|Year : 1990 | Volume
| Issue : 5 | Page : 371-374
Drugs resistance and penicillinase activity in skin isolated Staphylococcus aureus
Gopalkrishna Bhat, CN Nagesha, CN Pirvathi, KM Joseph, PG Shivananda
A study was carried out to evaluate the drug resistance pattern and penicillinase production in skin isolated Staphylococcus aurpus. The disk diffusion method showed prevalence of: multidrug resistance among S. aureus, strains, isolated from locafised skin abscesses. method for detection of penicilfinase could detect this enzyme m 98.60/o of the isolates all fo which were resistant to penicillin and ampicillin. C16xacillin resistance as detected by the agar dilution method was found in 1.4% of the isolates. On the whole cloxacillin and gentamy'cin were found to be the most effective 'antistaphylococcal antibotics.
Keywords: Multidrug resistant staphylococcus aureus, penicillinase, Methicillin resistance
|How to cite this article:|
Bhat G, Nagesha C N, Pirvathi C N, Joseph K M, Shivananda P G. Drugs resistance and penicillinase activity in skin isolated Staphylococcus aureus. Indian J Dermatol Venereol Leprol 1990;56:371-4
|How to cite this URL:|
Bhat G, Nagesha C N, Pirvathi C N, Joseph K M, Shivananda P G. Drugs resistance and penicillinase activity in skin isolated Staphylococcus aureus. Indian J Dermatol Venereol Leprol [serial online] 1990 [cited 2013 May 24];56:371-4. Available from: http://www.ijdvl.com/text.asp?1990/56/5/371/3576
Staphylococcus aureus is a versatile microorganism which is an important hospital and community pathogen.' Direct invasion through breaks in the skin or mucus membrane leads into the production of superficial local infections such as folliculitis, furuncles and abscesses. Antibiotic treatment of these infections has become difficult as multidrug resistance is a common feature in S. aureus.,, The enzyme penicillinase produced by S. aureus is responsible for its resistance to penicillin group of antibiotics. Thus, it becomes very important to know whether skin infections due to S. aureus can be treated using routine antibiotics. The present study was undertaken to evaluate the drug resistance pattern and penicillinase production in Skin isolated S. aureus with an aim to see whether common drugs can be used in the treatment of staphylococcal skin infections.
| Materials and methods|| |
A total of 209 strains of S. aureus isolated from skin infections at the Department of Microbiology, Kasturba Medical College, Mangalore were used in the present study. All the patients were otherwise healthy and none had been treated with antibiotics during the previous one month time. The isolation and identification of S. aureus was done according to the standard methods. Gram stain, catalase, oxidation - fermentation test and coagulase test were employed in the identification of S. aureus.
Antibiotic sensitivity of each S. aureus strain was determined by the standard disk diffusion test in Mueller- Hinton agar using the following antibiotic disks purchased from Hi Media Ltd, Bombay: penicillin (10U), ampicillin (10µg), chloramphenicol (30µg) tetracycline (30µg), erythromycin (15µg) and gentamicin (10µg). Sensitivity to cloxacillin was determined by using Muller-Hinton agar supplemented with 5% NaCl and cloxacillin (6 µglml) . Inoculum from each strain was prepared by suspending 24 hour agar plate culture in Mueller-Hinton broth and standardising the concentration by matching with Brown's opacity tube number 2. The inocula were spread on the plates using 4 mm diameter loop. The plates were examined after 24 hours of incubation at 35°c and any strain growing wa3 considered to be resistant. The plates were reexamined after 48 hours of incubation. In each test S. aureus ATCC 25923 was used as control.
Penicillinase testing was performed by using the method of Perret. Filter paper strips having the size 7cm x 4cm were soaked in saturated potato starch solution, dried and sterilized. Such prepared strips were soaked in penicillin G solution (1,00,000 u/ml) and were spread on petridishes. Overnight growth of the test organisms in nutrient agar were spread on the starch strips. After 10 minutes incubation at 37°c, the strips were flooded with 1:2 solution of Gram's iodine. The purple starch-iodine complex formed was broken up by penicilloic acid formed by the action of penicillinase on penicillin, resulting in discolourisation around the colonies. The results were recorded upto 10 minutes after the start. S. aureus ATCC 25923 and a penicillin resistant strain isolated from routine culture were used as negative and positive controls respectively.
| Results|| |
The number of S. aureus strains isolated from different skin infections is given in [Table - 1] . S. aureus was most commonly (33.5%) isolated from folliculitis. Out of 209 strains of S. aureus tested, 206 (98.6%) were resistant to penicillin and ampicillin, whereas only a small number of strains (1.4%) were resistant to cloxacillin [Table - 2]. Not a single strain was found to be sensitive to all the antibiotics used in the study. All the strains which were resistant to penicillin were also resistant to ampicillin. Among 3 strains of S. aureus showing resistance to cloxacillin, one showed resistance after 48 hours of incubation.
206 strains (98.6%) of S. aureus were found to produce enzyme penicillinase by the iodometric method. Among penicillinase producers, 10 strains were late positive. All the strains which were resistant to penicillin were found to produce penicillinase [Table - 3].
| Comments|| |
Developing drug resistance is a major obstacle in the treatment of S.aureus infections. There are many reports from our country regarding the increase of resistance in S.aureus.,. . The high incidence of drug resistance in S.aureus has been attributed to the indiscriminate use of antibiotics. 29.7% of the strains were found to be resistant to erythromycin, a commonly used antistaphylococcal antibiotic. The increased resistance to erythromycin could be due to its widespread use. The role of penicillinase production in development of resistance to penicillin group of antibiotics is evident as all of the strains which produced penicillinase were resistant to penicillin and ampicillin. So the strains isolated from clinical specimens could be tested for penicillinase by the simple iodometric method to know their sensitivity to penicillin.
Penicillinase positive S.aureus infections are currently being treated using penicillinase resistant drugs such as methicillin, oxacillin and nafcillin. S.aureus has been shown to develop resistance to these antibiotics as well., As each population might contain both methicillin sensitive and resistant bacteria which grow slowly, testing of methicillin sensitivity poses some problems, which are overcome by adapting some other methods like using lower incubation temperature of 30°c, longer incubation time to 48 hours and addition of more salt (5%) in the medium.,,The agar dilution method used in the present study detected cloxacillin resistance in 1.4% of the isolates, in which one strain grew in cloxacillin agar after 48 hours of incubation. The present study showed that cloxacillin and gentamycin are the most effective antibiotics against S.aureus. So cloxacillin can be recommended for the treatment of S.aureus infections, occurring in this part of country especially when sensitivity test reports are not available.
Anyhow, the antibiotic sensitivity pattern of S.aureus strains isolated from different geographical areas may be different.
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[Table - 1], [Table - 2], [Table - 3]