Community-acquired methicillin-resistant Staphylococcus aureus infections

A novel Staphylococcus aureus vaccine: iron surface determinant B induces rapid antibody responses in rhesus macaques and specific increased survival in a murine S. aureus sepsis model

Staphylococcus aureus is a major cause of nosocomial infections worldwide, and the rate of resistance to clinically relevant antibiotics, such as methicillin, is increasing; furthermore, there has been an increase in the number of methicillin-resistant S. aureus community-acquired infections. Effective treatment and prevention strategies are urgently needed. We investigated the potential of the S. aureus surface protein iron surface determinant B (IsdB) as a prophylactic vaccine against S. aureus infection. IsdB is an iron-sequestering protein that is conserved in diverse S. aureus clinical isolates, both methicillin resistant and methicillin sensitive, and it is expressed on the surface of all isolates tested. The vaccine was highly immunogenic in mice when it was formulated with amorphous aluminum hydroxyphosphate sulfate adjuvant, and the resulting antibody responses were associated with reproducible and significant protection in animal models of infection. The specificity of the protective immune responses in mice was demonstrated by using an S. aureus strain deficient for IsdB and HarA, a protein with a high level of identity to IsdB. We also demonstrated that IsdB is highly immunogenic in rhesus macaques, inducing a more-than-fivefold increase in antibody titers after a single immunization. Based on the data presented here, IsdB has excellent prospects for use as a vaccine against S. aureus disease in humans.

Clinical presentation of community-acquired methicillin-resistant Staphylococcus aureus in pregnancy

OBJECTIVE

The objective of this study was to review the presentation and management of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) in pregnant women.

METHODS

This was a chart review of pregnant patients who were diagnosed with MRSA between January 1, 2000, and July 30, 2004. Data collected included demographic characteristics, clinical presentation, culture results, and pathogen susceptibilities. Patients' pregnancy outcomes were compared with the general obstetric population during the study period.

RESULTS

Fifty-seven charts were available for review. There were 2 cases in 2000, 4 in 2001, 11 in 2002, 23 in 2003, and 17 through July of 2004. Comorbid conditions included human immunodeficiency virus and acquired immunodeficiency syndrome (13%), asthma (11%), and diabetes (9%). Diagnostic culture was most commonly obtained in the second trimester (46%); however 18% of cases occurred in the postpartum period. Skin and soft tissue infections accounted for 96% of cases. The most common site for a lesion was the extremities (44%), followed by the buttocks (25%), and breast (mastitis) (23%). Fifty-eight percent of patients had recurrent episodes. Sixty-three percent of patients required inpatient treatment. All MRSA isolates were sensitive to trimethoprim-sulfamethoxazole, vancomycin, and rifampin. Other antibiotics to which the isolates were susceptible included gentamicin (98%) and levofloxacin (84%). In comparison with the general obstetric population, patients with MRSA were more likely to be multiparous and to have had a cesarean delivery.

CONCLUSION

Community-acquired MRSA is an emerging problem in our obstetric population. Most commonly, it presents as a skin or soft tissue infection that involves multiple sites. Recurrent skin abscesses during pregnancy should raise prompt investigation for MRSA.

LEVEL OF EVIDENCE

II-3.

Necrotizing staphylococcal pneumonia in a neonate

Hospitalized neonates are commonly colonized soon after birth with Staphylococcus aureus. The majority of neonates do not develop infectious sequelae; however, premature neonates appear to be more susceptible to serious infections, such as pneumonia. We report a case of an extremely low birth weight infant who developed necrotizing pneumonia due to methicillin-resistant Staphylococcal aureus (MRSA). The MRSA isolate from this neonate is identical to the strains that have been causing primarily community-associated skin and soft tissue infections. The severe course of this patient may be attributed to the presence of the Panton-Valentine leukocidin gene, a well-known virulence factor leading to soft tissue and pulmonary infections.

Recently approved and investigational antibiotics for treatment of severe infections caused by Gram-positive bacteria

The development of resistance in the major pathogenic Gram-positive genera Staphylococcus and Streptococccus has led to the need for new agents that are able to overcome existing resistance mechanisms or that have novel mechanisms of action. There is currently a dearth of new agents that are active against resistant bacterial species. Agents that have recently been approved for clinical use include linezolid, the first oxazolidinone in clinical use, daptomycin, the first lipopeptide in clinical use, and telithromycin, a ketolide that is derived from clarithromycin. Agents currently in clinical development include tigecycline, a broad-spectrum intravenous tetracycline, ceftobiprole, a broad-spectrum cephalosporin that has activity against methicillin-resistant staphylococci, DX-619 and WCK-771, which are potent quinolones that have activity against quinolone-resistant staphylococci, oritavancin and dalbavancin, both of which are new glycopeptides, and iclaprim, which is a diaminopyrimidine. Additional agents that are in preclinical development against Gram-positive pathogens include quinoline-naphthyridine agents, which target novel DNA gyrase sites, other novel quinolones that have high potency, peptide deformylase inhibitors, and new lincosamide, oxazolidinone, lipopeptide and cephalosporin derivatives. Misuse of potent new agents will, however, result in the inevitable development of resistance to these agents; responsible use of potent new agents is required to prevent continuation of this vicious cycle.

Results of disk diffusion testing with cefoxitin correlate with presence of mecA in Staphylococcus spp

The cefoxitin disk diffusion (DD) test for predicting mecA-mediated oxacillin resistance in staphylococci was assessed during a three-phase study. In phase 1, one laboratory tested 62 and 53 strains of Staphylococcus aureus and coagulase-negative staphylococci (CoNS), respectively. These data were used to choose the provisional cefoxitin DD breakpoints (resistant/susceptible) of < or =19 mm/> or =20 mm for S. aureus and < or =24 mm/> or =25 mm for CoNS for the next phase of testing. In phase 2, 10 laboratories each tested approximately 40 in-house strains of staphylococci (half of which were S. aureus) using Mueller-Hinton agar from different manufacturers. In this phase, the sensitivity and specificity, respectively, of the cefoxitin disk test were 98 and 100% for S. aureus and 99 and 96% for CoNS. The cefoxitin DD test performed equivalently to oxacillin broth microdilution (BMD) and to oxacillin DD tests among S. aureus and mecA-positive CoNS strains but gave better results than oxacillin BMD or oxacillin DD for mecA-negative strains of CoNS. The cefoxitin DD test also was much easier to read and did not require the use of transmitted light for detection of resistance. Based on data from the first two phases, the Clinical and Laboratory Standards Institute (CLSI; formerly NCCLS) adopted the use of the cefoxitin DD test for predicting mecA-mediated oxacillin resistance in staphylococci and revised Table 2C in CLSI document M100-S14 to reflect the change. In the third phase, an additional 61 challenge strains of CoNS for which the oxacillin MICs were 0.5 to 2 microg/ml were tested in a single laboratory to determine the effectiveness of the cefoxitin DD test for this group of borderline-resistant isolates. These data were used to refine the description of the test in CLSI document M100-S15. The cefoxitin DD test is preferred over the oxacillin DD test for predicting mecA-mediated oxacillin resistance in S. aureus and CoNS.

Development of a new oligonucleotide array to identify staphylococcal strains at species level

The genus Staphylococcus is made up of 36 validated species which contain strains that are pathogenic, saprophytic, or used as starter cultures for the food industry. An oligonucleotide array targeting the manganese-dependent superoxide dismutase (sodA) gene was developed to overcome the drawbacks of the conventional methods of identification. Divergences of the sodA gene were used to design oligonucleotide probes, and we showed that each of the 36 species had a characteristic pattern of hybridization. To evaluate the array, we analyzed 38 clinical and 38 food or food plant Staphylococcus isolates identified by the phenotype-based system VITEK 2 (bioMérieux). This commercial kit failed to identify 8 (21%) of the clinical isolates and 32 (84%) of the food and food plant isolates. In contrast, the oligonucleotide array we designed provided an accurate and rapid method for the identification of staphylococcal strains, isolated from clinical, environmental, or food samples, at species level.

Cutaneous Community-acquired Methicillin-resistant Staphylococcus aureus Infection in Participants of Athletic Activities

OBJECTIVES

Cutaneous community-acquired methicillin-resistant Staphylococcus aureus (CAMRSA) has been identified in otherwise healthy individuals either with or without methicillin-resistant S. aureus (MRSA)-associated risk factors who participate in athletic activities. The purpose of this study was to describe the clinical features of CAMRSA skin infection that occurred in university student athletes, evaluate the potential mechanisms for the transmission of MRSA infection of the skin in participants of athletic activities, and review the measures for preventing the spread of cutaneous CAMRSA infection in athletes.

METHODS

A retrospective chart review of the student athletes from the University of Houston whose skin lesions were evaluated at the Health Center and grew MRSA was performed. The clinical characteristics and the postulated mechanisms of cutaneous MRSA infection in the athletes were compared with those previously published in reports of CAMRSA skin infection outbreaks in other sports participants.

RESULTS

Cutaneous CAMRSA infection occurred in seven student athletes (four women and three men) who were either weight lifters (three students) or members of a varsity sports team: volleyball (two women), basketball (one woman), and football (one man). The MRSA skin infection presented as solitary or multiple, tender, erythematous, fluctuant abscesses with surrounding cellulitis. The lesions were most frequently located in the axillary region (three weight lifters), on the buttocks (two women), or on the thighs (two women). The drainage from all of the skin lesions grew MRSA, which was susceptible to clindamycin, gentamicin, rifampin, trimethoprim/sulfamethoxazole, and vancomycin; five of the isolates were also susceptible to ciprofloxacin and levofloxacin. All of the bacterial strains were resistant to erythromycin, oxacillin, and penicillin. The cutaneous MRSA infections persisted or worsened in the six athletes who were empirically treated for methicillin-sensitive S. aureus at their initial visit. Complete resolution of the skin infection occurred after the abscesses had been drained and the athlete had been treated with systemic antimicrobial therapy for which the bacterial strain was susceptible.

CONCLUSIONS

Cutaneous CAMRSA infection typically presents as an abscess, with or without surrounding cellulitis, in otherwise healthy participants of athletic activities who have or do not have MRSA-associated risk factors. Athletes who have MRSA skin infections include weight lifters and team members from competitive sports such as basketball, fencing, football, rugby, volleyball, and wrestling. Bacterial culture of suspected infectious skin lesions should be performed to establish the diagnosis of cutaneous MRSA infection and to determine the antibiotic susceptibility of the bacterial isolate. Treatment of cutaneous MRSA infection involves drainage of the abscess (either spontaneously or after incision) and appropriate systemic antimicrobial therapy. Direct skin-to-skin physical contact with infectious lesions or drainage, skin damage that facilitates the entry of bacteria, and sharing of infected equipment, clothing, or personal items may result in the acquisition and transmission of MRSA infection in participants of athletic activities. Earlier detection and topical treatment of the athlete's skin wounds by their coaches, avoidance of contact with other participants' cutaneous lesions and their drainage, and good personal hygiene are measures that can potentially prevent the spread of cutaneous MRSA infection in participants of athletic activities.

Reducing the global burden of sepsis in infants and children: a clinical practice research agenda

OBJECTIVE

Sepsis remains a predominant cause of mortality and morbidity in children in the developing and industrialized world. This review discusses a clinical practice research agenda to reduce this global burden.

DESIGN

Summary of the literature with analysis by experts.

RESULTS

Many interventions have been proven effective in decreasing sepsis. Heterologous immunization with attenuated Bacillus Camille Guerin vaccine reduces all-cause mortality, and specific immunizations further reduce morbidity and mortality from many specific microbes. Antepartum antibiotics reduce the prevalence of cerebral palsy and mortality in infants. Administration of antibiotics to neonates with signs of sepsis reduces all-cause mortality five-fold and can also reduce mortality in the big four killers of children: severe pneumonia, diarrhea, malaria, or measles. Immunonutrition with zinc and vitamin A can further reduce morbidity in diarrhea and pneumonia and reduce mortality in measles. First-hour rapid intravenous fluid resuscitation achieves 100% survival in dengue shock, and time-sensitive fluid resuscitation and inotropic support reduces mortality ten-fold in meningococcal septic shock. Multiple organ failure occurs when late or inadequate resuscitation results in systemic thrombosis or when infection is not eradicated because of immunosuppression or inadequate source control.

CONCLUSIONS

The global burden of sepsis can be reduced by 1) prevention with improved heterologous or specific vaccines and vitamin or mineral supplement programs; 2) early recognition and treatment with appropriate antibiotics, intravenous fluid resuscitation, and inotropic support in organized healthcare-delivery systems; and 3) development of new diagnostics and therapeutics that reduce systemic thrombosis, improve immune function, and kill resistant organisms.