Biofilm formation by clinical isolates and the implications in chronic infections.
BACKGROUND
Biofilm formation is a major virulence factor contributing to the chronicity of infections. To date few studies have evaluated biofilm formation in infecting isolates of patients including both Gram-positive and Gram-negative multidrug-resistant (MDR) species in the context of numerous types of infectious syndromes. Herein, we investigated the biofilm forming capacity in a large collection of single patient infecting isolates and compared the relationship between biofilm formation to various strain characteristics.


METHODS
The biofilm-forming capacity of 205 randomly sampled clinical isolates from patients, collected from various anatomical sites, admitted for treatment at Brooke Army Medical Center (BAMC) from 2004-2011, including methicillin-resistant/methicillin susceptible Staphylococcus aureus (MRSA/MSSA) (n=23), Acinetobacter baumannii (n=53), Pseudomonas aeruginosa (n=36), Klebsiella pneumoniae (n=54), and Escherichia coli (n=39), were evaluated for biofilm formation using the high-throughput microtiter plate assay and scanning electron microscopy (SEM). Relationships between biofilm formation to clonal type, site of isolate collection, and MDR phenotype were evaluated. Furthermore, in patients with relapsing infections, serial strains were assessed for their ability to form biofilms in vitro.


RESULTS
Of the 205 clinical isolates tested, 126 strains (61.4%) were observed to form biofilms in vitro at levels greater than or equal to the Staphylococcus epidermidis, positive biofilm producing strain, with P. aeruginosa and S. aureus having the greatest number of biofilm producing strains. Biofilm formation was significantly associated with specific clonal types, the site of isolate collection, and strains positive for biofilm formation were more frequently observed to be MDR. In patients with relapsing infections, the majority of serial isolates recovered from these individuals were observed to be strong biofilm producers in vitro.


CONCLUSIONS
This study is the first to evaluate biofilm formation in a large collection of infecting clinical isolates representing diverse types of infections. Our results demonstrate: (1) biofilm formation is a heterogeneous property amongst clinical strains which is associated with certain clonal types, (2) biofilm forming strains are more frequently isolated from non-fluid tissues, in particular bone and soft tissues, (3) MDR pathogens are more often biofilm formers, and (4) strains from patients with persistent infections are positive for biofilm formation.
Department of Extremity Trauma and Regenerative Medicine, United States Army Institute of Surgical Research, Ft, Sam Houston, San Antonio, TX, USA. carlos.j.sanchez3@us.army.mil
Carlos J
CJ
Sanchez
Katrin
K
Mende
Miriam L
ML
Beckius
Kevin S
KS
Akers
Desiree R
DR
Romano
Joseph C
JC
Wenke
Clinton K
CK
Murray
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001424:Bacterial Infections / Q000382:microbiology*; D018441:Biofilms; D002908:Chronic Disease; D024881:Drug Resistance, Bacterial; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology*; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology*; D006801:Humans; D012008:Recurrence
D000900:Anti-Bacterial Agents