A comparative in vitro sensitivity study of “cefepime-tazobactam” and other antibiotics against Gram-negative isolates from intensive care unit

INTRODUCTION

The indiscriminate use of third and fourth -generation cephalosporin and carbapenems in the past few decades has led to widespread antibiotic resistance among Gram (−ve) bacteria; Thereby restricting the use of several classes of antibiotics and using the antibiotic of last resort, Colistin.^[1,2] Recently, some microorganisms have developed resistance to colistin leading to pan-drug resistant infections with an imperative demand for newer antibiotics.^[3-5] Beta-lactam resistance has been encountered as the most common form of resistance encountered among the microorganisms. The use of Beta-lactam/Beta-lactamase inhibitor is a better method to counter the resistance to Beta-lactams.^[6,7]

Among Indian hospitals, there is high resistance to extended-spectrum β lactamases (ESBLs), and a similar trend is being observed in carbapenems due to irrational use in most critical care units.^[8,9] Thus, an ever-increasing menace of Gram-negative antibiotic resistance is being encountered in Indian healthcare, which can be attributed to the indiscriminate usage of antibiotics, over-the-counter availability of all antibiotic agents, and the absence of national antibiotic policy to counter the skyrocketing antimicrobial resistance.^[10]

The discovery of new antibiotics is the need of the hour to counter the ever-increasing antibiotic resistance. A fourth-generation cephalosporin with a β-lactamase inhibitor combination provides coverage to OXA and AmpC enzymes over third -generation cephalosporins.^[7] Among newer BL/BLI combinations, cefepime/tazobactam is a new drug approved for use in Indian hospitals by the Drug Controller General of India.^[11] No clinical data is available in the literature for this drug combination, and very limited studies have been published on this drug combination to date. The aim of the research was to elucidate the in vitro sensitivity of “Cefepime-tazobactam” and some other antibiotics against Gram (−ve) isolates from the intensive care unit (ICU).

MATERIALS AND METHODS

Inclusion criteria

As multiple samples were sent from a single patient admitted to the ICU, we included only the first sample growing GNB from a single patient. Thus, non-repeat samples were included in this study [Figure 1].

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Figure 1:

Inclusion of the pathogenic GNB isolated from various samples obtained from patients admitted to the ICU (n = 1024). GNB: Gram negative bacteria, ICU: Intensive care unit, N: Number of samples.

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RESULTS

We included 480 total GNB isolated from blood, pus, body fluids, ETA, and sputum samples in our study cohort. The maximum number of GNB isolates tested for susceptibility to cefepime-tazobactam was obtained from endotracheal aspirate samples (120/480, 25%), followed by those isolated from bloodstream infections (115/480, 23.95%) and sputum (112/480, 23.33%), as shown in Figure 2.

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Figure 2:

The distribution of all the samples included in the study cohort (n = 480). n: Number of samples.

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The most common microorganism tested for susceptibility to cefepime-tazobactam was K. pneumoniae (182/480, 37.92%) followed by Acinetobacter baumannii (135/480, 28.12%) and P. aeruginosa (94/480, 19.58%). Figure 3 describes the distribution of the microorganisms from the various samples included in the study. The most common microorganism was K. pneumoniae, which was mostly isolated from endotracheal aspirate (75/182, 41.21%) followed by bloodstream infections (69/182, 37.91%). A. baumannii was isolated most commonly from ETA (68/135, 50.37%) followed by sputum samples (42/135, 31.11%), while P. aeruginosa was isolated mostly from endotracheal aspirate samples (43/94, 45.74%).

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Figure 3:

The distribution of pathogenic microorganisms isolated from various samples included in this study (n = 480). n: Number of samples. E.coli: Escherichia coli, K.pneumoniae, Klebsiella pneumonia, E.cloacae: Enterobacter cloacae, A.baumannii: Acinetobacter baumannii, P. aeruginosa, Pseudomonas aeruginosa.

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The microorganisms were further divided into two groups, namely, non-inducible Enterobacteriaceae group (which includes E. coli and K. pneumoniae) and the inducible Enterobacteriaceae group (which includes Enterobacter aerogenes and Serratia marcescens) and those belonging to non-inducible Enterobacteriaceae group (n = 217, 45.21%) were predominantly tested for susceptibility to cefepimetazobactam in comparison to inducible Enterobacteriaceae group (n = 36, 7.5%). We also analyzed the results of antibiotic susceptibility testing with cefepime-tazobactam and other first-line drugs against the isolates included in the study [Table 1]. The drug in question was also tested for susceptibility against non-fermenters (n = 229, 47.71%).

Table 1 also represents the antibiotic susceptibility of all Gram (−-ve) isolates to cefepime, cefoperazone-sulbactam, cefepime-tazobactam, meropenem, and imipenem. Serratia marcescens was the most susceptible isolate to all the antibiotics and was 75.0%–100.0% (12/16, 75.0% to 16/16, 100.0%) susceptible to all the five antibiotics. K. pneumoniae and E. aerogenes were most resistant to all the antibiotics tested against them. K. pneumoniae was most resistant to meropenem (41/182, 22.53%), followed by imipenem (42/182, 23.08%) and cefoperazone-sulbactam (49/182, 26.92%), and was predominantly found susceptible to cefepime-tazobactam (122/182, 67.04%). E. aerogenes was least susceptible by cefoperazone-sulbactam (2/18, 11.11%), followed by both carbapenems (3/18, 16.67%) each and cefepime (5/18, 27.47%) and primarily found susceptible to cefepimetazobactam (11/18, 61.11%). Overall, susceptibility to all the antibiotics in descending order was as follows: cefepimetazobactam (322/480, 67.08%), cefepime (137/480, 28.54%), cefoperazone-sulbactam (127/480, 26.46%), imipenem (120/480, 25.0%), and meropenem (116/480, 24.17%).

Table 2 describes the comparative activity of cefepimetazobactam and cefepime against the most common three microorganisms isolated from the samples involved in the present study. K. pneumoniae has been identified as the most susceptible (50/182, 27.47%) and most resistant (60/182, 32.96%) microbe to both the cefepime and cefepime-tazobactam. Seventy-two (72/182, 39.56%) isolates of K. pneumoniae were found susceptible to cefepime-tazobactam but were resistant to cefepime, while none of the isolates were found susceptible to cefepime and resistant to cefepime-tazobactam. A. baumannii (55/135, 40.74%) was found to be most susceptible to cefepimetazobactam but was resistant to cefepime.

DISCUSSION

There is serious global concern regarding the rise of antibiotic resistance in recent times,with few to no newer antibiotics in the pipeline. With the advent of increasing Carbapenem resistance, there is an increasing interest in new combinations like “cefepime-tazobactam.” Cefepime is a fourth generation, synthetic cephalosporin with broad-spectrum action.^[15] The antibiotic exhibits better action against the Gram (−ve) bacteria in comparison to the Gram-positive bacteria. Tazobactam is a beta-lactamase that inhibits the activity of the beta-lactamase enzymes including “group 1-cephalosporinases, group 2br-TEM beta-lactamases, and group 3-metallo-beta-lactamases.” “Cefepime-tazobactam” is expected to overcome ESBL, AmpC, and OXA enzyme production.^[16,17]

There is a lack of studies comparing the efficacy of drugs most commonly used in the ICU, which include a variety of cephalosporins, carbapenems, and BL/BLI combinations. This study reports a better susceptibility of the Gram (−ve) bacteria to cefepime-tazobactam in comparison to carbapenems, and other cephalosporins that are profusely used in the ICU setup, which agrees with research done by Sood et al.^[17] and Mushtaq et al.^[18] The common microorganisms isolated from various samples such as K. pneumoniae, A. baumannii, and P. aeruginosa showed better susceptibility to cefepime-tazobactam in comparison to cefepime alone. Therefore, similar findings were stated by Susan et al.,^[6] and other authors’^[17-19].

In the wake of increasing carbapenem resistance of ~ 25% susceptibility of the commonly isolated microorganisms reported in our study, the susceptibility of the microorganisms was better to cefepime-tazobactam (67.08%). This is in comparison to the research by Agarwal et al.^[15] where carbapenems showed comparable performance to cefepime-tazobactam. A similar study performed in patients with hematological malignancies by Benanti et al.^[20] also showed comparable results with both the antibiotics. However, the patients were shifted back on carbapenems early in the treatment. Other Indian studies by Ghafur et al.^[21] and Sharma et al.^[22] reported either equitable or better susceptibility of the microorganisms to both carbapenems and cefepime-tazobactam which are contradictory to our finding of better susceptibility of the organisms to cefepime-tazobactam. A similar rising trend of carbapenem resistance is noticed in research by Vu et al.^[23] that further compels us to identify new antibiotics to combat the drug resistance among the isolates. Vu et al.^[23] supported the use of cefepime-tazobactam in place of carbapenems to prevent the rapid emergence of drug resistance among commonly isolated microorganisms from the ICU settings.

The main limitations of the present analysis are: primary, it is a single-center study and does not represent the rate of drug resistance in a particular geographical region: secondary, due to the unavailability of any zone diameters for the antibiotics susceptibility of cefepime-tazobactam and no specific CLSI guidelines for the same, we had to improvise using the disc diameters of cefepime recommended in CLSI.

CONCLUSIONS

Our study defines a good in vitro activity of “cefepimetazobactam” against non-inducible, inducible, and nonfermenters in comparison to other BL/BLI combinations and carbapenems used routinely in ICUs. It is a potential antimicrobial agent for treating an array of Gram-negative bacteria-associated infections, and it improves the outcome of patients suffering from infections caused by GNB in comparison to other antimicrobial agents.