Abstract
BackgroundThe antimicrobial resistance of clinical, environmental and control strains of the WHO “Priority 1: Critical group” organisms, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa to various classes of antibiotics, colistin and surfactin (biosurfactant) was determined.MethodsAcinetobacter baumannii was isolated from environmental samples and antibiotic resistance profiling was performed to classify the test organisms [A. baumannii (n = 6), P. aeruginosa (n = 5), E. coli (n = 7) and K. pneumoniae (n = 7)] as multidrug resistant (MDR) or extreme drug resistant (XDR). All the bacterial isolates (n = 25) were screened for colistin resistance and the mobilised colistin resistance (mcr) genes. Biosurfactants produced by Bacillus amyloliquefaciens ST34 were solvent extracted and characterised using ultra-performance liquid chromatography (UPLC) coupled to electrospray ionisation mass spectrometry (ESI–MS). The susceptibility of strains, exhibiting antibiotic and colistin resistance, to the crude surfactin extract (cell-free supernatant) was then determined.ResultsAntibiotic resistance profiling classified four A. baumannii (67%), one K. pneumoniae (15%) and one P. aeruginosa (20%) isolate as XDR, with one E. coli (15%) and three K. pneumoniae (43%) strains classified as MDR. Many of the isolates [A. baumannii (25%), E. coli (80%), K. pneumoniae (100%) and P. aeruginosa (100%)] exhibited colistin resistance [minimum inhibitory concentrations (MICs) ≥ 4 mg/L]; however, only one E. coli strain isolated from a clinical environment harboured the mcr-1 gene. UPLC-MS analysis then indicated that the B. amyloliquefaciens ST34 produced C13–16 surfactin analogues, which were identified as Srf1 to Srf5. The crude surfactin extract (10.00 mg/mL) retained antimicrobial activity (100%) against the MDR, XDR and colistin resistant A. baumannii, P. aeruginosa, E. coli and K. pneumoniae strains.ConclusionClinical, environmental and control strains of A. baumannii, P. aeruginosa, E. coli and K. pneumoniae exhibiting MDR and XDR profiles and colistin resistance, were susceptible to surfactin analogues, confirming that this lipopeptide shows promise for application in clinical settings.
Highlights
The antimicrobial resistance of clinical, environmental and control strains of the World Health Organisation (WHO) “Priority 1: Critical group” organisms, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa to various classes of antibiotics, colistin and surfactin was determined
In order to confirm the identity of these isolates, as well as the reference and clinical strains of A. baumannii and the reference, clinical and environmental strains of E. coli, K. pneumoniae and P. aeruginosa, genus or species-specific conventional PCR and Deoxyribonucleic acid (DNA) sequencing was performed
Trimethoprim and polymyxin B are effective in inhibiting the growth of gram-negative bacteria, it should be noted that A. baumannii is known to exhibit rifampicin resistance [36, 37], trimethoprim resistance [37, 38] and remains viable at a polymyxin B concentration of 2 mg/L according to the Clinical and Laboratory Standard Institute (CLSI) [34] breakpoints
Summary
The antimicrobial resistance of clinical, environmental and control strains of the WHO “Priority 1: Critical group” organisms, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa to various classes of antibiotics, colistin and surfactin (biosurfactant) was determined. Carbapenem-resistant Acinetobacter baumannii (A. baumannii) was classified as one of the main “Priority 1: Critical group” organisms [1] as it is the primary opportunistic pathogen implicated in nosocomial infections such as; bacteraemia, pneumonia, endocarditis, meningitis and catheter associated urinary tract infections (UTIs) [2,3,4]. It is the primary species detected and isolated from hospital environments, including intensive care units (ICUs), with many other Acinetobacter species frequently isolated from soil, water, vegetables and animal sources [5]. A study by Tam et al [9] revealed that patients infected with MDR P. aeruginosa were hospitalised for a significantly longer time period and were at an increased risk for 30-day mortality
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