Abstract

Discharge of drug-resistant, biofilm-forming pathogens from hospital effluent water into municipal wastewater treatment plants poses a public health concern. This study examined the relationship between antibiotic resistance levels and biofilm formation of Acinetobacter baumannii strains isolated from hospital effluents. Antibiotic susceptibility of 71 A. baumannii isolates was evaluated by the Kirby-Bauer disk diffusion method. Minimum inhibitory concentrations (MICs) were determined by the agar dilution method, while the minimum biofilm eradication concentration (MBEC) was determined by the broth dilution method. Genotyping was performed for plasmid DNA. Biofilm formation was evaluated by the microtitre plate method and was quantified using crystal violet. A P-value of <0.05 was regarded as statistically significant in all tests. Extensively drug-resistant (XDR) strains made up 58% of the isolates, while multidrug-resistant (MDR) and pandrug-resistant (PDR) strains made up 50% of the isolates from final effluent. The MBEC of ciprofloxacin increased by 255-fold, while that of ceftazidime was as high as 63-1310-fold compared with their respective MICs. Isolates were classified into four plasmid pattern groups with no association between biofilm formation and plasmid type (P=0.0921). The degree of biofilm formation was independent of the level of antibiotic resistance, although MDR, XDR and PDR isolates produced significant biofilm biomass (P=0.2580). These results suggest that hospital effluent is a potential source of MDR biofilm-forming A. baumannii strains. Appropriate treatment and disposal of effluents are essential to prevent the presence of drug-resistant pathogens in wastewater.

Highlights

  • Antibiotic resistance is currently one of the greatest challenges facing global health

  • This study reports on the association between biofilm formation and antibiotic resistance of A. baumannii strains isolated from hospital effluent water from two hospitals in KwaZulu-Natal Province, South Africa

  • Of all nine categories of antimicrobials tested, only one isolate was non-resistant to at least one antibiotic in seven categories, none was susceptible to all antibiotics in all categories, while 17% were resistant to all antibiotics in all the categories (Supplementary Table S1)

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Summary

Introduction

Antibiotic resistance is currently one of the greatest challenges facing global health. It is estimated that antimicrobial resistance will lead to more deaths than other major causes of death, including cancer, at approximately 10 million by 2050 [1]. The high rate of abuse, misuse and inappropriate use of antibiotics together Pillay evade antimicrobial agents and the acquisition of plasmids harbouring resistance determinants within the microbial environment [6]. One of the most widely reported mechanisms for the selection of antibiotic-resistant bacteria through plasmid acquisition and evasion of drug action is the existence of microbial cells in community-like life forms known as biofilms [7]

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