In vitro cost-effective methods to detect carbapenemases in Enterobacteriaceae

Phenotypic Methods for the Detection of Metallo-Beta-Lactamase Production by Gram-negative Bacterial Isolates from Hospitalized Patients in A Tertiary Care Hospital in India

Drug-resistant bacteria are a global health concern owing to the high morbidity and mortality they can cause, especially in countries such as India. Gram-negative bacteria, including Enterobacteriaceae, Pseudomonas, and Acinetobacter, are primarily responsible for expanding the scope of drug resistance. These antibiotic-resistant pathogens are particularly associated with serious infections in hospitals. The production of carbapenemase by gram-negative bacteria appears to be the major reason for their resistance to carbapenems. The study was a prospective study done from March 2018 to December 2020. All the carbapenem-resistant isolates from various clinical samples were further tested for the production of carbapenemases/metallo-beta-lactamases production by various phenotypic tests like carbaNp, Imipenem–EDTA combined disc synergy test, Double-disc synergy test and E-test methods. Of all carbapenem-resistant gram-negative bacteria isolated from patients in a hospital in India, 237 (88.1%) carbapenemase producers were identified, among which 217 (91.5%) were metallo-beta-lactamase (MBL) producers. Therefore, the detection of MBL producers is important for preventing their infectious spread. The present study revealed that most MBL producers were isolated from patients of 0–9 to years of age (63.9%). The double-disc synergy test (DDST) and E-test MBL strips were more sensitive than the combined disc test in detecting MBLs. Because the DDST was the simplest and most effective method, it can be used for the routine laboratory screening of MBL producers in hospitals.

Detection of extensively drug-resistant and hypervirulent Klebsiella pneumoniae ST15, ST147, ST377 and ST442 in Iran

In this study, we focused on the emergence of extensively drug-resistant (XDR), pandrug-resistant (PDR), and hypervirulent Klebsiella pneumoniae (hvKP) in Iran. During 2018 to 2020 a total of 52 K. pneumoniae isolates were collected from different clinical specimens. The hvKP isolates were identified by PCR amplification of virulence and capsular serotype-specific genes. Hypermucoviscous K. pneumoniae (hmKP) were identified by string test. Carbapenem-resistant hvKP (CR-hvKP), multidrug-resistant hvKP (MDR-hvKP), extensively drug-resistant hvKP (XDR-hvKP), and pandrug-resistant hvKP (PDR-hvKP) were determined by disc diffusion method, Carba-NP test and PCR method. XDR-hvKP isolates were typed by multilocus sequence typing (MLST). Among all K. pneumoniae isolates 14 (26.9%) were identified as hvKP and 78.6% (11/14) of them were hmKP however, none of the classic K. pneumoniae (cKP) isolates were hmKP. The predominant capsular serotype of hvKP was K2 (42.85%) followed by K1 (35.71%). The prevalence of MDR-hvKP, XDR-hvKP and PDR-hvKP isolates were 6 (42.9%), 5 (35.7%) and 1 (7.1%), respectively. ESBL production was found in 85.7% of hvKP isolates and most of them carried bla TEM gene (78.6%) and 6 isolates (42.9%) were CR-hvKP. Among hvKP isolates, 1 (7.1%), 2 (14.3%), 3 (21.4%), 8 (28.6%), and 11 (78.6%) carried bla NDM-6, bla OXA-48, bla CTX-M, bla SHV, and bla TEM genes, respectively. According to MLST analysis, 2, 1, 1, and 1 XDR-hvKP isolates belonged to ST15, ST377, ST442, and ST147, respectively. The occurrence of such isolates is deeply concerning due to the combination of hypervirulence and extensively drug-resistance or pandrug-resistance.

Molecular characteristics of antibiotic-resistant Escherichia coli and Klebsiella pneumoniae strains isolated from hospitalized patients in Tehran, Iran

BACKGROUND

We evaluated the distribution of carbapenem and colistin resistance mechanisms of clinical E. coli and K. pneumoniae isolates from Iran.

METHODS

165 non-duplicate non-consecutive isolates of K. pneumoniae and E. coli were collected from hospitalized patients admitted to Iran's tertiary care hospitals from September 2016 to August 2018. The isolates were cultured from different clinical specimens, including wound, urine, blood, and tracheal aspirates. Antibiotic susceptibility testing was performed by disc diffusion and microdilution method according to the Clinical and Laboratory Standards Institute (CLSI) guideline. The presence of extended spectrum β-lactamases (ESBLs) genes, carbapenemase genes, as well as fosfomycin resistance genes, and colistin resistance genes was also examined by PCR-sequencing. The ability of biofilm formation was assessed with crystal violet staining method. The expression of colistin resistance genes were measured by quantitative reverse transcription-PCR (RT-qPCR) analysis to evaluate the association between gene upregulation and colistin resistance. Genotyping was performed using the multi-locus sequencing typing (MLST).

RESULTS

Colistin and tigecycline were the most effective antimicrobial agents with 90.3% and 82.4% susceptibility. Notably, 16 (9.7%) isolates showed resistance to colistin. Overall, 33 (20%), 31 (18.8%), and 95 (57.6%) isolates were categorized as strong, moderate, and weak biofilm-producer, respectively. Additionally, blaTEM, blaSHV, blaCTX-M, blaNDM-1, blaOXA-48-like and blaNDM-6 resistance genes were detected in 98 (59.4%), 54 (32.7%), 77 (46.7%), 3 (1.8%), 17 (10.30%) and 3 (1.8%) isolates, respectively. Inactivation of mgrB gene due to nonsense mutations and insertion of IS elements was observed in 6 colistin resistant isolates. Colistin resistance was found to be linked to upregulation of pmrA-C, pmrK, phoP, and phoQ genes. Three of blaNDM-1 and 3 of blaNDM-6 variants were found to be carried by IncL/M and IncF plasmid, respectively. MLST revealed that blaNDM positive isolates were clonally related and belonged to three distinct clonal complexes, including ST147, ST15 and ST3299.

CONCLUSIONS

The large-scale surveillance and effective infection control measures are also urgently needed to prevent the outbreak of diverse carbapenem- and colistin-resistant isolates in the future.