSSA were quite heterogeneous, only 2 out of 23 MSSA shared the same spa type. Two new MRSA spa types (t13149 and t13150) and 3 new MSSA spa types (t13182, t13193 and t13194) were identified. The predominant clonal complex was CC 5 which included multi-locus sequence types 1, 8 and 241.

Conclusion

In contrast to previous studies published from Kenya, there’s marked genetic diversity amongst clinical MRSA isolates in Nairobi including the presence of well-known epidemic MRSA clones. Given that these clones are resident within our referral hospitals, adherence to strict infection control measures needs to be ensured to reduce morbidity and mortality associated with hospital acquired MRSA infections.

Bacteremia in nonneutropenic pediatric oncology patients with central venous catheters in the ED

OBJECTIVE

To examine clinical characteristics associated with bacteremia in febrile nonneutropenic pediatric oncology patients with central venous catheters (CVCs) in the emergency department (ED).

BACKGROUND

Fever is the primary reason pediatric oncology patients present to the ED. The literature states that 0.9% to 39% of febrile nonneutropenic oncology patients are bacteremic, yet few studies have investigated infectious risk factors in this population.

METHODS

This was a retrospective cohort study in a pediatric ED, reviewing medical records from 2002 to 2014. Inclusion criteria were patients with cancer, temperature at least 38°C, presence of a CVC, absolute neutrophil count greater than 500 cells/μL, and age less than 22 years. Exclusion criteria were repeat ED visits within 72 hours, bloodwork results not reported by the laboratory, and patients without oncologic history documented at the study hospital. The primary outcome measure is a positive blood culture (+BC). Other variables include age, sex, CVC type, cancer diagnosis, absolute neutrophil count, vital signs, upper respiratory infection (URI) symptoms, and amount of intravenous (IV) normal saline (NS) administered in the ED. Data were analyzed using descriptive statistics and a multiple logistic regression model.

RESULTS

A total of 1322 ED visits were sampled, with 534 enrolled, and 39 visits had +BC (7.3%). Variables associated with an increased risk of +BC included the following: absence of URI symptoms (odds ratio [OR], 2.30; 95% CI, 1.13-4.69), neuroblastoma (OR, 3.65; 95% CI, 1.47-9.09), "other" cancer diagnosis (OR, 4.56; 95% CI, 1.93-10.76), tunneled externalized CVC (OR, 5.04; 95% CI, 2.25-11.28), and receiving at least 20 mL/kg IV NS (OR, 2.34; 95% CI, 1.2-4.55). The results of a multiple logistic regression model also showed these variables to be associated with +BC.

CONCLUSION

The absence of URI symptoms, presence of an externalized CVC, neuroblastoma or other cancer diagnosis, and receiving at least 20 mL/kg IV NS in the ED are associated with increased risk of bacteremia in nonneutropenic pediatric oncology patients with a CVC.

SCCmec-associated psm-mec mRNA promotes Staphylococcus epidermidis biofilm formation

Biofilm formation is considered the major pathogenic mechanism of Staphylococcus epidermidis-associated nosocomial infections. Reports have shown that SCCmec-associated psm-mec regulated methicillin-resistant Staphylococcus aureus virulence and biofilm formation. However, the role of psm-mec in S. epidermidis remains unclear. To this purpose, we analysed 165 clinical isolates of S. epidermidis to study the distribution, mutation and expression of psm-mec and the relationship between this gene and biofilm formation. Next, we constructed three psm-mec deletion mutants, one psm-mec transgene expression strain (p221) and two psm-mec point mutant strains (pM, pAG) to explore its effects on S. epidermidis biofilm formation. Then, the amount of biofilm formation, extracellular DNA (eDNA) and Triton X-100-induced autolysis of the constructed strains was measured. Results of psm-mec deletion and transgene expression showed that the gene regulated S. epidermidis biofilm formation. Compared with the control strains, the ability to form biofilm, Triton X-100-induced autolysis and the amount of eDNA increased in the p221 strain and the two psm-mec mutants pM and pAG expressed psm-mec mRNA without its protein, whereas no differences were observed among the three constructed strains, illustrating that psm-mec mRNA promoted S. epidermidis biofilm formation through up-regulation of bacterial autolysis and the release of eDNA. Our results reveal that acquisition of psm-mec promotes S. epidermidis biofilm formation.

Prevalence and antimicrobial susceptibility pattern of methicillin resistant Staphylococcus aureus isolated from clinical samples at Yekatit 12 Hospital Medical College, Addis Ababa, Ethiopia

BACKGROUND

Staphylococcus aureus particularly MRSA strains are one of the major causes of community and hospital acquired bacterial infections. They are also becoming increasingly multi-drug resistant and have recently developed resistance to vancomycin, which has been used successfully to treat MRSA for many years. In-vitro determination of drug resistance patterns of S. aureus is critical for the selection of effective drugs for the treatment of staphylococci infections. The main aim of this study was to determine the prevalence of methicillin resistant S. aureus strains from different clinical specimens from patients referred for routine culture and sensitivity testing.

METHOD

A cross sectional study was conducted among 1360 participants at Yekatit 12 Hospital Medical College in Ethiopia from September 2013 to April 2014. Clinical samples from various anatomical sites of study participants were cultured on blood agar and mannitol salt agar and identified to be S. aureus by using catalase, coagulase and DNAse tests. S. aureus isolates then were screened for MRSA using 30 μg cefoxitin disc and other 11 antimicrobial drugs by disc diffusion procedure, and agar dilution and E tests for vancomycin. All S. aureus isolates examined for beta-lactamase production by employing nitrocefin. Data were analyzed using SPSS version 20 software and logistic regressions were applied to assess any association between dependent and independent variables.

RESULTS

Of 1360 clinical specimens analyzed S. aureus was recovered from (194, 14.3 %). Rate of isolation of S. aureus with regard to clinical specimens was the highest in pus (118, 55.4 %).No S. aureus was isolated from CSF and urethral discharge. Out of 194 S. aureus isolates, (34, 17.5 %) were found out to be MRSA and the remaining (160, 82.5 %) were MSSA. Ninety eight (50.5 %) S. aureus were multi drug resistant and the highest isolates were resistant to penicillin (187, 96.4 %) and least resistant for clindamycin (23, 11.9 %) and vancomycin (10, 5.1 %). MRSA strains were 100 % resistant to penicillin G, erythromycin, trimethoprim-sulfamethoxazole and least resistant to vancomycin (10, 29.4 %). Out of 194 S. aureus isolates (153, 79.0 %) were beta-lactamase producers.

CONCLUSION

In this study S. aureus isolates exhibited very high degree of resistance to different antibiotics. The isolates were also multidrug resistant to several combinations of the tested antibiotics. The emergence of vancomycin resistant S. aureus highlights the value of prudent prescribing of antibiotics and avoiding their irrational use.

Ventilator-Associated Pneumonia Patients who Do Not Reduce Bacteria from the Lungs have a Worse Prognosis

The authors determined the significance of serial semi-quantitative bronchoalveolar lavage (BAL) culture results in patients undergoing therapy for ventilator-associated pneumonia. A total of 32 patients underwent at least 2 nonbronchoscopic BAL studies. Fourteen patients had methicillin-resistant Staphylococcus aureus(MRSA). Of these, 11 had more than 100 colony-forming units (cfu) of MRSA/mL of BAL from the follow-up BAL. Eighteen patients had an organism other than MRSA, and 7 of these patients had > 100 cfu of bacteria/mL of BAL from the follow-up BAL. Of the 18 patients with > 100 cfu of bacteria/mL of BAL at follow-up, 14 (79%) died, whereas only 5 of 14 (36%) patients who cleared their bacteria at follow-up died within 28 days. The inability to reduce the bacterial burden from the lower respiratory tract within the first few days of therapy for ventilator-associated pneumonia was associated with increased mortality.

Molecular Characteristics of Methicillin-Resistant Staphylococcus epidermidis on the Abdominal Skin of Females before Laparotomy

Staphylococcus epidermidis, especially methicillin-resistant strains, may be the source of surgical site infections and may be a reservoir of staphylococcal cassette chromosome mec (SCCmec) for S. aureus. The aim of this study was to investigate the prevalence of methicillin-resistant S. epidermidis (MRSE) on the abdominal skin of females before laparotomy and determine the molecular characteristics and antimicrobial susceptibility patterns of these isolates. MRSE was found in 54 of 157 isolates based on mecA gene detection, and there was no difference in icaA gene carriage rate between MRSE and methicillin-susceptible S. epidermidis (MSSE) isolates. Antimicrobial susceptibility profiles were determined by broth microdilution antimicrobial susceptibility testing according to the latest CLSI manuals. All MRSE isolates had unfavorable antimicrobial susceptibility patterns. Twenty-three MRSE strains (42.6%) were multi-drug resistant. SCCmec typing and pulsed field gel electrophoresis (PFGE) typing was performed. Thirty-nine (72.2%) had a single SCCmec type, whereas 1.9% had two types. Fourteen strains (25.9%) were non-typeable (NT). The most frequent MRSE genotype was SCCmec type IVa. High diversity with PFGE patterns was obtained for MRSE, and there were no isolates exhibiting identical pulsotype. The results confirm that methicillin-resistant strains are frequently present among S. epidermidis on the abdominal skin of females before laparotomy. Moreover, resistance profiles seem to have no association with the SCCmec types or PFGE types for most common antibiotics.

Oxacillin-Resistant and Multidrug-Resistant Staphylococcus aureus in Lima, Peru

In a hospital in Lima, Peru, a review of 103 Staphylococcus aureus infections was conducted during 2002. The prevalence of oxacillin-resistant S. aureus strains was 68%; 25% of strains were resistant to multiple drugs. Previous use of antibiotics and undergoing a surgical procedure during the current hospital stay were associated with the presence of an oxacillin-resistant S. aureus strain.

Antimicrobial Use Control Measures to Prevent and Control Antimicrobial Resistance in US Hospitals

Objective.

Clinical practice guidelines and recommended practices to control use of antibiotics have been published, but the effect of these practices on antimicrobial resistance (AMR) rates in hospitals is unknown. The objective of this study was to examine relationships between antimicrobial use control strategies and AMR rates in a national sample of US hospitals.

Design.

Cross-sectional, stratified study of a nationally representative sample of US hospitals.

Methods.

A survey instrument was sent to the person responsible for infection control at a sample of 670 US hospitals. The outcome was current prevalences of 4 epidemiologically important, drug-resistant pathogens, considered concurrently: methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, ceftazidime-resistant Klebsiella species, and quinolone (ciprofloxacin)-resistant Escherichia coli Five independent variables regarding hospital practices were selected from the survey: the extent to which hospitals (1) implement practices recommended in clinical practice guidelines and ensure best practices for antimicrobial use, (2) disseminate information on clinical practice guidelines for antimicrobial use, (3) use antimicrobial-related information technology, (4) use decision support tools, and (5) communicate to prescribers about antimicrobial use. Control variables included the hospitals' number of beds, teaching status, Veterans Affairs status, geographic region, and number of long-term care beds; and the presence of an intensive care unit, a burn unit, or transplant services. A generalized estimating equation modeled all resistance rates simultaneously to identify overall predictors of AMR levels at the facility.

Results.

Completed survey instruments were returned by 448 hospitals (67%). Four antimicrobial control measures were associated with higher prevalence of AMR. Implementation of recommended practices for antimicrobial use (P< .01) and optimization of the duration of empirical antibiotic prophylaxis (P<.01) were associated with a lower prevalence of AMR. Use of restrictive formularies (P = .05) and dissemination of clinical practice guideline information (P<.01) were associated with higher prevalence of AMR. Number of beds and Veterans Affairs status were also associated with higher AMR rates overall.

Conclusions.

Implementation of guideline-recommended practices to control antimicrobial use and optimize the duration of empirical therapy appears to help control AMR rates in US hospitals. A longitudinal study would confirm the results of this cross-sectional study. These results highlight the need for systems interventions and reengineering to ensure more-consistent application of guideline-recommended measures for antimicrobial use.

Spread of Clones of Multidrug-Resistant, Coagulase-Negative Staphylococci Within a University Hospital

Objective:

To detect putative clonal dissemination of multidrug-resistant, coagulase-negative staphylococci (CNS) in a university hospital in northern Sweden.

Methods:

All consecutive routine clinical samples from our hospital were screened during two periods (November and December 2001 and September and October 2002) for the presence of multidrug-resistant (defined as resistant to oxacillin, clindamycin, co-trimoxazole, gentamicin, and fusidic acid, but susceptible to vancomycin) isolates of CNS. Genetic similarity between isolates was analyzed using pulsed-field gel electrophoresis (PFGE) and a computer program.

Results:

Seventy multidrug-resistant isolates from 62 patients were identified, 28 during the 2001 period and 42 during the 2002 period. All isolates except one, which wasStaphylococcus haemolyticus, were identified asS. epidermidis. Multidrug-resistant CNS were isolated in samples obtained from 24 different wards. Two subgroups (group A and group B) ofS. epidermidisthat differed by approximately 40% in PFGE band similarity were identified. Group A consisted of 44 isolates with a PFGE band similarity of greater than 70% that included 6 subgroups consisting of 3 to 16 isolates that expressed a 100% similarity. These isolates were identified during both sampling periods in cultures performed in 18 different wards. A clonal origin could not be excluded for some of the remaining 26 isolates belonging to group B, but none had identical PFGE patterns, suggesting a more diverse origin.

Conclusion:

The results of this study suggest clonal spread of multidrug-resistant CNS within our hospital and that some clones are endemic in the hospital environment.

Costs and Outcomes Among Hemodialysis-Dependent Patients With Methicillin-Resistant or Methicillin-SusceptibleStaphylococcus aureusBacteremia

Objective:

Comorbid conditions have complicated previous analyses of the consequences of methicillin resistance for costs and outcomes ofStaphylococcus aureusbacteremia. We compared costs and outcomes of methicillin resistance in patients withS. aureusbacteremia and a single chronic condition.

Design, Setting, and Patients:

We conducted a prospective cohort study of hemodialysis-dependent patients with end-stage renal disease andS. aureusbacteremia hospitalized between July 1996 and August 2001. We used propensity scores to reduce bias when comparing patients with methicillin-resistant (MRSA) and methicillin-susceptible (MSSA)S. aureusbacteremia. Outcome measures were resource use, direct medical costs, and clinical outcomes at 12 weeks after initial hospitalization.

Results:

Fifty-four patients (37.8%) had MRSA and 89 patients (62.2%) had MSSA. Compared with patients with MSSA bacteremia, patients with MRSA bacteremia were more likely to have acquired the infection while hospitalized for another condition (27.8% vs 12.4%;P= .02). To attribute all inpatient costs toS. aureusbacteremia, we limited the analysis to 105 patients admitted for suspectedS. aureusbacteremia from a community setting. Adjusted costs were higher for MRSA bacteremia for the initial hospitalization ($21,251 vs $13,978;P= .012) and after 12 weeks ($25,518 vs $17,354;P= .015). At 12 weeks, patients with MRSA bacteremia were more likely to die (adjusted odds ratio, 5.4; 95% confidence interval, 1.5 to 18.7) than were patients with MSSA bacteremia.

Conclusions:

Community-dwelling, hemodialysis-dependent patients hospitalized with MRSA bacteremia face a higher mortality risk, longer hospital stays, and higher inpatient costs than do patients with MSSA bacteremia.

Pathogenesis of Staphylococcus aureus Bloodstream Infections

Staphylococcus aureus, a Gram-positive bacterium colonizing nares, skin, and the gastrointestinal tract, frequently invades the skin, soft tissues, and bloodstreams of humans. Even with surgical and antibiotic therapy, bloodstream infections are associated with significant mortality. The secretion of coagulases, proteins that associate with and activate the host hemostatic factor prothrombin, and the bacterial surface display of agglutinins, proteins that bind polymerized fibrin, are key virulence strategies for the pathogenesis of S. aureus bloodstream infections, which culminate in the establishment of abscess lesions. Pathogen-controlled processes, involving a wide spectrum of secreted factors, are responsible for the recruitment and destruction of immune cells, transforming abscess lesions into purulent exudate, with which staphylococci disseminate to produce new infectious lesions or to infect new hosts. Research on S. aureus bloodstream infections is a frontier for the characterization of protective vaccine antigens and the development of immune therapeutics aiming to prevent disease or improve outcomes.

Healthcare-Associated Methicillin-Resistant Staphylococcus aureus: Clinical characteristics and antibiotic resistance profile with emphasis on macrolide-lincosamide-streptogramin B resistance

OBJECTIVES

Healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen worldwide and its multidrug resistance is a major concern. This study aimed to determine the clinical characteristics and antibiotic susceptibility profile of healthcare-associated MRSA with emphasis on resistance to macrolide-lincosamide-streptogramin B (MLSB) phenotypes and vancomycin.

METHODS

This cross-sectional study was carried out between February 2014 and February 2015 across four tertiary care hospitals in Mangalore, South India. Healthcare-associated infections among 291 inpatients at these hospitals were identified according to the Centers for Disease Control and Prevention guidelines. Clinical specimens were collected based on infection type. S. aureus and MRSA isolates were identified and antibiotic susceptibility tests performed using the Kirby-Bauer disk diffusion method. The minimum inhibitory concentration of vancomycin was determined using the Agar dilution method and inducible clindamycin resistance was detected with a double-disk diffusion test (D-test).

RESULTS

Out of 291 healthcare-associated S. aureus cases, 88 were MRSA (30.2%). Of these, 54.6% were skin and soft tissue infections. All of the isolates were susceptible to teicoplanin and linezolid. Four MRSA isolates exhibited intermediate resistance to vancomycin (4.6%). Of the MRSA strains, 10 (11.4%) were constitutive MLSB phenotypes, 31 (35.2%) were inducible MLSB phenotypes and 14 (15.9%) were macrolide-streptogramin B phenotypes.

CONCLUSION

Healthcare-associated MRSA multidrug resistance was alarmingly high. In routine antibiotic susceptibility testing, a D-test should always be performed if an isolate is resistant to erythromycin but susceptible to clindamycin. Determination of the minimum inhibitory concentration of vancomycin is necessary when treating patients with MRSA infections.

Chinese herb medicine against Sortase A catalyzed transformations, a key role in gram-positive bacterial infection progress

Many Gram-positive bacteria can anchor their surface proteins to the cell wall peptidoglycan covalently by a common mechanism with Sortase A (SrtA), thus escaping from the host's identification of immune cells. SrtA can complete this anchoring process by cleaving LPXTG motif conserved among these surface proteins and thus these proteins anchor on the cell wall. Moreover, those SrtA mutants lose this capability to anchor these relative proteins, with these bacteria no longer infectious. Therefore, SrtA inhibitors can be promising anti-infective agents to cure bacterial infections. Chinese herb medicines (CHMs) (chosen from Science Citation Index) have exhibited inhibition on SrtA of Gram-positive pathogens irreversibly or reversibly. In general, CHMs are likely to have important long-term impact as new antibacterial compounds and sought after by academia and the pharmaceutical industry. This review mainly focuses on SrtA inhibitors from CHMs and the potential inhibiting mechanism related to chemical structures of compounds in CHMs.

Evaluation of Antimicrobial Resistance in Staphylococcus aureus Isolates by Years

Objective. Recently, community and hospital-acquired infections with Staphylococcus aureus have increased and raised antibiotic resistant isolates. In this study, we aimed to evaluate the antibiotic resistance profile of S. aureus isolates over several years in various clinical specimens from our hospital. Materials and Methods. S. aureus strains from 2009 to 2014 were isolated from various clinical samples at Yuzuncu Yil University, Dursun Odabas Medical Center, Microbiology Laboratory, and their antibiotic susceptibility test results were retrospectively investigated. The isolates were identified by conventional methods, and antibiotic susceptibility tests were performed by the Phoenix (Becton Dickinson, USA) automated system method according to Clinical and Laboratory Standards Institute (CLSI) standards. Results. A total of 1,116 S. aureus isolates were produced and methicillin-resistant S. aureus (MRSA) to 21% of all S. aureus isolates between 2009 and 2014. According to the results of susceptibility tests of all isolates of S. aureus, they have been identified as sensitive to vancomycin, daptomycin, linezolid, and levofloxacin. While the resistance rates to nitrofurantoin, quinupristin-dalfopristin, and trimethoprim-sulfamethoxazole were determined as 0.3%, 2.4%, and 6%, respectively, resistance rates to penicillin, erythromycin, rifampicin, gentamicin, and clindamycin were determined as 100%, 18%, 14%, 14%, and 11%, respectively. The highest percentage of methicillin resistance was determined as 30% in 2009, and the resistance was determined to have decreased in subsequent years (20%, 16%, 13%, 19%, and 21%) (p < 0.001). Conclusion. Currently, retrospective evaluations of causes of nosocomial infection should be done periodically. We think that any alteration of resistance over the years has to be identified, and all centers must determine their own resistance profiles, in order to guide empirical therapies. Reducing the rate of antibiotic resistance will contribute to reducing the cost of treatment.