Prevalence and Antimicrobial Susceptibility Pattern of Extended Spectrum Beta Lactamase (ESBL) and non-ESBL Producing Enteric Gram-Negative Bacteria and Activity of Nitrofurantoin in the era of ESBL

Background: Resistance in enteric Gram-negative bacteria is of a great concern and concise local data are lacking. Objectives: To determine prevalence and antimicrobial susceptibility pattern of Extended Spectrum Beta-Lactamase (ESBL) and non-ESBL producing enteric Gram-negative bacteria. Materials and Methods: In a descriptive study in Tehran, patients’ samples have been obtained and were inoculated on blood and MacConkey agar plates at microbiology laboratory hospital, and a total of 292 Gram-negative species were isolated at Microbiology Laboratory from patients’ specimens. Susceptibility pattern was determined by disk diffusion method based on Kirby-Bauer method on Mueller-Hinton agar plate. SPSS 16 software (descriptive analysis, Chi-square) was used for statistical analysis of this study. Results: Escherichia coli was the most common organism [189 (64.7%)], followed by Acinetobacter baumannii [40 (13.7%)], Pseudomonas aeruginosa [32 (11%)], Klebsiella pneumoniae [26 (8.9%)], Proteus mirabilis [4 (1.4%)], and Serratia marcescense [1 (0.3%)]. 122 (41.8%) of isolates were classified as ESBL - producers. E. coli accounted for most of the ESBL-producer bacteria, followed by K. pneumoniae. 170 (58.2%) of isolates were non-ESBL producers. All of the ESBL producer isolates were sensitive to imipenem, piperacillin-tazobactam and colistin whereas resistance to these antibiotics in the non-ESBL group was seen. The rate of resistance to nitrofurantoin in ESBL group was lower than of that in non-ESBL group. The majority of the ESBL isolates of resistant to trimethoprim-sulfamethoxazole, ciprofloxacin, the third generation cephalosprins (ceftriaxone, cefixime, and cefotaxime), gentamicin and amikacin, were sensitive to nitrofurantoin. Conclusion: Although all ESBL producer Gram-negative bacteria were sensitive to imipenem, piperacillin-tazobactam, and colistin, non-ESBL isolates showed resistant pattern. Interestingly, notable percent of mentioned resistant isolates were sensitive to nitrofurantoin.