Impact of heavy metals on inhibitory concentration of Escherichia coli-a case study of river Yamuna system, Delhi, India

The occurrence of resistant bacteria to specific heavy metals can be associated with increasing load of the metals in the environment. River Yamuna is polluted by various toxic heavy metals discharged by several industrial and agricultural sources. Therefore, the use of heavy metal-resistant bacteria as an indicator of metal pollution was tested in the present study. For the purpose of the study, the heavy metal resistance status of 42 Escherichia coli strains isolated from River Yamuna water from 7 sampling sites within a span of 2 years was determined using growth curves and plate dilution method in terms of minimum inhibitory concentration (MIC) values by comparing with MIC value of control strain. Seasonally, the lowest mean MIC value was observed for bacterial strains isolated in post-monsoon (December) 2013 and highest mean MIC value was observed for bacterial strains isolated in monsoon (August) 2015. Site-wise analysis of the maximum mean MIC values for all the isolated strains showed the highest mean Ni MIC value for the bacterial strains isolated from site S4 (ITO), highest mean Cu MIC, Cr MIC, and Fe MIC values for the bacterial strains isolated from site S2 (Najafgarh drain intermixing zone) and highest mean Cd MIC, Pb MIC, and Zn MIC values for the bacterial strains isolated from site S7 (Shahdara drain intermixing zone). Correlation analysis between mean MIC site-wise results with mean heavy metal site-wise concentrations showed significant positive correlation indicating that the higher the mean concentration of a given heavy metal at a given site, the higher the mean MIC value for the strains isolated from the same site indicating higher level of resistance. Overall, the present study has shown that the presence of heavy metals in River Yamuna caused due to indiscriminate discharge of various effluents from different kind of sources as well as due to insufficient treatment capacity of sewage treatment plants as well as common effluent treatment plants, has serious impacts on its bacterial microflora as it leads to the development of resistant strains.

Prevalence of community acquired urinary tract infections in Silchar Medical College, Assam, India and its antimicrobial susceptibility profile

BACKGROUND

This study was conducted to know the rate of prevalence of community acquired UTI infections in both males and females, Assam, North-East India.

MATERIALS AND METHODS

A 50 μl of urine sample from each of the subjects was streaked on cystine lactose electrolyte-deficient agar medium. The plates were incubated overnight at 37°C. Pure, isolated colonies of each type was separately cultured and characterized. The susceptibility of the clinical isolates to routinely prescribed antibiotics in the hospital was performed against various antibiotics.

RESULTS

Of the total 40 patients, 26 positive samples were obtained of which 19 females (73.07%) and 7 male (26.92%) patients were shown to be urine culture positive. The most commonly isolated bacterium was Escherichia coli with a frequency rate of (33.3%) followed by Staphyloccous aureus (22.2%), Klebsiella pnemoniae (11.1%), coagulase negative Staphylococcus (CoNS) (7.4%), Pseudomonas sp. (7.4%), Proteus myxofaciens (3.7%), Proteus mirabilis (3.7%), Edwardsiella tarda (3.7%), Morganella morganii (3.7%), and Citrobacter fruendii (3.7%). Analysis of the samples showed that UTI was more common in females of younger age group as compared with males. It was also observed that the patients responded effectively to imepenem (IE), cepefime, amikacin, norfloxacin, and co-trimoxazole antimicrobial agents against Gram-negative bacilli. Furthermore, the most effective antibiotics against Gram-positive cocci was found to be ampicillin, ciprofloxacin, IE, and penicillin G (benzyl penicillin).

CONCLUSIONS

Antibiotics have been in use for a long period and more often the misuse of antimicrobial drugs has today led to a general rise in the emergence of resistant bacteria.

In Vitro effects of various xenobiotics on Azotobacter chroococcum strains isolated from soils of southern Poland

Fourteen Azotobacter chroococcum strains isolated from soils of Southern Poland were studied concerning resistance to various xenobiotics: heavy metal ions: Cd(2+,) Cu(2+), Fe(3+), Mn(2+), Pb(2+), Zn(2+), pesticides: herbicides linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea) and combination of mecoprop ((RS)-2-(4-chloro-2-methylphenoxy)propanoic acid), dicamba (3,6-dichloro-2-methoxybenzoic acid) and MCPA (2-methyl-4-chlorophenoxyacetic acid), fungicide copper oxychloride, insecticide fenitrothion (O,O-Dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate) and eight antibiotics commonly used against Gram-negative bacteria. The tested soils were divided into seven groups of land use: forest, field crop, park, urban lawn, industrial area, garden and fallow land, and were analyzed for the following heavy metal ion concentrations using the atomic absorption spectrometry (AAS) technique: Cd(2+,) Cu(2+), Fe(3+), Mn(2+), Pb(2+), Zn(2+). All strains were resistant to Pb(2+), whereas other metals caused the growth inhibition of the analyzed strains. There was no significant relationship between metal concentrations in the analyzed soils and metal resistance of the isolates. Herbicide linuron did not inhibit the growth of A. chroococcum in any of the concentrations. All other pesticides caused the growth inhibition only in the concentrate forms. All isolates were sensitive to β-lactam antibiotic Meropenem, however high intraspecies differentiation was observed concerning resistance to other antibiotics. The obtained results require further study regarding resistance mechanisms and possible use of the xenobiotic-resistant strains in land rehabilitation.

Bacteria with dual resistance to elevated concentrations of heavy metals and antibiotics in Nigerian contaminated systems

Samples of soil, water, and sediments from industrial estates in Lagos were collected and analyzed for heavy metals and physicochemical composition. Bacteria that are resistant to elevated concentrations of metals (Cd(2+), Co(2+), Ni(2+), Cr(6+), and Hg(2+)) were isolated from the samples, and they were further screened for antibiotic sensitivity. The minimum tolerance concentrations (MTCs) of the isolates with dual resistance to the metals were determined. The physicochemistry of all the samples indicated were heavily polluted. Twenty-two of the 270 bacterial strains isolated showed dual resistances to antibiotics and heavy metals. The MTCs of isolates to the metals were 14 mM for Cd(2+), 15 mM for Co(2+) and Ni(2+), 17 mM for Cr(6+), and 10 mM for Hg(2+). Five strains (Pseudomonas aeruginosa, Actinomyces turicensis, Acinetobacter junni, Nocardia sp., and Micrococcus sp.) resisted all the 18 antibiotics tested. Whereas Rhodococcus sp. and Micrococcus sp. resisted 15 mM Ni(2+), P. aeruginosa resisted 10 mM Co(2+). To our knowledge, there has not been any report of bacterial strains resisting such high doses of metals coupled with wide range of antibiotics. Therefore, dual expressions of antibiotics and heavy-metal resistance make the isolates, potential seeds for decommissioning of sites polluted with industrial effluents rich in heavy metals, since the bacteria will be able to withstand in situ antibiosis that may prevail in such ecosystems.

Isolation and identification of enterococci from seawater samples: assessment of their resistance to antibiotics and heavy metals

A hundred Enterococcus strains were isolated from seawater samples collected from coastal areas of Istanbul. Isolates were identified to the species level using standard biochemical tests specified by Facklam and Collins. The species distribution was as follows Enterococcus faecalis (96%), Enterococcus gallinarum (3%) and Enterococcus solitarius (1%). The resistance of bacteria to both heavy metals (zinc [Zn], iron [Fe], cadmium [Cd], chrome [Cr], cobalt [Co]) and antibiotics (ampicillin 10 microg [AP], penicillin G 10 Units [PG], gentamycin 10 microg [GM], streptomycin 10 microg [S], chloramphenicol 10 microg [C], erythromycin 15 microg [E], kanamycin 30 microg [K], amikacin 30 microg [AK], nalidixic acid 30 microg [NA], and vancomycin 30 microg [VA]) was evaluated. None of the strains was resistant to VA. It was found that among the 100 isolates, those that exhibit resistance to antibiotics, particularly NA, S and K, were also resistant all the heavy metals tested. To our knowledge this is the first report focusing on determination of resistance of environmental enterococci found in Istanbul against heavy metals and antibiotics. Thus, combined expressions of antibiotic and heavy metal resistance may help to reinforce ecological and epidemiological studies and to determine the role of these strains in antibiotic and heavy metal resistance dissemination.

The prevalence of bacterial resistance in clinical, food, water and some environmental samples in Southwest Nigeria

The resistance pattern and mechanisms of bacterial isolates obtained from clinical origin, soil, industrial effluent, orange juice products and drinking water were studied using commonly used antibiotics. The microbial load of the water samples, industrial effluent and orange juice products were 1.0 x 10(1)-2.25 x 10(6), 2.15 x 10(5), and 3.5 x 10(4)-2.15 x 10(5) cfu mL(-1), respectively. The faecal coliform test revealed that only two out of twenty orange juice products had MPN of 2 and 20, the MPN of water ranged from 1-> or = 1800, while the effluent had MPN of > or = 1800. The bacterial isolates that were isolated include E. coli, S. aureus, P. vulgaris, S. marcescens, S. pyogenes, B. cereus, B. subtilis, Micrococcus sp., Klebsiella sp., P. aeruginosa, and Enterobacter sp. Also, clinical and soil isolates of P. aeruginosa were used in the study. Among the eight antibiotics tested for resistance on five strains of each bacterium, seven different resistance patterns were observed among the bacterial isolates obtained from water, effluent and orange juice products. Among the clinical and soil isolates of P. aeruginosa, four multiple-drug resistance patterns were obtained. Thirty strains of E. coli and S. aureus were tested for beta-lactamase production and fourteen strains, seven each of E. coli and S. aureus that had high Minimum Inhibitory Concentration values (MIC) for both Amoxycillin and Cloxacillin were positive.

Characterization of large plasmids encoding resistance to toxic heavy metals in Salmonella abortus equi

Salmonella abortus equi vaccine strains were found to be resistant to high levels of toxic heavy metals--arsenic, chromium, cadmium, and mercury. The two strains 157 and 158 were resistant to ampicillin also. Curing of these strains resulted in loss of one or more resistance marker indicating plasmid borne resistance. Plasmid profile of strain 157 showed presence of three plasmids of 85, 54, and 0.1 Kb, whereas 158 strain showed presence of 85 Kb and 2 Kb plasmids. Plasmids were isolated from strain 157 and introduced into E. coli DH5alpha with a transformation efficiency of 2 x 10(3) transformants/microg DNA. Interestingly the transformants were resistant to antibiotics, heavy metals (As, Cr, Cd, Hg) and was also able to utilize citrate, a trait specific to Salmonella species. We report and establish for the first time the transferable large plasmids encoding resistance to various heavy metals, antibiotics and biochemical nature of S. abortus equi.