Molecular and Phenotypic Evaluation of Antibiotic Resistance in Enteric Rods Isolated from the Oral Cavity

Abstract

Gram-negative enteric rods (GNERs) are transient members of the oral microbiota and are considered a superinfection in patients with periodontitis that poses local and systemic risks due to associations with infections and multidrug resistance, including extended-spectrum beta-lactamases. These pathogens often resist antibiotics such as amoxicillin, doxycycline, and ciprofloxacin, complicating dental treatments. Though their resistance patterns vary, links between specific resistance genes and phenotypic resistance remain unclear. Objectives: To determine the correlation between resistance genes (blaTEM, blaSHV, tetQ, tetM, qnrB, qnrS, and mph(A)) and phenotypic resistance in GNERs isolated from oral cavity samples. Methods: A total of 90 oral isolates of GNERs were isolated from patients in a dental clinic, and bacteria were identified by the BD BBL Crystal biochemical panel. The antibiotic susceptibility testing was conducted through broth microdilution following CLSI standards for drives such as amoxicillin, amoxicillin/clavulanic acid, doxycycline, ciprofloxacin, and azithromycin. Resistance genes, including blaTEM, blaSHV, tetQ, tetM, qnrS, qnrB, and mph(A), were detected using polymerase chain reaction and gel electrophoresis. The proportions of species, resistance genes, and minimum inhibitory concentration values were statistically analyzed. Conclusions: As expected, most enteric bacteria showed natural resistance to beta-lactams. Significant resistance to azithromycin was observed in some species. Genotypic and phenotypic profiles suggest the existence of alternative resistance mechanisms; therefore, other mechanisms associated with antibiotic resistance should be investigated.

Keywords: antibiotic resistance; enteric rods; genes; oral cavity.

Figure 1

Percentage of resistance to different antibiotics across several bacteria evaluated in this study. The antibiotics analyzed were amoxicillin (AMX), amoxicillin/clavulanic acid (AMC), ciprofloxacin (CIP), doxycycline (DO), and azithromycin (AZT) for the species evaluated. High resistance to AMX and AMC and minimal to no resistance to CIP was noted in all species.

Figure 2

Molecular and phenotypic evaluation of antibiotic resistance in enteric rods. Gp-po: gene present and phenotype observed; Gp-npo: gene present but no phenotype observed; Ga-po: gene absent and phenotype observed; Ga-npo: gene absent and no phenotype observed.