Prevalence, serotyping and antimicrobials resistance mechanism of Salmonella enterica isolated from clinical and environmental samples in Saudi Arabia

Abstract Salmonella is recognized as a common foodborne pathogen, causing major health problems in Saudi Arabia. Herein, we report epidemiology, antimicrobial susceptibility and the genetic basis of resistance among S. enterica strains isolated in Saudi Arabia. Isolation of Salmonella spp. from clinical and environmental samples resulted in isolation of 33 strains identified as S. enterica based on their biochemical characteristics and 16S-rDNA sequences. S. enterica serovar Enteritidis showed highest prevalence (39.4%), followed by S. Paratyphi (21.2%), S. Typhimurium (15.2%), S. Typhi and S. Arizona (12.1%), respectively. Most isolates were resistant to 1st and 2nd generation cephalosporin; and aminoglycosides. Moreover, several S. enterica isolates exhibited resistance to the first-line antibiotics used for Salmonellosis treatment including ampicillin, trimethoprim-sulfamethoxazole and chloramphenicol. In addition, the results revealed the emergence of two S. enterica isolates showing resistance to third-generation cephalosporin. Analysis of resistance determinants in S. enterica strains (n = 33) revealed that the resistance to β-lactam antibiotics, trimethoprim-sulfamethoxazole, chloramphenicol, and tetracycline, was attributed to the presence of carb-like, dfrA1, floR, tetA gene, respectively. On the other hand, fluoroquinolone resistance was related to the presence of mutations in gyrA and parC genes. These findings improve the information about foodborne Salmonella in Saudi Arabia, alarming the emergence of multi-drug resistant S. enterica strains, and provide useful data about the resistance mechanisms.

Analysis for the presence of determinants involved in the transport of mercury across bacterial membrane from polluted water bodies of India

Abstract Mercury, which is ubiquitous and recalcitrant to biodegradation processes, threatens human health by escaping to the environment via various natural and anthropogenic activities. Non-biodegradability of mercury pollutants has necessitated the development and implementation of economic alternatives with promising potential to remove metals from the environment. Enhancement of microbial based remediation strategies through genetic engineering approaches provides one such alternative with a promising future. In this study, bacterial isolates inhabiting polluted sites were screened for tolerance to varying concentrations of mercuric chloride. Following identification, several Pseudomonas and Klebsiella species were found to exhibit the highest tolerance to both organic and inorganic mercury. Screened bacterial isolates were examined for their genetic make-up in terms of the presence of genes (merP and merT) involved in the transport of mercury across the membrane either alone or in combination to deal with the toxic mercury. Gene sequence analysis revealed that the merP gene showed 86–99% homology, while the merT gene showed >98% homology with previously reported sequences. By exploring the genes involved in imparting metal resistance to bacteria, this study will serve to highlight the credentials that are particularly advantageous for their practical application to remediation of mercury from the environment.

Tetracycline and oxytetracycline resistance determinants detected in Bacillus cereus strains isolated from honey samples / Detección de determinantes de resistencia a tetraciclina y oxitetraciclina en cepas de Bacillus cereus aisladas de muestras de miel

The aim of this study was to investigate the presence of tetracycline and oxytetracycline resistance determinants in Bacillus cereus strains isolated from honey samples. Of a total of 77 isolates analyzed, 30 (39%) exhibited resistance to tetracyclines according to the results of a disk diffusion method. Resistant strains (n=30) were screened by PCR for the presence of the resistant determinants tetK, tetL, tetM, tetO, tetW, otrA and otrB and their MIC values for tetracycline, oxytetracycline and minocycline were assessed. According to the PCR results, 23 isolates (77%) presented at least one tetracycline or oxytetracycline resistance determinant. The tetK genotype was present in 10 isolates while the tetL, tetM, and otrA genotypes were present in 3, 2, and 5 isolates, respectively. In addition, 2 isolates of the tetK plus tetM genotype, 1 of the tetK plus tetL genotype, and 1 of the tetK plus otrA genotype were found. All isolates were tetW, tetO and otrB negatives. On the other hand, 7 isolates (23%) showed a tetracycline-resistant and/or minocyclineresistant phenotype (MIC) but did not carry any of the tet or otr determinants investigated in this study. This research has shown that B. cereus isolates from honey samples contain a variety of tetracycline and oxytetracycline resistance genes, including the tetK and tetL determinants which encode for efflux proteins, and tetM and otrA, which encode for ribosomal protection proteins. These findings indicate that strains isolated from honeys could represent a reservoir for tetracycline resistance genes. To our knowledge, this is the first report of tetracycline-resistant and oxytetracyclineresistant B. cereus strains carrying the tetK determinant, and also the first report of oxytetracycline-resistant and tetracycline- resistant Bacillus species carrying the otrA determinant.

El objetivo del presente estudio ha sido investigar la presencia de diversos determinantes de resistencia a tetraciclina y oxitetraciclina en las poblaciones de Bacillus cereus presentes en la miel. De un total de 77 aislamientos evaluados, 30 (39%) resultaron resistentes a tetraciclina y/o minociclina de acuerdo con los resultados de las pruebas de difusión en disco. Dentro del grupo que presentó un fenotipo resistente, se investigó la presencia de los determinantes tetK, tetL, tetM, tetO, tetW, otrA y otrB por PCR y se determinaron los valores de CIM para tetraciclina, oxitetraciclina y minociclina. De acuerdo con los resultados obtenidos por PCR, 23 aislamientos (77%) presentaron al menos un determinante de resistencia a tetraciclina o a oxitetraciclina; el genotipo tetK se encontró en 10 de esos aislamientos, mientras que los genotipos tetL, tetM y otrA se hallaron en 3, 2 y 5 aislamientos, respectivamente. Ningún aislamiento presentó los genotipos tetW, tetO ni otrB. Adicionalmente, se encontraron los genotipos tetK plus tetM (2 aislamientos); tetK plus tetL (1 aislamiento) y tetK plus otrA (1 aislamiento). Por otra parte, 7 cepas (23%) resultaron resistentes a tetraciclina, oxitetraciclina y/o minociclina por CIM, pero no presentaban ninguno de los determinantes tet u otr estudiados. Estos resultados indican la existencia de un alto porcentaje de cepas de B. cereus aisladas de miel con genes de resistencia a tetraciclina y oxitetraciclina, incluyendo los determinantes tetK, tetL, tetM y otrA. Este estudio constituye el primer registro de la presencia del determinante tetK de resistencia a tetraciclina en B. cereus, como así también la presencia del determinante otrA dentro del género Bacillus.

The involvement of tetA and tetE tetracycline resistance genes in plasmid and chromosomal resistance of Aeromonas in Brazilian strains

This study analyzed the involvement of tetA and tetE genes in the tetracycline resistance of 16 strains of genus Aeromonas, isolated from clinical and food sources. Polymerase chain reactions revealed that 37.5 percent of the samples were positive for tetA, and also 37.5 percent were tetE positive. One isolate was positive for both genes. Only the isolate A. caviae 5.2 had its resistance associated to the presence of a plasmid, pSS2. The molecular characterization of pSS2 involved the construction of its restriction map and the determination of its size. The digestion of pSS2 with HindIII originated two fragments (A and B) that were cloned separately into the pUC18 vector. The tetA gene was shown to be located on the HindIII-A fragment by PCR. After transforming a tetracycline-sensitive strain with pSS2, the transformants expressed the resistance phenotype and harbored a plasmid whose size was identical to that of pSS2. The results confirmed the association between pSS2 and the tetracycline resistance phenotype, and suggest a feasible dissemination of tetA and tetE among strains of Aeromonas. This study suggests the spreading tetA and tetE genes in Aeromonas in Brazil and describes a resistance plasmid that probably contributes to the dissemination of the resistance.