Comparison of phenotypic tests for the detection of metallo-beta-lactamases in clinical isolates of Pseudomonas aeruginosa

Evaluation of Three Carbapenemase-Phenotypic Detection Methods and Emergence of Diverse VIM and GES Variants among Pseudomonas aeruginosa Isolates in Tunisia

Background: Since 2012, few reports on the molecular epidemiology of Pseudomonas aeruginosa were reported in Tunisia. Objectives: This study aimed to evaluate carbapenem-resistance determinants and molecular epidemiology and to compare the carbapenemase-phenotypic detection methods of multidrug-resistant P. aeruginosa isolates. Methods: During a period of four years (2014 to 2017), all imipenem-ceftazidime-resistant P. aeruginosa isolates were retrospectively selected at the microbial laboratory of Charles Nicolle hospital of Tunis. These isolates were examined by the modified Hodge test, modified carbapenem inactivation method (mCIM), and another mCIM, called CIMTris, and their performance was evaluated using PCR analysis as the gold standard. Results: A total of 35 isolates were recovered among patients hospitalized in different units. All strains were colistin-susceptible.All carbapenem-resistant isolates showed a high-level resistance to carbapenems. CIMTris and mCIM showed 96.15% and 46.15% sensitivity and 44.44% and 100% specificity, respectively, for detecting carbapenemase production.Conclusions: CIMTris is a promising approach for detecting carbapenemase activity in P. aeruginosa and merits further testing. Moreover, this study described the first detection of GES-5- and GES-9-producing P. aeruginosa in Tunisia as well as the co-occurrence of the bla_GES-5 and bla_VIM-11 carbapenemase genes in one isolate. These findings are of great concern because the rapid dissemination of MDR strains represents a major therapeutic and epidemiological threat.

Comparison of four phenotypic methods for detection of metallo-β-lactamase-producing Gram-negative bacteria in rural teaching hospital

CONTEXT

Metallo-β-lactamase (MBL)-producing bacteria lead to resistance to carbapenem an antibiotic that used as the last resort for treatment of multidrug-resistant bacteria, extended spectrum beta-lactamases, and AmpC β-lactamase-producing Gram-negative bacteria (GNB). The emergence of MBL-producing GNB is challenge to microbiology laboratories because there are no standardized guidelines available to detect them. The aim of this study was to compare four phenotypic methods to detect MBL production in GNB and to determine antibiotic sensitivity of MBL-producing isolates.

MATERIALS AND METHODS

A total of 107 clinical isolates of GNB were tested for MBL production. Imipenem (IPM)-resistant GNB were taken as positive for MBL screening. MBL detection was done using ethylene diamine tetra acetic acid (EDTA) as MBL inhibitor. Four phenotypic methods were evaluated: (1) Combined disk synergy test (CDST) with 0.5M EDTA (CDST-0.5 M EDTA), (2) CDST with 0.1 M EDTA (CDST-0.1 M EDTA), (3) double-disk synergy test (DDST) with 0.5M EDTA (DDST-0.5 M EDTA), and (4) DDST with 0.1 M EDTA (DDST-0.1 M EDTA).

RESULTS

Out of 107 GNB, 30 were resistant to IPM considered as screening positive. Out of 30, 21 (70%) isolates were MBL positive by CDST-0.1 M EDTA, 19 (63.33%) by CDST-0.5M EDTA, 17 (56.67%) by DDST-0.1 M EDTA, and 16 (53.33%) by DDST-0.5M EDTA. All MBL-producing Gram-negative Bacilli were resistant to ampicillin/sulbactam. Polymyxin B was found to be the most sensitive drug.

CONCLUSION

CDST-0.1 M EDTA is the most sensitive method MBL detection. The detection of MBL-producing GNB is very important to control spread of the resistance.

Phenotypic and Molecular Survey of Metallo-beta-lactamase-producing Pseudomonas aeruginosa Isolated from Patients with Nosocomial and Non- Nosocomial Infections

BACKGROUND

Resistance to antimicrobial agents in Pseudomonas aeruginosa (P. aeruginosa) including carbapenems is a prominent problem in patients. The aim of this study is surveying Metallo-beta-lactamase (MBL)-producing P. aeruginosa isolated from patient specimens with nosocomial and non-nosocomial infections in Kurdistan province, Iran.

METHODS

In total, 146 Pseudomonas spp. were collected (December 2015 to August 2017). P. aeruginosa isolates were detected by phenotypic and polymerase chain reactions (PCR) of gyrB gene. Combination disk (CD) phenotypic test was used for the identification of MBL-producing strains and PCR was applied for identification of blaIMP and blaVIM genes in P. aeruginosa. Sensitivity and specificity of phenotypic tests were calculated as well. Fisher's exact test and logistic regression were used for data analysis (p≤0.05).

RESULTS

A total of 134 (91.78%) and 133 (91.09%) P. aeruginosa were detected using PCR and the phenotypic test, respectively. Fifty-six (41.79%) clinical isolates were isolated from patients with nosocomial infection. CD test proved that 67 out of 134 (50%) P. aeruginosa isolates were positive for MBL, of which 11 (8.20%) carried blaIMP gene. No significant relationship was found between MBL-producing P. aeruginosa and blaIMP genes; as well as between MBL-producing P. aeruginosa and blaIMP genes with age, sex, city of residence, inpatient/outpatient and specimen's type (p≥0.05).

CONCLUSION

Presence of MBL-producing P. aeruginosa strains and blaIMP genes were proved in this study; thus more precaution should be taken in the administration of carbapenem antibiotics to patients.

Low prevalence of metallo-beta-lactamase in Pseudomonas aeruginosa isolated from a tertiary burn care center in Tehran

Production of metallo-beta-lactamase (MBL) is one of the main mechanisms for resistance in carbapenem antibiotics. Detection of MBL-producer Pseudomonas aeruginosa is crucial in preventing its spread to other gram-negative bacteria. The aim of this study was to evaluate combination disc (CD) for identification of MBL-producer P. aeruginosa by polymerase chain reaction (PCR). A total of 255 imipenem resistant P. aeruginosa were collected from burn patients. Antibiotic susceptibility testing was conducted after purification and identification. Double-disc synergy test (DDST) with EDTA and combination disc test (CDT) with dipicolinic acid were performed for phenotypic detection of MBL and the PCR was carried out for blaVIM, blaIMP, blaNDM-1, blaSPM-1 genes. DDST with EDTA was negative in all cases, but 161 isolates were positive in CDT with dipicolinic acid. Further, blaVIM and blaIMP were detected in five and four strains, respectively. None of the isolates were positive for BlaNDM-1 and blaSPM-1. The results of this study showed that the prevalence of MBL is low in imipenem resistance P. aeruginosa and that other mechanisms could be involved in resistance to imipenem in this bacterium.