Errors in antibiotic sensitivity testing: Barking up the wrong tree.

Dear Editor,

We read a recently published study titled “Twelve-year trend of Escherichia coli antibiotic resistance in the Islamabad population” with an interest to know about the antibiotic susceptibility trend of uropathogenic Escherichia coli causing uncomplicated urinary tract infections (UTI) [1].

The study has reported the retrospective data of twelve years in two phases; first from 1st Jan 2005 to Dec 2010 and second from 1st Jan 2016 to 31st May 2021. However, there are few points in this study which need to be reviewed urgently-

Antimicrobial Susceptibility Testing (AST) is a standardized procedure which need to be performed and interpreted as per the recommended guidelines like Clinical and Laboratory Standards Institute (CLSI) or European Committee on Antimicrobial Susceptibility Testing (EUCAST). However, the authors in this study have not mentioned at all about any guidelines to conduct AST and interpretation of the results [2,3].

The Authors have wrongly chosen and documented the concentrations of different antibiotics (Table 1) which were tested against the uropathogenic E. coli strains. Moreover, the authors have just mentioned the name of antibiotic groups like Aminoglycosides and Cephalosporins but there are several antibiotics in each group which may not be tested using the same concentration. For instance, the potency of Gentamicin and Amikacin varies from each other.

Table 1

CLSI/EUCAST recommended potency of antibiotics.

S. No.	Antibiotics	Potency as mentioned in the present study	Recommended potency by CLSI/EUCAST
1	Amoxicillin/Clavulanic acid	625mg/1 gm	20/10 μg
2	Trimethoprim/Sulphamethoxazole	160/800 mg	1.25/23.75 μg
3	Aminoglycosides	80mg/500 mg	Gentamicin- 10 μgAmikacin- 30 μg
4	Nitrofurantoin	3 gm	300 μg
5	Cephalosporins	400 mg	30 μg
6	Sulbactams	1 gm/2 gm	Not to be used alone
7	Fosfomycin	100 mg	200 μg

Sulbactam, which is a beta-lactamase inhibitor and is recommended to be tested only in combination like Ampicillin-sulbactam etc., was tested alone and reported as 75% sensitive against uropathogenic E. coli in 2021 in this study [2,3].

There are different methods of performing antimicrobial susceptibility testing like diffusion method, dilution method, diffusion and dilution method etc. whereas the authors have not mentioned the name of method, opted in this study [4,5].

In conclusion, the authors have used non-recommended antibiotics concentrations and an unknown methodology and therefore, the results of this study can not be accepted as the antibiotic resistance being a most critical issue for public health.

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Author contributions

Both, Dr. Nitin Kumar and Mr. Harit Kumar have equally contributed in writing the final manuscript.

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Declaration of competing interest

The authors declare no conflicts of interest in this communication.