Subminimal inhibitory concentration (sub-MIC) of antibiotics can modify the phenotype of biofilm formation in bacteria. However, the relationship between resistance phenotypes, genotypes, and the biofilm formation phenotype in response to sub-MIC antibiotics remains unclear. Here, we collected 96 clinical isolates of Staphylococcus epidermidis (S. epidermidis) and investigated the erythromycin (ERY) susceptibility, the biofilm formation in respond to sub-MIC ERY, the presence and transcription expression of erm genes. Serial passage of induction resistance was used against ERY-susceptible isolates and biofilm formation in response to their new sub-MIC ERY was determined. The incidence of biofilm phenotype modification in ERY-resistant isolates was significantly higher than that of ERY-susceptible isolates [27/85 (31.8%) vs. 0/11 (0%), p = 0.031]. Yet, ERY-susceptible isolates displayed the phenomenon of biofilm phenotype modification (7/11), after induction of resistance to ERY. The ermC gene was absolutely dominant among the three macrolide resistant genes including erm (A, B, C) [6/96 (6.2%), 6/96 (6.2%), and 91/96 (94.8%), respectively]. With statistic stratification analysis, a linear and positive correlation was identified between the two factors in the biofilm-enhanced strains, a linear and negative correlation in biofilm-inhibited strains, and a weakly positive correlation in biofilm-unaffected strains (R(2) = 0.4992, 0.3686, and 0.0512, respectively). The results suggest that the ERY resistance phenotype and the transcription expression of ermC gene could be considered as important signs to estimate whether the biofilm formation phenotype in S. epidermidis clinical isolates can be easily affected by sub-MIC ERY.

The rapid emergence and dissemination of carbapenem resistance in Enterobacteriaceae complicates the treatment of infections caused by these organisms. We collected clinical isolates with meropenem inhibition zones of ≤ 22 mm from January 1, 2009, through December 31, 2010. We attempted to amplify the NDM-1 gene from these isolates and conducted the modified Hodge test (MHT). The minimal inhibitory concentration (MIC) of the MHT-positive strains was determined by the agar disk dilution method. The carbapenemase-encoding resistance genes of these strains were examined using polymerase chain reaction (PCR) analysis and a sequencing strategy to characterize these enzymes. The clonal relationship among isolates was analyzed by pulsed-field gel electrophoresis (PFGE). Among the 158 Enterobacteriaceae isolates that were collected, there were no NDM-1-positive strains and 26 MHT-positive strains. Among the latter, 18 strains were IMP-4-positive, and 1 was KPC-2-positive. In addition, 15 of the IMP-4-positive Klebsiella pneumoniae strains belonged to 4 PFGE genotypes, with 8 strains having the same genotype. These results suggest that nosocomial infections are one of the main reasons for the spread of these resistant strains.

Background: In recent years, the rising rates of resistance to antimicrobial drugs among pathogens have caused great difficulty for clinicians treating infectious diseases. The aim of the study was to assess the curative effect of fosfomycin in treating urinary tract infections (UTIs) in China. Methods: We collected clinical isolates of UTIs to determine their susceptibility to fosfomycin by the agar dilution method and to analyze extended-spectrum β-lactamase (ESBL)-producing isolates by the double-disc method on Mueller-Hinton agar. Fosfomycin-modifying enzyme analysis was conducted by PCR. Differences between the different groups were determined by the χ2 test. Results: We collected 433 UTI isolates, and the result showed that the susceptibility rates of clinical isolates were all above 80%. Only Klebsiella pneumoniae was fosA positive, with a positive rate of 26.7%. No correlation was found for the resistance between the antibiotic drugs tested and fosfomycin in the other bacteria, except for cefepime, levofloxacin and ciprofloxacin in Enterobacter cloacae and imipenem in K. pneumoniae. Conclusion: Our data suggest that fosfomycin may be a suitable antimicrobial agent for UTI isolates and ESBL-producing bacteria in our hospital.