Fibronectin-binding Protein F1 (prtF1) Gene Is Highly Distributed in Tetracycline-resistant, Erythromycin-sensitive Streptococcus pyogenes Isolates

@#Introduction: The internalization process of group A streptococci (GAS) into human cells is one of the crucial steps in the pathogenesis of GAS infections, which could also affect their susceptibility responses toward several antibiotics. Currently, data on the distribution of internalization-associated genes and susceptibility patterns are still lacking in Malaysia. This study investigated the distribution of fibronectin-binding protein F1 (prtF1) and streptococcal pyrogenic exotoxin B (speB) genes in GAS isolates with their susceptibility profiles and source of samples. Methods: We used 43 GAS isolates from our previous stock culture and performed antibiotic susceptibility testing by Kirby-Bauer disk diffusion method and interpreted the results according to the established guidelines. We detected virulence (prtF1 and speB) and resistance (ermA, ermB, mefA, tetM and lnuA) genes by PCR method using established primers and protocols. Results: High resistance rates were observed against doxycycline (58.1%) and clindamycin (16.3%). In comparison, 100.0% and 46.5% of GAS isolates carried speB and prtF1 genes, respectively. tetM and lnuA genes were detected in all respective resistant isolates (100% for each). No macrolide resistance genes were detected. Interestingly, prtF1 gene was highly distributed in doxycycline-resistant than doxycycline-sensitive isolates (60.0% versus 27.8%). Conclusions: High resistance rate of GAS toward doxycycline in our study may potentially reflect the uncontrol dissemination of tetM gene among our isolates. The presence of prtF1 gene among this strain would enhance its ability to evade the intracellular action of antibiotics, which may affect the management of GAS diseases. Thus, close monitoring of GAS by molecular methods is required in the future.

Conjugative transfer of resistance determinants among human and bovine Streptococcus agalactiae

Streptococcus agalactiae (GBS) is a major source of human perinatal diseases and bovine mastitis. Erythromycin (Ery) and tetracycline (Tet) are usually employed for preventing human and bovine infections although resistance to such agents has become common among GBS strains. Ery and Tet resistance genes are usually carried by conjugative transposons (CTns) belonging to the Tn916 family, but their presence and transferability among GBS strains have not been totally explored. Here we evaluated the presence of Tet resistance genes (tetM and tetO) and CTns among Ery-resistant (Ery-R) and Ery-susceptible (Ery-S) GBS strains isolated from human and bovine sources; and analyzed the ability for transferring resistance determinants between strains from both origins. Tet resistance and int-Tn genes were more common among Ery-R when compared to Ery-S isolates. Conjugative transfer of all resistance genes detected among the GBS strains included in this study (ermA, ermB, mef, tetM and tetO), in frequencies between 1.10-7 and 9.10-7, was possible from bovine donor strains to human recipient strain, but not the other way around. This is, to our knowledge, the first report of in vitro conjugation of Ery and Tet resistance genes among GBS strains recovered from different hosts.

Molecular characterization of tetracycline- and quinolone-resistant Aeromonas salmonicida isolated in Korea

The antibiotic resistance of 16 Aeromonas (A.) salmonicida strains isolated from diseased fish and environmental samples in Korea from 2006 to 2009 were investigated in this study. Tetracycline or quinolone resistance was observed in eight and 16 of the isolates, respectively, based on the measured minimal inhibitory concentrations. Among the tetracycline-resistant strains, seven of the isolates harbored tetA gene and one isolate harbored tetE gene. Additionally, quinolone-resistance determining regions (QRDRs) consisting of the gyrA and parC genes were amplified and sequenced. Among the quinolone-resistant A. salmonicida strains, 15 harbored point mutations in the gyrA codon 83 which were responsible for the corresponding amino acid substitutions of Ser83-->Arg83 or Ser83-->Asn83. We detected no point mutations in other QRDRs, such as gyrA codons 87 and 92, and parC codons 80 and 84. Genetic similarity was assessed via pulsed-field gel electrophoresis, and the results indicated high clonality among the Korean antibiotic-resistant strains of A. salmonicida.

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.

Antibiotic Susceptibility of Streptococcus pyogenes and Association of Ery-thromycin Resistance Phenotype with Resistance to Tetracycline / 대한진단검사의학회지

BACKGROUND: Streptococcus pyogenes is the most common bacterial cause of acute pharyngitis in children. The resistance rate and phenotype distribution of S. pyogenes could be different by geo-graphical locations and study periods. The purpose of this study was to determine the minimal inhibitory concentration (MIC), resistance rate to antimicrobial agents, and association of erythromycin (EM) resistance phenotype with resistance to tetracycline (TC) among S. pyogenes isolated in Jinju, Korea. METHODS: A total of 223 isolates of S. pyogenes were obtained from pediatric pharyngitis patients and asymptomatic carriers during the period from November 2001 to May 2002. Antibiotic susceptibility test was performed by the agar dilution and the disk diffusion methods against eight antimicro-bial agents. The phenotypes of EM resistance were determined by the double-disk diffusion test. RESULTS: Resistance rates of S. pyogenes to EM, clindamycin (CC), and TC were 48.9%, 22.0% and 29.6%, respectively. MIC(50) and MIC(90) were 0.25 mg/L and > or =256 mg/L of EM, or =256 mg/L of CC, and < or =0.5 mg/L and 64 mg/L of TC respectively. Almost all isolates were suscep-tible to penicillin, ampicillin, ofloxacin, levofloxacin and chloramphenicol. The M phenotype (55.0%) was slightly more common than the constitutive resistance (45.0%); the inducible resistance pheno-type was not detected. All strains of constitutive resistance phenotype were highly resistant to TC (MIC higher than 32 mg/L), while only 3.3% of M phenotype strains was resistant to TC. CONCLUSIONS: Almost all S. pyogenes isolated in the Jinju area were susceptible to penicillin, ampi-cillin, ofloxacin, levofloxacin and chloramphenicol, but resistance rates of S. pyogenes to EM, CC and TC were relatively high. This study showed that the EM phenotypes are associated with resistance to TC.