Complete-genome sequencing elucidates outbreak dynamics of CA-MRSA USA300 (ST8-spa t008) in an academic hospital of Paramaribo, Republic of Suriname.

We report the investigation of an outbreak situation of methicillin-resistant Staphylococcus aureus (MRSA) that occurred at the Academic Hospital Paramaribo (AZP) in the Republic of Suriname from April to May 2013. We performed whole genome sequencing with complete gap closure for chromosomes and plasmids on all isolates. The outbreak involved 12 patients and 1 healthcare worker/nurse at the AZP. In total 24 isolates were investigated. spa typing, genome-wide single nucleotide polymorphism (SNP) analysis, ad hoc whole genome multilocus sequence typing (wgMLST), stable core genome MLST (cgMLST) and in silico PFGE were used to determine phylogenetic relatedness and to identify transmission. Whole-genome sequencing (WGS) showed that all isolates were members of genomic variants of the North American USA300 clone. However, WGS revealed a heterogeneous population structure of USA300 circulating at the AZP. We observed up to 8 SNPs or up to 5 alleles of difference by wgMLST when the isolates were recovered from different body sites of the same patient or if direct transmission between patients was most likely. This work describes the usefulness of complete genome sequencing of bacterial chromosomes and plasmids providing an unprecedented level of detail during outbreak investigations not being visible by using conventional typing methods.

Antibiotic susceptibility of periodontal Streptococcus constellatus and Streptococcus intermedius clinical isolates.

BACKGROUND: Streptococcus constellatus and Streptococcus intermedius in subgingival dental plaque biofilms may contribute to forms of periodontitis that resist treatment with conventional mechanical root debridement/surgical procedures and may additionally participate in some extraoral infections. Because systemic antibiotics are often used in these clinical situations, and little is known of the antibiotic susceptibility of subgingival isolates of these two bacterial species, this study determined the in vitro susceptibility to six antibiotics of fresh S. constellatus and S. intermedius clinical isolates from human periodontitis lesions. METHODS: A total of 33 S. constellatus and 17 S. intermedius subgingival strains, each recovered from separate patients with severe chronic periodontitis (n = 50) before treatment, were subjected to antibiotic gradient strip susceptibility testing with amoxicillin, azithromycin, clindamycin, ciprofloxacin, and doxycycline on blood-supplemented Mueller-Hinton agar and to the inhibitory effects of metronidazole at 16 mg/L in an enriched Brucella blood agar dilution assay. Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing interpretative standards were used to assess the results. RESULTS: Clindamycin was the most active antibiotic against S. constellatus (minimum inhibitory concentration at 90% [MIC90] 0.25 mg/L), and amoxicillin was most active against S. intermedius (MIC90 0.125 mg/L). A total of 30% of the S. constellatus and S. intermedius clinical isolates were resistant in vitro to doxycycline, 98% were only intermediate in susceptibility to ciprofloxacin, and 90% were resistant to metronidazole at 16 mg/L. CONCLUSION: Subgingival S. constellatus and S. intermedius exhibited variable antibiotic susceptibility profiles, potentially complicating empirical selection of periodontitis antibiotic therapy in patients who are species positive.

Antibiotic resistance in human chronic periodontitis microbiota.

BACKGROUND: Patients with chronic periodontitis (CP) may yield multiple species of putative periodontal bacterial pathogens that vary in their antibiotic drug susceptibility. This study determines the occurrence of in vitro antibiotic resistance among selected subgingival periodontal pathogens in patients with CP. METHODS: Subgingival biofilm specimens from inflamed deep periodontal pockets were removed before treatment from 400 adults with CP in the United States. The samples were cultured, and selected periodontal pathogens were tested in vitro for susceptibility to amoxicillin at 8 mg/L, clindamycin at 4 mg/L, doxycycline at 4 mg/L, and metronidazole at 16 mg/L, with a post hoc combination of data for amoxicillin and metronidazole. Gram-negative enteric rods/pseudomonads were subjected to ciprofloxacin disk-diffusion testing. RESULTS: Overall, 74.2% of the patients with CP revealed subgingival periodontal pathogens resistant to at least one of the test antibiotics. One or more test species, most often Prevotella intermedia/nigrescens, Streptococcus constellatus, or Aggregatibacter actinomycetemcomitans, were resistant in vitro to doxycycline, amoxicillin, metronidazole, or clindamycin, in 55%, 43.3%, 30.3%, and 26.5% of the patients with CP, respectively. Fifteen percent of patients harbored subgingival periodontal pathogens resistant to both amoxicillin and metronidazole, which were mostly either S. constellatus (45 individuals) or ciprofloxacin-susceptible strains of Gram-negative enteric rods/pseudomonads (nine individuals). CONCLUSIONS: Patients with CP in the United States frequently yielded subgingival periodontal pathogens resistant in vitro to therapeutic concentrations of antibiotics commonly used in clinical periodontal practice. The wide variability found in periodontal pathogen antibiotic-resistance patterns should concern clinicians empirically selecting antibiotic treatment regimens for patients with CP.