Phenotypic Detection of Beta-lactamases among Proteus mirabilis, Enterobacter cloacae, and Citrobacter freundii Isolates from Urinary Samples in Gorgan, Northeast Iran

The data on members of the genera Proteus, Pseudomonas, Enterobacter, Citrobacter, and Staphylococcus as the etiologic agents of urinary tract infections (UTIs) is not much.  This study investigated the frequency of various beta-lactamases in urine isolates of Proteus mirabilis, Enterobacter cloacae, and Citrobacter freundii in Gorgan, Golestan province.

A total of 632 urine samples were collected from hospitalized patients in a teaching hospital. The samples were cultured on blood agar and Eosin Methylene blue agar and incubated overnight at 37°C. The cultures with a ≥105 CFU/mL bacterial count were defined as positive for UTI. Bacteria identification was performed using standard biochemical methods and the API20E enteric identification system. The antibiotic resistance pattern was determined by the Kirby-Bauer disk diffusion method, and a phenotypic confirmatory test was used for detecting ESBL, MBL, and AmpC beta-lactamases producers.

Out of 632 samples, 317 (50.1%) were positive for UTIs, and 27 (8.5%), 21 (6.6%), and 12 (3.7%) were positive for Enterobacter cloacae, Citrobacter freundii, and Proteus mirabilis isolates, respectively. All the isolates were sensitive to piperacillin-tazobactam and colistin. The prevalence of ESBL and AmpC beta-lactamases in P. mirabilis isolates was higher than the other isolates, but No MBL producers were detected.

In this study, the high frequency of ESBL and AmpC beta-lactamases in P. mirabilis isolates may suggest an increasing trend in resistance to cephalosporins and monobactams, which could have a significant impact on the management and treatment of UTI caused by this organism. Therefore, continuous monitoring is required to control the spread of β-lactamase-producing isolates in different geographical areas.