Antimicrobial susceptibility, virulence factors and biofilm formation among Staphylococcus aureus strains from hospital infections in Kerman, Iran

Öz

Amaç: Bu çalışma hastane kaynaklı Staphylococcus aureus suşlarının antimicrobial duyarlılık, virülans faktör ve biyofilm oluşturma özelliklerini belirlemeyi hedeflemektedir. Metotlar: İran, Kerman’da 30 adet, tekrarlamayan S. aureus suşu hastanelerden izole edildi. Antimicrobial duyarlılıklar disk diffüzyon metoduyla CLSI rehberinin sınırdeğerlerine göre çalışıldı. Vankomisin ve metisilin için minimum inhibitor konsantrasyonu (MİK) sıvı mikrodilüsyon ve E-test prosedürleri ile belirlendi. Bu suşlarla birlikte olan virülans faktörleri (proteaz, DNaz, lesitinaz, kapsül ve hemoliz) çalışıldı. Biyofilm değerlendirmesi mikrotitre tekniği ile miktarı belirleme şeklinde yapıldı. Bulgular: Toplam olarak 14 (% 46, 7) S. aureus suşu alt solunum yollarından, altı suş (% 20,0) üriner sistemden ve kalan 10 suş (% 33,3) yaralar, kan ve ortopedi hastalarından izole edildi. Bütün suşlar tigesikline duyarlıydı, sekiz suş (% 26,7) metisiline dirençli (MRSA) bulundu ve dört suş (% 13,3) vankomisine azalmış duyarlılık gösterdi. Suşların hiç biri vankomisine dirençli değildi (p≤0.05). MİK sonuçları; vankomisin için suşlardan dördünde (% 13,3) MİK 4 µg/mL olarak bulunurken beşinde (% 16,6) metisilin için MİK 32 µg/mL olarak bulundu. Suşlar aynı zamanda amoksisilin/klavulanik asit, tekrasiklin ve tobramisine dirençli idiler. MSSA suşları ile karşılaştırıldığında MRSA suşlarından 6’si (% 75,0) lesitinaz, yedisi (% 96,7) proteaz ve DNaz aktivitesi gösterdi. Yirmi suş (% 66,7) kuvvetli, yedi suş (% 23,3) orta ve üç suş (% 10,0) zayıf biyofilm yapmaktaydı.Sonuç: Bu sonuçlardan bu enfeksiyonlarda tedavi seçeneklerinin sınırlı olduğu anlaşılmaktadır. Bundan dolayı vankomisine duyarlılığı azalmış MRSA suşlarının etken olduğu enfeksiyonların izlenmesi ve yönetimi bu suşların hastane ortamına yayılmasının kontrolüyle yapılmalıdır

Anahtar Kelimeler

• Staphylococcus aureus, metisilin direnci, MİK, virülans faktörleri, biyofilm

Antimicrobial susceptibility, virulence factors and biofilm formation among Staphylococcus aureus isolates from hospital infections in Kerman, Iran

Abstract

Objective: The aims of present study were to determine the antimicrobial susceptibility, virulence factors and biofilm formation among MRSA hospital isolates of Staphylococcus aureus. Methods: Thirty non-repetitive strains of S. aureus isolated from three hospitals in Kerman, Iran. Antimicrobial sus­ceptibility was determined by disk diffusion breakpoints method according to CLSI guideline. The minimum inhibitory concentration (MIC) of vancomycin and methicillin were measured by the broth microdilution and E-test procedures. Virulence factors (protease, DNase, lecithinase, capsule and hemolysis) associated with the above isolates was studied. Biofilm was quantified by microtiter technique. Results: In total, 14 (46.7%) S. aureus were isolated from lower respiratory tract, six (20.0%) from urinary tract and re­maining 10 (33.3%) were recovered from wounds, blood and orthopedic patients. All of the isolates were susceptible to tigecycline, eight (26.7%) were found to be resistant to methicillin (MRSA) and 4 (13.3%) showed reduced susceptibility to vancomycin. No any vancomycin resistant isolate was detected (p≤0.05). MIC results showed that four of the isolates (13.3%) exhibited MIC 4 μg/mL to vancomycin while, five (16.6%) demonstrated MIC 32 μg/mL to methicillin. The iso­lates were also resistant to amoxicillin/clavulanic acid, tetracycline and tobramycin. It was found that, six (75 %) of MRSA strains produced lecithinase, seven (96.7%) demonstrated protease and DNase activities as compared to MSSA isolates. Biofilm analysis revealed that twenty (66.7%) isolates formed strong, seven (23.3%) formed moderate and three (10.0%) had weak biofilm. Conclusion: From the results, it can be concluded that, treatment options available for these infections are limited; therefore, monitoring, and management of infections due to MRSA with reduced susceptibility to vancomycin, must be done in order to control spread of these strains in the hospital environment.

Keywords

• Staphylococcus aureus
• methicillin resistance
• MIC
• virulence factor
• biofilm

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