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

Biofilm inhibitory and eradicating activity of wound care products against Staphylococcus aureus and Staphylococcus epidermidis biofilms in an in vitro chronic wound model

AIMS

Although several factors contribute to wound healing, bacterial infections and the presence of biofilm can significantly affect healing. Despite that this clearly indicates that therapies should address biofilm in wounds, only few wound care products have been evaluated for their antibiofilm effect. For this reason, we developed a rapid quantification approach to investigate the efficacy of wound care products on wounds infected with Staphylococcus spp.

METHODS AND RESULTS

An in vitro chronic wound infection model was used in which a fluorescent Staph. aureus strain was used to allow the rapid quantification of the bacterial burden after treatment. A good correlation was observed between the fluorescence signal and the bacterial counts. When evaluated in this model, several commonly used wound dressings and wound care products inhibited biofilm formation resulting in a decrease between one and seven log CFU per biofilm compared with biofilm formed in the absence of products. In contrast, most dressings only moderately affected mature biofilms.

CONCLUSION

Our model allowed the rapid quantification of the bacterial burden after treatment. However, the efficacy of treatment varied between the different types of dressings and/or wound care products.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our model can be used to compare the efficacy of wound care products to inhibit biofilm formation and/or eradicate mature biofilms. In addition, the results indicate that treatment of infected wounds should be started as soon as possible and that novel products with more potent antibiofilm activity are needed.

Structures of SdrD from Staphylococcus aureus reveal the molecular mechanism of how the cell surface receptors recognize their ligands

Staphylococcus aureus is the most important Gram-positive colonizer of human skin and nasal passage, causing high morbidity and mortality. SD-repeat containing protein D (SdrD), an MSCRAMM (Microbial Surface Components Recognizing Adhesive Matrix Molecules) family surface protein, plays an important role in S. aureus adhesion and pathogenesis, while its binding target and molecular mechanism remain largely unknown. Here we solved the crystal structures of SdrD N2-N3 domain and N2-N3-B1 domain. Through structural analysis and comparisons, we characterized the ligand binding site of SdrD, and proposed a featured sequence motif of its potential ligands. In addition, the structures revealed for the first time the interactions between B1 domain and N2-N3 domain among B domain-containing MSCRAMMs. Our results may help in understanding the roles SdrD plays in S. aureus adhesion and shed light on the development of novel antibiotics.

Community-associated MRSA: what makes them special?

While infections with methicillin-resistant Staphylococcus aureus (MRSA) were traditionally restricted to the hospital setting, novel MRSA strains emerged over the last two decades that have the capacity to infect otherwise healthy people outside of the hospital setting. These community-associated (CA-)MRSA strains combine methicillin resistance with enhanced virulence and fitness. Interestingly, CA-MRSA strains emerged globally and from different backgrounds, indicating that the "trade-off" between maintaining sufficient levels of methicillin resistance and obtaining enhanced virulence at a low fitness cost was achieved on several occasions in convergent evolution. However, frequently this process comprised similar changes. First and foremost, all CA-MRSA strains typically carry a novel type of methicillin resistance locus that appears to cause less of a fitness burden. Additionally, acquisition of specific toxin genes, most notably that encoding Panton-Valentine leukocidin (PVL), and adaptation of gene expression of genome-encoded toxins, such as alpha-toxin and phenol-soluble modulins (PSMs), further contributed to the evolution of CA-MRSA. Finally, the exceptional epidemiological success of the USA300 CA-MRSA clone in particular may have been due to yet another gene acquisition, namely that of the speG gene, which is located on the arginine catabolic mobile element (ACME) and involved in detoxifying harmful host-derived polyamines.

Effect of pulsed light treatments on the growth and resistance behavior of Listeria monocytogenes 10403S, Listeria innocua, and Escherichia coli ATCC 25922 in a liquid substrate

Pulsed light (PL) treatment can effectively inactivate a large proportion of contaminating bacteria on surfaces and in clear solutions. An important issue that needs to be investigated is whether repeated exposure to PL treatment causes any changes to the growth and resistance behavior of the bacteria surviving the treatment. To test this, three challenge microorganisms were used: Listeria monocytogenes, Listeria innocua, and Escherichia coli. Cells of the challenge bacteria were treated with either low or high PL doses. Survivors of the PL treatment were enumerated, isolated, regrown, and exposed again to PL treatment. PL inactivation curves were generated for the survivors of each exposure cycle (as well as controls) to examine possible differences induced by repeated treatments. Growth curves of L. monocytogenes, L. innocua, and E. coli isolates recovered from exposure to either 1.1 or 10.1 J/cm(2) were not significantly different from the growth curves of untreated cells. Reduction levels of up to 4 and up to 6 log CFU were obtained after exposure to 1.1 and 10.1 J/cm(2), respectively, both for the controls and the repeatedly treated and recovered isolates. These results show that PL did not significantly change the growth kinetics or resistance to PL of the target microorganisms after up to 10 exposures. These findings have significance for the practical application of PL treatment, as they indicate that this technology does not select for microorganisms with increased resistance.

Metabolic profiling for detection of Staphylococcus aureus infection and antibiotic resistance

Due to slow diagnostics, physicians must optimize antibiotic therapies based on clinical evaluation of patients without specific information on causative bacteria. We have investigated metabolomic analysis of blood for the detection of acute bacterial infection and early differentiation between ineffective and effective antibiotic treatment. A vital and timely therapeutic difficulty was thereby addressed: the ability to rapidly detect treatment failures because of antibiotic-resistant bacteria. Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) were used in vitro and for infecting mice, while natural MSSA infection was studied in humans. Samples of bacterial growth media, the blood of infected mice and of humans were analyzed with combined Gas Chromatography/Mass Spectrometry. Multivariate data analysis was used to reveal the metabolic profiles of infection and the responses to different antibiotic treatments. In vitro experiments resulted in the detection of 256 putative metabolites and mice infection experiments resulted in the detection of 474 putative metabolites. Importantly, ineffective and effective antibiotic treatments were differentiated already two hours after treatment start in both experimental systems. That is, the ineffective treatment of MRSA using cloxacillin and untreated controls produced one metabolic profile while all effective treatment combinations using cloxacillin or vancomycin for MSSA or MRSA produced another profile. For further evaluation of the concept, blood samples of humans admitted to intensive care with severe sepsis were analyzed. One hundred thirty-three putative metabolites differentiated severe MSSA sepsis (n = 6) from severe Escherichia coli sepsis (n = 10) and identified treatment responses over time. Combined analysis of human, in vitro, and mice samples identified 25 metabolites indicative of effective treatment of S. aureus sepsis. Taken together, this study provides a proof of concept of the utility of analyzing metabolite patterns in blood for early differentiation between ineffective and effective antibiotic treatment in acute S. aureus infections.

Host cell invasion by Staphylococcus aureus stimulates the shedding of microvesicles

During severe sepsis, microvesicles that are positive for tissue factor (TF) are at increased levels within blood and in pulmonary lavage. These microvesicles potentially disperse TF, the major initiator of the coagulation cascade, throughout multiple organ systems, initiating fibrin deposition and resultant ischemia. The source of these microvesicles has remained incompletely defined. Although TF(+) microvesicles are shed from cells that express nascent TF transcript in response to injury, recent findings revealed that circulating, full-length TF protein is detectable prior to these nascent transcripts. This finding suggested that the protein is released from constitutive sources as an acute response. We examined whether Staphylococcus aureus, the Gram-positive bacteria that is emerging as one of the most common etiologic agents in sepsis, is capable of stimulating the release of TF(+) microvesicles from a pulmonary cell line that constitutively expresses TF protein. We found that host cell invasion stimulated an acute release of TF(+) microvesicles and that these microvesicles mediated the transfer of the protein to TF-negative endothelial cells. We also found that transfer was inhibited by cholesterol-lowering simvastatin. Taken together, our findings reveal that S. aureus pathogenesis extends to the acute release of TF(+) microvesicles and that inhibiting dispersal by this mechanism may provide a therapeutic target.

Hyaluronidase expression and biofilm involvement in Staphylococcus aureus UAMS-1 and its sarA, agr and sarA agr regulatory mutants

In a previous study, two proteins identified as hyaluronidases were detected in spent media by MS and found to be in greater quantity in the sarA and sarA agr mutant strains when compared with the parent and agr mutant strains of Staphylococcus aureus UAMS-1. In the present study, spent media and total RNA were isolated from UAMS-1 and its regulatory mutants and analysed for hyaluronidase activity and steady-state hyaluronidase (hysA) RNA message levels. Hyaluronidase activity was observed throughout all time points examined regardless of the regulatory effects of sarA and agr but activity was always substantially higher in the sarA and sarA agr mutant strains than in the UAMS-1 parent and agr mutant strains. Northern analysis did not detect hysA message for either the UAMS-1 parent or the agr mutant strains at any time point examined, while steady-state hysA message levels were detected throughout growth for the sarA mutant strain, but only at exponential and early post-exponential growth for the sarA agr mutant strain. An in vitro biofilm plate assay, pre-coated with human plasma as a source of hyaluronic acid, demonstrated no significant increase in biofilm for a sarA mutant strain of S. aureus UAMS-1 defective in hyaluronidase activity when compared with the sarA mutant strain. These data indicate that, while hysA message levels and hyaluronidase activity are elevated in the sarA mutant strains of S. aureus UAMS-1, the increase in activity did not contribute to the biofilm-negative phenotype observed in the sarA mutant strain of S. aureus UAMS-1.

Use of Triplex PCR for Rapid Detection of PVL and Differentiation of MRSA from Methicillin Resistant Coagulase Negative Staphylococci

INTRODUCTION

Methicillin-Resistant Staphylococcus aureus (MRSA) has become a major public health problem in both hospitals and communities. Panton - Valentine Leucocidin (PVL) has been reported to be an important marker for the highly pathogenic community acquired S. aureus infections. A rapid detection of these MRSA is very important for its treatment. The specific detection of MRSA is always a problem due to the prevalence of methicillin resistance among the coagulase negative Staphylococci. Hence, this study was done to develop a rapid triplex PCR for the detection of PVL positive MRSA and for the simultaneous differentiation of MRSA from Coagulase Negative Staphylococci (CoNS).

MATERIALS AND METHODS

We developed a triplex PCR for the specific detection of PVL positive Community Acquired (CA) - MRSA and for its simultaneous differentiation from the coagulase negative Staphylococci. We used PCR for targeting the fem A gene which is specific for S. aureus, mecA which is specific for methicillin-resistance and luk - PV which is specific for the PVL toxin. The method was evaluated with a total of 100 clinical isolates of Staphylococcus spp.

RESULTS

The triplex PCR was successfully standardized by using the reference strains and it was evaluated by using clinical strains. The method was found to be rapid, highly sensitive (100%), specific (99%) and cost effective.

CONCLUSION

Triplex PCR can be used as a diagnostic tool for the detection of the highly pathogenic strains of CA-MRSA.

Characterization of the humoral immune response during Staphylococcus aureus bacteremia and global gene expression by Staphylococcus aureus in human blood

Attempts to develop an efficient anti-staphylococcal vaccine in humans have so far been unsuccessful. Therefore, more knowledge of the antigens that are expressed by Staphylococcus aureus in human blood and induce an immune response in patients is required. In this study we further characterize the serial levels of IgG and IgA antibodies against 56 staphylococcal antigens in multiple serum samples of 21 patients with a S. aureus bacteremia, compare peak IgG levels between patients and 30 non-infected controls, and analyze the expression of 3626 genes by two genetically distinct isolates in human blood. The serum antibody levels were measured using a bead-based flow cytometry technique (xMAP®, Luminex corporation). Gene expression levels were analyzed using a microarray (BµG@s microarray). The initial levels and time taken to reach peak IgG and IgA antibody levels were heterogeneous in bacteremia patients. The antigen SA0688 was associated with the highest median initial-to-peak antibody fold-increase for IgG (5.05-fold) and the second highest increase for IgA (2.07-fold). Peak IgG levels against 27 antigens, including the antigen SA0688, were significantly elevated in bacteremia patients versus controls (P≤0.05). Expression of diverse genes, including SA0688, was ubiquitously high in both isolates at all time points during incubation in blood. However, only a limited number of genes were specifically up- or downregulated in both isolates when cultured in blood, compared to the start of incubation in blood or during incubation in BHI broth. In conclusion, most staphylococcal antigens tested in this study, including many known virulence factors, do not induce uniform increases in the antibody levels in bacteremia patients. In addition, the expression of these antigens by S. aureus is not significantly altered by incubation in human blood over time. One immunogenic and ubiquitously expressed antigen is the putative iron-regulated ABC transporter SA0688.

Random mutagenesis and topology analysis of the autoinducing peptide biosynthesis proteins in Staphylococcus aureus

The Staphylococcus aureus accessory gene regulator (agr) is a peptide signalling system that regulates the production of secreted virulence factors required to cause infections. The signal controlling agr function is a 7-9 residue thiolactone-containing peptide called an autoinducing peptide (AIP) that is biosynthesized from the AgrD precursor by the membrane peptidase AgrB. To gain insight into AgrB and AgrD function, the agrBD genes were mutagenized and screened for deficiencies in AIP production. In total, single-site mutations at 14 different residues in AgrD were identified and another 20 within AgrB. In AgrD, novel mutations were characterized in the N-terminal leader and throughout the central region encoding the AIP signal. In AgrB, most mutations blocked peptidase activity, but mutations in the K129-K131 residues were defective in a later step in AIP biosynthesis, separating the peptidase function from thiolactone ring formation and AIP transport. With the identification of residues in AgrB essential for AgrD processing, we reevaluated the membrane topology and the new model predicts four transmembrane helices and a potential re-entrant loop on the cytoplasmic face. Finally, co-immunoprecipitation studies indicate that AgrB forms oligomeric structures within the membrane. These studies provide further insight into the unique structural and functional properties of AgrB.

The role of the Panton-Valentine leucocidin toxin in staphylococcal disease: a systematic review and meta-analysis

BACKGROUND

Invasive community-onset staphylococcal disease has emerged worldwide associated with Panton-Valentine leucocidin (PVL) toxin. Whether PVL is pathogenic or an epidemiological marker is unclear. We investigate the role of PVL in disease, colonisation, and clinical outcome.

METHODS

We searched Medline and Embase for original research reporting the prevalence of PVL genes among Staphylococcus aureus pneumonia, bacteraemia, musculoskeletal infection, skin and soft-tissue infection, or colonisation published before Oct 1, 2011. We calculated odds ratios (ORs) to compare patients with PVL-positive colonisation and each infection relative to the odds of PVL-positive skin and soft-tissue infection. We did meta-analyses to estimate odds of infection or colonisation with a PVL-positive strain with fixed-effects or random-effects models, depending on the results of tests for heterogeneity.

RESULTS

Of 509 articles identified by our search strategy, 76 studies from 31 countries met our inclusion criteria. PVL strains are strongly associated with skin and soft-tissue infections, but are comparatively rare in pneumonia (OR 0·37, 95% CI 0·22-0·63), musculoskeletal infections (0·44, 0·19-0·99), bacteraemias (0·10, 0·06-0·18), and colonising strains (0·07, 0·01-0·31). PVL-positive skin and soft-tissue infections are more likely to be treated surgically than are PVL-negative infections, and children with PVL-positive musculoskeletal disease might have increased morbidity. For other forms of disease we identified no evidence that PVL affects outcome.

INTERPRETATION

PVL genes are consistently associated with skin and soft-tissue infections and are comparatively rare in invasive disease. This finding challenges the view that PVL mainly causes invasive disease with poor prognosis. Population-based studies are needed to define the role of PVL in mild, moderate, and severe disease and to inform control strategies.

FUNDING

None.

Methicillin-resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus is one of the leading causes of surgical site infection (SSI). Over the past decade there has been an increase in methicillin-resistant S. aureus (MRSA). This is a subpopulation of the bacterium with unique resistance and virulence characteristics. Nasal colonisation with either S. aureus or MRSA has been demonstrated to be an important independent risk factor associated with the increasing incidence and severity of SSI after orthopaedic surgery. Furthermore, there is an economic burden related to SSI following orthopaedic surgery, with MRSA-associated SSI leading to longer hospital stays and increased hospital costs. Although there is some controversy about the effectiveness of screening and eradication programmes, the literature suggests that patients should be screened and MRSA-positive patients treated before surgical admission in order to reduce the risk of SSI.

Cite this article: Bone Joint J 2013;95-B:4–9.

The antibiotic resistance profiles of bacterial strains isolated from patients with hospital-acquired bloodstream and urinary tract infections

Treatment of nosocomial infections is becoming difficult due to the increasing trend of antibiotics resistance. Current knowledge on antibiotic resistance pattern is essential for appropriate therapy. We aimed to evaluate antibiotic resistance profiles in nosocomial bloodstream and urinary tract pathogens. A total of 129 blood stream and 300 urinary tract positive samples were obtained from patients referring to Besat hospital over a two-year period (2009 and 2010). Antibiotic sensitivity was ascertained using the Kirby-Bauer disk diffusion technique according to CLSI guidelines. Patient's data such as gender and age were recorded. The ratio of gram-negative to gram-positive bacteria in BSIs was 1.6 : 1. The most prevalent BSI pathogen was Coagulase-Negative Staphylococci (CoNS). The highest resistance rate of CoNS was against penicillin (91.1%) followed by ampicillin (75.6%), and the lowest rate was against vancomycin (4.4%). Escherichia coli was the most prevalent pathogen isolated from urinary tract infections (UTIs). Ratio of gram-negative to gram-positive bacteria was 3.2 : 1. The highest resistance rate of E. coli isolates was against nalidixic acid (57.7%). The present study showed that CoNS and E. coli are the most common causative agents of nosocomial BSIs and UTIs, and control of infection needs to be addressed in both antibiotic prescription and general hygiene.

Coagulase-negative staphylococci as reservoirs of genes facilitating MRSA infection: Staphylococcal commensal species such as Staphylococcus epidermidis are being recognized as important sources of genes promoting MRSA colonization and virulence

Recent research has suggested that Staphylococcus epidermidis is a reservoir of genes that, after horizontal transfer, facilitate the potential of Staphylococcus aureus to colonize, survive during infection, or resist antibiotic treatment, traits that are notably manifest in methicillin-resistant S. aureus (MRSA). S. aureus is a dangerous human pathogen and notorious for acquiring antibiotic resistance. MRSA in particular is one of the most frequent causes of morbidity and death in hospitalized patients. S. aureus is an extremely versatile pathogen with a multitude of mechanisms to cause disease and circumvent immune defenses. In contrast, most other staphylococci, such as S. epidermidis, are commonly benign commensals and only occasionally cause disease. Recent findings highlight the key importance of efforts to better understand how genes of staphylococci other than S. aureus contribute to survival in the human host, how they are transferred to S. aureus, and why this exchange appears to be uni-directional.

Methicillin-resistant Staphylococcus aureus (MRSA) detected at four U.S. wastewater treatment plants

BACKGROUND

The incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is increasing in the United States, and it is possible that municipal wastewater could be a reservoir of this microorganism. To date, no U.S. studies have evaluated the occurrence of MRSA in wastewater.

OBJECTIVE

We examined the occurrence of MRSA and methicillin-susceptible S. aureus (MSSA) at U.S. wastewater treatment plants.

METHODS

We collected wastewater samples from two Mid-Atlantic and two Midwest wastewater treatment plants between October 2009 and October 2010. Samples were analyzed for MRSA and MSSA using membrane filtration. Isolates were confirmed using biochemical tests and PCR (polymerase chain reaction). Antimicrobial susceptibility testing was performed by Sensititre® microbroth dilution. Staphylococcal cassette chromosome mec (SCCmec) typing, Panton-Valentine leucocidin (PVL) screening, and pulsed field gel electrophoresis (PFGE) were performed to further characterize the strains. Data were analyzed by two-sample proportion tests and analysis of variance.

RESULTS

We detected MRSA (n = 240) and MSSA (n = 119) in 22 of 44 (50%) and 24 of 44 (55%) wastewater samples, respectively. The odds of samples being MRSA-positive decreased as treatment progressed: 10 of 12 (83%) influent samples were MRSA-positive, while only one of 12 (8%) effluent samples was MRSA-positive. Ninety-three percent and 29% of unique MRSA and MSSA isolates, respectively, were multidrug resistant. SCCmec types II and IV, the pvl gene, and USA types 100, 300, and 700 (PFGE strain types commonly found in the United States) were identified among the MRSA isolates.

CONCLUSIONS

Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater. Because of increasing use of reclaimed wastewater, further study is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater.

Characterization of methicillin-resistant Staphylococcus aureus from skin and soft tissue infections in patients in Nairobi, Kenya

BACKGROUND

Skin and soft tissue infections (SSTIs) are among the most common infectious diseases and a frequent cause of hospital visits. In this study we sought to assess the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) and antibiotic susceptibility patterns in SSTIs in patients attending hospitals in Kenya.

METHODS

Eighty-two S. aureus isolates recovered from SSTIs from both inpatients and outpatients were screened for antibiotic susceptibility, possession of staphylococcal cassette chromosome mec (SCCmec) gene type, and the Panton-Valentine leukocidin (PVL) toxin gene. The prevalence of MRSA was investigated in relation to the type of patient and infection type, as well as the type of health care facility.

RESULTS

Of 60 boil cultures, 39 (65%) grew S. aureus, of out of which 34 (87.2%) were MRSA. Of the 60 abscess cultures, 14 (23.3%) grew S. aureus, of which 10 (71.4%) were MRSA. Of 34 cellulitis cultures, 18 (52.9%) grew S. aureus, of which 16 (88.8%) were MRSA. Of 25 ulcer cultures, 11 (44%) grew S. aureus, of which nine (81.8%) were MRSA. Sixty-nine of 82 S. aureus (84.1%) were MRSA, with 52 (75.4%) possessing SCCmec II type and 14 (20.3%) being positive for the PVL gene. Based on hospitals, it was noted that most MRSA were isolated at publicly funded health care facilities serving an economically disadvantaged segment of Nairobi's population, such as those living in urban informal settlements. All 82 S. aureus were susceptible to vancomycin and resistant in high numbers to macrolides, aminoglycosides, and quinolones. Bacterial isolates were mostly susceptible to vancomycin, ciprofloxacin and co-trimoxazole, and none was resistant to vancomycin. However, most organisms showed decreased susceptibility to erythromycin and clindamycin.

CONCLUSIONS

These findings suggest that SCCmec II MRSA and a PVL strain of MRSA are significant pathogens in patients with SSTIs presenting to hospitals in Kenya, and that MRSA cases are prevalent at publicly funded health care facilities.

Interactions of Staphylococci with Osteoblasts and Phagocytes in the Pathogenesis of Implant-Associated Osteomyelitis

In spite of great advancements in the field of biomaterials and in surgical techniques, the implant of medical devices is still associated with a high risk of bacterial infection. Implant-associated osteomyelitis is a deep infection of bone around the implant. The continuous inflammatory destruction of bone tissues characterizes this serious bone infectious disease. Staphylococcus aureus and Staphylococcus epidermidis are the most prevalent etiologic agents of implant-associated infections, together with the emerging pathogen Staphylococcus lugdunensis. Various interactions between staphylococci, osteoblasts, and phagocytes occurring in the peri-prosthesis environment play a crucial role in the pathogenesis of implant-associated osteomyelitis. Here we focus on two main events: internalization of staphylococci into osteoblasts, and bacterial interactions with phagocytic cells.

Epidemiology of methicillin-resistant Staphylococcus aureus carrying the novel mecC gene in Denmark corroborates a zoonotic reservoir with transmission to humans

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of healthcare-associated (HA), community-associated (CA) and livestock-associated (LA) infections. Recently, the discovery of human and bovine MRSA isolates carrying a new mecA gene homologue, mecA(LGA251) (now designated mecC), has caused concern because they are not detected by conventional, confirmatory tests for MRSA. Very little is known about their frequency, epidemiology and possible transmission between livestock and humans. In this study, the epidemiology of the mecC isolates in Denmark was investigated by screening the national collections of MRSA cases (from 1988 onwards) and S. aureus bacteraemia cases (from 1958 onwards). Isolates carrying mecC were only recovered infrequently before 2003 (n = 2) but now seem to be increasing, with 110 cases in 2003-2011. Clinical data on mecC-carrying MRSA demonstrated that mecC-MRSA were primarily community-acquired (CA-MRSA) and affected persons typically living in rural areas, being older than other CA-MRSA patients. Among 22 cases in Region Zealand, four reported contact with cattle and sheep. Two of these persons lived on farms with livestock positive for mecC-carrying MRSA, sharing spa type (t843), MLVA (MT429) and PFGE pattern with the human isolates. These observations indicate that mecC-carrying MRSA can be exchanged between humans and ruminants.

Immunity induced by Staphylococcus aureus surface protein A was protective against lethal challenge of Staphylococcus aureus in BALB/c mice

Staphylococcus aureus is the most common cause of hospital-acquired bacteremia. Due to emergence of antibiotic-resistant strains, these infections present a serious public health threat. In this study, to develop a broadly protective vaccine, we tested whether immune responses induced by several proteins associated with S. aureus toxicity could protect mice from lethal challenge with human clinical S. aureus isolate USA300. We found that the surface protein A (SasA) of S. aureus could protect mice from lethal challenge of the bacteria.

Prevalence of Bacterial Pathogens in Aseer Region, Kingdom of Saudi Arabia: Emphasis on Antimicrobial Susceptibility of Staphylococcus aureus

OBJECTIVES

This short study aims to determine the prevalence of various bacterial pathogens causing infections in the Aseer regions, and to also assess the distribution of Staphylococcus aureus in relation to different body sites as well as their in vitro antimicrobial susceptibility profile.

METHODS

Clinical specimens (n=9831) from various infections diagnosed at Aseer Central Hospital (ACH) and Abha General Hospital (AGH), were analyzed bacteriologically. Confirmed S. aureus isolates (n=210) were tested against 44 antibacterial agents as per standard methods.

RESULTS

Bacterial pathogens were recovered from 24.9% of the samples. The results revealed that Escherichia coli, Klebsiella pneumoniae, Enterococcus spp. and S. aureus to be the main etiological agents, while purulent exudates of wounds and abscesses were the main source of S. aureus. Out of the 210 S. aureus isolates; 77 (38.5%) were recovered from purulent exudates of wounds and abscesses of the examined patients and 53 (26.5%) were from high vaginal discharges, while other body sites exhibited different rates of S. aureus. On the other hand, 45% of the 210 S. aureus isolates were found to be multidrug resistant S. aureus (MRSA).

CONCLUSION

The results from this study revealed that Escherichia coli and staphylococci were the main etiological agents, while purulent exudates of wounds and abscesses were the main source of S. aureus. Also, a higher rate of MRSA was detected.

Haemin represses the haemolytic activity of Staphylococcus aureus in an Sae-dependent manner

Staphylococcus aureus is a major human pathogen and a common cause of nosocomial infections. This facultative pathogen produces a large arsenal of virulence factors, including the haemolysins, which allow the bacterium to lyse erythrocytes and thereby release large amounts of the haem-containing haemoglobin. The released haem is thought to be the main iron source of this organism during the course of infection, and is considered to be crucial for bacterial proliferation in vivo. High concentrations of haem and its degradation products, on the other hand, are known to be toxic for S. aureus, making it essential for the pathogen to tightly control haem release from red blood cells. Here we show that S. aureus responds to haemin by downregulating the expression of haemolysins. Subinhibitory concentrations of haemin were found to significantly reduce transcription of the haemolysin genes hlb (encoding β-haemolysin) and hlgA (encoding the S-class component of γ-haemolysin), while hla (encoding α-haemolysin) and RNAIII (encoding δ-haemolysin) transcription did not appear to be affected. The presence of haemin also reduced the haemolytic potential of the supernatants of S. aureus LS1 cultures. Inactivation of the sae locus in LS1 abolished the haemin effect on the transcription of haemolysin genes, indicating that the two-component regulatory system is required for this regulatory effect. Iron limitation, on the other hand, was found to induce the expression of haemolysins, and this effect was again abolished in the sae mutant, indicating that S. aureus modulates its haemolysin production in response to iron and haem availability in an Sae-dependent manner.

MRSA virulence and spread

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most frequent causes of hospital- and community-associated infections. Resistance to the entire class of β-lactam antibiotics, such as methicillin and penicillin, makes MRSA infections difficult to treat. Hospital-associated MRSA strains are often multi-drug-resistant, leaving only lower efficiency drugs such as vancomycin as treatments options. Like many other S. aureus strains, MRSA strains produce a series of virulence factors, such as toxins and adhesion proteins. Recent findings have shed some new light on the molecular events that underlie MRSA epidemic waves. Newly emerging MRSA clones appear to have acquired phenotypic traits that render them more virulent or able to colonize better, either via mobile genetic elements or via adaptation of gene expression. Acquisition of Panton-Valentine leukocidin genes and increased expression of core genome-encoded toxins are being discussed as potentially contributing to the success of the recently emerged community-associated MRSA strains. However, the molecular factors underlying the spread of hospital- and community-associated MRSA strains are still far from being completely understood, a situation calling for enhanced research efforts in that area.

Antibiotic-resistance Staphylococcus aureus isolated from cow's milk in the Hawassa area, South Ethiopia

BACKGROUND

Quarter milk samples from cows were examined to determine the prevalence of Staphylococcus aureus (SA) and different antibiotic resistant pattern were determined in a cross-sectional study design.

OBJECTIVE

The objective of this study was to isolate Staphylococcus aureus from samples of cow's milk obtained from Hawassa area and to determine their antibiotic susceptibility patterns.

METHOD

A total of 160 milk (CCP1-CCP5) samples were collected and screened for the presence of S. aureus. Gram staining, oxidase, catalase, DNase, haemolysis and coagulase tests were employed for bacterial identification.

RESULTS

All the samples were contaminated with S. aureus. A total of 78 S. aureus isolates were obtained during this study. The levels of contamination with S. aureus were higher in milk obtained from CCP1, CCP2, CCP3, CCP4 and CCP5 at Hawassa area farms (18.0%, 25.6%, 27.0%, 21.8% and 7.7%) respectively. A large percentage of the S. aureus isolates (25.6% and 27.0%) were from CCP2 and CCP3. All strains were resistant to Penicillin G (PG) (10 μg), Ampicillin (AP) (10 μg), Amoxicillin-Clavulanic acid (AC) (30 μg), Ciprofloxacin (CIP) (5 μg), Erythromycin (E) (15 μg), Ceftriaxone (CRO) (30 μg), Trimethoprime-Sulfamethoxazole (TMP-SMZ) (25 μg) Oxacillin (Ox) (1 μg) and Vancomycin (V) (30 μg), 67.9%, 70.9%, 30.9%, 0%, 32.1%, 23.1%, 7.7%, 60.3% and 38.5% respectively.

CONCLUSION

The proportion of isolates resistant to CIP, TMP-SMZ, CRO, AC, E and V were low compared to AP, PG and Ox. S. aureus is normally resident in humans; therefore, the S. aureus present in the cow's milk may have resulted from transmission between the two species, emphasizing the need to improve sanitary conditions in the milking environment.

Comparative pharmacodynamics of the new oxazolidinone tedizolid phosphate and linezolid in a neutropenic murine Staphylococcus aureus pneumonia model

Tedizolid phosphate (TR-701) is a novel oxazolidinone prodrug (converted to the active form tedizolid [TR-700]) with potent Staphylococcus aureus activity. The current studies characterized and compared the in vivo pharmacokinetic/pharmacodynamic (PD) characteristics of TR-701/TR-700 and linezolid against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in the neutropenic murine pneumonia model. The pharmacokinetic properties of both drugs were linear over a dose range of 0.625 to 40 mg/kg of body weight. Protein binding was 30% for linezolid and 85% for TR-700. Mice were infected with one of 11 isolates of S. aureus, including MSSA and community- and hospital-acquired MRSA strains. Each drug was administered by oral-gastric gavage every 12 h (q12h). The dosing regimens ranged from 1.25 to 80 mg/kg/12 h for linezolid and 0.625 to 160 mg/kg/12 h for TR-701. At the start of therapy, mice had 6.24 ± 0.40 log(10) CFU/lungs, which increased to 7.92 ± 1.02 log(10) CFU/lungs in untreated animals over a 24-h period. A sigmoid maximum-effect (E(max)) model was used to determine the antimicrobial exposure associated with net stasis (static dose [SD]) and 1-log-unit reduction in organism relative to the burden at the start of therapy. The static dose pharmacodynamic targets for linezolid and TR-700 were nearly identical, at a free drug (non-protein-bound) area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC ratio) of 19 and 20, respectively. The 1-log-unit kill endpoints were also similar, at 46.1 for linezolid and 34.6 for TR-700. The exposure targets were also comparable for both MSSA and MRSA isolates. These dosing goals support further clinical trial examination of TR-701 in MSSA and MRSA pneumonia.

A case of acute cholecystitis caused by methicillin-resistant Staphylococcus aureus in an immunocompromised patient

Although infections with Staphylococcus aureus can implicate multiple organ systems, involvement of the biliary tract is rare. A case of acute cholecystitis and bacteremia with methicillin-resistant S aureus (MRSA) in a patient with HIV infection is presented. The MRSA isolate was found to be a community-associated strain. The present case highlights the invasive nature of staphylococcal infections and the emerging importance of community-associated MRSA strains.

Staphylococcus aureus ocular infection: methicillin-resistance, clinical features, and antibiotic susceptibilities

Background

Methicillin-resistant Staphylococcus aureus (MRSA) infection is an important public health issue. The study aimed to determine the prevalence of ocular infections caused by MRSA and to identify the clinical characteristics and antibiotic susceptibility of ocular MRSA infections by comparing those of ocular methicillin-sensitive S. aureus (MSSA) infections.

Methodology/Principal Findings

The medical records of the patients (n = 519) with culture-proven S. aureus ocular infections seen between January 1, 1999 and December 31, 2008 in Chang Gung Memorial Hospital were retrospectively reviewed. Two hundred and seventy-four patients with MRSA and 245 with MSSA ocular infections were identified. The average rate of MRSA in S. aureus infections was 52.8% and the trend was stable over the ten years (P value for trend  = 0.228). MRSA ocular infections were significantly more common among the patients with healthcare exposure (P = 0.024), but 66.1% (181/274) patients with MRSA ocular infections had no healthcare exposure. The most common clinical presentation for both MRSA and MSSA ocular infections was keratitis; MRSA and MSSA caused a similar disease spectrum except for lid infections. MRSA was significantly more resistant than MSSA to clindamycin, erythromycin and sulfamethoxazole/trimethoprim (all P<0.001).

Conclusions/significance

We demonstrated a paralleled trend of ocular MRSA infection in a highly prevalent MRSA country by hospital-based survey. Except for lid disorder, MRSA shared similar spectrum of ocular pathology with MSSA. Since S. aureus is a common ocular pathogen, our results raise clinician’s attention to the existence of highly prevalent MRSA.

Colistin in burn intensive care: back to the future?

Colistin is a venerable antibiotic whose fortunes have been revived by its excellent activity, the diminishing output of novel clinically effective antibiotics and the increasing importance of MDR infection in burn surgery, both in the civilian and military arenas. This review synthesizes current evidence on the usage of colistin in burn surgery including the structure-activity relationship; dosing, pharmacokinetics/pharmacodynamic (PK/PD), analytic methods, resistance and current research efforts into the redevelopment of this antibiotic, to distil recommendations for future research and clinical efficacy.

Nosocomial Gram-positive antimicrobial susceptibility pattern at a referral teaching hospital in Tehran, Iran

Aims: The aim of the study was to evaluate epidemiology and susceptibility patterns of nosocomial Gram-positive infections in a referral teaching hospital. Methods: Over a 1 year period, Gram-positive microorganisms isolated from specimens of hospitalized patients with documented nosocomial infection underwent antimicrobial susceptibility testing using the disk diffusion test. In addition, possible risk factors for developing multidrug-resistant bacteria were evaluated. Results: During the study period, a total of 137 nosocomial infections were detected. Staphylococcus aureus was the most frequently isolated microorganism (56.2%), followed by Enterococcus spp. (21.9%) and Staphylococcus epidermidis (15.3%). All S. aureus strains were sensitive to vancomycin, teicoplanin, linezolid and chloramphenicol. More than 50% of enterococci strains were resistant to vancomycin and teicoplanin. Possible risk factors for multidrug resistance among isolated pathogens were history of antibiotic use and intubation of patient for mechanical ventilation. Conclusion: This study showed high rates of antimicrobial resistance among nosocomial Gram-positive pathogens, complicating antibiotic therapy and its outcomes.

Original submitted 26 March 2012; Revised submitted 27 April 2012

Daptomycin: local application in implant-associated infection and complicated osteomyelitis

BACKGROUND

The rise of highly resistant bacteria creates a persistent urge to develop new antimicrobial agents. This paper investigates the application of the lipopeptide antibiotic daptomycin in infections involving the human bone.

METHODS

Compressive and tensile strength testing of daptomycin-laden PMMA was performed referring to the ISO 5833. The microstructure of the antibiotic-laden PMMA was evaluated by scanning electron microscopy. Intracellular activity of daptomycin was determined by a human osteoblast infection model. Elution kinetics of the antibiotic-laden bone cement was measured by using a continuous flow chamber setup.

RESULTS

There was no significant negative effect of adding 1.225% and 7.5% per weight of daptomycin to the PMMA. There was no significant difference in intracellular activity comparing gentamicin to daptomycin. Elution of daptomycin from PMMA showed within the first-hour initial peak values of 15-20 μg/mL.

CONCLUSION

Daptomycin has a certain degree of activity in the intracellular environment of osteoblasts. Daptomycin admixed to PMMA remains bactericidal and does not significantly impair structural characteristics of the PMMA. The results of this paper suggest that daptomycin might be a potent alternative for treating osteomyelitis and implant-associated infection in trauma and orthopedic surgery caused by multiresistant strains.

Development of novel antibacterial agents against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious threat to public health because of its resistance to multiple antibiotics most commonly used to treat infection. In this study, we report the unique ability of the cyclooxygenase-2 (COX-2) inhibitor celecoxib to kill Staphylococcus aureus and MRSA with modest potency. We hypothesize that the anti-Staphylococcus activity of celecoxib could be pharmacologically exploited to develop novel anti-MRSA agents with a distinct mechanism. Examination of an in-house, celecoxib-based focused compound library in conjunction with structural modifications led to the identification of compound 46 as the lead agent with high antibacterial potency against a panel of Staphylococcus pathogens and different strains of MRSA. Moreover, this killing effect is bacteria-specific, as human cancer cells are resistant to 46. In addition, a single intraperitoneal administration of compound 46 at 30 mg/kg improved the survival of MRSA-infected C57BL/6 mice. In light of its high potency in eradicating MRSA in vitro and its in vivo activity, compound 46 and its analogues warrant continued preclinical development as a potential therapeutic intervention against MRSA.

Successful Treatment of Polymicrobial Calcaneal Osteomyelitis with Telavancin, Rifampin, and Meropenem

OBJECTIVE:

To report a case of multidrug-resistant osteomyelitis successfully treated with telavancin, rifampin, and meropenem.

CASE SUMMARY:

An 18-year-old male with spina bifida was treated primarily in the outpatient setting over the course of 133 days with multiple antimicrobials for a recurrent right calcaneal wound and osteomyelitis infection. Initial cultures were positive for methicillin-resistant Staphylococcus aureus and coagulase-negative Staphylococcus, which were treated with intravenous vancomycin 1 g every 12 hours, increased after 13 days to 1.5 g every 12 hours with addition of rifampin 300 mg twice daily, both of which were discontinued on day 22 due to leukopenia (white blood cell count 3.0 × 103/μL) and neutropenia (absolute neutrophil count 0.2 × 103/μL). Daptomycin 8 mg/kg/day was then initiated with rifampin 300 mg twice daily; treatment was discontinued after 49 days due to an elevated creatine kinase level of 1831 U/L (baseline 86). Intravenous meropenem 1 g every 8 hours was again initiated on day 83 following additional identification of quinolone-resistant Pseudomonas aeruginosa from the soft tissue of the right foot. Intravenous vancomycin 1 g every 12 hours was also restarted at this time for persistent coagulase-negative Staphylococcus and oral rifampin 300 mg twice daily was again added. Adverse events again required the discontinuation of vancomycin on day 91. The eventual drug therapy regimen consisted of telavancin 750 mg/day for 42 days, meropenem for 50 days, and oral rifampin for 50 days. At the end of treatment, the patient's right heel wound had almost completely closed. He was without recurrence or treatment-related adverse events at follow-up 1 year later.

DISCUSSION:

Antimicrobial selection for osteomyelitis infections presents a challenge to the clinician due to patient intolerance, increasing antimicrobial resistance, and variable antimicrobial penetration at the site of infection. To our knowledge, this is the first case report of the successful use of a regimen including telavancin for the treatment of a recurrent, coagulase-negative Staphylococcus osteomyelitis infection.

CONCLUSIONS:

In this complex case involving a polymicrobial infection of the right calcaneal bone and surrounding soft tissue, eventual drug therapy including telavancin, meropenem, and rifampin resulted in a successful clinical response.

Geographic variability and anti-staphylococcal activity of the chrysophaentins and their synthetic fragments

Drug-resistant Staphylococcus aureus is a continuing public health concern, both in the hospital and community settings. Antibacterial compounds that possess novel structural scaffolds and are effective against multiple S. aureus strains, including current drug-resistant ones, are needed. Previously, we have described the chrysophaentins, a family of bisdiarylbutene macrocycles from the chrysophyte alga Chrysophaeum taylori that inhibit the growth of S. aureus and methicillin-resistant S. aureus (MRSA). In this study we have analyzed the geographic variability of chrysophaentin production in C. taylori located at different sites on the island of St. John, U.S. Virgin Islands, and identified two new linear chrysophaentin analogs, E2 and E3. In addition, we have expanded the structure activity relationship through synthesis of fragments comprising conserved portions of the chrysophaentins, and determined the antimicrobial activity of natural chrysophaentins and their synthetic analogs against five diverse S. aureus strains. We find that the chrysophaentins show similar activity against all S. aureus strains, regardless of their drug sensitivity profiles. The synthetic chrysophaentin fragments indeed mimic the natural compounds in their spectrum of antibacterial activity, and therefore represent logical starting points for future medicinal chemistry studies of the natural products and their analogs.

Sublytic concentrations of Staphylococcus aureus Panton-Valentine leukocidin alter human PMN gene expression and enhance bactericidal capacity

CA-MRSA infections are often caused by strains encoding PVL, which can cause lysis of PMNs and other myeloid cells in vitro, a function considered widely as the primary means by which PVL might contribute to disease. However, at sublytic concentrations, PVL can function as a PMN agonist. To better understand this phenomenon, we investigated the ability of PVL to alter human PMN function. PMNs exposed to PVL had enhanced capacity to produce O(2)(-) in response to fMLF, but unlike priming by LPS, this response did not require TLR signal transduction. On the other hand, there was subcellular redistribution of NADPH oxidase components in PMNs following exposure of these cells to PVL--a finding consistent with priming. Importantly, PMNs primed with PVL had an enhanced ability to bind/ingest and kill Staphylococcus aureus. Priming of PMNs with other agonists, such as IL-8 or GM-CSF, altered the ability of PVL to cause formation of pores in the plasma membranes of these cells. Microarray analysis revealed significant changes in the human PMN transcriptome following exposure to PVL, including up-regulation of molecules that regulate the inflammatory response. Consistent with the microarray data, mediators of the inflammatory response were released from PMNs after stimulation with PVL. We conclude that exposure of human PMNs to sublytic concentrations of PVL elicits a proinflammatory response that is regulated in part at the level of gene expression. We propose that PVL-mediated priming of PMNs enhances the host innate immune response.

Comparative in vivo efficacies of epithelial lining fluid exposures of tedizolid, linezolid, and vancomycin for methicillin-resistant Staphylococcus aureus in a mouse pneumonia model

The antibacterial efficacies of tedizolid phosphate (TZD), linezolid, and vancomycin regimens simulating human exposures at the infection site against methicillin-resistant Staphylococcus aureus (MRSA) were compared in an in vivo mouse pneumonia model. Immunocompetent BALB/c mice were orally inoculated with one of three strains of MRSA and subsequently administered 20 mg/kg TZD every 24 hours (q24h), 120 mg/kg linezolid q12h, or 25 mg/kg vancomycin q12h over 24 h. These regimens produced epithelial lining fluid exposures comparable to human exposures observed following intravenous regimens of 200 mg TZD q24h, 600 mg linezolid q12h, and 1 g vancomycin q12h. The differences in CFU after 24 h of treatment were compared between control and treatment groups. Vehicle-dosed control groups increased in bacterial density an average of 1.1 logs. All treatments reduced the bacterial density at 24 h with an average of 1.2, 1.6, and 0.1 logs for TZD, linezolid, and vancomycin, respectively. The efficacy of TZD versus linezolid regimens against the three MRSA isolates was not statistically different (P > 0.05), although both treatments were significantly different from controls. In contrast, the vancomycin regimen was significantly different from TZD against one MRSA isolate and from linezolid against all isolates. The vancomycin regimen was less protective than either the TZD or linezolid regimens, with overall survival of 61.1% versus 94.7% or 89.5%, respectively. At human simulated exposures to epithelial lining fluid, vancomycin resulted in minimal reductions in bacterial counts and higher mortality compared to those of either TZD or linezolid. TZD and linezolid showed similar efficacies in this MRSA pneumonia model.

Methicillin-Resistant Staphylococcus aureus Associated with Animals and Its Relevance to Human Health

Staphylococcus aureus is a typical human pathogen. Some animal S. aureus lineages have derived from human strains following profound genetic adaptation determining a change in host specificity. Due to the close relationship of animals with the environmental microbiome and resistome, animal staphylococcal strains also represent a source of resistance determinants. Methicillin-resistant S. aureus (MRSA) emerged 50 years ago as a nosocomial pathogen but in the last decade it has also become a frequent cause of infections in the community. The recent finding that MRSA frequently colonizes animals, especially livestock, has been a reason for concern, as it has revealed an expanded reservoir of MRSA. While MRSA strains recovered from companion animals are generally similar to human nosocomial MRSA, MRSA strains recovered from food animals appear to be specific animal-adapted clones. Since 2005, MRSA belonging to ST398 was recognized as a colonizer of pigs and human subjects professionally exposed to pig farming. The “pig” MRSA was also found to colonize other species of farmed animals, including horses, cattle, and poultry and was therefore designated livestock-associated (LA)-MRSA. LA-MRSA ST398 can cause infections in humans in contact with animals, and can infect hospitalized people, although at the moment this occurrence is relatively rare. Other animal-adapted MRSA clones have been detected in livestock, such as ST1 and ST9. Recently, ST130 MRSA isolated from bovine mastitis has been found to carry a novel mecA gene that eludes detection by conventional PCR tests. Similar ST130 strains have been isolated from human infections in UK, Denmark, and Germany at low frequency. It is plausible that the increased attention to animal MRSA will reveal other strains with peculiar characteristics that can pose a risk to human health.

Staphylococcus epidermidis colonization is highly clonal across US cardiac centers

BACKGROUND

Little is known about the clonality of Staphylococcus epidermidis in the United States, although it is the predominant pathogen in infections involving prosthetic materials, including ventricular assist devices (VADs).

METHODS

Seventy-five VAD recipients at 4 geographically diverse US cardiac centers were prospectively followed up to 1 year of VAD support. The anterior nares, sternum, and (future) driveline exit site were cultured for S. epidermidis before VAD insertion and at 7 times after surgery. Infection isolates were also collected. Isolates were typed by pulsed-field gel electrophoresis. A subset underwent susceptibility testing and staphylococcal chromosomal cassette mec and multilocus sequence typing.

RESULTS

A total of 1559 cultures yielded 565 S. epidermidis isolates; 254 of 548 typed isolates (46%) belonged to 1 of 7 clonal types as defined by pulsed-field gel electrophoresis. These clones were identified in up to 27 people distributed across all 4 cardiac centers. They caused 3 of 6 VAD-related infections. Disseminated clones were more antibiotic resistant than were less prevalent isolates (eg, 79% vs 54% methicillin resistant; P = .0021).

CONCLUSIONS

This study revealed that healthcare-associated S. epidermidis infection is remarkably clonal. We describe S. epidermidis clones that are highly resistant to antibiotics distributed across US cardiac centers. These clones may have determinants that enhance transmissibility, persistence, or invasiveness. Clinical Trials Registration. NCT01471795.

Prevalence and population structure of Staphylococcus aureus nasal carriage in healthcare workers in a general population. The Tromsø Staph and Skin Study

Healthcare workers (HCWs) may be a reservoir for Staphylococcus aureus transmission to patients. We examined whether HCW status is associated with S. aureus nasal carriage and population structure (spa types) in 1302 women (334 HCWs) and 977 men (71 HCWs) aged 30–69 years participating in the population-based Tromsø Study in 2007–2008. Multivariable logistic regression models were used. While no methicillin-resistant S. aureus (MRSA) was isolated, overall, 26·2% of HCWs and 26·0% of non-HCWs were S. aureus nasal carriers. For women overall and women residing with children, the odds ratios for nasal carriage were 1·54 [95% confidence interval (CI) 1·09–2·19] and 1·86 (95% CI 1·14–3·04), respectively, in HCWs compared to non-HCWs. Moreover, HCWs vs. non-HCWs had a 2·17 and 3·16 times higher risk of spa types t012 and t015, respectively. This supports the view that HCWs have an increased risk of S. aureus nasal carriage depending on gender, family status and spa type.

Antistaphylococcal activity of bacteriophage derived chimeric protein P128

Background

Bacterial drug resistance is one of the most significant challenges to human health today. In particular, effective antibacterial agents against methicillin-resistant Staphylococcus aureus (MRSA) are urgently needed. A causal relationship between nasal commensal S. aureus and infection has been reported. Accordingly, elimination of nasal S. aureus reduces the risk of infection. Enzymes that degrade bacterial cell walls show promise as antibacterial agents. Bacteriophage-encoded bacterial cell wall-degrading enzymes exhibit intrinsic bactericidal activity. P128 is a chimeric protein that combines the lethal activity of the phage tail-associated muralytic enzyme of Phage K and the staphylococcal cell wall targeting-domain (SH3b) of lysostaphin.

Here we report results of in vitro studies evaluating the susceptibility of staphylococcal strains to this novel protein.

Results

Using the broth microdilution method adapted for lysostaphin, we found that P128 is effective against S. aureus clinical strains including MRSA, methicillin-sensitive S. aureus (MSSA), and a mupirocin-resistant S. aureus. Minimum bactericidal concentrations and minimum inhibitory concentrations of P128 (1-64 μg/mL) were similar across the 32 S. aureus strains tested, demonstrating its bactericidal nature.

In time-kill assays, P128 reduced colony-forming units by 99.99% within 1 h and inhibited growth up to 24 h.

In an assay simulating topical application of P128 to skin or other biological surfaces, P128 hydrogel was efficacious when layered on cells seeded on solid media. P128 hydrogel was lethal to Staphylococci recovered from nares of healthy people and treated without any processing or culturing steps, indicating its in situ efficacy. This methodology used for in vitro assessment of P128 as an agent for eradicating nasal carriage is unique.

Conclusions

The novel chimeric protein P128 is a staphylococcal cell wall-degrading enzyme under development for clearance of S. aureus nasal colonization and MRSA infection. The protein is active against globally prevalent antibiotic-resistant clinical isolates and other clinically significant staphylococcal species including S. epidermidis. The P128 hydrogel formulation was bactericidal against Staphylococci including S. aureus recovered from the nares of 31 healthy people, demonstrating its in situ efficacy.