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May 1987, Volume 37, Issue 5

Original Article


Aqeel Ahmad  ( Department of Microbiology, University of Karachi, Karachi-32. )
Khursheed Ali Khan  ( Department of Microbiology, University of Karachi, Karachi-32. )
Tahir Saeed Haroon  ( Department of Dermatology, Jinnah Postgraduate Medical Centre, Karachi. )


Of 162 cases of impetigo 134 (82.7%) had impetigo contagiosa and 28 (17.3%) were of bullous type. Staphylococcus aureus was isolated from 113 (69.75%), Streptococcus pyogenes from 30 (18.51%) and both of these from 19 (11.74%) cases.
All isolates were tested for their resistance pattern to 13 antibiotics in varying concentrations ranging from 0.01-100 yg/mI. The minimum inhibitory concentration required to inhibit the growth of 90%, 75%, 50% and 25% of isplates were investigated. Amp icillin, bacitracin and erythromycin had low activity. Procain penicillin, dexycycline, gentamicin and chloramphenicol were found most effective of the antibiotics used.
The study indicates that resistance is being commonly used antibiotics (JPMA 37: 129, 1987).


Impetigo is a contagious superficial in­fection of the skin caused by Staphylococcus, Streptococcus or both. The relative prevalence of these two organisms varies greatly, that of staph impetigo relatively frequent throughout the world and pure strep impetigo less frequent, intemperate climate, than mixed Streptococci1. In strep impetigo, isolation of Staphylococci has been regarded as secondary invader but their association may be synergistic, and that either organism may be the primary invader2.
Certain strains of Staphylococcus and Streptococcus have been attributed to be the main cause of impetigo but rarely with skin infection of other types as staphylococci, causing impetigo, acquired by these organisms against majority of the are lipase negative while those causing deep skin lesion are lipase positive.
There are two types of impetigo known as Impetigo contagiosa of Tilbury Fox and bullous impetigo differentiated on the basis of epidemio­logical and clinical picture2,3.
Impetigo heals spontaneously in 2-8 weeks without treatment2. Complications are rare. The only serious hazard is the acute glo­merulonephritis but its incidence in impetigo is under 1%4.
Indiscriminate use of antibiotics has led to the multiple antibiotic resistance in bacteria.5 Antibiotic resistance is due to the natural occur­rence of an extra piece of DNA called plasmid that usually causes the cell to produce enzymes which inactivate the specific antibiotics. In Staphylococcus aureus the resistance spreads by phage mediated transduction6.
The present research work deals with the study of 162 cases of impetigo caused by Staphy­lococcus aureus, Streptococcus pyogenes, or both and the determination of their resistance pattern to various antibiotics.


The clinical material was collected with the help of sterile cotton swabs after cleaning the lesion thoroughly with 95% ethanol. The pus was streaked on Staphylococcus medium 110 (Oxoid) and blood agal’ and incubated at 37°C for 18-24 hours. The suspected colonies showing charac­teristic growth and hemolysis were isolated and identified. Out of 162 cases, 113 were identified as Staphylococcus aureus and 30 Streptococcus pyogenes. From 19 cases of impetigo, both S. aureus and S. pyogenes were isolated.
Master plates of the isolated cultures were prepared (25 spots per plate). The impressions were transferred by replica device to the plates containing varying concentrations of different antibiotics and plane plates (which served as control). Plates were incubated overnight at 37°C and the results recorded. The MICs of each isolate against 13 antibiotics were determined. MIC (Minimal Inhibitory concentration) is the lowest concentration of the antibiotic which inhibits visible growth of the organism.


One hundred and sixty two patients suf­fering from impetigo were seen at Dermatology Department, Jinnah Postgraduate Medical Centre, Karachi. The clinical material was collected and cultures isolated and identified.
The study includes 134 (82.72%) cases of Tilbery Fox Variety and 28 (17.28%) of bullous type. Incidence of infection was very high in young children (Table 1).

In majority of cases the infection was found on face (usually around mouth), head and hands but less frequently on other parts of the body.
Out of 162 cases, 54 acquired the infection from their family members, 51 had past history of recurrence and 60 were suffering from scabies. 55 cases presented with fever and 56 had
The incidence of infection peaks during summers probably due to the high temperature and humidity. Recurrence of infection in low income group of the population may be due to poor personal hygiene.
Staphylococcus aureus accounted for 113(69.75%) cases and Streptococcus pyogenes for 30 (18.51%). Mixed infection of S. aureus and S.   pyogenes was found in 19 (11.74%) cases. A total of 181 isolates of S. aureus and S. pyogenes were recovered from 162 patients (Table II).

Isolated cultures were tested for their resistance pattern to 13 antibiotics in varying concentrations ranging from 0.0 1-100 jig/mi. The Minimum Inhibitory Concentration of various antibiotics required to inhibit the growth of 90%, 75%, 50% and 25% isolates have been shown in Table III.

The data shows that ampidillin, bacitracin and erythxomycin had low activity. For MIC90 (Minimal Inhibitory Concentration for 90% isolates) concentration of 50 ug/ml or higher was required.
Doxycycline, procain penicillin, genta­micin and chioramphenicol were most effective, tetracycline comparatively less. Carbencillin had MIC90 of 35 ug/ml and neomycin and suiphame­thaxazole MIC90 of 25 ug/ml.
The data shows that the organisms are acquiring resistance to the majority of commonly used antibiotics. Most of the isolates were found to be resistant to the concentration attained in blood during therapy.


The high incidence of antibiotic resistance among bacteria from patients has helped in selection and dissemination of transferable antibiotic resistance among pathogenic bacteria. Overcrowding in cities like Karachi and hospitali­zation of patients provide ideal conditions for dissemination of resistant organisms and indiscri­minate use of antibiotics results in selective survival of resistant strain7.
The data shows that ampiciffin had MIC75 of 60 jig/mi, MIC90 of 80 Ug/mI and erythromycin MIC75 of 20 ug/mi and MIC90 of 50 ug/ml (Table III). These concentrations are much higher than those attained in serum during therapy.
The majority of isolated cultures showed resistance to ampicillin, bacitracin, erythromycin,
carb encillin, neo mycin and suiphamethaxazole. Some culture were found resistant to streptomycin and tetracycline and had MIC as high as 60 jig/mi a few others showed MIC of 30 jig/mI of chloram­phenicol, kanamycin and gentamicin.
The invitro susceptibility of the isolates (both S. aureus and S. pyogenes) has been shown in Table Ii!. Procain penicillin was found most effective among the antibiotics used with MIC90 of 1 jig/mi. For doxycycline and gentamicin MIC90 was 4 pg/mi. However, a few isolates were found resistant to 4 pg/mi for gentamicin. Chioramphenicol and kanamycin had MIC90 of 8 jig/mi and 6 pg/mI. A few isolates to these anti­biotics were inhibited at 20 jig/mi.
This data shows that organisms are acquir­ing resistance to a majority of the commonly used antibiotics. The MIC of most of the isolates were much higher than that of the concentration of antibiotics attained in blood during therapy8 and consequently response was very poor.
Inadequacy of facilities in the hospitals for proper selection of antibiotics and the non-availability of the proper drugs contribute to the proliferation of antibiotics resistant organisms.


1. Ferrieri, P.,Dajani, A. S., Wannamaker, L.W. and Chapman, S.S. Natural history of impetigo. 1. Site sequence of acquisition and familial patterns of spread of cutaneous streptococci. J. Clin. Invest., 1972; 51:2851.
2. Dajani, A.S. Endemic superficial pyoderma in children. Arch. Dermatol., 108:517.
3. Dillon, H.C. Jr. Impetigo contagiosa; suppurative and non-suppurative complication. I. Clinical, bacteriologic, and epidemiologic characteristics of Impetigo. Am. J. Dis. Child., 1968; 115:539.
4. Rasmussen, J.E. and Maibach, HI. Impetigo and other pyodermas, in clinical dermatology. Edited by, DJ. Philadelphia, Harper and Row, V.3, p.4.
5. Watanabe, T. Infectious drug resistance. Sci. Am.1967; 217:19.
6. Lacey, R.W. Antibiotic resistance plasmids of Staph viococcus aureus and their clinical impor­tance. Bactorol. Rev.,1975;39:1.
7. Sydney, S., Lacey, R.W. and Bakhtiar, M. Beta­lactam antibiotics penicillin and cephalosporin in perspective. London, Hodder and Stoughton, 1980; p.224.
8. Davis, S., Reeves, I.\\ P., William, J.D. and Richard, W. Laboratory method in antimicrobial chemo­ therapy. NewYork, Churchill Livingstone, 1978; p.151.

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