مونا قاضی

The emergence of drug resistance and treatment- renitent Mycobacterium tuberculosis has made controlling the disease a challenge. World Health Organization (WHO) estimates that approximately 500,000 new cases of tuberculosis occur annually. Considering that mechanisms involved in drug resistance are yet to be elucidated and results of the studies are not consistent, we decided to investigate the correlation between mutations in thyA gene and resistance to para- aminosalicylic acid (PAS).

In this descriptive cross- sectional study, a total of 255 positive MTB specimens were isolated during a three- year period using standard microscopic and culture methods from which 68 Multidrug resistant (MDR) and extensively drug resistant (XDR) tuberculosis samples were selected through drug susceptibility testing. Then, to determine potential mutations in thyA gene, the fragment was amplified using conventional PCR and products were sequenced. Afterward, mutations which have been induced amino acid substitutions were evaluated with various protein prediction tools. Also, the correlation between mutations and drug resistance was statistically determined using chi-square test.

From 255 clinical TB samples, 68 (26.7%, CI 21.3%) MDR / or XDR-TB strains were isolated. In total, 13 (19.1%) were PAS- resistant and 5 (38.4%) of them had different nucleotide mutations in thyA gene. All of the mutations were statistically correlated with drug resistance. Moreover, the results of bioinformatics showed that identified mutations could lead to the structural and functional disruption of the protein.

According to our results, mutations in thyA gene have appeared to be associated with resistance to PAS. Also, our findings have shed light on the potential of the analysis of short genomic regions and new computational tools in unraveling the molecular mechanisms of drug resistance.

Stenotrophomonas maltophilia (S. maltophilia) is a non-fermenting gram-negative bacterium that has rapidly emerged as an important hospital pathogen in hospitalized patients and is considered a global threat due to the increase of intrinsic antibiotic resistance. The present study was conducted to determine the antibiotic resistance profile of S. maltophilia isolates collected from blood cultures of patients referred to Qazvin hospitals.

In this study, 28 blood samples with the early diagnosis of S. maltophilia were collected. First, the identification of bacteria was performed by using culture and common biochemical tests. The final confirmation of the samples was done by examining 23S rRNA gene using the molecular PCR method. Finally, antibiogram was performed using disc diffusion method according to CLSI 2022 guidelines.

60.71% of patients with positive blood culture were male. The resistance rates to levofloxacin, minocycline and trimethoprim-sulfamethoxazole were 10.71%, 7.14% and 3.57%, respectively.

Considering the appropriate effectiveness of the trimethoprim-sulfamethoxazole, it can be concluded that the isolates are still sensitive to this antibiotic and it is still considered as the best therapeutic option. It is necessary to evaluate the levels of antibiotic resistance using standard methods before prescribing the antibiotics in order to prevent the emergence and spread of resistant strains in the community and the possibility of treatment failure.

Abstract

Pseudomonas aeruginosalung infection is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). The type III secretion system is an important and identified virulence determinant of P. aeruginosa that delivers effector proteins into targeted host cells. Three effector proteins have been described in P. aeruginosa: exoS, exoT, exoU. Unlike many studies that have been done on bacterial virulence factors in acute conditions, fewer studies have been done on virulence factors of bacteria in chronic disease and conditions such as cystic fibrosis.

this study investigated 51 sputum samples containing P. aeruginosa from child patients with cystic fibrosis for their possession of genes associated with the type III secretion system (exoU, exoS, exoT). PCR assays using specific primers were used to determine the distribution of the type III secretion toxin-encoding genes exoU, exoT and exoS for the test strains.

In this study from 51 samples, 34 of samples (6.66%) were resistant to trimethoprim, 19 of samples (2.37%) were resistant to gentamicin, and 11 samples (5.21%) were resistant to amikacin and cefepime, 10 samples (6.19%) were resistant to tobramycin, 8 cases (6.15%) were resistant to ciprofloxacin, 7 samples (7.13%) were resistant to imipenem, 5 (8/9%) were resistant to ceftazidime and 3 cases (8.5%) were resistant to meropenem. In the current study, from the total of 51 sputum samples, 46 samples (90%) possessed the exoT gene, 40 samples (75%) possessed the exoS genewhereas 13 samples (25%) possessed the exoU gene.

In this study, the resistance against antibiotics of aminoglycosides (gentamicin), fluoroquinolone (ciprofloxacin) and broad-spectrum cephalosporins (cefepime or Ceftazidime) was observed in 13/7% of the samples showing the emergence of multi-drug resistance in these samples. Our results demonstrated that most of our isolates harbored type III secretion toxin-encoding genes, but isolates containing the ExoS-encoding gene are significantly more common among CF patient isolates indicating that ExoS-secreting strains are selected for survival in CF patient airways.