Ecological and Public Health Implications of the Discharge of Multidrug-Resistant Bacteria and Physicochemical Contaminants from Treated Wastewater Effluents in the Eastern Cape, South Africa

This study assessed the prevalence of fecal indicator bacteria (FIB) and Vibrio species, as well as the physicochemical qualities of the discharged effluents of two wastewater treatment facilities, in the Eastern Cape, South Africa over a one-year sampling period using standard methods. Bacteriological assessment revealed presumptive E. coli counts ranging from 3 to 1.2 × 105 CFU/100 mL, while counts of Vibrio spp. ranged from 11 to 1.4 × 104 CFU/100 mL. Molecular identification of the isolates by polymerase chain reactions (PCR) yielded positive reaction rates of 76.2% (381/500) and 69.8% (279/400) for E. coli and Vibrio species, respectively. The antibiotic susceptibility profiles of 205 randomly selected PCR-confirmed Vibrio isolates against 18 antibiotics revealed resistance frequencies ranging from 0.5% (imipenem) to 96.1% (penicillin G), based on recommended breakpoint concentrations. About 81% (166/205) of the Vibrio isolates exhibited multidrug resistance (resistance to three or more classes of antibiotics), while nine different antibiotic resistance genes were detected by PCR. The physicochemical qualities of the effluents also ranged as follows: pH (6.5–7.6), temperature (12–27 °C), turbidity (1.5–65.7 mg/L), total dissolved solids (95–171 mg/L), dissolved oxygen (2.1–9.8), electrical conductivity (134–267 µS/cm), free chlorine (0.08–0.72 mg/L), biochemical oxygen demand (0.12–9.81 mg/L), nitrate (1.04–21.5 mg/L), nitrite (0.11–0.76 mg/L), phosphate (1.03–18.3 mg/L) and chemical oxygen demand (27–680 mg/L). The discharged effluents fell short of the regulatory guidelines for some of the parameters assessed. We conclude that the discharged effluents are potential sources of environmental pollution and can contribute to drug resistant bacteria load in the receiving watershed, with the associated ecological and human health risks

Prevalence of Multidrug-Resistant Bacteria (Enteropathogens) Recovered from a Blend of Pig Manure and Pinewood Saw Dust during Anaerobic Co-Digestion in a Steel Biodigester

South Africa adopts intensive livestock farming, embracing the employment of huge quantities of antibiotics to meet the increased demand for meat. Therefore, bacteria occurring in the animal products and manure might develop antibiotic resistance, a scenario which threatens public health. The study investigated the occurrence of Gram-negative bacteria from eighteen pooled samples withdrawn from a single-stage steel biodigester co-digesting pig manure (75%) and pine wood saw dust (25%). The viable counts for each bacterium were determined using the spread plate technique. The bacterial isolates were characterised based on cultural, morphological and biochemical characteristics, using the Analytical Profile Index 20 e test kit. In addition, isolates were characterised based on susceptibility to 14 conventional antibiotics via the disc diffusion method. The MAR index was calculated for each bacterial isolate. The bacterial counts ranged from 104 to 106 cfu/mL, indicating manure as a potential source of contamination. Overall, 159 bacterial isolates were recovered, which displayed diverse susceptibility patterns with marked sensitivity to amoxicillin (100% E. coli), streptomycin (96.15% for Yersinia spp.; 93.33% for Salmonella spp.) and 75% Campylobacter spp. to nitrofurantoin. Varying resistance rates were equally observed, but a common resistance was demonstrated to erythromycin (100% of Salmonella and Yersinia spp.), 90.63% of E. coli and 78.57% of Campylobacter spp. A total of 91.19% of the bacterial isolates had a MAR index > 0.2, represented by 94 MAR phenotypes. The findings revealed multidrug resistance in bacteria from the piggery source, suggesting they can contribute immensely to the spread of multidrug resistance; thus, it serves as a pointer to the need for the enforcement of regulatory antibiotic use in piggery farms. Therefore, to curb the level of multidrug resistance, the piggery farm should implement control measures in the study area

Occurrence and Multidrug Resistance in Strains of <i>Listeria monocytogenes</i> Recovered from the Anaerobic Co-Digestion Sludge Contained in a Single Stage Steel Biodigester: Implications for Antimicrobial Stewardship

L. monocytogenes is a zoonotic foodborne pathogen with inherent adaptability to tolerate environmental and physiological stresses, thereby causing severe disease outbreaks. Antibiotic resistant foodborne pathogens are a challenge to the food industry. A total of 18 samples were pooled from a bio-digester co-digesting swine manure/pinewood sawdust, and evaluated for the occurrence of bacterium plus total viable counts using the spread plate method. The recovered bacterial isolates were presumptively identified by growth on selective medium and confirmed by biochemical characterisation, leading to the isolation of 43 L. monocytogenes. The isolates were characterized based on their susceptibility to antibiotics via the Kirby-Bauer disc diffusion technique against a panel of 14 antibiotics. Equally, the multiple antibiotic resistance (MAR) index was calculated, and MAR phenotypes generated. The bacterial counts were between 102 and104 cfu/mL. Complete susceptibility (100%) was demonstrated to ampicillin, gentamicin and sulfamethoxazole, which are the drugs of choice in the treatment of listeriosis. In addition, intermediate sensitivity occurred at 25.58% to cefotaxime, and the highest resistance (51.16%) was exhibited against nalidixic acid. The MAR index ranged from 0 to 0.71. Overall, 41.86% of the Listeria isolates displayed multidrug resistance, with 18 different MAR phenotypes, demonstrating CIP, E, C, TET, AUG, S, CTX, NA, AML, NI as the greatest MAR phenotype. It can be concluded that the isolates yielding MAR > 0.2 originated from the farm, where antibiotics had been in routine use. Therefore, strict monitoring of antibiotics use in the farm is crucial to mitigate further increase in antibiotic resistance amongst these bacterial isolates

A Systematic Analysis of Research on Arcobacter: Public Health Implications from a Food–Environment Interphase Perspective

This review maps the global research landscape of the public health implications of Arcobacter from the food–environment interphase using content analytics and integrated science mapping. The search term “Arcobacter” was used to retrieve relevant articles published in Web of Science and Scopus between 1991 to 2019. The number of articles included in the review was 524, with 1304 authors, 172 journal sources, and a collaborative index of 2.55. The annual growth rate of the publications was 9.74%. The most contributing author in the field was Houf K., with 40 publications, 26 h-index, and 2020 total citations. The most productive country was the USA (13.33%). The majority of the articles were published in English (96%) and in the Journal of Food Protection (8.02%). The highest research outputs were in the field of Microbiology (264). The frequently occurred keywords were Arcobacter, poultry, shellfish, cattle, and chicken. This study revealed a fair increase in the growth rate of Arcobacter-related research—especially in the area of isolation and detection of the pathogen in foods and food environments, as well as the pathogenesis and genetic diversity of the pathogen. Research themes in the area of prevalence and epidemiology seem to be underexplored

In Vitro Assessment of the Combination of Antibiotics against Some Integron-Harbouring Enterobacteriaceae from Environmental Sources

One strategy for combating antimicrobial resistance in many infections is to combine antibacterial compounds to create combinations that outperform each molecule alone. In this study, we examine and study the inhibitory effect of combining two drugs belonging to different antibiotic classes to obtain a possible potentiating effect against some Enterobacteriaceae isolates harbouring integrons recovered from rivers and effluents of hospital and wastewater treatment plants in Eastern Cape Province, South Africa. These integrons could easily enable the isolates to acquire genes that confer additional resistance against conventional antibiotics. The minimum inhibitory concentration of the various antibiotics was determined using the broth microdilution, while the checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs). A total of 26.3% (10/38) of the interactions were categorised as synergistic, while 73.7% (28/38) were indifferent. None of the combinations were antagonistic. The time–kill assays revealed all the synergistic interactions as bactericidal. Therefore, the combinations of gentamicin with tetracycline, ciprofloxacin, and ceftazidime against multidrug-resistant (MDR) Klebsiella pneumoniae, tetracycline–ceftazidime combination against MDR Escherichia coli, colistin combinations with ceftazidime and gentamicin, and tetracycline–gentamicin combinations against MDR Citrobacter freundii may be future therapeutic alternatives. Hence, the synergistic combinations reported in this study must be assessed further in vivo before their clinical applications

In vitro assessment of the synergism between extracts of Cocos nucifera husk and some standard antibiotics

Objective: To evaluate the interactions between the crude extracts of Cocos nucifera (C. nucifera) and six front line antibiotics (ampicillin sodium salt, penicillin G sodium, amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection. Methods: The pulverized husk of C. nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water (aqueous). The antibacterial susceptibility of the crude extracts of C. nucifera was tested against environmental and clinical strains (6) obtained from the South African Bureau of Standards (SABS), Vibrio (6) and Listeria pathogens (6). The agar-well diffusion method was used for screening the extracts for their antibacterial activity. The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined. Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity. The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods. Results: With the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a −5.6 ± 0.2 log10 CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations. Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%. The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%. There was no specificity in the observed synergy to a particular class of antibiotics. Conclusions: This investigation suggests the crude extracts of C. nucifera to be a potential broad spectrum antimicrobial compound. Therefore, further study is needed to isolate the pure compounds from these crude extracts

Modelling the Potential Risk of Infection Associated with Listeria monocytogenes in Irrigation Water and Agricultural Soil in Two District Municipalities in South Africa

Listeria monocytogenes (L. monocytogenes) is the etiologic agent of listeriosis which significantly affects immunocompromised individuals. The potential risk of infection attributed to L. monocytogenes in irrigation water and agricultural soil, which are key transmission pathways of microbial hazards to the human population, was evaluated using the quantitative microbial risk assessment modelling. A Monte Carlo simulation with 10,000 iterations was used to characterize the risks. High counts of L. monocytogenes in irrigation water (mean: 11.96 &times; 102 CFU/100 mL; range: 0.00 to 56.67 &times; 102 CFU/100 mL) and agricultural soil samples (mean: 19.64 &times; 102 CFU/g; range: 1.33 &times; 102 to 62.33 &times; 102 CFU/g) were documented. Consequently, a high annual infection risk of 5.50 &times; 10&minus;2 (0.00 to 48.30 &times; 10&minus;2), 54.50 &times; 10&minus;2 (9.10 &times; 10&minus;3 to 1.00) and 70.50 &times; 10&minus;2 (3.60 &times; 10&minus;2 to 1.00) was observed for adults exposed to contaminated irrigation water, adults exposed to contaminated agricultural soil and children exposed to agricultural soil, respectively. This study, therefore, documents a huge public health threat attributed to the high probability of infection in humans exposed to L. monocytogenes in irrigation water and agricultural soil in Amathole and Chris Hani District Municipalities in the Eastern Cape province of South Africa