Methicillin, cloxacillin, flucloxacillin, and cefoxitin are stable, penicillinase-producing β-lactam antibiotics; Staphylococcus aureus strains resistant to these agents are designated as methicillin-resistant S aureus (MRSA). Based on genotypic and phenotypic differences there are 2 strains of MRSA: hospital acquired and community acquired.
The potential for nosocomial transmission and the limited number of antibiotics available to treat MRSA are problematic. Moreover, MRSA has emerged worldwide as a major nosocomial pathogen that contributes to morbidity and mortality. Methicillin-resistant S aureus infection in vesiculobullous disorders such as pemphigus vulgaris (PV) and toxic epidermal necrolysis (TEN) is known to contribute to mortality.1
The reported prevalence of MRSA in India ranges from 12% to 38.44%.2-4 We frequently encounter MRSA in dermatology inpatients, especially those with a vesiculobullous disorder. The primary objective of this study was to determine the prevalence of MRSA in dermatology inpatients with a vesiculobullous disorder; the secondary objective was to determine if MRSA contributes to mortality.
Materials and Methods
A 1-year prospective, cross-sectional, descriptive study was conducted in a tertiary-care center. The study population included all dermatology inpatients with a vesiculobullous disorder. Patients with a vesiculobullous disorder secondary to a primary viral or bacterial disorder were excluded. Permission to conduct the study was granted by the institution’s Human Ethics Committee.
All patients underwent a detailed history and clinical examination. Routine hematology testing, urinalysis, measurement of the blood glucose level, and other investigations relevant to the vesiculobullous disorder were performed. Special investigations were Gram staining, culture, and susceptibility testing of material from a nasal swab and a swab of a representative skin lesion.
Detection of MRSA
Skin lesions were thoroughly cleaned with sterile normal saline. Specimens of pus were drawn with a sterile swab for Gram staining, culture, and susceptibility testing and were analyzed in the institution’s microbiology department. A direct colony suspension (equivalent to McFarland Standard No. 0.5) was inoculated on a Mueller-Hinton agar plate, incorporating cefoxitin, linezolid, vancomycin, amikacin, and rifampicin supplemented with sodium chloride 2% and incubated at 37°C for 24 hours. Staphylococcus aureus colonies were identified by their smooth, convex, shiny, and opaque appearance with a golden yellow pigment, as well as by coagulase positivity, mannitol fermentation, and production of phosphatase.
Methicillin-resistant S aureus was defined as an isolate having a minimum inhibitory concentration of more than 2 μg/mL of cefoxitin; a methicillin-sensitive S aureus isolate was defined as having a minimum inhibitory concentration of less than or equal to 2 μg/mL of cefoxitin. Specimens showing moderate to heavy growth of MRSA were included in the study. For specimens showing mild growth, testing was repeated; if no growth was seen on repeat testing, results were interpreted as negative.
Data were collected and analyzed for frequency and percentage; P<.05 was considered significant.
Results
The number of patients analyzed in the study period was 43. Table 1 shows their salient demographic characteristics, clinical features, and findings of the investigation. The youngest patient was aged 13 years; the oldest was aged 80 years. The male to female ratio was 0.65 to 1. The most common primary lesion was a combined vesicle and bulla (34 patients [79.1%]); the most common secondary lesion was a combination of erosion with crusting (22 patients [51.2%]).
Table 2 lists the types of vesiculobullous disorders seen in this study. Pemphigus vulgaris was the most common (21 patients [48.8%])(Figure 1). Drug-induced vesiculobullous disorders (eg, TEN) were noted in 11 patients (25.6%)(Figure 2).
Figure 1. Multiple erosions and crusts in a patient with pemphigus vulgaris from which methicillin-resistant Staphylococcus aureus was isolated.
Figure 2. Fluid-filled blisters and denuded skin in toxic epidermal necrolysis from which methicillin-resistant Staphylococcus aureus was isolated.
Table 2 also lists pathogens cultured in the study group. There were 24 bacterial isolates, of which S aureus accounted for 22 (91.7%). Methicillin-resistant S aureus was cultured in 14 patients (32.6%); culture was sterile in 19 patients (44.2%).
Among the 22 cultured staphylococcal species, MRSA accounted for 14 (63.6%) and constituted 58.3% (14/24) of all bacterial isolates. The nasal swab for MRSA was positive in 4 PV patients (9.3%), 2 TEN patients (4.6%), and 1 bullous pemphigoid patient (2.3%). Methicillin-resistant S aureus was most commonly cultured in PV patients (8/14 [57.1%]).
All MRSA strains (100%) were sensitive to vancomycin and linezolid; 34 (79.1%) were sensitive to amikacin. Additionally, 100% of MRSA strains were resistant to oxacillin, cloxacillin, and cefoxitin.
Three patients with PV (7.0%) and 1 patient with TEN (2.3%) died during the course of the study; only 1 death (2.3%) occurred in a patient who had a positive MRSA culture.