Methicillin-resistant Staphylococcus Aureus Infection

Molecular Epidemiological Survey of Prophages in MRSA Isolates in Taiwan

Introduction

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) type SCCmec IV or V is increasing in Taiwan. It has been suggested that the surface protein SasX is responsible for their transmission. However, the sasX gene was not detected in our SCCmec IV or V isolates. Since sasX was originally found in S. epidermidis and believed to be transferred to S. aureus by a prophage, studies were conducted to detect and type this prophage in our clinical isolates.

Materials and Methods

A total of 1192 MRSA isolates collected from 2006 to 2014 were examined. Multiplex PCRs were performed to determine SCCmec, sasX, and prophage types.

Results

The prevalence of SCCmec IV and V isolates was increased in recent years (from 2006 to 2014). The sasX gene was present in most SCCmec III isolates but was absent in SCCmec IV or V isolates. The Sa5 prophage was found only in SCCmec IV and SCCmec V (or V_t) isolates, and the Sa6 prophage was mainly present in SCCmec III isolates. MRSA isolates harboring prophage combinations Sa1, Sa2, and Sa3; Sa2 and Sa3; Sa2, Sa3, and Sa7; or Sa2 and Sa7 were mainly of SCCmec II, and those that harbored prophage combinations Sa3 and Sa6; Sa3, Sa6, and Sa7; or Sa3 and Sa7 were mostly of SCCmec III. The numbers of SCCmec II isolates containing prophages Sa2, Sa3, and Sa7 and those of SCCmec III isolates containing prophages Sa3 and Sa6 or Sa3, Sa6, and Sa7 were decreased from 2010 to 2014. The number of SCCmec IV isolates with prophage Sa3 or prophages Sa3 and Sa5 was decreased, but that of those with prophage Sa6 or prophages Sa2 and Sa3 was increased from 2010 to 2014.

Conclusion

The sasX gene was found to play no role in clonal selection of MRSA. The finding that different SCCmec types of MRSA harbored different types of prophages suggests that these prophages may affect the survival and clonal expansion of certain types of MRSA.

Studies of Staphylococcus aureus FabI inhibitors: fragment-based approach based on holographic structure-activity relationship analyses

AIM

FabI is a key enzyme in the fatty acid metabolism of Gram-positive bacteria such as Staphylococcus aureus and is an established drug target for known antibiotics such as triclosan. However, due to increasing antibacterial resistance, there is an urgent demand for new drug discovery. Recently, aminopyridine derivatives have been proposed as promising competitive inhibitors of FabI.

METHODS

In the present study, holographic structure-activity relationship (HQSAR) analyses were employed for determining structural contributions of a series containing 105 FabI inhibitors.

RESULTS & CONCLUSION

The final HQSAR model was robust and predictive according to statistical validation (q² and r²_pred equal to 0.696 and 0.854, respectively) and could be further employed to generate fragment contribution maps. Then, final HQSAR model together with FabI active site information can be useful for designing novel bioactive ligands.

Mechanism and inhibition of saFabI, the enoyl reductase from Staphylococcus aureus

Approximately one-third of the world's population carries Staphylococcus aureus. The recent emergence of extreme drug resistant strains that are resistant to the "antibiotic of last resort", vancomycin, has caused a further increase in the pressing need to discover new drugs against this organism. The S. aureus enoyl reductase, saFabI, is a validated target for drug discovery. To drive the development of potent and selective saFabI inhibitors, we have studied the mechanism of the enzyme and analyzed the interaction of saFabI with triclosan and two related diphenyl ether inhibitors. Results from kinetic assays reveal that saFabI is NADPH-dependent, and prefers acyl carrier protein substrates carrying fatty acids with long acyl chains. On the basis of product inhibition studies, we propose that the reaction proceeds via an ordered sequential ternary complex, with the ACP substrate binding first, followed by NADPH. The interaction of NADPH with the enzyme has been further explored by site-directed mutagenesis, and residues R40 and K41 have been shown to be involved in determining the specificity of the enzyme for NADPH compared to NADH. Finally, in preliminary inhibition studies, we have shown that triclosan, 5-ethyl-2-phenoxyphenol (EPP), and 5-chloro-2-phenoxyphenol (CPP) are all nanomolar slow-onset inhibitors of saFabI. These compounds inhibit the growth of S. aureus with MIC values of 0.03-0.06 microg/mL. Upon selection for resistance, three novel safabI mutations, A95V, I193S, and F204S, were identified. Strains containing these mutations had MIC values approximately 100-fold larger than that of the wild-type strain, whereas the purified mutant enzymes had K i values 5-3000-fold larger than that of wild-type saFabI. The increase in both MIC and K i values caused by the mutations supports the proposal that saFabI is the intracellular target for the diphenyl ether-based inhibitors.

Risk factors for postoperative mediastinitis due to methicillin-resistant Staphylococcus aureus

Risk factors for developing postoperative mediastinitis (POM) due to methicillin-resistant Staphylococcus aureus (MRSA) were analyzed in a case-case control study of patients who underwent median sternotomy during the period from 1994 through 2000. Three patient groups were studied. The first consisted of 64 patients with POM due to MRSA; the second consisted of 79 patients with POM due to methicillin-susceptible S. aureus (MSSA); and the third consisted of 80 uninfected control patients. In multivariable analysis, patients who were diabetic (adjusted OR, 2.86; 95% CI, 1.22-6.70), female (OR, 2.70; 95% CI, 1.25-5.88), and >70 years old (OR, 3.43; 95% CI, 1.53-7.71) were more likely to develop POM due to MRSA. In contrast, the only independent risk factor associated with POM due to MSSA was obesity (OR, 2.49; 95% CI, 1.25-4.96). Antimicrobial prophylaxis consisted primarily of cephalosporin antibiotics (administered to 97% of the patients). Changes in perioperative antimicrobial prophylaxis, in addition to other interventions, should be considered for prevention of POM due to MRSA in targeted, high-risk populations.

Antimicrobial resistance and aging: beginning of the end of the antibiotic era?

Throughout the history of mankind, infectious diseases have remained a major cause of death and disability. Although industrialized nations, such as the United States, have experienced significant reductions in infection-related mortality and morbidity since the beginning of the "antibiotic era," death and complications from infectious diseases remain a serious problem for older persons. Pneumonia is the major infection-related cause of death in older persons, and urinary tract infection is the most common bacterial infection seen in geriatric patients. Other serious and common infections in older people include intra-abdominal sepsis, bacterial meningitis, infective endocarditis, infected pressure ulcers, septic arthritis, tuberculosis, and herpes zoster. As a consequence, frequent prescribing of antibiotics for older patients is common practice. The large volume of antibiotics prescribed has contributed to the emergence of highly resistant pathogens among geriatric patients, including methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae, vancomycin-resistant enterococci, and multiple-drug-resistant gram-negative bacilli. Unless preventive strategies coupled with newer drug development are established soon, eventually clinicians will be encountering infections caused by highly resistant pathogens for which no effective antibiotics will be available. Clinicians could then be experiencing the same frustrations of not being able to treat infections effectively as were seen in the "pre-antibiotic era."

Antimicrobial therapy in the elderly

This article focuses on the special characteristics of infection in the elderly and provides an update of the principles of antibiotic selection, use of specific antibiotics, and empiric use of antimicrobials in the treatment of infectious diseases in this particularly vulnerable group. Antituberculous, antifungal, and antiviral agents are mentioned briefly; detailed information regarding these classes of agents in reference to aging can be found in standard reviews of antimicrobial therapy in the elderly.

The economic impact of Staphylococcus aureus infection in New York City hospitals

We modeled estimates of the incidence, deaths, and direct medical costs of Staphylococcus aureus infections in hospitalized patients in the New York City metropolitan area in 1995 by using hospital discharge data collected by the New York State Department of Health and standard sources for the costs of health care. We also examined the relative impact of methicillin-resistant versus -sensitive strains of S. aureus and of community-acquired versus nosocomial infections. S. aureus-associated hospitalizations resulted in approximately twice the length of stay, deaths, and medical costs of typical hospitalizations; methicillin-resistant and -sensitive infections had similar direct medical costs, but resistant infections caused more deaths (21% versus 8%). Community-acquired and nosocomial infections had similar death rates, but community-acquired infections appeared to have increased direct medical costs per patient ($35,300 versus $28,800). The results of our study indicate that reducing the incidence of methicillin-resistant and -sensitive nosocomial infections would reduce the societal costs of S. aureus infection.

Methicillin-resistant Staphylococcus aureus infection in palliative care

Our objective was to assess the impact of methicillin-resistant Staphylococcus aureus (MRSA) infection in palliative care. The study was conducted at three hospices in south London, totalling 118 beds, and the following two methods were used. Firstly, a retrospective review of the notes of patients who were known to be MRSA positive at admission or were subsequently found to be MRSA positive was taken. Secondly, a prospective study of factors influencing bed occupancy in one hospice was conducted. The proportion of admissions who were MRSA positive ranged from 4% to 8% in the three hospices. Seven of the 43 patients who had MRSA suffered clinically significant infections. Risk factors for colonization and bacteraemia were similar to the general population. Sites of infection were variable and multiple and treatment regimes for eradication were variable, with varying outcomes. MRSA infection appeared to delay admission because of the need for single rooms, of which there are few Time spent cleaning rooms after discharge or death also reduced the number of available beds. It was concluded that MRSA infection is associated with significant morbidity in a small number of palliative care patients. Beds unavailable because of MRSA should be considered in bed occupancy figures, otherwise bed occupancy may appear artificially low. The psychological and financial impact of the infection in palliative care patients needs further evaluation.

Approach to fever and infection in the nursing home

OBJECTIVE

To summarize current information on the scope, epidemiology, clinical manifestations, diagnostic approach, and general management of infectious diseases in nursing home residents, as well as the specific treatment of common infections occurring in the nursing home setting.

DESIGN

Survey and literature review of the diagnostic and therapeutic problems of nursing home residents with infections.

CONCLUSIONS

Older persons residing in nursing homes as well as other types of long-term care facilities are at increased risk for infections. Moreover, infection is the most frequent reason for patients to be transferred from nursing homes to an acute-care facility. The most common infections that are acquired in nursing homes are urinary tract infection (cystitis pyelonephritis), respiratory infections (pneumonia, bronchitis), and skin/soft tissue infections (infected pressure ulcers, cellulitis). Most serious infections in this setting are caused by bacteria; however, influenza and other respiratory viruses as well as herpes zoster may cause significant morbidity in older nursing home residents. Mycobacterium tuberculosis infects nursing home residents at a higher rate than it infects older community dwellers. Infections in older nursing home residents may manifest clinically, with atypical symptoms and signs, including the absence of fever. Rapid diagnostic evaluation and early therapeutic intervention are essential for minimizing the high mortality and morbidity associated with infections in this older population; most nursing home residents with serious infections should be considered for hospitalization.

New aspects of old pathogens of pneumonia

Changes in the microorganism or in the host have resulted in exciting new aspects of several old pathogens of pneumonia. Penicillin-resistant Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus, and "toxic strep" are examples of changes in the microorganisms. Host changes have resulted in Mycoplasma pneumoniae now emerging as a cause of pneumonia in the elderly.

Prevalence of oral methicillin-resistant Staphylococcus aureus in an institutionalized veterans population

Methicillin-resistant Staphylococcus aureus (MRSA) is a nosocomial pathogen now of great concern in nursing homes and other institutional settings. MRSA has been well-documented to inhabit the nares, skin wounds, and respiratory tract, but little is known about its presence in the oral cavity. In this study, all patients admitted to an 80-bed VA extended care facility were cultured weekly for 12 weeks to detect the presence of MRSA in the nares, wounds, in-dwelling devices, and the oral cavity. Of a total of 107 participating subjects, 20 cultured positive for oral MRSA, yielding a prevalence of 18.7%, compared with 19.6% prevalence in the nares--the traditionally accepted screening site for MRSA. There was a 91.6% agreement between oral and nasal carriage in subjects, but four of 107 subjects (3.7%) cultured positive for oral MRSA without evidence of nasal carriage. These results suggest that oral MRSA may be more common than previously thought in high-risk settings, with a prevalence comparable with that of nasal infection. Further investigation is necessary to characterize the factors associated with the presence of MRSA in the oral cavity.

Enhancing infection control for elderly and medically compromised patients

Some patients may be at risk for complications from relatively common infectious diseases. Influenza, tuberculosis and methicillin-resistant Staphylococcus aureus infection can lead to illness and even death in elderly, medically compromised and institutionalized individuals. Dental personnel caring for these individuals should adopt preventive strategies that are simple and inexpensive in addition to standard infection control guidelines.