Investigation of a cluster of Candida albicans invasive Candidiasis in a neonatal intensive care unit by pulsed-field gel electrophoresis

Nosocomial invasive candidiasis (IC) has emerged as a major problem in neonatal intensive care units (NICUs). We investigated herein the temporal clustering of six cases of neonatal IC due to Candida albicans in an NICU. Eighteen isolates obtained from the six neonates and two isolates from two health care workers (HCWs) working at the same unit and suffering from fingers' onychomycosis were genotyped by electrophoretic karyotyping (EK) and restriction endonuclease analysis of genomic DNA by using Sfi I (PFGE-Sfi I). PFGE-Sfi I was more effective in discriminating between temporally related isolates. It showed that (i) both HCWs had specific strains excluding them as a source of infections in neonates. (ii) Isolates collected from three neonates were identical providing evidence of their clonal origin and the occurrence of a horizontal transmission of C. albicans in the unit. (iii) The three remaining neonates had specific strains confirming that the IC cases were coincidental. (iv) Microevolution occurred in one catheter-related candidemia case. Our results illustrate the relevance of the molecular approach to investigate suspected outbreaks in hospital surveys and the effectiveness of PFGE-Sfi I for typing of epidemiologically related C. albicans isolates.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

Use of molecular methods in identification of Candida Species and evaluation of fluconazole resistance

The aim of this study was to evaluate the use of one of the molecular typing methods such as PCR (polymerase chain reaction) following by RFLP (restriction fragment length polymorphism) analysis in the identification of Candida species and then to differentiate the identified azole susceptible and resistant Candida albicans strains by using AP-PCR (arbitrarily primed-polymerase chain reaction). The identification of Candida species by PCR and RFLP analysis was based on the size and primary structural variation of rDNA intergenic spacer regions (ITS). Forty-four clinical Candida isolates comprising 5 species were included to the study. The amplification products were digested individually with 3 different restriction enzymes: HaeIII, DdeI, and BfaI. All the isolates tested yielded the expected band patterns by PCR and RFLP analysis. The results obtained from this study demonstrate that Candida species can be differentiated as C. albicans and non-C. albicans strains only by using HaeIII restriction enzyme and BfaI maintains the differentiation of these non-C. albicans species. After identification Candida species with RFLP analysis, C. albicans strains were included to the AP-PCR test. By using AP-PCR, fluconazole susceptible and resistant strains were differentiated. Nine fluconazole susceptible and 24 fluconazole resistant C. albicans were included to the study. Fluconazole resistant strains had more bands when evaluating with the agarose gel electrophoresis but there were no specific discriminatory band patterns to warrant the differentiation of the resistance. The identification of Candida species with the amplification of intergenic spacer region and RFLP analysis is a practical, short, and a reliable method when comparing to the conventional time-consuming Candida species identification methods. The fluconazole susceptibility testing with AP-PCR seems to be a promising method but further studies must be performed for more specific results.

Effect of fluoride on cariogenic oral microorganisms (an in vitro study)

The effect of sodium fluoride and sodium monofluorophosphate at concentrations of 1, 5, 10, 50, 100 and 1000 mg/l in phosphate buffer (pH 6.5) as well as in UHT milk were studied on cultures and suspensions of Streptococcus mutans, Lactobacillus acidophilus and Candida albicans. Using serial tenfold dilutions up to 10(-7) of 24-48 hour cultures, a subsequent 0, 60 and 120 min incubation caused no decrease in the number of CFUs. Growth kinetic studies in the Bioscreen biophotometer (Labsystem, Finland) revealed that sodium fluoride in different concentrations (from 0.875 mg/l up to 500 mg/l) influenced the growth dynamics of S. mutans and C. albicans: the exponential phase flattened out at the highest fluoride concentrations (500 mg/l) present in the growth media. The lag phase of C. albicans became longer. The results of these experiments indicate that sodium fluoride administered at higher concentrations than the usual caries preventive dosage made the generation time of cariogenic oral bacteria and fungi longer, slowing down their multiplication.

Influence of the hospital environment on yeast colonization in nursing students

Fungemias have increased in recent decades, with high indices of morbidity and mortality. The agents of fungal infection isolated most often are yeasts, which can be acquired by direct contact with already colonized individuals. The present study aimed to detect yeast colonization in nursing students, and to study the possible influence of the hospital environment on colonization. The nasal cavities and hands of 22 students were sampled before and after a 62-day hospital training period. The yeast colonies that developed were identified using standard techniques. In total, 47 yeast samples were isolated, which were part of the normal flora of 15 (68%) students. Candida albicans was the species isolated most often (P < 0.05), comprising 59.6% of all isolates. The hospital environment affected colonization, as following the training period there was a significant increase in the number of microorganisms isolated, and also replacement of less virulent species by C. albicans. Our results are important because hospital infections of fungal origin are emerging today, and cross-transmission appears to be an important factor. In this situation, prophylactic measures are necessary to control the nosocomial microbial flora and thus reduce the incidence of hospital infections.

Candida glabrata: review of epidemiology, pathogenesis, and clinical disease with comparison to C. albicans

Until recently, Candida glabrata was considered a relatively nonpathogenic commensal fungal organism of human mucosal tissues. However, with the increased use of immunosuppressive agents, mucosal and systemic infections caused by C. glabrata have increased significantly, especially in the human immunodeficiency virus-infected population. A major obstacle in C. glabrata infections is their innate resistance to azole antimycotic therapy, which is very effective in treating infections caused by other Candida species. Candida glabrata, formerly known as Torulopsis glabrata, contrasts with other Candida species in its nondimorphic blastoconidial morphology and haploid genome. C. glabrata currently ranks second or third as the causative agent of superficial (oral, esophageal, vaginal, or urinary) or systemic candidal infections, which are often nosocomial. Currently, however, there are few recognized virulence factors of C. glabrata and little is known about the host defense mechanisms that protect against infection. Two established animal models (systemic and vaginal) have been established to study treatment, pathogenesis, and immunity. Treatment of C. glabrata infections can include azoles but often requires amphotericin B or flucytosine. This review summarizes all known clinical and experimental information about C. glabrata infections with comparisons to C. albicans as a means of contrasting the two species commonly observed and emphasizing the many recognized differences.

Molecular methods for epidemiological and diagnostic studies of fungal infections

Over the past two decades there has been a remarkable increase in the incidence of invasive fungal infections. Molecular methods, such as karyotyping, restriction analysis and polymerase chain reaction (PCR), have now been applied to improve our current understanding of the epidemiology of these fungal infections. For example, investigations on nosocomial outbreaks of fungal infections have been greatly facilitated by molecular methods. In addition, the ability to diagnose and identify deep-seated mycoses may be enhanced by the use of molecular techniques. In the near future it is possible that PCR-based methods will supplement, or perhaps even replace, traditional methods for detection of Candida albicans blood stream infections, invasive aspergillosis and Pneumocystis carinii pneumonia. This review examines the progress of molecular biology into the clinical arena of fungal epidemiology, laboratory identification and diagnosis.

Nosocomial Candida glabrata colonization: an epidemiologic study

Candida glabrata has emerged as an important nosocomial pathogen, yet little is known about its epidemiology. We prospectively followed 98 patients admitted to a medical intensive care unit and the bone marrow transplant unit of a university hospital. Samples from environmental surfaces and the hands of hospital personnel were also cultured. Patients with newly acquired C. glabrata strains were compared to controls who were culture negative for C. glabrata. C. glabrata was recovered from multiple sites from 24 patients and three environmental surfaces. Sixteen patients (17%) acquired C. glabrata after admission to the study units. Significant risk factors for the nosocomial acquisition of C. glabrata were prolonged duration of hospitalization in the unit and prior antimicrobial use. Strain delineation by restriction enzyme analysis revealed 28 different strains of C. glabrata; three strain types were common to nine patients. The environmental isolates were of the same strain type and common to five patients (four patients with newly acquired strains). These results suggest the possibility of exogenous nosocomial acquisition of C. glabrata, including the possible acquisition from the hospital environment. Transmission may be by indirect contact since identical strains of C. glabrata were recovered from patients who were geographically and temporally associated.

Evaluation of pulsed-field gel electrophoresis as a typing system for Candida rugosa: comparison of karyotype and restriction fragment length polymorphisms

Nosocomial infections with Candida species have emerged as an increasingly important cause of morbidity and mortality in intensive care units. Ten Candida rugosa isolates from a previously documented cluster of C. rugosa infections in one hospital (nine burn unit isolates and one isolate from another hospital ward) and eight C. rugosa isolates recovered in a referral fungus testing laboratory (comparison isolates) from distinct geographic areas were investigated by molecular techniques. Isolates were from multiple anatomic sites. Pulsed-field gel electrophoresis (PFGE) of whole-cell DNA was performed with the 18 C. rugosa isolates as a marker of strain identity. The PFGE karyotypes of the C. rugosa isolates were demonstrated from four to seven chromosome bands. Karyotyping revealed the same PFGE pattern for the nine outbreak isolates from the burn unit, confirming clonal strain transmission. The isolate from the other hospital ward had a distinct karyotype. Distinct PFGE karyotype patterns were demonstrated for the eight comparison isolates. Restriction fragment length polymorphisms (RFLP) generated from whole-cell DNA digested with SfiI demonstrated the same RFLP pattern among outbreak isolates. Among comparison isolates, karyotyping distinguished some isolates that were indistinguishable by RFLP patterns. Karyotyping by PFGE appears to be the most useful molecular typing tool for discrimination among strains of C. rugosa and will be a useful marker for evaluating the epidemiology of future C. rugosa infections.

Control of endemic glycopeptide-resistant enterococci

OBJECTIVE

To evaluate the epidemiology of, and control measures for, vancomycin-resistant Enterococcus (VRE) in a renal unit.

DESIGN

A 3-month, prospective, prevalence culture survey of patients on a 24-bed renal unit.

SETTING

A 975-bed community teaching hospital.

PATIENTS

Patients admitted to the renal unit over a 3-month period. Patients identified with VRE were each matched with four patients without VRE isolated over the study period. INTERVENTIONS/CONTROL MEASURES: Resistant-organism barrier precautions. To eradicate carriage of VRE, two patients with VRE stool colonization were treated with 5 days of oral doxycycline (100 mg twice per day) and rifampin (300 mg/day).

RESULTS

Seven patients with VRE (8 isolates) were identified. Five isolates were Enterococcus faecium (vancomycin MIC = 16 to 256 micrograms/mL), two were Enterococcus faecalis (MICs = 16 and 124 micrograms/mL), and one was Enterococcus gallinarum (MIC = 8.0 micrograms/mL). Eradication of carriage with VRE was accomplished in two patients treated with doxycycline and rifampin. In the final 30 days of the culture survey and at 9 months, there were no further patients with VRE identified.

CONCLUSIONS

Resistant-organism precautions and elimination of patient carriage may be useful measures for controlling the spread of low-prevalence endemic vancomycin-resistant Enterococcus.

Validity of contour-clamped homogeneous electric field electrophoresis as a typing system for Candida albicans

Instigated by an increase in serious human Candida infections and aided by advances in technology, there has been renewed interest in the study of the epidemiology of fungal infections. Among the newer techniques available, contour-clamped homogeneous electric field (CHEF) electrophoresis has shown great promise as a tool for typing strains of Candida albicans. However, few studies have addressed the reproducibility of the preparatory and electrophoretic methods. Through a series of analyses on clinical isolates of C. albicans, we were able to demonstrate that (a) sample preparation induced no appreciable artifacts in CHEF banding patterns; (b) the electrophoretic patterns were reproducible over time; (c) changes in colony morphology were not associated with changes in the electrophoretic pattern, and (d) the method was more sensitive than restriction enzyme analysis (REA) for demonstrating strain differences. CHEF electrophoresis is a sensitive and reproducible tool for the study of Candida epidemiology. Further use and study of this methodology is warranted.