Abstract:
Pseudomonas aeruginosa is a gram-negative rod that can cause severe infections which are
associated with high mortality rates in immunocompromised patients. It is a frequent cause
of nosocomial infections where the spread of organisms is a common source of outbreaks.
One of the clinical significance of P. aeruginosa is its ability to form a biofilm on living or
non-living tissues and to differentiate into layered structures of sessile multicellular
bacterial cells bound by exopolysaccharide matrix (EPS). The genome size of P.
aeruginosa varies from 5.2 to 7.1 Mbp. This degree of variation highlights the importance
of typing methods used to study the evolution and epidemiology of this organism. This
study aimed at typing 100 clinical P. aeruginosa isolates recovered from several site of
infections obtained from American University of Beirut Medical Center (AUBMC). The
relatedness of the isolates was inspected by aligning their PFGE types (PT) in a
dendrogram. The phylogenetic tree revealed the presence of two major groups (I and II),
one of which contained only 2 isolates. The second major group (II) consisted of 8
subgroups (represented from A to H) with C, F, G and H being further divide into 2 clones
each. None of the isolates were genetically identical with 100% similarity index. A strong
correlation was detected between respiratory tract P. aeruginosa strains and the cluster II-G
of certain restriction patterns. In addition to a moderate correlation between urine samples
and PFGE cluster II-C. Antimicrobial susceptibility testing showed the distribution of the
P. aeruginosa samples into 32 antibiotypes. Tetracycline was considered an ineffective
drug against P. aeruginosa due to the high resistance percentage (95%), followed by
carbenicillin (49%). The most effective antibiotic was imipenem due to the least percentage
of resistance (20%), followed by ceftazidime (23%). Another objective of this study was to investigate the presence of a relationship between the strength of attachment of P.
aeruginosa to stainless steel surfaces and their corresponding antibiotic susceptibility
profile. A weak correlation has been detected between multiple drug resistance and strength
of attachment to surfaces. Significance of such a result is that even antibiotic susceptible P.
aeruginosa could have the potential of attaching strongly to surfaces and hence forming
biofilm. This study showed the importance of PFGE in characterizing the genetic diversity
and assessing the risk of environmental reservoirs of P. aeruginosa and the banding
patterns established will serve as a database to better understand the evolutionary
epidemiology of this important human pathogen in Lebanon.
