Difficulty in detecting low levels of polymyxin resistance in clinical Klebsiella pneumoniae isolates: evaluation of Rapid Polymyxin NP test, Colispot Test and SuperPolymyxin medium

Challenges in the Detection of Polymyxin Resistance: From Today to the Future

Antimicrobial resistance is known to be one of the greatest global threats to human health, and is one of the main causes of death worldwide. In this scenario, polymyxins are last-resort antibiotics to treat infections caused by multidrug-resistant bacteria. Currently, the reference test to evaluate the susceptibility of isolates to polymyxins is the broth microdilution method; however, this technique has numerous complications and challenges for use in laboratory routines. Several phenotypic methods have been reported as being promising for implementation in routine diagnostics, including the BMD commercial test, rapid polymyxin NP test, polymyxin elution test, culture medium with polymyxins, and the Polymyxin Drop Test, which require materials for use in routines and must be easy to perform. Furthermore, Sensititre®, molecular tests, MALDI-TOF MS, and Raman spectroscopy present reliable results, but the equipment is not found in most microbiology laboratories. In this context, this review discusses the main laboratory methodologies that allow the detection of resistance to polymyxins, elucidating the challenges and perspectives.

Detection of polymyxins resistance among Enterobacterales: evaluation of available methods and proposal of a new rapid and feasible methodology

BACKGROUND

Fast and accurate detection of polymyxins resistance is necessary as they remain the last resources to treat infections caused by Carbapenem-resistant Enterobacterales in many regions. We evaluated the rapid colorimetric polymyxin B elution (RCPE) and developed its miniaturized version, RCPE microelution (RCPEm), aiming to detect polymyxins resistance among Enterobacterales.

METHODS

The methodologies consist of exposing the bacterial population in a solution (NP solution) where polymyxin B disks were previously eluted to obtain a concentration of 2 µg/mL for RCPE and 3 µg/mL for RCPEm.

RESULTS

Two hundred sixty-seven Enterobacterales were evaluated, 90 (33.7%) resistant to polymyxin B by broth microdilution. It was observed 0.6% of major error (ME) by RCPE, with a specificity of 99.4%. The miniaturized version (RCPEm) presented the same ME and specificity values, but slightly higher sensitivity (97.8% vs. 95.6%) with 2.2% of very major error (VME).

CONCLUSIONS

RCPE and RCPEm proved to be useful alternatives to determine polymyxin B susceptibility in clinical microbiology laboratories, presenting low cost, being easy to perform, and demanding short incubation time.

Evaluation of Early Reading of Broth Microdilution Technique for Polymyxin B

Delay in the results of standard phenotypic susceptibility tests is the main obstacle to adequate antibiotic treatment. For this reason, the European Committee for Antimicrobial Susceptibility Testing has proposed the Rapid Antimicrobial Susceptibility Testing for the disk diffusion method directly from blood culture. However, to date, there are no studies evaluating early readings of polymyxin B broth microdilution (BMD), the only standardized methodology for assessing susceptibility to polymyxins. This study aimed to evaluate modifications in the BMD technique for polymyxin B using fewer antibiotic dilutions and reading after an incubation time of 8-9 hr (early reading) in comparison to 16-20 hr of incubation (standard reading) for isolates of Enterobacterales, Acinetobacter baumannii complex, and Pseudomonas aeruginosa. A total of 192 isolates of gram-negative bacteria were evaluated and the minimum inhibitory concentrations were read after early and standard incubations. The early reading presented 93.2% of essential agreement and 97.9% of categorical agreement with the standard reading of BMD. Only three isolates (2.2%) presented major errors and only one (1.7%) presented a very major error. These results indicate a high agreement between the early and the standard reading times of BMD of polymyxin B.

Distribution of mcr-1 Harboring Hypervirulent Klebsiella pneumoniae in Clinical Specimens and Lytic Activity of Bacteriophage KpnM Against Isolates

Background

The World Health Organization (WHO) has declared the multi-drug resistant (MDR) Klebsiella pneumoniae as one of the critical bacterial pathogens. The dearth of new antibiotics and inadequate therapeutic options necessitate finding alternative options. Bacteriophages are known as enemies of bacteria and are well-recognized to fight MDR pathogens.

Methods

A total of 150 samples were collected from different clinical specimens through a convenient sampling technique. Isolation, identification, and antibiotic susceptibility testing (AST) of K. pneumoniae were done by standard and validated microbiological procedures. Molecular identification of virulence factors and antibiotic resistance genes (ARGs) was carried out through polymerase chain reaction (PCR) by using specific primers. For bacteriophage isolation, hospital sewage samples were processed for phage enrichment, purification, and further characterization ie, transmission electron microscopy (TEM) and stability testing, etc. followed by evaluation of the lytic potential of the phage.

Results

Overall, a total of 41% of isolates of K. pneumoniae were observed as hypervirulent K. pneumoniae (hvKp). Among hvKp, a total of 12 (42%) were detected as MDR hvKp. A total of 37% of all MDR isolates were found resistant to colistin, and 66% of the colistin resistance isolates were recorded as mcr-1 positive. Isolated phage KpnM had shown lytic activity against 53 (79%) K. pneumoniae isolates. Remarkably, all 8 mcr-1 harboring MDR hvKp and non-hvKp isolates were susceptible to KpnM phage.

Conclusion

Significant distribution of mcr-1 harboring hypervirulent Klebsiella pneumoniae was observed in clinical specimens, which is worrisome for the health system of the country. Characterized phage KpnM exhibited encouraging results and showed the lytic activity against the mcr-1 harboring hvKp isolates, which may be used as a prospective alternative control strategy to fight this ominous bacterium.

Evaluation of phenotypic methods for detection of polymyxin B-resistant bacteria

Determination of sensitivity to polymyxins has always been a challenge, especially in clinical laboratory routines. This study evaluated two rapid, simple, and inexpensive phenotypic methods to test polymyxin B (PMB) susceptibility in Enterobacterales and non-fermenting Gram-negative bacilli. One hundred isolates were used in the tests. The isolates were collected in three hospitals in southern and southeastern Brazil from 1995 to 2019. We compared broth microdilution (reference method) with the broth disk elution test and modified drop test, using polymyxin B -disk or PMB -powder in 2 concentrations (12 and 16 μg/ml). For the broth disk elution and modified drop test with the concentration of 12 μg/ml, categorical agreement values exceeded 90%. The modified drop test with a concentration of 12 μg/ml and broth disk elution may be excellent for initial screening of polymyxin-resistance in laboratory routines. Moreover, these methods are simple and use inexpensive supplies, and may optimize therapeutic decisions.

Polymyxin NP tests (from colonies and directly from blood cultures): accurate and rapid methodologies to detect polymyxin B susceptibility among Enterobacterales

Detection of polymyxins susceptibility is challenging. We aimed to evaluate Rapid Polymyxin NP from colonies (NP-colony) and directly from positive blood bottles (NP-bottle), using polymyxin B instead of colistin among Enterobacterales. Both had similar and acceptable accuracy. This is the first study performing NP-bottle using polymyxin B instead of colistin.