316. Epidemiology of Resistance to Metronidazole in Clinical Isolates of Bacteroides fragilis in a New York City Hospital
Session: Poster Abstract Session: HAI: Multi Drug Resistant Gram Negatives
Thursday, October 27, 2016
Room: Poster Hall
Background:

Bacteroides fragilis (B. fragilis) is an important cause of clinical infection. Recently there have been increasing reports of resistance to metronidazole (MTZ), the antibiotic of choice. We reviewed the microbiologic and clinical epidemiology of B. fragilis to determine trends in resistance to MTZ at our institution.

Methods: Retrospective review of B. fragilis isolates from the NYU Langone Medical Center Clinical Microbiology Lab from 2010-2015. Sensitivity was performed by E-test using the CLSI breakpoints. MIC50, MIC90 and GM were calculated for each year and compared by ANOVA using SPSS 13.

Results:

There were 574 positive cultures of B. fragilis, of which 402 non-duplicate isolates were analyzed. The majority of cultures were from patients 50 years of age and above. 388 (96.5%) isolates were sensitive, 13 (3%) were resistant and 1 showed intermediate sensitivity to MTZ. MTZ-resistant isolates were found in all age groups. The overall distribution of MICs differed significantly by year (p<0.000). A trend towards increasing resistance and a gradual increase in MIC and GM over time was seen (Table 1).Isolates recovered from blood were more likely to be resistant to MTZ than those recovered from other sites of infection, 6.4 % vs 2 % 42% of the resistant strains were resistant to clindamycin , 92% to penicillin, 8% to amoxicillin-clavulonic acid. All strains were sensitive to carbapenems.

Table 1: Increase in MIC Range, GM, MIC50, MIC90 and Resistance by Year (MIC=µ/ml)

Year

Number of Isolates

Range

Geometric Mean

MIC50

MIC90

%Resistant

(CLSI >16)

2010

67

0.02-256

0.55

0.5

1.5

1.5

2011

54

0.02-12

0.62

0.5

2

0

2012

60

0.09-512

0.76

0.5

2

5

2013

65

0.01-512

0.86

0.75

2

1.5

2014

75

0.09-512

1.33

1

4

6.6

2015

81

0.04-512

0.97

1

3

3.7

Conclusion: Over the last 5 years there has been a gradual increase in MIC to MTZ in B. fragilis isolates and increased frequency of high-level resistance. The rates of resistance at our institution were higher than those previously reported from Europe and North America. Further understanding of the mechanism of B. fragilis MTZ resistance and the factors that are associated with the development of MTZ resistance are critical to reversing this trend and preventing further spread of this problem, as well as providing improved antibiotic stewardship guidance.

Sharon Vuppula, MD, Carla Lee, MD, MPH and Henry Pollack, MD, Pediatric Infectious Disease, NYU Langone Medical Center, New York, NY

Disclosures:

S. Vuppula, None

C. Lee, None

H. Pollack, None

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