Macrolide and tetracycline resistance in clinical strains of Streptococcus agalactiae isolated in Tunisia

Abstract

clinical strains of Streptococcus agalactiae, recovered from female genital specimens and from gastric fluid or ear specimens from infected newborns, were isolated at the Laboratory of Microbiology of Charles Nicolle Hospital of Tunis. They were investigated to determine the prevalence of antibiotic resistance and to characterize the mechanisms of resistance to macrolide and tetracycline. All strains were susceptible to penicillin, ampicillin and quinupristin-dalfopristin. They were resistant to chloramphenicol (3.1 %), rifampicin (19.1 %), erythromycin (40 %) and tetracycline (97.3 %); 3.1 % were highly resistant to streptomycin and 1.3 % to gentamicin. Among the erythromycin-resistant isolates, 78.7 % showed a constitutive macrolide-lincosamide-streptogramin B (MLS B ) phenotype with high-level resistance to macrolides and clindamycin (MIC 50 .256 mg ml ) and low MICs of clindamycin (MIC 50 58 mg ml "1 ) and 2.2 % showed an M phenotype with a low erythromycin-resistance level (MIC range512-32 mg ml "1 ) and low MICs of clindamycin (MIC range: 0.75-1 mg ml). All strains were susceptible to quinupristin-dalfopristin and linezolid (MIC 90 : 0.75 mg ml "1 for each). MLS B phenotypes were genotypically confirmed by the presence of the erm(B) gene and the M phenotype by the mef(A) gene. Resistance to tetracycline was mainly due to the tet(M) gene (93.1 %) encoding a ribosome protection mechanism. This determinant is commonly associated with the conjugative transposon Tn916 (P¡0.0002). tet(O) and tet(T) existed in a minority (2.2 % and 0.4 %, respectively). The efflux mechanism presented by tet(L) was less frequently present (4.5 %). No significant association was found between erm(B) and tet(M) genes.

ANTIMICROBIAL SUSCEPTIBILITY OF Streptococcus agalactiae ISOLATED FROM PREGNANT WOMEN

“…High resistance to this drug was reported in other countries, including Tunisia (97.3%) 19 and Iran (96%) 16 . Currently, its use is restricted because the emergence of resistance appears to be related to the high use of antibiotics 19 .…”

Molecular epidemiology and mechanisms of antibiotic resistance inEnterococcusspp.,Staphylococcusspp., andStreptococcusspp. in Africa: a systematic review from a One Health perspective

“…Other resistance genes, including erm (B) ( n = 79) and tet (O) ( n = 50), were detected. All isolates were, however, susceptible to β‐lactams and quinupristin–dalfopristin . Between 2005 and 2007, 160 ERY‐resistant S. agalactiae were isolated from humans, with a high resistance rate of 84.3% (135/160) to MLS B…”

Resistance to the tetracyclines and macrolide-lincosamide-streptogramin group of antibiotics and its genetic linkage – a review

“…clarithromycin and azithromycin) have a broader spectrum and are used in human medicine for the treatment of upper and lower respiratory tract infections, infections of the skin and soft tissue, sexually transmitted diseases, community-acquired pneumonia and atypical Mycobacterium infections. Together with lincosamides, macrolides are also used for the treatment of group B streptocoocal infections, or for the intrapartum prevention of Streptococcus agalactiae neonatal infections in penicillin hypersensitive patients [12,13]. In combination with fluoroquinolones, erythromycin is commonly used in the therapy of severe infections caused by Campylobacter spp.…”