Antimicrobial susceptibility of Staphylococcus aureus isolated from children with impetigo in China from 2003 to 2007 shows community‐associated methicillin‐resistant Staphylococcus aureus to be uncommon and heterogeneous

Background The number of patients with impetigo caused by community‐associated methicillin‐resistant Staphylococcus aureus (CA‐MRSA) has been increasing. Objectives To investigate the antimicrobial susceptibility of S. aureus causing impetigo in children in China from 2003 to 2007 and further characterize isolates of CA‐MRSA. Materials and methods We examined 984 S. aureus isolates for antimicrobial susceptibility to 11 antimicrobials using the agar dilution method. CA‐MRSA isolates were analysed for Panton–Valentine leucocidin (PVL) genes, and staphylococcal cassette chromosome mec (SCCmec) typing was performed. Results The largest proportion (94·5%) of strains were resistant to penicillin, followed by erythromycin (86·2%) and clindamycin (69·6%). In total 772 of 984 (78·5%) S. aureus strains were multiresistant. The incidence of CA‐MRSA was 1·1%, with a high rate of resistance to clindamycin (90·9%) and tetracycline (72·7%), but all were susceptible to ciprofloxacin. The susceptibility profiles of MRSA to other antimicrobial agents were similar to those of methicillin‐sensitive S. aureus (MSSA). None of the S. aureus strains were resistant to vancomycin and fusidic acid; moreover, only one strain was resistant to mupirocin. Typing of the SCCmec showed that 54·5% were type IV, 18·2% were type V and 9·1% were type VI. All the PVL‐positive CA‐MRSA carried SCCmec type IV. Conclusions CA‐MRSA is still relatively uncommon and heterogeneous in children in China. Penicillin and erythromycin are no longer appropriate agents. Effective antibiotic agents for patients with impetigo are mupirocin and fusidic acid.     

Susceptibility of Staphylococcus aureus to fusidic acid: Canadian data

BACKGROUND: Ongoing antimicrobial surveillance is important to ensure proper management of infectious diseases. There are inherent issues in estimating the relevant incidence of antimicrobial resistance from surveillance data and special issues for topical preparations. OBJECTIVE: To perform semiannual surveillance of fusidic acid susceptibility of Staphylococcus aureus strains in a Canadian tertiary care hospital. METHODS: S. aureus strains were collected twice yearly from routine cultures. Routine antimicrobial susceptibility testing was performed by an automated method. Fusidic acid susceptibility testing was performed by disk diffusion. RESULTS: Between 1999 and 2005, 2,302 S. aureus strains were tested, of which 240 were methicillin resistant (MRSA). Among all strains tested, 65 (2.8%) were resistant to fusidic acid. Ten of the MRSA strains (4.2%) were resistant to fusidic acid. Although from different patients, these were shown to be part of a hospital outbreak and were epidemiologically linked. CONCLUSIONS: There has been no trend toward increasing fusidic acid resistance in our hospital over this period.     

葡萄球菌烫伤样皮肤综合征208例临床分析

目的回顾分析208例葡萄球菌烫伤样皮肤综合征患儿的临床资料,对部分病原菌进行表皮剥脱毒素及药敏检测,了解本地区致病菌分泌表皮剥脱毒素血清型别及药敏情况。方法记录所有病例的临床资料,并对其中30株金黄色葡萄球菌(以下简称SA)应用反向乳胶凝集法检测表皮剥脱毒素,对51株SA应用琼脂稀释法进行了14种抗生素的药敏试验。结果 30株SA中,21株表皮剥脱毒素A,B均阳性,8株单纯表皮剥脱毒素B阳性。51株SA药敏青霉素耐药率为96.08%,对红霉素耐药率为82.35%。对苯唑青霉素、头孢类抗生素、莫匹罗星、万古霉素和夫西地酸均未发现耐药菌。结论引起本病的SA以表皮剥脱毒素A,B均阳性的菌株为主。青霉素和红霉素耐药率较高,不适合治疗本病。头孢菌素、万古霉素和夫西地酸可作为可选择的抗生素。     

Outbreak of bullous impetigo caused by Staphylococcus aureus strains of phage type 3C/71 in a maternity ward linked to nasal carriage of a healthcare worker

We describe an outbreak of bullous impetigo (BI) that occurred in a maternity unit and show phenotypic and genotypic properties and relatedness of isolated Staphylococcus aureus strains. Clinical material was obtained from 11 affected neonates. Additionally, nasal swabs from 67 healthy care workers (HCWs) as well as 107 environmental swabs were investigated. All isolates were screened for exfoliative toxin genes (eta, etb), antibiotic susceptibility and phage typed. Chromosomal DNA was genotyped by MLVF method and PCR/RFLP of coagulase gene were tested. Affected neonates were infected by two clusters of eta-positive S. aureus of phage type 3C/71: (1) MLVF type A isolates resistant only to penicillin, and (2) MLVF type B isolates resistant to penicillin and erythromycin/clindamycin. All isolates were susceptible to methicillin. We found 19 of 67 HCWs to be S. aureus nasal carriers. Two nasal isolates from HCWs were related to the outbreak on the basis of phage typing, PCR detection of eta/etb genes, antibiotyping and genotyping. Additionally, environmental swabs from the maternity unit revealed a 3C/71 S. aureus in the mattress of a baby bed. This is the first documented case of an outbreak of BI caused by phage type 3C/71 eta-positive strain of S. aureus.     

Impetigo: A Reassessment of Etiology and Therapy

Traditional concepts regarding the bacteriology and therapy of nonbullous impetigo have been reexamined. Although in the United States the disease is considered primarily of streptococcal origin and amenable to penicillin therapy, we found that Staphylococcus aureus was the most common isolate in 71 patients studied. Only two patients yielded pure cultures of group A beta-hemolytic streptococci. All but two isolates of S. aureus were resistant to penicillin; one of these two isolates was also resistant to erythromycin. Erythromycin appeared to be more efficacious than penicillin for the treatment of impetigo.     

Prevalence of Staphylococcus aureus toxins and nasal carriage in furuncles and impetigo

BACKGROUND: The precise role of Staphylococcus aureus toxins and nasal carriage in common skin infections remains unclear. OBJECTIVES: To seek correlations between toxin expression, S. aureus nasal carriage and clinical manifestations in patients with community-acquired furuncles and impetigo. METHODS: From November 2004 to August 2005, we studied clinical data and bacteriological samples prospectively collected from 121 patients presenting with furuncles or impetigo. RESULTS: Sixty-four patients (31 with furuncles and 33 with impetigo) had S. aureus-positive skin culture. Panton-Valentine leukocidin (PVL) genes were present in 13 of 31 (42%) isolates from furuncles and were associated with epidemic furunculosis. Exfoliative toxin genes were present in 10 of 10 (100%) and 12 of 21 (57%) bullous and nonbullous impetigo isolates, respectively. Nasal carriage of S. aureus was found in 58% of patients overall. It was strongly associated with chronic furunculosis but not with simple furuncles (88% vs. 29%, P < 0.007). Skin and nose isolates from a given patient always had identical characteristics. Methicillin-resistant S. aureus accounted for four of 64 (6%) positive skin cultures. CONCLUSIONS: PVL is not involved in all types of furuncles but is associated with epidemic furunculosis. Both bullous and nonbullous forms of impetigo are associated with exfoliative toxins. Staphylococcus aureus nasal carriage is associated with the chronicity of furuncles.     

The bacteriology of acne vulgaris and antimicrobial susceptibility of Propionibacterium acnes and Staphylococcus epidermidis isolated from acne lesions

We examined the species of bacteria aerobically and anaerobically isolated from 30 acne lesions and determined antimicrobial susceptibilities of Propionibacterium acnes (P. acnes) and Staphylococcus epidermidis (S. epidermidis) using nine antimicrobial agents. Among the bacteria isolated, S. epidermidis was most dominant. Both P. acnes and S. epidermidis were isolated from half of the acne lesions. The MIC of seven antimicrobials (ampicillin, erythromycin, roxithromycin, clindamycin, tetracycline, minocycline, nadifloxacin) against P. acnes was under 3.13 micrograms/ml. There were very few resistant strains of P. acnes, but many of S. epidermidis. More than 30% of the S. epidermidis isolates were resistant to erythromycin, roxithromycin, and clindamycin. After long-term systemic antibiotic therapy, the resistant strains of S. epidermidis increased, but P. acnes resistance was still limited. When we use antimicrobial agents for the treatment of acne, it should be noticed that not only P. acnes but also S. epidermidis in the acne lesions may acquire resistance to antimicrobials.     

Impetigo Contagiosa: A Comparison of Erythromycin and Dicloxacillin Therapy

One hundred patients with impetigo were prospectively enrolled in a study to determine the current etiology and comparative therapeutic efficacy of two oral antimicrobial agents active against both group A beta-hemolytic streptococci (GABS) and Staphylococcus aureus. After obtaining a bacterial culture from a representative impetiginous lesion, the children were randomized to receive 10 days of either erythromycin (40 mg/kg/day) or dicloxacillin (25 mg/kg/day). S. aureus alone was isolated from 46 children, and in association with GABS from 25 children. GABS alone was isolated from nine patients. Of the 59 evaluable children with S. aureus isolates, 28 of 29 treated with erythromycin and 29 of 30 treated with dicloxacillin were cured or improved on follow-up examination. Thus, we conclude that erythromycin is the drug of choice for impetigo in our midwestern locale because of its high efficacy and relatively low cost.     

北京地区儿童皮肤感染金黄色葡萄球菌的耐药研究

目的 分析儿童皮肤感染金黄色葡萄球菌的耐药现状及社区获得性耐甲氧西林金黄色葡萄球菌的流行情况。方法 对600例感染性皮肤病患儿皮损分泌物进行细菌培养。应用琼脂稀释法检测抗生素及环丙沙星对培养出的金黄色葡萄球菌的最小抑菌浓度。结果 600例患儿皮损共培养出金黄色葡萄球菌451株，对13种抗生素及环丙沙星的药敏试验结果显示，对青霉素耐药率为93.8%，对红霉素耐药率为87.6%，对克林霉素为71.6%，对四环素、氯霉素、庆大霉素和环丙沙星的耐药率依次为37.3%，13.3%，6.4%和2.2%，对苯唑西林、头孢唑啉、头孢呋辛和莫匹罗星耐药率分别为1.6%，0.4%，0.2%和0.2%，未发现头孢曲松、万古霉素和夫西地酸耐药菌株。结论 儿童社区获得性耐甲氧西林金黄色葡萄球菌分离率为1.6%。治疗社区来源的皮肤金黄色葡萄球菌感染性皮肤病，全身治疗首选耐青霉素酶的半合成青霉素和头孢菌素，外用治疗可选择莫匹罗星或夫西地酸。     

Characteristics of Streptococcus species isolated from infectious skin diseases

During the period from January of 1995 to June of 1998, 27 beta-hemolytic streptococci were isolated from 25 cases of infectious skin diseases including secondary infections, impetigo, phlegmone, and paronychia. The rate of beta-hemolytic streptococci among all kinds of the isolates was found to be similar during those 4 years, ranging from 3.5% to 5.6%. Staphylococcus aureus were found to coexist with beta-hemolytic streptococci in 20 (80%) out of 25 cases. beta-hemolytic streptococci were also often associated with coagulase-negative staphylococci, gram-positive rods, or other species. Twelve cases (48%) carried beta-hemolytic streptococci predominantly. Most beta-hemolytic streptococci showed high susceptibilities to all antimicrobials tested; however S. agalactiae showed no susceptibility to gentamicin. The evaluation of characteristics of Streptococcus species is very important for selecting the right antimicrobial agents and the proper term of chemotherapy.     

广东省汕头市92株淋球菌药物敏感性检测

目的：了解汕头地区2009年淋球菌对多种抗菌药物耐药的发生率及产β-内酰胺酶淋球菌（PPNG）和四环素高度耐药淋球菌（TRNG）的流行状况.方法：采用琼脂稀释法测定5种抗菌药物最低抑菌浓度（MIC）,纸片酸度法测定青霉素产β-内酰胺酶菌株.结果：92株淋球菌对青霉素耐药率为84.8%、四环素耐药率为89.1%、环丙沙星耐药率为92.4%;未发现大观霉素及头孢曲松耐药菌株.检出PPNG高达31株（33.7%）.TRNG为47株（51.1%）.青霉素﹑四环素和环丙沙星的MIC50及MIC90均已超过耐药标准.结论：大观霉素和头孢曲松为汕头地区治疗淋病的首选药物.     

解脲脲原体生物群与体外抗菌药物敏感性关系的初步研究

目的探讨解脲脲原体两大生物群与体外抗菌药物敏感性的相关性。方法采用微量肉汤稀释法测定体外抗菌药物敏感性,并以多条带抗原(MB-Ag)基因为靶位,设计分群引物,对UU菌株进行分群。结果两大生物群对五种抗菌药物MIC值范围基本一致,个别MIC90值存在差异。UU两大生物群对四环素、多西环素、洛美沙星的耐药率差异无显著性意义,但对红霉素、阿奇霉素耐药率差异有统计学意义(P分别为0.0008和<0.0001)。结论UU两大生物群对抗菌药物的耐药性可能存在差异,支持UU分成两个独立的物种。     

Streptococci isolated from various skin lesions: the interaction with Staphylococcus aureus strains

We isolated 73 streptococcus strains (41 from infections, and 32 from colonization) from various skin diseases between March, 1994, and June, 1998. In 29 out of 41 cases of infective origin, Staphylococcus aureus strains were simultaneously isolated. Twenty-four out of 28 patients with impetigo were suffering from atopic dermatitis. We confirmed that impetigo lesions where Streptococcus pyogenes was dominant in number always showed thick-walled pustules on an erythematous base; these skin lesions were considered to be an early manifestation of streptococcal impetigo. We further confirmed that thick-crusted lesions in streptococcal impetigo, where S. aureus exceeded S. pyogenes in number, were a late manifestation. Antimicrobial agents such as minocycline, fusidic acid, ofloxacin and tosufloxacin, were more effective against S. aureus strains than against β-hemolytic streptococcal strains. In contrast, ampicillin, cefdinir, imipenem, erythromycin and vancomycin were more effective against β-hemolytic streptococcal strains.     

Antibiotic susceptibility of Staphylococcus aureus strains responsible for community-acquired skin infections

BACKGROUND: The appearance and worldwide spread of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) skin infections warrant new studies of antibiotic resistance among strains of S. aureus responsible for cutaneous infections seen in general practice. PATIENTS AND METHODS: A prospective, multicentre study was performed from December 2003 to August 2004 in outpatients of both sexes presenting with a common bacterial skin infection presumed due to S. aureus (primary or secondary impetigo, ecthyma, paronychia, folliculitis, furunculosis). The investigators (n=50) were GPs from seven French regions. Clinical data (history, previous hospitalisation, type of infection, site, previous treatment, etc.) were collected using a standard questionnaire. A bacteriological sample was taken in attempt to isolate S. aureus after which antibiograms were prepared and minimal inhibiting concentrations determined (11 antibiotics). RESULTS: Four hundred and eighty patients of mean age 42 years (range: 2-94 years) were included. S. aureus was isolated from cultures in 205 of 477 samples, i.e. in 197 patients (eight had two strains of S. aureus). Patients with S. aureus had a primary skin infection in 104/197 cases (53%) (24 impetigo, 20 paronychia, 45 folliculitis or furunculosis) and a secondary infection in 93/197 cases (47%), with 4.9% patients being hospitalized within the preceding six months (median: 10 days). Percentages of resistant S. aureus strains were as follows: penicillin: 86%, erythromycin: 32%, ciprofloxacin: 9.3%, tetracycline: 5.8%, oxacillin: 5.8% (representing MRSA strains), fusidic acid: 4.4%, clindamycin: 3.4%, mupirocin: 1% and gentamicin: 0.5%. All S. aureus strains were sensitive to vancomycin and rifampicin. Except for one strain also resistant to tetracycline and fusidic acid, all MRSA strains were also resistant to ciprofloxacin. DISCUSSION: Multiresistant bacterial strains could become a concern in the community in France in the near future. In our study, only 14/197 (6.8%) S. aureus strains were sensitive to all tested antibiotics, whereas 21/197 (10.7%) were resistant to at least three of them. Compared to a French study performed in private practice in 2000, the level of MRSA is growing only slowly (5.8% versus 3.9%), whereas the percentage of strains of Peni-R/Oxa-S S. aureus are stable (80.5%). CONCLUSION: Common bacterial infections of the skin due to MRSA or to multiresistant S. aureus are not rare in France and have tended to increase slowly in recent years.     

Methicillin-resistant Staphylococcus aureus in community-acquired pyoderma

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen. It can also cause community-acquired infections. Indian reports about MRSA in community-acquired infections are rare. AIM: To evaluate the rate of MRSA in community-acquired pyoderma and the nasal colonisation with S. aureus in such patients. METHODS: Two hundred and fifty patients with community-acquired pyoderma, who attended outreach camps around Mangalore, south India between January 2000 and July 2001, were studied. Swabs collected from the skin lesions and anterior nares were inoculated onto blood agar and MacConkey's agar. Antimicrobial sensitivity testing was performed using Kirby-Bauer disk diffusion, agar dilution, and agar screen. RESULTS: Of 250 pyoderma cases, S. aureus was isolated from 202 (80.8%) patients. Twenty-two (10.9%) S. aureus isolates were methicillin resistant, 179 (88.6%) were resistant to penicillin, and 114 (56.4%) were resistant to erythromycin. S. aureus colonization in the anterior nares was observed in 136 (54.4%) cases, 11.8% of which were MRSA. Antibiograms of clinical isolates of S. aureus matched with nasal isolates in 99 (49%) cases. CONCLUSION: The emergence of MRSA in the community is a warning. A high nasal carriage rate may contribute to recurrent pyoderma. A correct antimicrobial policy and the avoidance of inappropriate antimicrobial usage are mandatory to reduce the spread of MRSA in the community.     

Trends of chromosomally mediated antimicrobial resistance in Neisseria gonorrhoeae in Canada: 1994-1999

BACKGROUND AND OBJECTIVES: We monitored the trends of chromosomally mediated resistant Neisseria gonorrhoeae (CMRNG) in Canada. Chromosomally resistant N. gonorrhoeae (CMRNG) were defined as having resistance to 3 antibiotics: penicillin (minimum inhibitory concentration [MIC] > or =2.0 mg/L), tetracycline (MIC > or =2.0 mg/L and < or =8.0 mg/L), and erythromycin (MIC > or =2.0 mg/L). GOAL: The goal was to provide surveillance data for public health interventions for the control of gonococcal infections. STUDY DESIGN: Antibiotic susceptibility tests were performed on N. gonorrhoeae isolates obtained from 1994 to 1999 in Canada. Strains were further characterized by auxotype (A), serovar (S), and plasmid profile (P). RESULTS: Between 1994 and 1999, 19.2% of strains were CMRNG, 12.9% had a combined resistance to tetracycline and erythromycin, and 4.7% were resistant to tetracycline. The incidence of ciprofloxacin resistance and azithromycin resistance was 2.3% and 0.8%, respectively. CONCLUSION: This survey of N. gonorrhoeae provides strain characterization data and temporal trends of strains in the Canadian population. CMRNG strains are on the rise, and the continual monitoring and characterization of these strains is important for the evaluation of current recommended antibiotic therapies used in Canada.     

葡萄球菌性烫伤样皮肤综合征的致病金黄色葡萄球菌剥脱毒素基因型及耐药研究

目的 探讨葡萄球菌性烫伤样皮肤综合征（SSSS）致病的金黄色葡萄球菌（简称金葡菌）分泌表皮剥脱毒素（ET）的主要类型及耐药情况。方法 108株金葡菌分离自SSSS（36例）、脓疱疮（36例）及皮肤脓肿（36例）。用多重PCR法测定致病金葡菌菌株产ETA、ETB、ETD基因型，Kirby-Bauer纸片法检测其对20种抗生素的敏感性。结果 36株来源于SSSS的金葡菌 100％ （36/36）为产ET菌株，其中单产ETA 2株（6％），ETB 7株（19％），兼产ETA和ETB 27株（75％）。来源于脓疱疮的36株金葡菌78％ （28/36）为产ET菌株，单产ETA 5株（14％），兼产ETA和ETB 23株（64％），未发现单产ETB金葡菌。而分离自皮肤脓肿的36株金葡菌仅2.8%（1/36）产ET，为兼产ETA和ETB菌株。108株金葡菌均未检测到ETD。金葡菌产ET的型别分布在三组疾病间差异有统计学意义（χ2 = 89.4，P ＜ 0.01），且分离自SSSS的金葡菌株产ET的比例明显高于脓疱疮组（χ2 = 9.0，P < 0.01）和脓肿组（χ2 = 68.1，P < 0.01）。三组病例的致病金葡菌对青霉素、氨苄西林、大环内酯类及克林霉素高度耐药，但对头孢类抗生素均敏感。脓肿组发现2例耐甲氧西林金葡菌株（MRSA）。结论 SSSS及脓疱疮患儿的致病金葡菌主要为产ET菌株，并以兼产ETA和ETB菌株为主。     

Adherence characteristics and susceptibility to antimicrobial agents of Staphylococcus aureus strains isolated from skin infections and atopic dermatitis

We examined the adherence characteristics and susceptibility to various antimicrobial agents of 130 strains of Staphylococcus aureus isolated from infective skin lesions and 135 strains of S. aureus isolated from non-infective eczematous lesions of atopic dermatitis (AD) patients. The isolation rate of methicillin-resistant S. aureus (MRSA) was 27.7% in strains from clinical sources excluding AD and 31.1% in those from AD. Coagulase type II strains were most frequently observed in MRSA strains isolated from all sources excluding AD, and coagulase type III strains were most frequently observed in those isolated from AD. We proposed that antimicrobial treatment for AD patients should be carefully designed to prevent MRSA infection. Plasma coagulation ability was lowest in S. aureus strains isolated from abscesses, suggesting that the lower production of fibrin observed in abscesses may assist the infiltration of neutrophils into skin tissues and that a decrease in plasma coagulation ability may enable abscess formation. Adherence to polypropylene tubes with slime production was most evident in S. aureus strains isolated from felon and least evident in those isolated from cellulitis and lymphangitis. Tube adherence was characteristic of the S. aureus strains attached to superficial skin tissues, but not necessarily for strains that had infiltrated the deep skin tissues. Fusidic acid demonstrated significant antimicrobial activity against the MRSA strains, but rifampicin was the strongest antimicrobial agent.     

Incidence of methicillin-resistant Staphylococcus aureus in community-onset paediatric skin infections: a retrospective study 2000-2005

BACKGROUND: A dramatic increase in the incidence of methicillin-resistant Staphylococcus aureus (MRSA) in community-onset skin infections has been reported over the last 10 years in the USA. The emergence of MRSA has been recently described in France. The aims of this study were to assess the incidence of MRSA in community-onset skin infections and to analyse the characteristics of MRSA skin infections in a French paediatric population. PATIENTS AND METHODS: This is a retrospective study covering the period January 2000 to December 2005. Patients aged under 15 years with S. aureus isolated from skin and a clinical diagnosis of skin infection were included. RESULTS: One hundred and thirty-four children were included with a median age of 3.4 years. There were no significant differences in MRSA prevalence between the different years of the study. The overall prevalence of MRSA was 8.2% (n=11/134). None of the isolated strains presented an antimicrobial susceptibility profile suggestive of the ST80-type community-acquired MRSA described in France. Three MRSA strains were isolated from serious superantigen-mediated skin infections. The antimicrobial susceptibility and genetic profile (tst-positive agr2 MSRA) for one strain of S. aureus militated strongly in favour of an MRSA ST5 clone skin infection. CONCLUSION: In this study we found no evidence of epidemic spread of MRSA in community-onset childhood skin infections between 2000-2005. Nevertheless, we report three cases of serious MRSA-induced superantigen-associated skin infection. This argues in favour of the presence of virulent community MRSA clones in France.     

Assessment of Streptococcus pyogenes microcolony formation in infected skin by confocal laser scanning microscopy

BACKGROUND: Streptococcus pyogenes and Staphylococcus aureus are often simultaneously detected from many cases of non-bullous impetigo with atopic dermatitis. OBJECTIVES: Using confocal laser scanning microscopy (CLSM), to investigate formation of S. pyogenes microcolonies in skin lesions. METHODS: The S. pyogenes cells in the stationary growth phase alone were strongly stained with fluorescein isothiocyanate-concanavalin A (FITC-ConA), and this staining was reduced by pretreatment with amylase. Although the components of sugars in glycocalyx produced by S. pyogenes cells are unknown, we suggested that the materials stained by FITC-ConA were consistent with the presence of ConA-reactive sugars in glycocalyx produced by S. pyogenes cells. RESULTS: S. pyogenes cells associated with streptococcal impetigo skin and croton-oil inflamed mouse skin formed microcolonies encircled by materials (glycocalyx) that stained strongly with FITC-ConA, and these findings were consistent with those in biofilms. In croton-oil inflamed mouse skin, polymorphonuclear leukocytes (PMNs) infiltrated to just below the epidermis in the cefdinir-treated group but only to the middle dermis in the cefdinir-non-treated group. In this case S. pyogenes and S. aureus cells formed separate microcolonies and existed independently in the outer walls of pustule lesions of streptococcal impetigo. CONCLUSION: In skin infections, S. pyogenes and S. aureus formed aggregates of microcolonies (similar to that in biofilms) encircled by glycocalyx, which can make the infection hard to eradicate using an antimicrobial agent alone. The effect of conventional antimicrobial agents against biofilm is mainly due to the increase of the invasion of PMNs into the biofilm.