Update on methods used for mycological testing: wide diversity and opportunities for improvement persist

Past analysis of laboratory methods used for mycology specimens revealed significant variation in practices, many of which fell short of recommended procedures. In 2016 these findings led to a set of recommendations for laboratories to consider modification of their methods where appropriate, to analyse current laboratory methods used by participants in the Royal College of Pathologists of Australasia Quality Assurance Programs (RCPAQAP) Mycology module, and to compare these to the 2016 recommendations. Seven test items, with 105-107 participants each, were analysed. Several laboratories (7-12%) did not handle specimens as recommended in an appropriate biological safety cabinet. Direct microscopy was not performed on tissue specimens 23-25% of the time. The most used staining method was potassium hydroxide with an optical brightener for fluorescent microscopy (49%) followed by Gram stain (33%). While 17-25% of laboratories used three or more media, use of four or more was uncommon (<3%). Between 9-13% of participants used only a single non-inhibitory medium for cultures. Urine specimens were incubated longer than recommended with 57% of laboratories incubating for >7days and 24% >21 days. Duration of incubation was shorter than recommended for several specimen types with 36% of skin specimens and 37-48% of tissue specimens being kept ≤21 days. For cultures kept >7 days, 13% were inspected daily, but for those incubating >14 days only 3%. The methods of several laboratories remain outside recommended practice. An updated set of recommendations are made.

Comparison of subclinical dermatophyte infection in short- and long-haired cats

Background and Aim

Long-haired cats may have an increased risk of dermatophytosis due to insufficient grooming and their thick hair coat trapping fungal spores. The prevalence of subclinical dermatophytosis in long-haired cats was evaluated using fungal culture and Wood's lamp test. Hematology and blood chemistry results were compared between cats negative and positive for dermatophytosis.

Materials and Methods

A total of 127 cats (median age, 3 years [range, 10 months-10 years]) without feline leukemia virus or feline immunodeficiency virus infection were classified into short-haired (n=64) and long-haired (n=63) groups. Hair samples were cultured on a fungal culture medium (dermatophyte test medium, enhanced sporulation agar, and Sabouraud agar).

Results

The prevalence of dermatophytosis in short-haired and long-haired cats was 6.25% (95% confidence interval [CI], 2.15-12.28) and 34.92% (95% CI, 22.94-46.90), respectively. The odds of long-haired cats having dermatophytosis were 8.05 (95% CI, 2.44-33.97) times greater than that in short-haired cats. The number of positive dermatophytosis found in domestic short-haired cats (2/50, 4.0%) was significantly lower than that in Persian cats (17/47, 36.17%; p<0.001) and long-haired mixed breed cats (3/7, 42.86%; p=0.011). The overall sensitivity and specificity of the Wood's lamp test for diagnosing Microsporum canis infection were 37.5% (95% CI, 21.2-57.3%) and 96.1% (95% CI, 90.4-98.5%), respectively. Cats with dermatophytosis had significantly lower hematocrit and serum albumin levels than cats without dermatophytosis.

Conclusion

Subclinical dermatophytosis was more common in long-haired cats; therefore, dermatophyte examinations should be performed routinely.

Limited effectiveness of four oral antifungal drugs (fluconazole, griseofulvin, itraconazole and terbinafine) in the current epidemic of altered dermatophytosis in India: results of a randomized pragmatic trial

BACKGROUND

Dermatophytic infections have undergone unprecedented changes in India in the recent past. Clinical trials to find out the effectiveness of the four main oral antifungal drugs are lacking.

OBJECTIVES

We tested the effectiveness of oral fluconazole, griseofulvin, itraconazole and terbinafine in chronic and chronic relapsing tinea corporis, tinea cruris and tinea faciei in an investigator-initiated, randomized, pragmatic trial.

METHODS

Two hundred patients with microscopy-confirmed tinea were allocated to four groups (50 patients in each group): fluconazole 5 mg kg^-1 per day, griseofulvin 10 mg kg^-1 per day, itraconazole 5 mg kg^-1 per day and terbinafine 7·5 mg kg^-1 per day. Allocation was performed by concealed block randomization and the patients were treated for 8 weeks or until cure. Effectiveness was calculated based on intention-to-treat analysis. The trial was registered with the Clinical Trials Registry India (CTRI/2017/04/008281).

RESULTS

At 4 weeks, all drugs were similarly ineffective, with cure rates being 8% or less (P = 0·42). At 8 weeks, the numbers of patients cured were as follows: fluconazole 21 (42%), griseofulvin seven (14%), itraconazole 33 (66%) and terbinafine 14 (28%) (P < 0·001). Itraconazole was superior to fluconazole, griseofulvin and terbinafine (adjusted P ≤ 0·048). Relapse rates after 4 and 8 weeks of cure with the four treatments were not different (P ≥ 0·42). Numbers needed to treat (vs. griseofulvin), calculated on the basis of cure rates at 8 weeks, were as follows: fluconazole 4, itraconazole 2 and terbinafine 8.

CONCLUSIONS

The results show limited effectiveness of all four antifungal drugs. In view of cure rates and the number needed to treat, itraconazole is the most effective drug, followed by fluconazole (daily), terbinafine and then griseofulvin, in chronic and chronic relapsing dermatophytosis in India. What is already known about this topic? Oral antifungal drugs are considered to have a high cure rate in tinea corporis, tinea cruris and tinea faciei. Unprecedented changes have been noticed in the last few years in India in the morphology, course and treatment responsiveness of tinea; however, data about the effectiveness of oral antifungals are lacking. What does this study add? Our results show limited effectiveness of four oral antifungal drugs (fluconazole, griseofulvin, itraconazole and terbinafine) in the current epidemic of altered dermatophytosis in India. Among the four drugs tested, oral itraconazole is the most effective. Linked Comment: Elewski. Br J Dermatol 2020; 183:798-799.

New Developments in Bacterial, Viral, and Fungal Cutaneous Infections

PURPOSE OF REVIEW

This review highlights clinically relevant updates to common and significant bacterial, viral, and fungal cutaneous infection within the past 5 years. Recent developments are presented so that the clinician may provide evidence-based, high-quality patient care.

RECENT FINDINGS

New resistance patterns in cutaneous pathogens have recently emerged as a result of inappropriate antimicrobial use. Several new FDA-approved antimicrobials have been approved to treat such infections, including multi-drug resistant pathogens. Several organizational guidelines for cutaneous infection management have been updated with new recommendations for screening, diagnostic, and treatment strategies.

SUMMARY

Clinicians should be aware of the most recent evidence and guidelines for the management of cutaneous infections in order to reduce the emergence of antimicrobial resistance and most effectively treat their patients.

Descriptive epidemiology and test characteristics of cats diagnosed with Microsporum canis dermatophytosis in a Northwestern US animal shelter

OBJECTIVES

The aims of this descriptive study were to identify risk factors for feline Microsporum canis infection at shelter intake, to describe screening test accuracy, and to refine confirmatory testing time frames.

METHODS

Database records for the general feline population and intake data, medical records and fungal culture logs for cats diagnosed with M canis at a limited admissions shelter were accessed retrospectively for a period of 2 years.

RESULTS

The feline population at the study shelter had a prevalence of M canis of 1.8% (95% confidence interval [CI] 1.6-2.0%). Kittens were eight (95% CI 4.8-13.5) times more likely to present with dermatophytosis than adults. Although more cats presented with M canis during summer and autumn, season was not significant when the model was controlled for age. Owner-surrendered cats were half as likely (95% CI 0.41-0.77) as transported cats to be diagnosed with M canis. Wood's lamp examinations had a sensitivity of 66.8% (95% CI 60.2-73.4) and a specificity of 74.8% (95% CI 64.2-85.1) compared with dermatophyte test medium (DTM) culture. In 78.8% (95% CI 61-91) of littermate or household groups with mixed Wood's lamp results, all cats were DTM culture positive. Under consistent incubation conditions, 202/202 diagnostic DTM plates for M canis-infected cats showed recognizable colony growth before 7 days (median 4 days), and 19/19 fomite carrier cat cultures showed growth before 12 days (median 5 days).

CONCLUSIONS AND RELEVANCE

Applying the results of this study to shelter protocols could optimize diagnostic approaches and shorten the length of stay for shelter cats and kittens, resulting in streamlined shelter operations and improved feline welfare.

Host- and pathogen-dependent susceptibility and predisposition to dermatophytosis

Dermatophytes are a highly specialized group of keratinophilic and keratinolytic filamentous fungi causing a ringworm disease called dermatophytosis or superficial mycoses. Although dermatophyte infections do not threaten the host's life, they lower its quality in humans by causing discomfort related to cosmetic problems and through their epidemiological significance, whereas in farm animals they are responsible for economic losses and constitute a source of the spread of spores. Evidence from countless observational studies that have been conducted over the last 90 years indicates that dermatophytes infect humans of every age, race, gender and socioeconomic status with strikingly high rates, as well as both farmed and wild animals in various health conditions and with various epidemiological statuses. However, the prevalence of superficial fungal infections is highly variable, since it depends on several parameters associated with the infected individual and the dermatophyte, their mutual interactions, and epidemiological and geographical factors. The curious disparity in dermatophyte infection patterns has prompted many investigators to search for a link between the host, the host's predispositions and susceptibility to the disease, and the dermatophyte species and virulence. Thus, the question arises as to whether, in addition to the generally recognized factors predisposing hosts to diseases, there are some other predispositions to dermatophyte infections in a species-specific host. In this review, we describe recent findings about the mechanism of dermatophyte infections, focusing on the adaptation of the fungi to the host and conditions predisposing each side to the disease.

THE PREVALENCE OF ONYCHOMYCOSIS IN THE ZAGREB AREA - THE ROLE OF SABOURAUD AGAR WITHOUT CYCLOHEXIMIDE IN DIAGNOSIS AND THERAPY

SUMMARY – Mycological analysis is considered the gold standard in the diagnosis of very common fungal diseases of nails. The purpose of the article is to present the prevalence of onychomycosis obtained by using direct microscopic examination (DME) and cultivation on Sabouraud media without cycloheximide. The quantitative retrospective research was conducted on 2706 patients of both sexes (mostly middle-aged to elderly) with various toenail lesions, who had undergone mycological analyses in the Mycological Laboratory of our Department of Dermatovenereology in 2013 and 2014. Analysis of the results obtained revealed that there were 35.4% of positive DME results; of these, there were 39.2% of dermatophytes, 59.1% of yeasts and 1.7% of molds. The percentage of dermatophytes (Trichophyton spp.) was twice as high in men as in women. A considerable percentage (12%) of mixed isolates was also observed. Particularly worrisome was the high percentage (one-third) of suppressed and insufficiently developed dermatophytes (a possible indicator of inappropriate preparation of patients for mycological analysis). Cultivation on culture media without cycloheximide requires frequent inspections because of the fast-growing molds while not allowing sporulation for a great number of dermatophytes. However, it has certain advantages, i.e. it offers an insight into the wide range of the present fungi. As part of the biofilm, they can be potentially pathogenic in dystrophic nails under certain circumstances because, according to our results, the percentage of dermatophytes does not change substantially with aging; however, what does change is the percentage of molds, yeasts and mixed isolates.

Evaluation of incubation time for Microsporum canis dermatophyte cultures

Objectives The goal of this study was to determine how frequently Microsporum canis was isolated after 1, 2 and 3 weeks of incubation on dermatophyte culture medium either from untreated cats or cats during treatment. Methods This was an observational retrospective study. Toothbrush fungal culture results were examined from two data pools: untreated cats with suspect skin lesions and weekly fungal cultures from cats being treated for dermatophytosis. Results Results from 13,772 fungal cultures were reviewed and 2876 (20.9%) were positive for M canis. Of these, 2800 were confirmed as positive within 14 days of incubation and only 76 (2.6%) required >14 days for confirmation of M canis. In pretreatment specimens, 98.2% (1057/1076) of M canis isolates were recovered within 14 days of incubation in specimens from cats not known to have received prior antifungal treatment. For cats receiving treatment, 96.8% (1743/1800) of M canis isolates were recovered within 14 days of incubation. Of the 57 cultures that required >14 days for finalization, 21 required extra incubation time because cultures were grossly abnormal, 12 had concurrent contaminant growth delaying microscopic confirmation and 24 had no growth in the first 14 days. Of these 24, 19 had 1-2 colony-forming units (cfu)/plate and the remaining five plates had 5 to >10 cfu/plate, all with abnormal morphology. Conclusions and relevance The findings of this study show that it is not necessary to hold pretreatment or post-treatment fungal cultures for 21 days before finalizing cultures for no growth. Growth requiring >14 days had grossly abnormal morphology.

Comparison of real-time PCR with fungal culture for the diagnosis of Microsporum canis dermatophytosis in shelter cats: a field study

Objectives Fungal culture requires at least 14 days for a final result, compared with 1-3 days for PCR. The study compared a commercial real-time dermatophyte PCR panel with fungal culture in cats in a shelter setting for: (1) diagnosis of Microsporum canis infection; and (2) determination of mycological cure. Methods This was a cross-sectional, observational study of cats with suspicious skin lesions or suspected exposure to dermatophytosis. Hair samples were collected for fungal culture and PCR prior to treatment and at weekly intervals until two negative culture results were obtained. Results One hundred and thirty-two cats were included, of which 28 (21.2%) were culture positive and 104 (78.8%) culture-negative for M canis. PCR correctly identified all culture-positive cats and 92/104 culture negative cats; there were 12 false-positive PCR results. The sensitivity and specificity of PCR were 100% (95% confidence interval [CI] 87.7-100) and 88.5% (95% CI 80.7-93.9), respectively. Data from 17 cats were available for assessment of mycological cure. At the time of the first and second negative fungal cultures, 14/17 (82.4%) and 11/17 (64.7%) tested PCR positive, respectively. Conclusions and relevance PCR showed high sensitivity and specificity for diagnosis of M canis dermatophytosis compared with fungal culture, but was unreliable for identifying mycological cure. False-positive results were relatively common. There were no false-negative PCR results and a negative PCR test was a reliable finding in this study. The ability to rapidly diagnose or rule out dermatophytosis could be a valuable tool to increase life-saving capacity in animal shelters.

Reappraisal of Conventional Diagnosis for Dermatophytes

Dermatophytoses include a wide variety of diseases involving glabrous skin, nails and hair. These superficial infections are a common cause of consultation in dermatology. In many cases, their diagnosis is not clinically obvious, and mycological analysis therefore is required. Direct microscopic examination of the samples using clearing agents provides a quick response to the clinician and is usually combined with cultures on specific media, which must be used to overcome the growth of contaminating moulds that may hamper the recovery of dermatophytes. Accurate identification of the causative agent (i.e. at the species level), currently based on morphological criteria, is necessary not only to initiate an appropriate treatment but also for setting prophylactic measures. However, conventional methods often lack sensitivity and species identification may require up to 4 weeks if subcultures are needed. Histological analysis, which is considered the "gold standard" for the diagnosis of onychomycoses, is seldom performed, and as direct examination, it does not allow precise identification of the pathogen. Nevertheless, a particular attention to the quality of clinical specimens is warranted. Moreover, the sensitivity of direct examination may be greatly enhanced by the use of fluorochromes such as calcofluor white. Likewise, sensitivity of the cultures could be enhanced by the use of culture media containing antifungal deactivators. With the generalization of molecular identification by gene sequencing or MALDI-TOF mass spectrometry, the contribution of historical biochemical or physiological tests to species identification of atypical isolates is now limited. Nevertheless, despite the recent availability of several PCR-based kits and an extensive literature on molecular methods allowing the detection of fungal DNA or both detection and direct identification of the main dermatophyte species, the biological diagnosis of dermatophytosis in 2016 still relies on both direct examination and cultures of appropriate clinical specimens.