Growing Prevalence of Providencia stuartii at Detroit Medical Center, 2005-2009

Background: Providencia stuartii is usually a urinary pathogen isolated from patients residing in healthcare facilities and can also be a cause of bacteremia. P. stuartii is associated with both intrinsic and acquired resistance determinants. Tigecycline and colistin are sometimes the only available agents that retain activity against certain multi-drug resistant (MDR) Gram-negative pathogens, but both have poor activity against Providencia spp.�

Objective: The objective of this study was to determine if increasing use of tigecycline and colistin in our health system was associated with increasing prevalence of P. stuartii.

Methods: Trend analysis of the prevalence of P. stuartii at the Detroit Medical Center (DMC), an 8-hospital healthcare system with over 2,200 inpatient beds, was conducted from 2005-2009. A broth micro-dilution Microscan� automated system was used for species identification and antibiotic susceptibility testing. Antibiograms and all cultures processing were conducted according to CLSI criteria. Defined daily doses (DDD) of tigecycline and colistin for the study period were obtained from pharmacy data.

Results: During the 5-year study period, the prevalence of P. stuartii at the DMC significantly increased (Table) (p for trend < 0.001). Tigecycline's and colistin's DDDs also increased significantly during the study period (p for trend < 0.001). The increase in P. stuartii was associated with the increased use of colistin, although this was not statistically significant (r=0.6, p=0.28). No significant association was found between the increase of P. stuartii and the use of tigecycline.

�Conclusions: The prevalence of P. stuartii at the DMC increased significantly during the 5-year study period and was correlated with the increased use of colistin. This association might be due to the broad spectrum activity of colistin against gram-negative bacteria, and lack of activity against P. stuartii.

Table I - P. stuartii antibiogram, Detroit Medical Center, 2005-2009

Yr	P. stuartii No. of isolates	P. stuartii� No. of cases/1,000 Pt days	Susceptibility prevalence (%)													DDD
			AMP	Pip/ Tazo	CZL	CRX	CTR	CAZ	CFP	AZT	MER	AMK	GEN	CIP	Trim/ Sulfa	COL DDD	TIG DDD
2005	168	0.52	12	96	9	53	98	95	98	98	100	100	35	34	65	0	0
2006	171	0.5	18	95	17	60	98	90	98	95	100	99	47	32	66	185	363
2007	139	0.41	19	98	14	61	98	96	96	90	100	98	43	32	71	1994	1745
2008	217	0.65	9	98	8	46	99	95	93	96	100	100	41	30	59	5138	1059
2009	288	0.91	16	98	12	44	93	95	93	94	100	100	40	28	60	4459	1105

AMP: Ampicillin; Pip/Tazo: Piperacillin/Tazobactam; CZL: Cefazolin; CRX: Cefuroxime; CTR: Ceftriaxone; CAZ: Ceftazidime; CFP: Cefepime; AZT: Aztreonam; MER: Meropenem; AMK: Amikacin; GEN: Gentamicin; CIP: Ciprofloxacin; Trim/Sulfa:Trimethoprim/Sulfamethoxazole; COL: Colistin; TIG: Tigecycline.