Title : Biofilm formation in clinical isolates of cephalosporinase-producing proteus mirabilis
Objective: Infections caused by Proteus mirabilis are difficult to treat due to the acquisition of various antibiotic resistance mechanisms. The present work aims to examine the correlation between biofilm formation and antibiotic resistance in clinical isolates of Proteus mirabilis.
Methodology: This is a prospective study spanning a period of three months (June-July-August 2018). The study population is composed of 16 patients hospitalized for 48 hours or more in the intensive care unit. The strains isolated from different samples are purified and then identified by the Api 20E strips.
Sensitivity to antibiotics is determined according to the recommendations of the antibiogram committee of the French Society of Microbiology 2019 (CA-SFM / EUCAST)
The sensitivity tests of the isolated strains of Proteus mirabilis to imipenem were carried out using the micro-dilution method (CLSI, 2015).
The phenotypic demonstration of the presence of an extended-spectrum β-lactamase and a cephalosporinase is carried out by the synergy test (Robin et al., 2012) and the cloxacillin test (EUCAST, 2019), respectively. Thus, this work aimed to test the ability of these strains to form biofilms by the crystal violet technique.
Results: During the study period, Proteus mirabilis represented 9% (n=8) of all isolated germs (86 germs). Antibiogram results for the β-lactam family showed that the strains studied are resistant to ticarcillin/clavulanic acid combinations ; piperacillin/tazobactam as well as piperacillin, cefoxitin, ceftazidime and aztreonam. Resistance to tobramycin and ciprofloxacin concerned all the strains studied. With respect to gentamicin and amikacin, resistance has been observed in four strains. However, only two strains showed a resistance to the trimethoprim/sulfamethoxasole combination. The intermediate resistance observed to imipenem was confirmed by the evaluation of the MIC levels (2 to 4μg/ml) to this antibiotic. The β-lactam resistance phenotypes were the expression of a cephalosporinase alone or associated with that of a broad-spectrum β-lactamase.
For the study of the ability of the strains to form biofilms, the quantification of the biomass carried out revealed that all the strains of Proteus mirabilis isolated have the power to form single-species biofilms and are assigned to the group of highly producing biofilms.
Conclusion: Since most multidrug-resistant, cephalosporinase-producing strains of Proteus mirabilis were highly biofilm-forming, it appears that acquisition of specific antimicrobial resistance can enhance biofilm formation. Proper management of antibiotics is necessary against the spread of multidrug resistance and the appearance of new enzymes.