Prevalence of ?-Lactamase Production and Antimicrobial Susceptibility of Multidrug Resistant Clinical Isolates of Non-Fermenting Gram Negative Bacteria From Hospitalized Patients in Kerman/Iran

Background: Non-fermenting Gram–negative bacteria are unable to ferment sugars in order to generate energy. They are ubiquitous in nature, and have a wide geographic distribution. They are also common in hospital settings, and may be isolated from humidifiers, ventilator machines, dialysis machines and other equipment, as well as from the skin of hospital personnel.
Objectives: This study focused on the isolation of multidrug resistant (MDR) non-fermenting Gram negative bacteria from clinical samples. Antimicrobial susceptibility, detection of extended spectrum β-lactamases (ESBL), and the presence of CTX-M and Metallo β-lactamase (MBL) in the isolated bacteria were evaluated.
Materials and Methods: Agar dilution method was used to test the susceptibility of the isolates to 10 antibacterial agents. All the isolates that were resistant to ≥ 3 antibacterial agents from different classes were regarded as MDR (111 isolates) and were selected for further studies.
β-lactamase and ESBL production were detected by nitrocefin discs, combined discs (CD) and double discs plus CD (DCDT). blaCTX-M and MBL were detected by PCR and EDTA synergy methods respectively.
Result: Among the MDR isolates the isolation frequency of Pseudomonas aeruoginosa, Stenotrophomonas maltophilia and Acinetoacter baumannii were 83.7%, 9.9% and 6.3% respectively. Resistance to imipenem (0.9%) and Ceftazidim (13.6%) was low, but resistance to other β-lactams was high, and 29.7% were resistant to ≥ 6 antibacterial agents from different classes simultaneously. β-lactamase was produced by 41.4% of the MDR isolates. Detection of ESBLs by a CD (59.4%) or DCDT test (46.8%) was not significantly different, but with a combination of CD and DCDT a higher percentage of ESBLs in the isolates (P ≤ 0.00) could be detected. The blaCTX-M and MBL phenotype were detected in two different strains of P. aeruoginosa.
Conclusions: The presence of a high percentage of isolates producing ESBLs which are resistant to different antibacterial agents may result in treatment failure in infected patients. Careful detection of antimicrobial resistant strains is needed in order to avoid underestimation or misidentification of ESBLs. An effective hospital infection control policy is also necessary in order to prevent further resistance to antimicrobials in the region.

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