Nasal staphylococci and sepsis in hospital patients

An induced mutation of ABC-transporter component VraF(K84E) contributes to vancomycin resistance and virulence in Staphylococcus aureus strain MW2

Staphylococcus aureus is a notorious pathogen responsible for various severe diseases. Due to the emergence of drug-resistant strains, the prevention and treatment of S. aureus infections have become increasingly challenging. Vancomycin is considered to be one of the last-resort drugs for treating most methicillin-resistant S. aureus (MRSA), so it is of great significance to further reveal the mechanism of vancomycin resistance. VraFG is one of the few important ABC (ATP-binding cassette) transporters in S. aureus that can form TCS (two-component systems)/ABC transporter modules. ABC transporters can couple the energy released from ATP hydrolysis to translocate solutes across the cell membrane. In this study, we obtained a strain with decreased vancomycin susceptibility after serial passaging and selection. Subsequently, whole-genome sequencing was performed on this laboratory-derived strain MWA2 and a novel single point mutation was discovered in vraF gene, leading to decreased sensitivity to vancomycin and daptomycin. Furthermore, the mutation reduces autolysis of S. aureus and downregulates the expression of lytM, isaA, and atlA. Additionally, we observed that the mutant has a less net negative surface charge than wild-type strain. We also noted an increase in the expression of the dlt operon and mprF gene, which are associated with cell surface charge and serve to hinder the binding of cationic peptides by promoting electrostatic repulsion. Moreover, this mutation has been shown to enhance hemolytic activity, expand subcutaneous abscesses, reflecting an increased virulence. This study confirms the impact of a point mutation of VraF on S. aureus antibiotic resistance and virulence, contributing to a broader understanding of ABC transporter function and providing new targets for treating S. aureus infections.

Severe cellulitis from methicillin-resistant Staphylococcus aureus (MRSA) in a couple of preterm twins: a case report

BACKGROUND

Preterms are at risk of systemic infections as the barrier function of their immature skin is insufficient. The long period of hospitalization and the huge number of invasive procedures represent a risk factor for complications. Among the nosocomial infections of the skin, methicillin-resistant Staphylococcus aureus (MRSA) is associated with significant morbidity and mortality. We report a clinical case of cellulitis and abscess in two preterm twins caused by MRSA in a tertiary level Neonatal Intensive Care Unit (NICU).

CASE PRESENTATION

Two preterm female babies developed cellulitis from MRSA within the first month of extrauterine life. The first one (BW 990 g) showed signs of clinical instability 4 days before the detection of a hyperaemic and painful mass on the thorax. The second one (BW 1240 g) showed signs of clinical instability contextually to the detection of an erythematous, oedematous and painful area in the right submandibular space. In both cases the diagnosis of cellulitis was confirmed by ultrasound. A broad spectrum, multidrug antimicrobial therapy was administered till complete resolution.

CONCLUSIONS

Due to the characteristic antibiotic resistance of MRSA and the potential complications of those infections in such delicate patients, basic prevention measures still represent the key to avoid the spreading of neonatal MRSA infections in NICUs, which include hand hygiene and strict precautions, as well as screening of patients for MRSA on admission and during hospital stay, routine prophylactic topical antibiotic of patients, enhanced environmental cleaning, cohorting and isolation of positive patients, barrier precautions, avoidance of ward crowding, and, in some units, surveillance, education and decolonization of healthcare workers and visiting parents.

Association between methicillin-resistant Staphylococcus aureus nasal carriage and infection after pancreatic surgery

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) infections after pancreatectomy are relatively rare; however, they can be fatal when associated with pseudoaneurysms. For the past 12 years, we have been investigating nasal MRSA carriage by polymerase chain reaction testing, postoperatively in patients admitted to the intensive care units, to prevent nosocomial infections. Here, we investigated the relationship between MRSA nasal carriage and postoperative MRSA infection at the surgical site, following pancreatectomy.

METHODS

This single-center retrospective study analyzed 313 pancreatectomies (220 pancreaticoduodenectomies and 93 distal pancreatectomies), performed at our hospital between January 2011 and June 2022. The incidence of surgical site infection (SSI) and postoperative MRSA infection were compared between the nasal MRSA-positive and nasal MRSA-negative groups.

RESULTS

MRSA nasal carriage was identified in 24 cases (7.6%), and the frequency of SSIs in the nasal MRSA-positive and MRSA-negative groups were 50% and 36.7%, respectively, with no significant difference (p = .273). However, the frequency of MRSA infection among the SSI cases was significantly higher in the nasal MRSA-positive group (16.7%) than in the nasal MRSA-negative group (1.7%) (p = .003).

CONCLUSION

It should be noted that MRSA carriers have a significantly higher frequency of MRSA-positive SSIs.

Development of a novel circular mRNA vaccine of six protein combinations against Staphylococcus aureus

Staphylococcus aureus is an extraordinarily versatile pathogen, which is currently the most common cause of nosocomial and community infections. Considering that increased antibiotic resistance may hasten the spread of S. aureus, developing an effective vaccine can possibly aid in its control. The RNA vaccine coding immunodominance epitopes from bacteria provide a potential method to induce T and B cell immune responses by translating them into cells. Furthermore, using bioinformatics to create circular RNA vaccines can ensure that the translation of the vaccine is potent and durable. In this study, 7 cytotoxic T lymphocyte (CTL) epitopes, 4 helper T lymphocyte (HTL) epitopes, and 15 B cell epitopes from 6 proteins that are closely associated with the S. aureus virulence and invasion and critical to natural immune responses were mapped. To verify their interactions, all epitopes were docked with the corresponding MHC alleles. The final vaccine was composed of 26 epitopes and the adjuvant β-defencin, and a disulfide bond was also introduced to improve its stability. After the prediction of structure and characteristics, the developed vaccine was docked with TLR2 and TLR4, which induce immunological responses in S. aureus infection. According to the molecular dynamic simulation, the vaccine might interact strongly with TLRs. Meanwhile, it performed well in immunological simulation and population coverage prediction. Finally, the vaccine was converted into a circular RNA using a series of helper sequences to aid in vaccine circulation translation. Hopefully, this proposed structure will be proven to serve a viable vaccine against S. aureus.Communicated by Ramaswamy H. Sarma.

Community-Acquired Methicillin-Resistant Staphylococcus aureus in Hospitals: Age-Specificity and Potential Zoonotic-Zooanthroponotic Transmission Dynamics

Methicillin-resistant Staphylococcus aureus (MRSA) lineages are a devastating clinical and public health issue. Data on local lineage profiles are limited. We report on the frequency of community-acquired and hospital-acquired cases (CA-MRSA, HA-MRSA). We studied 147 isolates from King Khalid tertiary care hospitals (KKH), each from a case in a patient and including 33 patients at the Maternity and Children's Hospital (MCH). Of the 147 isolates, 87 males (59%) and 60 females (41%) were in KKH. The overwhelming majority (80%; n = 119/147) were CA-MRSA in KKH. Intriguingly, despite significant differences between males (70%) and females (53%), lineage-acquisition remained age-specific around 58-60 years in both genders. However, while CA-MRSA dominated early in life (0-20, 70% MCH), it increased with age in KKH adults; 21-50 (28%), >50 (59%) until the overall 80% (n = 144/180). Major specimens included skin-wounds, surgeries (70.3%), blood (13.5%), sputum (8.8%), very rarely urine (4.1%), and nasal (3.4%), albeit most patients showed severe enteritis and necrotizing pneumonia. Antibiograms showed high beta lactam resistances, including amoxicillin-clavulanate (83%), oxacillin (84%), cefoxitin FOX (100%), penicillin and ampicillin (~100%), as well as high resistance (82%) to carbapenem. Fortunately, high susceptibility was seen to non-beta lactams and, to a lesser extent, gentamicin, erythromycin, and fusidic acid; 33%, 34%, and 38%, respectively, in KKH. A similar pattern was seen in MCH except for a low resistance pattern to gentamicin CN, clindamycin CD, erythromycin E, and tobramycin TOB; 34%, 31%, 39%, and 41%, respectively, except for fusidic acid. These findings have significant clinical implications for MRSA patient management strategies. Clinical- and lineage-profiles imply host-selection and zoonotic-zooanthroponotic transmission dynamics. Future molecular typing, sequencing, and characterization of dominant clone(s) is imperative.

MRSA lineage USA300 isolated from bloodstream infections exhibit altered virulence regulation

The epidemic community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 lineage has recently become a leading cause of hospital-associated bloodstream infections (BSIs). Here, we leveraged this recent introduction into hospitals and the limited genetic variation across USA300 isolates to identify mutations that contribute to its success in a new environment. We found that USA300 BSI isolates exhibit altered virulence regulation. Using comparative genomics to delineate the genes involved in this phenotype, we discovered repeated and independent mutations in the transcriptional regulator sarZ. Mutations in sarZ resulted in increased virulence of USA300 BSI isolates in a murine model of BSI. The sarZ mutations derepressed the expression and production of the surface protein ClfB, which was critical for the pathogenesis of USA300 BSI isolates. Altogether, these findings highlight ongoing evolution of a major MRSA lineage and suggest USA300 strains can optimize their fitness through altered regulation of virulence.

Changes in the Use of Antibiotics for Methicillin-Resistant Staphylococcus aureus Bloodstream Infections in Children: A 5-Year Retrospective, Single Center Study

Monitoring antibiotic use in the pediatric population is a challenge, especially when determining a relationship between specific pathogens, infections, and antibiotic use. We retrospectively analyzed the consumption of anti-methicillin-resistant Staphylococcus aureus (MRSA) drugs from 2017 to 2021 at Istituto Giannina Gaslini by means of defined daily dose (DDD) adopted for adults by World Health Organization. We observed a statistically significant increase in the use of daptomycin and ceftaroline, combined with a decrease in the use of vancomycin. In the same period, we observed an increase in the proportion of bloodstream infections due to MRSA with vancomycin minimally inhibitory concentration (MIC mg/L) = 1, that represented the 100% of cases in 2021. This aspect was combined with the observation that in the 59% of cases, where vancomycin plasma concentrations were evaluated, it was not possible to achieve a ratio of the 24-h area under the concentration-time curve and MIC (AUC_0-24/MIC) of vancomycin ≥ 400 mg/L. This study confirms that DDD can be used in pediatrics to monitor antibiotic consumption in relationship with infections epidemiology. Moreover, it describes the presence of vancomycin MIC creep for MRSA also in pediatrics and the difficulties in obtaining effective vancomycin plasma concentrations in children.

Genetic Diversity of Staphylococcus aureus Strains from a Tertiary Care Hospital in Rawalpindi, Pakistan

Staphylococcus aureus is an important healthcare-associated bacterium that causes a multitude of infections in humans such as superficial skin and soft tissue infections, necrotizing pneumonia, foodborne illnesses and postsurgical infections. Treatment of S. aureus infections has become more complicated due to the emergence of Methicillin-Resistant Staphylococcus aureus (MRSA), some of which are multidrug resistant. The present study aimed to characterize S. aureus isolates from a tertiary care hospital in the Rawalpindi district of Pakistan. Staphylococci were isolated from 300 clinical samples collected from January 2018 to January 2019 and S. aureus isolates were tested for antimicrobial susceptibility and analyzed using Pulsed-Field Gel Electrophoresis (PFGE), Multi-Locus Sequence Typing (MLST), staphylococcal cassette chromosome mec (SCCmec) and spa typing. Approximately 25.3% (76/300) of the clinical samples were positive for S. aureus; of those, 88.2% (67/76) were mecA+ (MRSA). In addition to the β-lactam antibiotics, high levels of resistance were also found to the fluoroquinolones (ciprofloxacin, gatifloxacin and levofloxacin (73.7% each)). Of the 23 different spa types identified, the majority of isolates belonged to spa type t632 and t657 (9/66; 13.6% each spa type). ST772-t657 (Bengal Bay clone) was the most commonly identified clone in this study although other clones circulating around different regions of the world were also found indicating the diversity in MRSA isolates from this area of Pakistan. This study emphasizes the need to monitor MRSA in the clinical setting for improved infection control and treatment options.

Corynebacterium pseudodiphtheriticum Exploits Staphylococcus aureus Virulence Components in a Novel Polymicrobial Defense Strategy

While some individuals are nasally colonized with S. aureus, the underlying factors that determine colonization are not understood. There is increasing evidence that indicates that resident bacteria play a role; some commensal species can eradicate S. aureus from the nasal cavity. Among these, Corynebacterium pseudodiphtheriticum can eliminate S. aureus from the human nose. We sought to understand this phenomenon at a molecular level and found that C. pseudodiphtheriticum produces a factor(s) that specifically kills S. aureus. While resistant S. aureus isolates were recovered at a low frequency, resistance came at the cost of attenuated virulence in these strains. Molecular dissection of the specific strategies used by C. pseudodiphtheriticum to kill S. aureus could lead to the development of novel treatments or therapies. Furthermore, commensal competition that requires virulence components of the competitor may represent an exciting and unexplored possibility for development of novel antimicrobial compounds.

Commensal bacteria in the human nasal cavity are known to suppress opportunistic pathogen colonization by competing for limited space and nutrients. It has become increasingly apparent that some commensal bacteria also produce toxic compounds that directly inhibit or kill incoming competitors. Numerous studies suggest that microbial species-specific interactions can affect human nasal colonization by the opportunistic pathogen Staphylococcus aureus. However, the complex and dynamic molecular interactions that mediate these effects on S. aureus nasal colonization are often difficult to study and remain poorly understood. Here, we show that Corynebacterium pseudodiphtheriticum, a common member of the normal nasal microbiota, mediates contact-independent bactericidal activity against S. aureus, including methicillin-resistant S. aureus (MRSA). Bacterial interaction assays revealed that S. aureus isolates that were spontaneously resistant to C. pseudodiphtheriticum killing could be recovered at a low frequency. To better understand the pathways associated with killing and resistance, a S. aureus transposon mutant library was utilized to select for resistant mutant strains. We found that insertional inactivation of agrC, which codes for the sensor kinase of the Agr quorum sensing (Agr QS) system that regulates expression of many virulence factors in S. aureus, conferred resistance to killing. Analysis of the spontaneously resistant S. aureus isolates revealed that each showed decreased expression of the Agr QS components. Targeted analysis of pathways regulated by Agr QS revealed that loss of the phenol-soluble modulins (PSMs), which are effectors of Agr QS, also conferred resistance to bactericidal activity. Transmission electron microscopy analysis revealed that C. pseudodiphtheriticum induced dramatic changes to S. aureus cell surface morphology that likely resulted in cell lysis. Taken together, these data suggest that C. pseudodiphtheriticum-mediated killing of S. aureus requires S. aureus virulence components. While S. aureus can overcome targeted killing, this occurs at the cost of attenuated virulence; loss of Agr QS activity would phenotypically resemble a S. aureus commensal state that would be unlikely to be associated with disease. Commensal competition resulting in dampened virulence of the competitor may represent an exciting and unexplored possibility for development of novel antimicrobial compounds.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Introduction to the Centers for Disease Control and Prevention and the Healthcare Infection Control Practices Advisory Committee Guideline for the Prevention of Surgical Site Infections

Surgical site infection (SSI) is a common type of health-care-associated infection (HAI) and adds considerably to the individual, social, and economic costs of surgical treatment. This document serves to introduce the updated Guideline for the Prevention of SSI from the Centers for Disease Control and Prevention (CDC) and the Healthcare Infection Control Practices Advisory Committee (HICPAC). The Core section of the guideline addresses issues relevant to multiple surgical specialties and procedures. The second procedure-specific section focuses on a high-volume, high-burden procedure: Prosthetic joint arthroplasty. While many elements of the 1999 guideline remain current, others warrant updating to incorporate new knowledge and changes in the patient population, operative techniques, emerging pathogens, and guideline development methodology.

Vaccine development to prevent Staphylococcus aureus surgical-site infections

BACKGROUND

Staphylococcus aureus surgical-site infections (SSIs) are a major cause of poor health outcomes, including mortality, across surgical specialties. Despite current advances as a result of preventive interventions, the disease burden of S. aureus SSI remains high, and increasing antibiotic resistance continues to be a concern. Prophylactic S. aureus vaccines may represent an opportunity to prevent SSI.

METHODS

A review of SSI pathophysiology was undertaken in the context of evaluating new approaches to developing a prophylactic vaccine to prevent S. aureus SSI.

RESULTS

A prophylactic vaccine ideally would provide protective immunity at the time of the surgical incision to prevent initiation and progression of infection. Although the pathogenicity of S. aureus is attributed to many virulence factors, previous attempts to develop S. aureus vaccines targeted only a single virulence mechanism. The field has now moved towards multiple-antigen vaccine strategies, and promising results have been observed in early-phase clinical studies that supported the recent initiation of an efficacy trial to prevent SSI.

CONCLUSION

There is an unmet medical need for novel S. aureus SSI prevention measures. Advances in understanding of S. aureus SSI pathophysiology could lead to the development of effective and safe prophylactic multiple-antigen vaccines to prevent S. aureus SSI.

Methicillin-resistant Staphylococcus aureus carrying the new mecC gene--a meta-analysis

In 2011, a new mecA gene homolog, named mecC gene, was found in isolates from both humans and animals. The discovery of methicillin-resistant Staphylococcus aureus (MRSA) carrying the mecC gene has caused speculations about the origin, epidemiology, and impact of these isolates. The objective of this work is to perform a meta-analysis on the prevalence of mecC MRSA, based on previously published results. Meta-analysis showed that the overall pooled prevalence is 0.009% (95% confidence interval=0.05-0.013) and that there was evidence of heterogeneity (P<0.01, I(2)=97%). In conclusion, the very low reported prevalence provides an important baseline to monitor the epidemiology of this emerging form of MRSA.

The Current State of Screening and Decolonization for the Prevention of Staphylococcus aureus Surgical Site Infection After Total Hip and Knee Arthroplasty

The most common pathogens in surgical site infections after total hip and knee arthroplasty are methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), and coagulase-negative staphylococci. Patients colonized with MSSA or MRSA have an increased risk for a staphylococcal infection at the site of a total hip or knee arthroplasty. Most colonized individuals who develop a staphylococcal infection at the site of a total hip or total knee arthroplasty have molecularly identical S. aureus isolates in their nares and wounds. Screening and nasal decolonization of S. aureus can potentially reduce the rates of staphylococcal surgical site infection after total hip and total knee arthroplasty.

Mild Staphylococcus aureus Skin Infection Improves the Course of Subsequent Endogenous S. aureus Bacteremia in Mice

Staphylococcus aureus carriers with S. aureus bacteremia may have a reduced mortality risk compared to non-carriers. A role for the immune system is suggested. Here, we study in mice the effect of mild S. aureus skin infection prior to endogenous or exogenous S. aureus bacteremia, and evaluate protection in relation to anti-staphylococcal antibody levels. Skin infections once or twice by a clinical S. aureus isolate (isolate P) or S. aureus strain 8325-4 were induced in mice free of S. aureus and anti-staphylococcal antibodies. Five weeks later, immunoglobulin G (IgG) levels in blood against 25 S. aureus antigens were determined, and LD50 or LD100 bacteremia caused by S. aureus isolate P was induced. S. aureus skin infections led to elevated levels of anti-staphylococcal IgG in blood. One skin infection improved the course of subsequent severe endogenous bacteremia only. A second skin infection further improved animal survival rate, which was associated with increased pre-bacteremia IgG levels against Efb, IsaA, LukD, LukE, Nuc, PrsA and WTA. In conclusion, S. aureus isolate P skin infection in mice reduces the severity of subsequent endogenous S. aureus bacteremia only. Although cellular immune effects cannot be rules out, anti-staphylococcal IgG against specified antigens may contribute to this effect.

Cost-Effectiveness of Perioperative Mupirocin Nasal Ointment in Cardiothoracic Surgery

Objective:

To assess the cost-effectiveness of perioperative intranasal application of mupirocin calcium ointment in cardiothoracic surgery.

Design:

Cost-effectiveness analysis based on results of an intervention study with historical controls.

Setting:

University Hospital Rotterdam, a tertiary referral center for cardiac and pulmonary surgery.

Patients:

Consecutive patients undergoing cardiothoracic surgery between August 1, 1989, and February 1, 1991 (control group, n=928), and between March 1, 1991, and August 1, 1992 (intervention group, n=868).

Intervention:

Perioperative nasal application of mupirocin calcium ointment started on the day before surgery, continued for 5 days, twice daily.

Results:

Postoperative costs were increased significantly in patients with a surgical-site infection (SSI), compared with uninfected patients (P<.001). Mean SSI-attributable costs were estimated at $16,878 (95% confidence interval, $15,575-$18,181). The incidence of SSIs was 7.3% in the control group and 2.8% in the intervention group, mupirocin effectiveness being 62%. The costs of mupirocin were $11 per patient. Thus, the savings per SSI prevented were $16,633. To validate this comparative estimate of SSI-attributable costs, a noncomparative analysis of the postoperative length of stay (POLS) was performed, according to the Appropriateness Evaluation Protocol. Approximately 50% of the comparative SSI-attributable POLS were judged SSI-attributable in the noncomparative analysis. Sensitivity analyses, testing for the robustness of our conclusions, indicated that the presented model is rather insensitive to variations in the incidence of SSIs and for the effectiveness and costs of mupirocin. SSI-attributable costs were shown to be the only variable with substantial effect on the cost-effectiveness ratio. Perioperative mupirocin would result in net costs instead of savings only if SSI-attributable costs were less than $245.

Conclusions:

SSIs in patients undergoing cardiothoracic surgery are associated with a substantial increase in postoperative costs. Provided that perioperative mupirocin reduces the SSI rate, this measure will be highly cost-effective in most centers providing cardiothoracic surgical services.

LTX-109 is a novel agent for nasal decolonization of methicillin-resistant and -sensitive Staphylococcus aureus

Nasal decolonization has a proven effect on the prevention of severe Staphylococcus aureus infections and the control of methicillin-resistant S. aureus (MRSA). However, rising rates of resistance to antibiotics highlight the need for new substances for nasal decolonization. LTX-109 is a broad-spectrum, fast-acting bactericidal antimicrobial drug for topical treatment, which causes membrane disruption and cell lysis. This mechanism of action is not associated with cross-resistance and has a low propensity for development of resistance. In the present study, persistent nasal MRSA and methicillin-sensitive S. aureus (MSSA) carriers were treated for 3 days with vehicle or with 1%, 2%, or 5% LTX-109. A significant effect on nasal decolonization was observed already after 2 days of LTX-109 treatment in subjects treated with 2% or 5% LTX-109 compared to vehicle (P ≤ 0.0012 by Dunnett's test). No safety issues were noted during the 9-week follow-up period. Minimal reversible epithelial lesions were observed in the nasal cavity. The systemic exposure was very low, with a maximum concentration of drug in plasma (Cmax) at 1 to 2 h postdosing (3.72 to 11.7 ng/ml). One week after treatment initiation, LTX-109 was not detectable in any subject. Intranasal treatment of S. aureus with LTX-109 is safe and reduces the bacterial load already after a single day of treatment. Hence, LTX-109 has potential as a new and effective antimicrobial agent with a low propensity of resistance development that can prevent infections by MSSA/MRSA during hospitalization. (This study has been registered at ClinicalTrials.gov under registration no. NCT01158235.).

Does the nose know? An update on MRSA decolonization strategies

Colonization with methicillin-resistant Staphylococcus aureus (MRSA) is an important step in the pathogenesis of active infection and is a key factor in the epidemiology of MRSA infection. Decolonization of patients found to have MRSA carriage may be of value in certain patient populations, especially those undergoing elective surgery. However, the most commonly used agent for decolonization, mupirocin, comes with a considerable risk of resistance if widely employed. Recent studies of other novel agents for decolonization show promise, but further research is necessary. This review focuses on the pathogenesis from MRSA colonization to infection, identifies the risk factors for colonization, and summarizes decolonization strategies, including novel approaches that may have a role in decreasing MRSA disease burden.

Identification and functional characterization of a novel monotreme- specific antibacterial protein expressed during lactation

Monotremes are the only oviparous mammals and exhibit a fascinating combination of reptilian and mammalian characters. They represent a component of synapsidal reproduction by laying shelled eggs which are incubated outside the mother’s body. This is accompanied by a prototherian lactation process, marking them as representatives of early mammals. The only extant monotremes are the platypus, and the short- and long- beaked echidnas, and their distributions are limited to Australia and New Guinea. Apart for a short weaning period, milk is the sole source of nutrition and protection for the hatchlings which are altricial and immunologically naive. The duration of lactation in these mammals is prolonged relative to the gestational length and period of incubation of eggs. Much of the development of monotreme young occurs in the non-sterile ex-utero environment. Therefore the role of milk in the growth, development and disease protection of the young is of significant interest. By sequencing the cDNA of cells harvested from monotreme milk, we have identified a novel monotreme- specific transcript, and the corresponding gene was designated as the EchAMP. The expression profile of this gene in various tissues revealed that it is highly expressed in milk cells. The peptides corresponding to the EchAMP protein have been identified in a sample of echidna milk In silico analysis indicated putative antimicrobial potential for the cognate protein of EchAMP. This was further confirmed by in vitro assays using a host of bacteria. Interestingly, EchAMP did not display any activity against a commensal gut floral species. These results support the hypothesis of enhancement of survival of the young by antimicrobial bioactives of mammary gland origin and thus emphasize the protective, non- nutritional role of milk in mammals.

WFDC2 is differentially expressed in the mammary gland of the tammar wallaby and provides immune protection to the mammary gland and the developing pouch young

WAP four disulfide core domain 2 (WFDC2) is a four disulfide core (4-DSC) protein secreted in the milk of the tammar wallaby. It is comprised of two 4-DSC domains assigned domain III at the NH2-terminal end and domain II at the COOH-terminal end. The WFDC2 gene was expressed only during pregnancy, early lactation, towards the end of lactation and involution. The WFDC2 protein showed antibacterial activity against Staphylococcus aureus, Salmonella enterica and Pseudomonas aeruginosa and this activity resided with domain II. There was no antibacterial activity detected against Enterococcus faecalis. The observed expression pattern of tammar WFDC2 and its antibacterial activity suggests a role to either reduce mastitis in the mammary gland caused by S. aureus or to protect the gut of the young at a time when it is not immune-competent. The latter effect could be achieved without disturbing the balance of commensal gut flora such as E. faecalis.

Methicillin-susceptible Staphylococcus aureus clone related to the early pandemic phage type 80/81 causing an outbreak among residents of three occupational centres in Barcelona, Spain

In the 1950s an unusually virulent and transmissible penicillin-resistant Staphylococcus aureus clone harbouring Panton-Valentine leukocidin (PVL) genes, known as phage type 80/81 and subsequently identified as multilocus sequence type (ST) 30, emerged and caused serious infections in hospitals and the community. We describe an outbreak of skin infections caused by a PVL-positive, methicillin-susceptible S. aureus (MSSA) strain of ST1472, related to phage type 80/81, in three associated occupational centres. After identification of the first patient an active case-finding strategy was initiated among the three centres. Epidemiological and clinical features were indistinguishable from outbreaks currently caused by community-acquired methicillin-resistant S. aureus. The S. aureus was cultured and identified from nasal swabs and skin lesions by conventional methods; PVL was detected using a PCR assay. Pulsed-field gel electrophoresis and DNA-array-based genotyping were applied to MSSA isolates. MSSA was identified in nasal swabs from 49 of 133 individuals (37%). A single pulsed-field gel electrophoresis pattern, belonging to ST1472 (CC30) and PVL positivity, were detected in 20 individuals, including eight of 18 skin cultures, i.e. 15% of the screened individuals were colonized by the epidemic strain. Nasal and cutaneous decontamination with 5% nasal mupirocin ointment and 2% aqueous chlorhexidine was implemented for all individuals. Patients with active skin infections were treated with a first-generation cephalosporin. General recommendations were made to prevent cross-transmission. No new cases were reported over the following 90 days.

Negotiating hospital infections: the debate between ecological balance and eradication strategies in British hospitals, 1947-1969

This paper reviews and contrasts two strategies of infection control that emerged in response to the growing use of antibiotics within British hospitals, c. 1946-1969. At this time, we argue, the hospital became an arena within which representatives of the medical sciences and clinical practices contested not so much the content of knowledge but the way that knowledge translated into practice. Key to our story are the conceptual assumptions about antibiotics put forward by clinicians, on the one hand, and microbiologists on the other. The former embraced antibiotics as the latest weapon in their fight to eradicate disease. For clinicians, the use of antibiotics were utilised within a conceptual frame that prioritised the value of the individual patient before them. Microbiologists, in contrast, understood antibiotics quite differently. They adopted a complex understanding of the way antibiotics functioned within the hospital environment that emphasised the relational and ecological aspects of their use. Despite their broader environmental focus, microbiologists focus on the ways in which bacteria travelled led to ever greater emphasis to be placed on the "healthy" body which, having been exposed to antibiotics, became a dangerous carrier of resistant staphylococcal strains. The surrounding debate regarding the appropriate use of antibiotics reveals the complex relationship between hospital, the medical sciences and clinical practice. We conclude that the history of hospital infections invites a more fundamental reflection on global hospital cultures, antibiotic prescription practices, and the fostering of an interdisciplinary spirit among the professional groups living and working in the hospital.

Staphylococcal disease and nasal carriage in the Royal Air Force

1. The nasal carriage of Staph. aureus and its relation to disease was studied in new recruits, boy apprentices and trained men of the Royal Air Force.

2. The proportions of Staph. aureus that were penicillin-resistant ranged from 15% in new recruits to 29% in trained men. In a school for apprentices the rate in new arrivals was 18%, and 23% for boys after the initial training. We were unable to find when these changes occurred.

3. 31% of strains isolated from septic lesions were penicillin-resistant and the rate was similar in all types of unit. Resistant strains were not apparently more virulent than sensitive strains.

4. About 1% of all strains isolated were resistant to tetracycline and streptomycin and much smaller proportions to chloramphenicol and erythromycin.

5. The phage-group distribution was similar for nasal and lesion strains, but nearly half the penicillin-resistant lesion strains belonged to Group I, and types 52A and 3C/55/71 were much commoner in lesions than in the nose.

6. Penicillin-resistant strains were more readily acquired and more rapidly lost than the sensitive strains.

7. Nasal carriers suffered from septic lesions more frequently than non-carriers, and those with a lesion tended to suffer further lesions. There was no evidence of cross-infection among bedroom contacts.

8. The proportion of penicillin-resistant strains rose from 30 to 40% between admission to and discharge from service hospitals. Resistant strains were not carried for long after discharge.

9. Penicillin treatment resulted in a fall in the total carrier rate and a rise in the resistance rate. Phage type analysis showed that this was mainly due to elimination of sensitive strains and recolonization with resistant strains.

We are greatly indebted to Miss Susan Green for the large amount of work that she did in the laboratory. We should like to thank also many Royal Air Force medical officers for their assistance, in particular Wing Commander E. S. Odbert, Wing Commander M. White, Squadron Leader M. Shearer and Flight Lieutenant A. J. Zuckerman; and the Director-General of the Royal Air Force Medical Services for permission to publish the results.

A study of post-operative wound infection in a provincial general hospital

1. A survey of post-operative wound infection was done in 1959–60 on 559 surgical patients admitted to a provincial general hospital.

2. Clinical evidence of post-operative wound sepsis was observed in 71(12·7 %), suppuration in 51(9·1 %) and staphyloccocal wound sepsis in 48 (8·6 %).

3. Seventeen of the patients died in hospital. Although 5 of these had septic wounds, the sepsis did not appear to have been the cause of death.

4. Contrary to some reported findings, the post-operative wound sepsis rate was considerably lower in patients who were staphylococcal nasal carriers on admission to hospital than in non-carriers. Nine out of 153 carriers (5·9 %) developed wound sepsis and 36 out of 385 non-carriers (9·4 %). When allowance is made for 3 highly probable self-infections, the incidence of wound cross-infection was 3 % in carriers and 9 % in non-carriers.

5. The excess of sepsis in non-carriers could not be explained in terms of different age or sex distribution in carrier and non-carrier groups, nor by differences in the types of operation undergone or in degree of exposure to staphylococcal contamination.

6. The excess of sepsis in non-carriers was accounted for by the patients whose wounds had drains rather than by clean-stitched wounds.

7. Those carriers who harboured a staphylococcus of the 80/81 group in the nose on admission to hospital had a higher incidence of wound sepsis than carriers of other phage types or staphylococcus.

8. Three probable instances of wound self-infection occurred, and in the early stages of the survey at least 5 wound infections were probably directly caused by two members of the theatre staff carrying staphylococci of the 80/81 group in the nose and with existing skin sepsis or a recent history.

9. The survey findings and a study of the literature suggested: (a) that the acquisition of a nasal staphylococcus in hospital was probably, as a rule, evidence of exposure to staphylococeal contamination and not a determinant of wound sepsis, unless the patient also became a skin carrier; (b) that a small proportion of patients are self-infected, some are directly infected by theatre personnel, and the wounds of other patients are directly or indirectly contaminated by staphylococci from the ward environment; (c) that wool or cotton fluff contaminated with staphyloccoci may cause wound sepsis by falling into open wounds and as foreign bodies induce a significant reduction in the minimum pus-forming dose of staphylococci; (d) that before ascribing high or low sepsis rates to factors such as the nasal carrier state, the relevant groups should be shown not to differ materially in respect of other factors known to influence the incidence of wound sepsis.

We gratefully acknowledge the help and encouragement of our surgical colleagues Mr H. P. Guerrier, Mr P. J. W. Monks, Mr J. Macpherson and Mr C. C. Jeffery; and of Dr C. P. Warren, consultant pathologist to the Torbay Hospital, Mrs M. Stamp, Matron, Sister E. M. Cottrell, first Infection Control Sister at the Torbay Hospital, and her successor Mr H. Street.

Acknowledgement is also due to the South Western Regional Hospital Board for its encouragement and for a research grant for technical aid, without which the surveys described would not have been possible.

Staphylococcus aureus isolates from blood and anterior nares induce similar innate immune responses in endothelial cells

To evaluate the possibility to distinguish virulent from non-virulent isolates, gene expression in human umbilical vein endothelial cells (HUVEC) induced by invasive and colonizing isolates of Staphylococcus aureus was compared. Gene expression in HUVEC was analyzed by microarray analysis after 4 h of infection with Staphylococcus aureus, isolated from healthy nasal carriers (n = 5) and from blood of septic patients (n = 5), to explore possible differences between the groups of bacteria in interaction with HUVEC. All isolates were spa-typed to disclose strain relatedness. Moreover, the isolates were characterized with DNA microarray to determine the presence of virulence genes and to investigate the potential genes of importance in HUVEC interaction. The expression of 41 genes was up-regulated, and four were down-regulated in HUVEC by all isolates. Most of the up-regulated genes encode cytokines, chemokines, interferon-induced proteins, proteins regulating apoptosis and cell proliferation. There was no difference in the gene expression pattern between HUVEC infected with invasive or colonizing isolates. Furthermore, there was no difference in the presence of bacterial virulence genes between the two groups. In conclusion, our data indicate that S. aureus isolates induce comparable expression patterns in HUVEC, irrespective of invasiveness or presence of virulence genes.

The role of nasal carriage in Staphylococcus aureus burn wound colonization

Thermal injury destroys the physical skin barrier that normally prevents invasion of microorganisms. This and concomitant depression of local and systemic host cellular and humoral immune responses are important factors that contribute to colonization and infection of the burn wound. One of the most common burn wound pathogens is Staphylococcus aureus. Staphylococcus aureus is both a human commensal and a frequent cause of infections leading to mild to life-threatening diseases. Despite a variety of infection control measures, for example patient cohorting and contact precaution at burn centres, S. aureus is still frequently encountered in burn wounds. Colonization with S. aureus has been associated with delayed wound healing, increased need for surgical interventions, and prolonged length of stay at burn centres. In this minireview, we focus on S. aureus nasal carriage in relation to S. aureus burn wound colonization and subsequent infection, and its impact on strategies for infection control.

Pathogenesis of methicillin-resistant Staphylococcus aureus infection

Staphylococcus aureus is a versatile pathogen capable of causing a wide range of human diseases. However, the role of different virulence factors in the development of staphylococcal infections remains incompletely understood. Some clonal types are well equipped to cause disease across the globe, whereas others are facile at causing disease among community members. In this review, general aspects of staphylococcal pathogenesis are addressed, with emphasis on methicillin-resistant strains. Although methicillin-resistant S. aureus (MRSA) strains are not necessarily more virulent than methicillin-sensitive S. aureus strains, some MRSA strains contain factors or genetic backgrounds that may enhance their virulence or may enable them to cause particular clinical syndromes. We examine these pathogenic factors.

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA): new issues for infection control

The emergence and clonal expansion of strains of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) have created new challenges with their entrance to hospitals. The increased virulence of CA-MRSA in concert with the depressed immunity of inpatients may cause added morbidity and mortality expected from healthcare-associated infections. Questions about changing prophylactic and empirical therapy as well as the use of intravenous immunoglobulin for life-threatening infections are addressed.

Carriage of multiple subtypes of methicillin-resistant Staphylococcus aureus by intensive care unit patients

OBJECTIVE

To determine how consistently patients are colonized with methicillin-resistant Staphylococcus aureus (MRSA) at various sites and how many subtypes can be carried simultaneously by a single patient.

SETTING

A 28-bed Intensive care unit in a tertiary-care referral hospital.

METHODS

A total of 1,181 patients were screened by culture of swab specimens obtained from the nose, throat, groin, and axilla on admission to the intensive care unit (ICU), twice weekly during their ICU stay, and at discharge.

RESULTS

MRSA was isolated at least once from 224 patients. Of these isolates, 359 were selected from 32 patients to be subtyped using pulsed-field gel electrophoresis. The rate of compliance with collection of swab specimens was 79.9%. The combination of sites colonized varied frequently over time for many patients. Of patients who had swab specimens obtained twice in 1 day, 8.7% had discordant results from the 2 swab sets. No patient had a clinical isolate that was not of an identical subtype to an isolate from an anatomical site that was sampled for screening. Half the patients carried multiple subtypes during their stay, with up to 4 subtypes per patient.

CONCLUSIONS

The findings of this study may indicate that these patients have been colonized with MRSA on more than one occasion, possibly because of multiple breaches in infection control procedure. In MRSA-colonized patients, anatomical sites were intermittently colonized and carriage of multiple subtypes was common. These findings indicate that MRSA carriage is not a fixed state but may vary over time.

Emergence and resurgence of meticillin-resistant Staphylococcus aureus as a public-health threat

Staphylococcus aureus is a gram-positive bacterium that colonises the skin and is present in the anterior nares in about 25-30% of healthy people. Dependent on its intrinsic virulence or the ability of the host to contain its opportunistic behaviour, S aureus can cause a range of diseases in man. The bacterium readily acquires resistance against all classes of antibiotics by one of two distinct mechanisms: mutation of an existing bacterial gene or horizontal transfer of a resistance gene from another bacterium. Several mobile genetic elements carrying exogenous antibiotic resistance genes might mediate resistance acquisition. Of all the resistance traits S aureus has acquired since the introduction of antimicrobial chemotherapy in the 1930s, meticillin resistance is clinically the most important, since a single genetic element confers resistance to the most commonly prescribed class of antimicrobials--the beta-lactam antibiotics, which include penicillins, cephalosporins, and carbapenems.

Randomized clinical trial of preoperative intranasal mupirocin to reduce surgical-site infection after digestive surgery

BACKGROUND

Compromised patients subjected to major digestive surgery frequently develop infective complications caused by methicillin-resistant Staphylococcus aureus (MRSA), which may have dangerous consequences. This was a prospective randomized study to determine whether intranasal mupirocin could reduce postoperative infective complications in patients having digestive surgery.

METHODS

A total of 395 patients who underwent abdominal digestive surgery were assigned randomly into two groups: a treated group (193 patients) and controls (202). Patients in the treated group were given 30 mg mupirocin calcium hydrate ointment topically to each nostril three times a day on each of the 3 days before operation. The untreated group received no mupirocin treatment.

RESULTS

Most infections were due to Gram-negative bacteria in both groups. There were 21 Gram-positive infections detected at the surgical site, ten in the treated group and 11 in control patients. The incidence of pneumonia was significantly different between the groups (none in the treated group and five in control patients; P = 0.028). Four of five patients with pneumonia had a sputum culture containing MRSA.

CONCLUSION

Intranasal mupirocin treatment had no significant impact on surgical-site infection after digestive surgery.

Differences between Staphylococcus aureus isolates from medical and nonmedical hospital personnel

It is unclear whether the levels of Staphylococcus aureus colonization of hospital personnel with patient exposure are increased or whether personnel become colonized with more antibiotic-resistant strains. Differences in nasal and hand carriage of S. aureus between medical and nonmedical hospital personnel were examined. No differences in nasal carriage between the two groups were found; however, there was a trend that suggested differences in the rates of hand carriage of S. aureus (18% of nonmedical personnel and 10% of medical personnel). Medical personnel were colonized with more antibiotic-resistant isolates than nonmedical personnel (mean, 2.8 versus 2.1 isolates [P < 0.03]), and the strain profiles indicated that they tended to be more clonal in origin, suggesting that exposure to hospital isolates alters the colonization profile.

The role of methicillin-resistant Staphylococcus aureus in orthopaedic implant surgery

The problems presented by methicillin-resistant Staphylococcus aureus (MRSA) must be accommodated in both prophylactic and treatment regimens for orthopaedic implant surgery. The rationale of pre-admission nasal swabbing in directing prophylaxis for orthopaedic patients is discussed. The potential advantage of nasal mupirocin for Staphylococcus aureus and MRSA carriers is described. Methicillin-resistant Staphylococcus epidermidis is commented upon as another hazard in orthopaedics. Criteria for choosing glycopeptides in the treatment of implant infections are discussed, and need to be defined in orthopaedic units. Treatment regimens are briefly described.

The significance of nasal carriage of Staphylococcus aureus as risk factor for human skin infections

The present study was designed to investigate the significance and the relationship between nasal carriage of Staphylococcus aureus and staphylococcal skin infections. Thirty-one S. aureus strains, isolated from 12 patients with chronic and recurrent skin infections, one patient with septicemia and one patient with otitis externa were studied. The staphylococcal strains were isolated from the site of infection and from the anterior nares of each patient. The identity of both strains of each pair could be demonstrated by determination of phenotypic properties and by genotyping of the isolates. The phenotypic properties included hemolytic activities, antibiotic resistance data, and the production of enterotoxins. The identity was additionally confirmed by phage-typing, by determination of the size and the number of repeats of the X region of spa gene, by determination of gene polymorphisms of coa gene and by macrorestriction analysis of the chromosomal DNA of the isolates by pulsed-field gel electrophoresis. The present results showed an identity of the S. aureus obtained from anterior nares and from skin infection of each patient indicating the importance of nasal carriage of these bacteria for development of human skin infection.