Molecular testing of Klebsiella pneumoniae contaminating tissue allografts recovered from deceased donors

Molecular typing methods & resistance mechanisms of MDR Klebsiella pneumoniae

The emergence and transmission of carbapenem-resistant Klebsiella pneumoniae (CRKP) have been recognized as a major public health concern. Here, we investigated the molecular epidemiology and its correlation with the mechanisms of resistance in CRKP isolates by compiling studies on the molecular epidemiology of CRKP strains worldwide. CRKP is increasing worldwide, with poorly characterized epidemiology in many parts of the world. Biofilm formation, high efflux pump gene expression, elevated rates of resistance, and the presence of different virulence factors in various clones of K. pneumoniae strains are important health concerns in clinical settings. A wide range of techniques has been implemented to study the global epidemiology of CRKP, such as conjugation assays, 16S-23S rDNA, string tests, capsular genotyping, multilocus sequence typing, whole-genome sequencing-based surveys, sequence-based PCR, and pulsed-field gel electrophoresis. There is an urgent need to conduct global epidemiological studies on multidrug-resistant infections of K. pneumoniae across all healthcare institutions worldwide to develop infection prevention and control strategies. In this review, we discuss different typing methods and resistance mechanisms to explore the epidemiology of K. pneumoniae pertaining to human infections.

Biofilm formation and antibiotic susceptibility of Staphylococcus and Bacillus species isolated from human allogeneic skin

Human skin banks around the world face a serious problem with the high number of allogeneic skins that are discarded and cannot be used for grafting due to persistent bacterial contamination even after antibiotic treatment. The biofilm formation capacity of these microorganisms may contribute to the antibiotic tolerance; however, this is not yet widely discussed in the literature. Thisstudy analyzed bacterial strains isolated from allogeneic human skin samples,which were obtained from a hospital skin bank that had already been discardeddue to microbial contamination. Biofilm formation and susceptibility topenicillin, tetracycline, and gentamicin were evaluated by crystal violetbiomass quantification and determination of the minimum inhibitoryconcentration (MIC), minimum biofilm inhibitory concentration (MBIC), andminimum biofilm eradication concentration (MBEC) by the broth microdilutionmethod with resazurin dye. A total of 216 bacterial strains were evaluated, and204 (94.45%) of them were classified as biofilm formers with varying degrees ofadhesion. MBICs were at least 512 times higher than MICs, and MBECs were atleast 512 times higher than MBICs. Thus, the presence of biofilm in allogeneicskin likely contributes to the inefficiency of the applied treatments as antibiotictolerance is known to be much higher when bacteria are in the biofilmconformation. Thus, antibiotic treatment protocols in skin banks shouldconsider biofilm formation and should include compounds with antibiofilmaction.

Prevalence of β-lactamase-encoding genes and molecular typing of Acinetobacter baumannii isolates carrying carbapenemase OXA-24 in children

Background

β-Lactam antibiotics have been broadly used for the treatment of Acinetobacter baumannii infections, resulting in development of β-lactam inactivating β-lactamases. Here, we described antibiotic resistance rate, prevalence of β-lactamase-encoding genes, and clonal relationships of A. baumannii strains isolated from children referred to Children’s Medical Center in Tehran, Iran, during 2019–2020.

Methods

A total of 60 non-replicate A. baumannii isolates were recovered from clinical specimens of pediatric patients. Antibiotic susceptibility testing was done by the disc diffusion method. Colistin susceptibility of isolates was performed by the broth microdilution method. β-lactamase-encoding genes were characterized by PCR. The presence of ISAba1 element upstream of the several oxacillinase genes was also checked. Genetic relatedness of isolates was determined by using random amplification of polymorphic DNA (RAPD) typing.

Results

The antimicrobial susceptibility tests showed that 83.3% of A. baumannii isolates were MDR, and 40% XDR. Both MDR and XDR A. baumannii isolates were susceptible to colistin. The frequency of bla_OXA-51-like, bla_OXA-23-like, bla_TEM, bla_OXA-24-like, bla_PER, bla_SHV, bla_CTX-M, bla_OXA-58-like, and bla_IMP was 100, 93.33, 60, 36.67, 28.33, 8.33, 5, 3.33, and 1.67%, respectively. Coexistence of ISAba1/bla_OXA-23-like and ISAba1/bla_OXA-51-like was observed in 65% and 85% of isolates, respectively. RAPD analysis revealed 4 common types and 2 single types of A. baumannii isolates.

Conclusions

The multiple clones harboring bla_OXA-23-like, ISAba1-bla_OXA-51-like, and ISAba1-bla_OXA-23-like were responsible for the spread of A. baumannii isolates in our clinical wards. Dissemination of the well-established clones is worrisome and would become therapeutic challenges due to the possible transferring genetic elements associated with resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-021-00480-5.

Clonal relatedness and resistance characteristics of OXA-24 and -58 producing carbapenem-resistant Acinetobacter baumannii isolates in Tehran, Iran

AIMS

The present study was conducted to investigate the mechanism of carbapenem resistance and the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii (CRAB) isolates collected from two nearby hospitals in Tehran, Iran.

METHODS AND RESULTS

A total of 180 CRAB isolates were studied. Antimicrobial susceptibility testing was performed using disk diffusion and Epsilometer tests. The detection of OXA-23, -24 and -58 was implemented for all isolates using polymerase chain reaction. Subsequently, isolates harbouring OXA-24 and -58 were investigated for the presence of resistance determinants of Ambler class A, metallo-β-lactamases (MBLs), and carbapenem-hydrolysing class D β-lactamases, ISAba1, and the genetic relatedness between them was analysed using pulsed-field gel electrophoresis (PFGE). All isolates were found to be resistant to imipenem with a MIC of ≥8 µg ml^-1 and were susceptible to colistin with a MIC of ≤1·5 µg ml^-1 . Sixty percent of the isolates had OXA-23. OXA-24 and -58 were detected in 31 of 180 CRAB isolates. These chosen isolates were devoid of MBLs and bla_SHV , bla_{C TX-M} , bla_VEB ESBL genes. The PER determinant was detected in 38% of isolates as the most common extended spectrum β-lactamases (ESBLs). Of these isolates, 51·6% had OXA-23, and ISAba1 was found to be upstream of OXA-23 and OXA-51 in 16 and 8 isolates, respectively. The band patterns produced by PFGE showed nine clonal pulsotypes distributed between the two hospitals.

CONCLUSION

The findings showed that the refractory CRAB isolates were transmitted intra- and inter-hospital, particularly in the ICU due to shortcomings in infection control surveillance.

SIGNIFICANCE AND IMPACT OF THE STUDY

Carbapenem resistance is a substantial threat in the treatment of infections caused by A. baumannii due to limitations in the therapeutic options.