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"Considering the high rates of biofilm and antimicrobial resistance of biofilm-forming isolates in biomedical device associated infections, it was determined that it would not be sufficient to evaluate only the MIC results for susceptibility results" Öcal et al (2022).
Biofilm formation during CLABSI episodes

Abstract:

In view of the significant negative impact of biofilm-mediated infection on patient health and the necessity of a reliable phenotypic method to detect biofilm producers, this study aimed to demonstrate phenotypic and molecular biofilm formation in coagulase-negative staphylococci (CoNS) isolated from catheter related infections and to compare the methods used with each other. The study was also aimed to determine the biofilm eradication effect of vancomycin in order to guide for the treatment. For the detection of biofilm formation, a total of 154 CoNS clinical isolates of which 30 being causative agents of catheter related bloodstream infection (CRBSI) (isolated from both the catheter tip and blood cultures of 15 patients), 89 being isolated from peripheral blood cultures of patients without a central venous catheter (CVC) (13 of them were bloodstream infection agents, 76 of them were contaminant), and 35 being isolated as catheter colonizer, were screened by tissue culture plate (TCP), Congo red agar (CRA) method and polymerase chain reaction (icaA, icaD and IS256). Vancomycin minimum inhibitory concentration (MIC) and minimum biofilm eradicating concentration (MBEC) values were determined. The pulsed field gel electrophoresis (PFGE) method was used to show the clonal relationship between CoNS isolated from the catheter tips and peripheral blood of patients with CRBSI. Of the 154 CoNS isolates included in the study, 38.9% were Staphylococcus epidermidis (n= 60), 34.4% were Staphylococcus haemolyticus (n= 53), 20.7% were Staphylococcus hominis (n= 32), and 3.8% were detected as Staphylococcus capitis (n= 6). In our study, biofilm formation was shown in 31.8% with the CRA method and in 68.1% with the TCP method. By TCP method, 22% (n= 34) were determined as weak, 31.2% (n= 48) medium and 14.9% (n= 23) strong biofilm producers. While the sensitivity of the CRA method was found to be low for isolates that were determined as weak positive in the microplate method, the high sensitivity of the CRA method for isolates with medium and strong positivity was found remarkable. The positivity rates of icaA, icaD and IS256 genes in a total of 154 CoNS isolates were found to be 40 (25.9%), 57 (37%) and 77 (50%), respectively. In total, at least one gene positivity was detected in 107 (69.5%) isolates. Single gene positivity was detected in 55 (35.7%), two gene positivity in 35 (22.7%) and three gene positivity was detected in 17 (11%) of the included CoNS. Biofilm formation (four weak, four medium, two strong) was detected by microplate method in 10 of 47 CoNS isolates (five S.epidermidis, three S.hominis, one S.haemolyticus and one S.capitis) in which no genes were detected. Vancomycin MBEC/ MIC values were found to be high and it was observed that as the biofilm forming power of the isolates increased, the MBEC/MIC ratio also increased. The CoNS isolated from the catheter samples and blood of patients diagnosed with CRBSI had a 100% similar profile with PFGE except for one unevaluable isolate. The tissue culture plate (TCP) method was found to be most sensitive, accurate and reproducible screening method for detection of biofilm formation by staphylococci and has the advantage of being a quantitative model to study the adherence of staphylococci. The presence of the icaAD and IS256 gene is not always associated with in vitro biofilm formation. For this reason, it is more appropriate to use more than one method together for the evaluation of biofilm formation. It was thought that the use of reliable methods to specifically detect biofilms could be helpful in diseases that are difficult to treat. Considering the high rates of biofilm and antimicrobial resistance of biofilm-forming isolates in biomedical device associated infections, it was determined that it would not be sufficient to evaluate only the MIC results for susceptibility results.

Reference:

Öcal D, Tekeli A, Dolapçı İ. Kateter İlişkili Kan Dolaşımı Enfeksiyonlarından İzole Edilen Koagülaz Negatif Stafilokokların Biyofilm Oluşturma Özelliklerinin Araştırılması . Mikrobiyol Bul. 2022 Jul;56(3):506-524. Turkish. doi: 10.5578/mb.20229710. PMID: 35960241.