Evaluation of BOX-PCR and ERIC-PCR as Molecular Typing Tools for Pathogenic Leptospira

Isolation, identification, antibiotic resistance profile and molecular analysis of Ornithobacterium rhinotracheal isolates from turkeys

BACKGROUND

Ornithobacterium rhinotracheal (ORT) infects numerous birds, particularly chickens and turkeys. ORT is an emerging bacterial pathogen of global concern in the poultry industry. As ORT is rapidly spreading throughout commercial poultry, it requires intensive studies of its epidemiology, diagnostic procedures, molecular typing, virulence genes and antimicrobial resistance.

OBJECTIVES

The present study was conducted in isolation and identification of ORT from slaughtered turkeys.

METHODS

Cleft palate swabs of 200 were collected from slaughtered turkeys and cultured on blood agar. ORT was characterized using biochemical tests and PCR targeting the ORT 16S rRNA gene. Virulence genes of isolates were determined targeting adenylate kinase (adk), copA and virulence-associated protein D (vapD) genes. Additionally, diversity of ORT isolates was performed by enterobacterial repetitive intergenic consensus (ERIC) and RAPD PCR. Disk diffusion was used to determine the antibiotic sensitivity of the isolates.

RESULTS

ORT was identified in 23 (11.5%) samples using both the biochemical tests and PCR. The result of detecting virulence genes showed that all the isolates (23: 100%) had the adk gene, whereas two (8.7%) isolates had the copA gene, and seven (30.43%) isolates had the vapD gene. Molecular typing of isolates revealed 21 different patterns by RAPD PCR assay using M13 primer and 20 distinct patterns by ERIC PCR test. Both ERIC and RAPD PCR were distinctive methods for investigating the genetic diversity of ORT isolates. The antibiotic resistance test showed that 18 (78.26%) isolates were resistant to gentamicin, amikacin, cefazolin, streptomycin and penicillin. All isolates (100%) were resistant to cloxacillin and fosfomycin.

CONCLUSIONS

This study showed the prevalence of ORT in turkey and high resistance of this bacterium to many common veterinary antibiotics. Moreover, both ERIC and RAPD PCR are distinctive methods for investigating the genetic diversity of ORT isolates. These data may help monitor antibiotic resistance and typing of ORT in epidemiological studies and serve as the foundation for designing region-specific vaccines for future use.

Genetic diversity, mating type and pathogenicity of two Phytophthora species infecting black pepper in India

Phytophthora capsici and P. tropicalis are the two species of Phytophthora associated with foot rot disease of black pepper in India. High genetic diversity amongst the Phytophthora species contributes to its wide host range and variability in the virulence pattern. In the present study, genetic diversity of Phytophthora species infecting black pepper was analysed using RAMS (Random Amplified Microsatellites) and REP (Repetitive Extragenic Palindromic)-PCR fingerprinting. Forty-eight isolates, 24 each of P. capsici and P. tropicalis collected from major black pepper growing states, such as Karnataka, Kerala, Tamil Nadu and Goa, were used in the study. The analyses revealed a total of 160 loci of which 150 (93.75%) were polymorphic. UPGMA cluster and PCoA analysis based on combined RAMS and REP-PCR data clearly grouped the P. capsici and P. tropicalis isolates into two clusters which were further divided into four sub-clusters viz., I & II (P. capsici) and III & IV (P. tropicalis). The study clearly indicated that all the isolates were genetically unique and the entire population was heterogeneous. REP-PCR primers showed more polymorphic loci than RAMS primers. Further, sixteen isolates were selected for morphological and infectivity analyses under in vitro conditions. The isolates exhibited varied colony morphology, sporangial shapes and belonged to A1 mating type. Under in vitro conditions, all the sixteen black pepper Phytophthora isolates could infect nutmeg, tomato, chilli, pumpkin, and cucumber and few of the isolates could infect cardamom. None of the isolates could infect coconut, areca nut and vanilla.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03843-1.

Detection of clinically relevant carbapenemase encoding genes in carbapenem-resistant Enterobacter cloacae complex and Klebsiella pneumoniae isolated from farmed freshwater fish

AIMS

The present study was aimed to detect clinically relevant carbapenemase encoding genes in carbapenem-resistant Enterobacter cloacae complex (CR-ECC), Klebsiella pneumoniae (CR-KP), and Serratia plymuthica (CR-SP) isolated from farmed freshwater fish.

METHODS AND RESULTS

Out of 243 spatially diverse freshwater fish samples analysed, 5.3% were contaminated with CR-ECC, 1.6% with CR-KP, and 0.4% with CR-SP. The CR-ECC was further identified as E. asburiae (38.5%), E. mori (23.1%), E. cloacae (15.4%), E. hormaechei (15.4%), and E. kobei (7.7%) by 16S rRNA gene sequencing. The CR-ECC were resistant to carbapenems and cefoxitin, whereas CR-KP and CR-SP were multi-drug resistant (MDR). The CR-ECC harboured the carbapenemase gene blaIMI alone or in combination with blaTEM, blaEBC, blaCIT, blaACC, and tet(E). Whereas, CR-KP harboured carbapenemase gene, blaNDM-5 along with blaOXA-48, blaSHV, blaOXA-1, blaCTX-M-15, tet(A), sul1, and qnrB. No carbapenemase-encoding genes were detected in CR-SP. The MLST analysis showed that CR-KP belonged to ST231 and ST1561 lineages, while CR-ECC did not show exact match with any reported STs. The plasmid replicons predominantly detected were IncF and IncI1. Broth mating assays of CR-KP and CR-ECC with recipient Escherichia coli J53 indicated that blaNDM-5 was transferable but not blaIMI.

CONCLUSION

This study highlights the low-level contamination of carbapenem-resistant Enterobacterales (CRE) harbouring clinically relevant carbapenemase-encoding genes in farmed freshwater fish from India. The CR-ECC of fish origin did not show the potential to spread carbapenem resistance.

Description and host-range determination of phage PseuPha1, a new species of Pakpunavirus infecting multidrug-resistant clinical strains of Pseudomonas aeruginosa

A new phage PseuPha1, infecting multiple multi-drug resistant strains of Pseudomonas aeruginosa with strong anti-biofilm activities, was isolated from wastewater in India. PseuPha1 showed optimal multiplicity of infection at 10^-3, maintained the infectivity at wide ranges of pH (6-9) and temperature (4-37 ⁰C), and exhibited 50 minutes latent period and a burst size of 200 when tested against P. aeruginosa PAO1. PseuPha1 shared 86.1-89.5% pairwise intergenomic similarity with Pakpunavirus species (n = 11) listed by the International Committee on Taxonomy of Viruses and established distinct phyletic lineages during phylogenetic analyses of phage proteins. While genomic data validated the taxonomic novelty and lytic attributes of PseuPha1, BOX-PCR profiling asserted the genetic heterogeneity of susceptible clinical P. aeruginosa. Our data supported the affiliation of PseuPha1 as a new Pakpunavirus species and provided the first line of evidence for its virulence and infectivity that can be harnessed in wound therapeutics.

The Emergence of Carbapenem-Resistant Gram-Negative Bacteria in Mizoram, Northeast India

(Background) Numerous reports on carbapenem resistance in different parts of India have been published, yet there are insufficient studies on the prevalence of antibiotic resistance in the northeast region of the country. This study evaluated the emergence of carbapenem resistance in the clinical isolates collected in Mizoram. (Results) A total of 141 Gram-negative clinical isolates were collected from the two hospitals, including the Civil Hospital in Lunglei and the Synod Hospital in Aizawl. The isolates include Escherichia coli (n = 62, 43.9%), Klebsiella spp. (n = 43, 30.4%), Pseudomonas aeruginosa (n = 9, 6.3%), Serratia marcescens (n = 3, 2.1%), Proteus mirabilis (n = 2, 1.4%), Shigella spp. (n = 4, 2.8%), Enterobacter spp. (n = 6, 4.2%) and Acinetobacter spp. (n = 12, 8.5%). The isolates were found to be resistant to meropenem (11%), colistin (48%), tigecycline (25%) and cefotaxime (50%). A total of four E. coli and one Shigella sonnei encoded the blaOXA-48-like gene. The blaCTX-M-1 gene was detected in 13 isolates, of which eight were E. coli, two Shigella flexneri, and one isolates each of K. pneumoniae, K. oxytoca and Shigella sonnei, respectively. (Conclusion) Carbapenem-resistant Enterobacteriaceae are common among other parts of India, despite limited access to antibiotics, the emergence of resistance in the northeastern region is worrying.

Common Colonization Genes Profiling and BOX-PCR Based Genotyping of Streptococcus agalactiae from Pregnant Women in Tehran, Iran

Background: Streptococcus agalactiae or group B streptococcus (GBS) is a prominent cause of severe neonatal infections. GBS is a part of the intestinal and vaginal normal flora. Maternal colonization is recognized as the main path of GBS transmission. GBS is a pathobiont that changes from a non-symptomatic mucosal carriage state to a significant bacterial pathogen, causing major infections. Objectives: This study aimed to investigate the concomitant presence of major colonization genes, including ftsA, ftsB, lmb, and sfbA, and to determine the genetic relatedness of clinical GBS isolates. Methods: The GBS isolates were obtained from urinary and placental samples of pregnant women with a urinary tract infection, who were admitted to a hospital in Tehran, Iran. The presence of some major colonization factors was investigated via multiplex PCR assay. Genotyping of the isolates was performed using the BOX-PCR fingerprint technique with a BOX-A1R primer. Next, the data were analyzed using the UPGMA method and the coefficient of Jaccard in NTSYS software. Results: A total of 60 GBS isolates were examined in this study. The concomitant presence of target colonization genes was observed in all isolates. The BOX-PCR discriminated GBS isolates into six different genetic clusters at a 60% cutoff point. The majority of isolates (80%) from both clinical samples were clustered into genotypes 2, 6, and 4, while the rest (20%) were distributed equally into three different genotypes. Conclusions: Determining the colonization associated genes and genetic polymorphism in a different geographical area provides the epidemiological basis for the prevention of GBS infections in pregnant women and infants.

ESBL-Producing Escherichia coli Carrying CTX-M Genes Circulating among Livestock, Dogs, and Wild Mammals in Small-Scale Farms of Central Chile

Antibiotic-resistant bacteria of critical importance for global health such as extended-spectrum beta-lactamases-producing (ESBL)-Escherichia coli have been detected in livestock, dogs, and wildlife worldwide. However, the dynamics of ESBL-E. coli between these animals remains poorly understood, particularly in small-scale farms of low and middle-income countries where contact between species can be frequent. We compared the prevalence of fecal carriage of ESBL-E. coli among 332 livestock (207 cows, 15 pigs, 60 horses, 40 sheep, 6 goats, 4 chickens), 82 dogs, and wildlife including 131 European rabbits, 30 rodents, and 12 Andean foxes sharing territory in peri-urban localities of central Chile. The prevalence was lower in livestock (3.0%) and wildlife (0.5%) compared to dogs (24%). Among 47 ESBL-E. coli isolates recovered, CTX-M-group 1 was the main ESBL genotype identified, followed by CTX-M-groups 2, 9, 8, and 25. ERIC-PCR showed no cluster of E. coli clones by either host species nor locality. To our knowledge, this is the first report of ESBL-E. coli among sheep, cattle, dogs, and rodents of Chile, confirming their fecal carriage among domestic and wild animals in small-scale farms. The high prevalence of ESBL-E. coli in dogs encourages further investigation on their role as potential reservoirs of this bacteria in agricultural settings.

Comparative Assessment of Different PCR-Based Typing Methods of Pseudomonas aeruginosa Isolates

Introduction

Pseudomonas aeruginosa is one of the important causes of nosocomial infections. Analyzing the diversity of these isolates is important to control the diseases caused by them. Studies of molecular epidemiology depend on the application of typing methods.

Purpose

This study aims to assess the performance of PCR- based typing techniques (RAPD, ribotyping, tDNA, and ERIC) in determining the genetic diversity of 44 P. aeruginosa urinary isolates.

Methods

Performance parameters were analyzed for each of the tested methods. The banding pattern was assessed by calculating polymorphism, genotypic gene diversity and the effective multiplex ratio. Moreover, strain diversity, typeability, and discriminatory power were used to measure the efficiency of typing methods. The congruence among typing methods was calculated by Rand’s and Wallace coefficients.

Results

P-640 among RAPD primers and Ribo-2 among ribotyping primers were more informative as they gave high strain diversity, the highest number of clusters, and highest discriminatory power (ISD=70.45%, 29 clusters at 70% cutoff, DI=0.97 and ISD=75%, 25 clusters at 70% cutoff DI=0.969, respectively). Comparison of typing methods showed that RAPD-PCR gave the highest mean percent polymorphism per assay (76.85%) followed by ERIC-PCR. ERIC-PCR outperformed in most marker parameters; highest mean number of alleles, number of monomorphic bands per assay unit, mean genotypic gene diversity, effective multiplex ratio, and assay efficiency index. Calculated congruence revealed that individual methods demonstrate moderate to poor predictive power. Interestingly, this power increased by combining data obtained from another method.

Conclusion

RAPD primer (P-640) had more discrimination power followed by ribo-2 and ERIC. The performance and predictive power of typing methods can be improved by combining data obtained from different methods as ERIC+OPA-02 and ERIC+P-640 combinations gave complete typeability and discrimination of isolates. ERIC, ERIC+OPA-02, and ERIC+P-640 combinations can provide finer discrimination and classification of P. aeruginosa strains than the other tested methods.

Probiotics inspired from natural ecosystem to inhibit the growth of Vibrio spp. causing white gut syndrome in Litopenaeus vannamei

Probiotics inspired by host-microbe interactions in the natural ecosystem are propitious in controlling bacterial infections in aquaculture and veterinary systems. Here we report the isolation and characterization of pathogenic Vibrio spp. and lactic acid bacteria from an intensive culture system of Litopenaeus vannamei and natural ecosystem, respectively. The pathogen isolated from the gut of L. vannamei showing the symptoms of white gut disease were identified as V. parahaemolyticus and V. campbelli. Both the pathogens expressed the virulence genes, rtxA, and tcpA and were showing multiple antibiotic resistance (MAR) index of more than 0.5. The lactic acid bacteria isolated from the sediment and gut of benthic organisms (shrimp and polychaetes) collected from a tropical estuary were classified as member of 9 OTUs such as Pediococcus stilessi, Lactobacillus fermentum, L. rhamnosus, Weissella cibaria, Enterococcus durans, E. fecalis, Streptococcus gallolyticus and L. garvieae. Majority of these isolates were facultative in nature and were able to tolerate gastric juice and bile salt. Out of 83 bacteria isolated from sediment and gut, 36 showed abilities to reduce the pH of culture medium to less than five. Many of these isolates (34 Nos.) showed production of hydrolytic enzymes and secondary metabolites with antagonistic activity against both the pathogens (1 No.) or separately toward V. parahaemolyticus (9 Nos.) and V. campbelli (11 Nos.). Overall, the current study proposes a natural ecosystem as a potential source of lactic acid bacteria with probiotic potentials to prevent the vibriosis disease outbreaks in shrimp aquaculture systems. Further studies are required to understand the abilities of lactic acid bacteria to colonize shrimp intestine, stimulate immune system and manipulate microbiome.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02618-2.

Molecular Characterization of Carbapenemase-Producing Klebsiella pneumoniae Isolated from Egyptian Pediatric Cancer Patients Including a Strain with a Rare Gene-Combination of β-Lactamases

PURPOSE

Healthcare-associated infections caused by multi-drug-resistant (MDR) pathogens are a global threat. We aim to assess the clonal relatedness among carbapenemase-producing Klebsiella pneumoniae (CPKP) strains infecting Egyptian pediatric cancer patients.

MATERIALS AND METHODS

Identification and antimicrobial susceptibility testing of 149 Gram-negative isolates obtained from pediatric cancer patients were performed by VITEK 2. Genes encoding carbapenemases and extended-spectrum β-lactamases were detected by PCR and verified by DNA sequencing of representative samples. The transferability of the plasmids harboring bla OXA-48, from representative clinical samples, was evaluated by performing a conjugation experiment followed by PCR and MIC shift determination. Clonal relationships among the bla OXA-48-harboring K. pneumoniae isolates were determined by enterobacterial repetitive intergenic consensus (ERIC)-PCR and pulsed-field gel electrophoresis (PFGE).

RESULTS

Carbapenem resistance was observed in 59% of the isolates. The most prevalent species was K. pneumoniae (45.6%) and 57% of them were isolated from ICU. Fifty-nine % of the K. pneumoniae isolates were carbapenemase-producers and bla OXA-48 was detected in (58%) of them. One isolate co-harbored bla OXA-48, bla NDM-1, and bla IMP-1 genes for the first time in Egypt. PCR and meropenem MIC shift confirmed the success of the transferability of representative plasmids to E. coli K12. ERIC and PFGE identified 93% and 100% of the K. pneumoniae with a similarity coefficient ≥85%, respectively, including strains with indistinguishable patterns, suggesting possible clonal dissemination.

CONCLUSION

Our findings underline the dissemination of diverse clones of MDR CPKP among Egyptian pediatric cancer patients. Hence, routine molecular characterizations followed by strict implementation of infection control measures are crucial to tackling this threat.

Molecular determination of genetic diversity among Campylobacter jejuni and Campylobacter coli isolated from milk, water, and meat samples using enterobacterial repetitive intergenic consensus PCR (ERIC-PCR)

Consumption of contaminated meat, milk, and water are among the major routes of human campylobacteriosis. This study aimed to determined the genetic diversity of C. coli and C. jejuni isolated from meat, milk, and water samples collected from different locations. From the 376 samples (meat = 248, cow milk = 72, and water = 56) collected, a total of 1238 presumptive Campylobacter isolates were recovered and the presence of the genus Campylobacter were detected in 402 isolates, and from which, 85 and 67 isolates were identified asC. jejuni and C. coli respectively. Of which, 71 isolates identified as C. coli (n = 35) and C. jejuni (n = 36) were randomly selected from meat, milk, and water samples and were genotyped using enterobacterial repetitive intergenic consensus PCR (ERIC-PCR). The digital images of the ERIC-PCR genotype were analyzed by GelJ v.2.0 software. The diversity and similarity of the isolates were assessed via an unweighted-pair group method using average linkages clustering algorithm. The results showed that the 36 C. jejuni strains separated into 29 ERIC-genotypes and 4 clusters while the 35 C. coli were delineated into 29 ERIC-genotypes and 6 clusters. The study revealed the genetic diversity among C. coli and C. jejuni strains recovered from different matrices characterized by Gelj.

Molecular characterization of antimicrobial resistance and enterobacterial repetitive intergenic consensus-PCR as a molecular typing tool for Salmonella spp. isolated from poultry and humans

Background and Aim:

Salmonella spp. are one of the most important food-borne pathogens in the world, emerging as a major public health concern. Moreover, multidrug-resistant (MDR) strains have been isolated from salmonellosis outbreaks, which compromise its treatment success. This study was conducted to characterize the phenotypic and genotypic antibiotic resistance profile of Salmonella strains isolated from broilers and humans from the regions of Tolima and Santander (Colombia).

Materials and Methods:

Salmonella spp. strains (n=49) were confirmed through molecular detection by amplification of the invA gene. Phenotypic antibiotic resistance was determined by the automated method and the agar diffusion method, and the presence of resistance genes was evaluated by PCR. Genotypic characterization was conducted using the enterobacterial repetitive intergenic consensus (ERIC)-PCR method, from which a dendrogram was generated and the possible phylogenetic relationships were established.

Results:

Salmonella isolates were classified as MDR strains exhibiting resistance to four antibiotic classes, penicillins, aminoglycosides, sulfonamides, and cephalosporins, and the human strains were resistant to gentamicin. At the genotypic level, the isolates contained the genes bla_CMY2, bla_CTX-M, bla_PSE-1, bla_TEM, aadA1, srtB, dfrA1, sul2, and floR. The genotyping results obtained by ERIC-PCR allowed the grouping of strains according to the source of isolation.

Conclusion:

The Salmonella spp. strains exhibited resistance to multiple antibiotics, as well as multiple genes associated with them, and the ERIC-PCR method was a technique that was helpful in generating clusters with biological significance.

Outbreak of Ralstonia mannitolilytica bacteraemia in patients undergoing haemodialysis at a tertiary hospital in Pretoria, South Africa

Background

Ralstonia species are Gram-negative bacilli of low virulence. These organisms are capable of causing healthcare associated infections through contaminated solutions. In this study, we aimed to determine the source of Ralstonia mannitolilytica bacteraemia in affected patients in a haemodialysis unit.

Methods

Our laboratory noted an increase in cases of bacteraemia caused by Ralstonia mannitililytica between May and June 2016. All affected patients underwent haemodialysis at the haemodialysis unit of an academic hospital. The reverse osmosis filter of the haemodialysis water system was found to be dysfunctional. We collected water for culture at various points of the dialysis system to determine the source of the organism implicated. ERIC-PCR was used to determine relatedness of patient and environmental isolates.

Results

Sixteen patients were found to have Ralstonia mannitolilytica bacteraemia during the outbreak period. We cultured Ralstonia spp. from water collected in the dialysis system. This isolate and patient isolates were found to have the identical molecular banding pattern.

Conclusions

All patients were septic and received directed antibiotic therapy. There was 1 mortality. The source of the R. mannitolilytica infection in these patients was most likely the dialysis water as the identical organism was cultured from the dialysis water and the patients. The hospital management intervened and repaired the dialysis water system following which no further cases of R. mannitolilytca infections were detected. A multidisciplinary approach is required to control healthcare associated infections such as these. Routine maintenance of water systems in the hospital is essential to prevent clinical infections with R.mannitolilytica.

Effectiveness of six molecular typing methods as epidemiological tools for the study of Salmonella isolates in two Colombian regions

Aim:

The aim of this study was the genotypic characterization of the strains of Salmonella spp. isolated from broiler chickens and humans with gastroenteritis from two regions of Colombia, by BOXA1R-polymerase chain reaction (PCR) and random amplification of polymorphic DNA (RAPD)-PCR methods.

Materials and Methods:

Forty-nine strains of Salmonella were assessed, 15 from poultry farms in Santander region, and 34 from Tolima region isolated from poultry farms (n=24) and the stool samples of people with gastroenteritis (n=10). BOXA1R primers were selected for repetitive element-based PCR (REP-PCR) and five arbitrary primers, namely, GTG 5, OPB 15, OPP 16, OPS 11, and P 1254 were used for RAPD-PCR to generate DNA fingerprints from the isolates. Fingerprint data from each typing method were under composite analysis and the diversity of the data was analyzed by grouping (clustering). The dendrogram was generated by the unweighted group method with analysis of the arithmetic mean based on the Dice similarity coefficient. In addition, Simpson’s index was evaluated to discriminate the power of the methods.

Results:

OPP 16 primer and composite analysis proved to be superior compared to other REP-PCR typing methods. The best discriminatory index was observed when GTG 5 (0.92) and OPP 16 (0.85) primers were used alone or combined with RAPD-PCR and BOX-PCR (0.99).

Conclusion:

This study indicated that OPP 16 and GTG 5 primers provide suitable molecular typing results for the discrimination of the genetic relationship among Salmonella spp. isolates and may be useful for epidemiological studies.

Zinc biosorption, biochemical and molecular characterization of plant growth-promoting zinc-tolerant bacteria

Zinc plays a key role in plant nutrition at low levels; however, at higher concentrations Zn ions can be highly phytotoxic and plant growth-promoting rhizobacteria can be used to reduce such metal toxicity. In the present investigation we had reported the zinc biosorption and molecular characterization of plant growth-promoting zinc-tolerant bacteria. Initially, thirty bacteria having zinc solubilizing ability were screened for MIC against zinc ion and displayed high value of MIC ranging from 2.5 to 62.5 mM. Biochemically, all the 30 isolates showed significant difference in the 6 biochemical tests performed. The molecular diversity studies based on the repetitive DNA PCR viz, REP, ERIC and BOX elements showed significant genetic diversity among these 30 zinc-tolerant bacteria. These ZTB strains also showed multiple PGP activities and all ZTB strains were found positive for production of IAA, GA₃ and ammonia, whereas 24 were found positive for ACC deaminase activity, 8 showed siderophore production and 9 ZTB isolates were positive for HCN production. Out of 30 isolates, 24 showed phosphorus solubilization activity, 30 showed potash solubilization, 15 showed silica solubilization and 27 showed phytase production activities. All the 30 ZTB stains showed zinc solubilization up to 0.25% insoluble ZnO in the medium, whereas at 2% ZnO in MSM only 12 isolates showed solubilization which were further selected for zinc biosorption and pot studies. The heavy metal removal studies revealed that ZTB stains were able to remove zinc ions effectively from the medium efficiently and the highest zinc biosorption (< 90%) was recorded with the bacterial strain Z-15. Further, the inoculation of ZTB strains under zinc stress conditions (pot containing 1000 mg/kg Zn) resulted in significant increase of shoot length, root length and total chlorophyll content in maize seedlings compared with the uninoculated control. The partial 16S rDNA sequence of the potential ZTB isolates viz. Z-15, Z-24, Z-28 and Z-29 revealed their identity as Serratia sp. The ability of these zinc-tolerant bacteria to tolerate the toxic level of zinc may serve as suitable candidates for developing microbial formulations for the growth of crop plants in Zn-contaminated areas.

Identification and molecular characterization of Azotobacter chroococcum and Azotobacter salinestris using ARDRA, REP, ERIC, and BOX

Azotobacter chroococcum and A. salinestris do not possess significant and distinct morphological and physiological differences and are often mistaken with each other in microbiological research. In this study, 12 isolates of Azotobacter isolated by standard protocol from soils were identified morphologically and physiologically as A. chroococcum. The isolates were more closely investigated for the molecular differentiation and diversity of A. chroococcum and A. salinestris. For this purpose, the ARDRA technique including HpaII, RsaI, and AluI restriction enzymes, and REP, ERIC, and BOX markers were used. The nifD and nifH genes were also utilized to evaluate the molecular identification of these two species. The 16S rDNA evaluation showed that only four out of the 12 isolates were identified as A. chroococcum and the rest were A. salinestris. The results revealed that HpaII was able to differentiate A. chroococcum from A. salinestris whereas RsaI and AluI were not able to separate them. Moreover, BOX and REP markers were able to differentiate between A. chroococcum and A. salinestris. However, ERIC marker and nifD and nifH genes were unable to separate these species. According to the results, HpaII restriction enzyme is suggested to save time and cost. BOX and REP markers are recommended for differentiation and clear discrimination not only between A. chroococcum and A. salinestris but also among their strains.