Marwa Abdallah1, Sanaa M I Zaki 2, Abeer El-Sayed 2, Dina Erfan2

Egyptian Dermatology Online Journal 3 (2): 3, December 2007

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Abstract

Background: Organisms causing bacterial infections complicating dermatoses differ among in- and outpatients. They constantly change their antibiotic sensitivity, thereby posing additional concern about disease outcome.

Objective: The aim of the present study was to detect the types of bacteria commonly complicating skin diseases of Egyptian in- and outpatients of the dermatology department and to test their sensitivity to a panel of the most commonly used antibiotics.

Patients & Methods: Direct film was prepared and samples were cultured aerobically and anaerobically from the deeper parts of the suppurative exudate of secondarily infected skin of 37 outpatients and 23 inpatients suffering from various dermatoses. This was followed by antibiotic sensitivity testing in addition to testing of gram positive and gram negative organisms for beta lactamase and extended beta lacamase (ESβL) production, respectively.

Results: Staphylococcus aureus (83.3%) and Gram-negative enteric bacteria (21.7%) were the most common isolated organisms from all cases. Streptococcus pyogenes, Pseudomonas aeruginosa and Enterococci were detected in 15%, 6.7% and 5% of cases respectively. There was significant difference between in- and/outpatients as regards the antibiotic sensitivity pattern of both S.aureus and the Enterobacteriaceae group. S.aureus strains isolated from inpatients showed more resistance to amoxicillin/clavulonic acid, cefaclor, fusidic acid, methicillin, ofloxacin and tobramycin (p<0.05). The rate of methicillin resisitant staph aureus (MRSA) in hospitalized patients was (26.3%) versus (9.7%) in outpatients (p<0.05). Enterobacteriaceae strains from hospitalized patients were more resistant to cefaclor, levofloxacin and ofloxacin (p<0.05).

Collectively, the incidence of β-lactamase production by Gram-positive cocci was (96%) in both groups, while the incidence of ESβL production by Gram-negative bacilli was (29.4%), being higher in inpatients than outpatients.

In conclusion, this study shows that S.aureus is the most common cause of secondary infection in all skin lesions. The incidence of Enterobacteriaceae infection was more in inpatients with higher levels of ESβL production. Resistance of different bacterial isolates to antibiotics was also higher in inpatients.

Introduction

An intact stratum corneum prevents invasion of skin by normal skin flora or pathogenic microorganisms. Skin diseases that are usually complicated by secondary bacterial invasion can be broadly classified into itchy skin conditions in which scratching provides a portal of entry to microorganisms such as scabies and pediculosis, and those characterized by absence of skin barrier, such as eczema, pemphigus and ulcers [1].

The most common causes of secondary bacterial infections of the skin are staphylococci and streptococci. Secondary infections to skin lesions can be potentially life threatening and may progress rapidly; therefore, their early recognition and proper medical and surgical management are important [7].

The current work aims at isolation and identification of bacteria causing secondary infection of skin diseases in Egyptian patients visiting the outpatient clinic, or admitted as inpatients in the dermatology department, Ain Shams University Hospital. Determination of antibiotic sensitivity for these bacteria, testing the β-lactamase production by the Gram-positive cocci, and the extended spectrum β-lactamase (ESβL) production by the Gram-negative bacilli will be done in an attempt to detect whether there are differences among outpatients, which represent patients in the normal community and inpatients, who reflex nosocomial skin diseases.

Subjects And Methods

Patients: Included in the present study were patients attending the outpatient clinic or those admitted as inpatients in the dermarology department, Ain Shams University Hospital suffering from different skin diseases which are complicated by secondary bacterial infections. The study was conducted during the period from April 2005 to December 2005. All patients were subjected to full history taking, clinical and bacteriological examination.

Methods: A sample from the suppurative exudates of infected skin lesions was taken by means of sterile disposable swab and inoculated into peptone water as transport medium for aerobic bacteria between the clinic and the bacteriological laboratory. Another sample was taken by another swab and inoculated into thioglycolate broth as transport medium for anaerobic bacteria.

Direct films were prepared from the samples and were stained with Gram stain and examined by oil immersion of light microscope for the presence and morphology of microorganisms.

The samples were cultured aerobically at 37°C for 18-24 hours on Blood agar medium and Mac Conkey's agar medium. The second sample was cultured anaerobically on Colombia blood agar medium in anaerobic jar using an anaerobic gas pack for 48 hours at 37°C. Bacteriological identification of the colonies was done according to Colee et al.[14].

All isolated organisms were tested for antibiotic sensitivity by disc diffusion method using commercially prepared discs 6 mm in diameter (Oxoid-England). Interpretation of results was done according to National Committee for Clinical Laboratory Standards [30,31].

Gram-positive cocci were tested for production of β-lactamase by nitrocefin discs (Mast Diagnostic-England) for rapid detection of β-lactamase. Positive results: Development of a red colour in the area of the disc where the culture was applied. Negative results: No colour change.

All Gram-negative bacilli were tested for the production of extended spectrum β-lactamase (ESβL) enzyme by ESβL detection discs (Mast Diagnostics-England), which contain three paired sets of cartridges, each cartridge containing 50 discs. The diameter of any observed zones of inhibition was measured and recorded:

     *CAZ:  Ceftazidime, CLAV:  Clavulonic acid        

An index number > 1.5 means positive ESβL and < 1.5 indicates negative ESβL. The calculations were repeated with the results from the remaining sets of discs. A positive result from any or all of the sets of MAST ID ESβL detection discs indicated ESβL production [16].

Statistical analysis

Analysis of the data was performed by SSPS version 12, where the data were expressed as mean ± standard deviation. Unpaired student t-test was used for between groups comparison of numerical variables, while Chi square test or Fischer exact test were used for comparison between categorical variables. P-value < 0.05 was considered significant.

Results

This study was conducted on 60 patients suffering from secondary bacterial infection of skin diseases; 37 outpatients (61.7%) and 23 inpatients (38.3%). Thirty five patients were males (58.3%) and 25 were females (41.7%), their ages ranged from 2 months to 75 years (mean 27 19).

Outpatients suffered from eczema (n=10), pediculosis (n=6), scabies (n=5), papular urticaria (n=4), sweat rash (n=4), kerion (n=3) and viral infections of the skin (herpes simplex and chicken pox, n=3). The inpatient group was suffering from pemphigus (14 patients), psoriasis (two with generalized pustular psoriasis and one with extensive chronic plaque psoriasis) in addition to 6 patients with skin ulcers due to pyoderma gangrenosum, vasculitis, lymphedema and dermatitis artefacta (Table1). All inpatients, with the exception of those with lymphoedema and dermatitis artefacta, were receiving immunosuppressive therapy.
 

Table (1): Incidence of infection by different bacterial isolates in the different primary skin lesions (click)

Bacterial isolates from secondarily-infected skin diseases:

The commonest encountered organism was Staphylococcus aureus (61.8%) followed by Gram-negative bacilli of the family Enterobactericeae (16%), then Strept. pyogenes (11.1%), Pseudomonas aeruginosa (5%), Enterococci (3.7%), and the least isolated were anaerobic Gram-positive cocci and coagulase negative staphylococci (CONS) (each representing 1.2%).

As regards Enterobactericeae, E.coli and Proteus species were the most commonly isolated organisms, (30.8%) for each. Other less frequently encountered organisms included Serratia marcescens (15.3%), while Klebsiella pneumoniae, Citrobacter freundii and Enterobacter aerogens were the least isolated (each represented 7.7%).

On comparing the type of primary skin lesion with the organism causing secondary bacterial infection, a non-statistically significant difference was detected (p>0.05). S.aureus was the commonest organism isolated from all cases (83.3%) followed by the Enterobacteriaceaea group (21.7%), Strept.pyogenes (15%) and P.aerugnosa was isolated from (6.7%) of the cases. Enterococci, CONS and anaerobic Gram-positive cocci were the least isolated (5%, 1.7%, and 1.7% respectively). Mixed infections are responsible for overlap in percentage (Table 1).

In pemphigus, S.aureus was the most commonly isolated organism (92.9%), followed by Enterobactericeae (35.7%) and Pseudomonas (14.3%), while Enterococci, Strept.pyogenes and anaerobic Gram-positive cocci were the least isolated, only one isolate of each was detected. In eczema patients, S.aureus was the commonest isolated organism (90%) followed by Strept.pyogenes (40%) and Enterobacteriaceae (20%), while no other organisms were isolated. In skin ulcers the commonest isolated organism was also S.aureus (50%), followed by Enterobacteriaceae (37.5%) and P.aeruginosa (25%) no other organisms were found. In scabies, S.aureus was the commonest isolated organism (80%), followed by Strept.pyogenes (40%), and Enterobacteriaceae (20%).However in viral infections of the skin Enterobacteriaceae were the most common isolated organisms (66.7%). In kerion, papular urticaria and sweat rash S.aureus was the only isolated organism (Table 1).

As regards the distribution of bacterial isolates and the anatomical site from where they were detected, Enterobacreiaceae group and Strept.pyogenes were found more frequently in the lower limbs than in other sites (Table 2)

Table (2): Distribution of bacterial isolates according to the anatomical site of secondary infection.

As we compared the type and incidence of secondary bacterial infection between in- and outpatients, only Enterobactericeae group were more common among inpatients (P<0.05). There was no statistically significant difference (P>0.05) between inpatients and outpatients as regard percentage of mixed infection although it was higher in inpatients (Table3).
 

P: P value           S: Significant      NS: Non-significant

Table (3): Comparison between inpatients and outpatients as regards the incidence of secondary infection by the different bacterial isolates

Testing for antibiotic sensitivity of isolated organisms:

On testing for the antibiotic sensitivity of staphylococci, all S.aureus isolates had good sensitivity to clindamycin, chloramphenicol, and vancomycin, while they were resistant to penicillin, ampicillin, tetracycline and cefotaxime; without a significant difference between in- and outpatients. A significant difference between in- and outpatients was found as regards their sensitivity to amoxicillin/clavulonic acid, cefaclor, fusidic acid, methicillin, ofloxacin and tobramycin (p<0.05). Both groups were resistant to erythromycin, incidence in inpatients being higher. A larger percentage of inpatients were resistant to amoxicillin/clavulonic acid and fusidic acid compared to outpatients. Both groups were sensitive to cefaclor, methicillin, ofloxacin and tobramycin, but a larger percentage of the outpatient group was sensitive to these antibiotics (Table 4).