Antibiotic Resistance: the Bermuda Experience

Antibiotic resistance is a worldwide problem (2, 5, 8, 10). Virtually every developed nation has reported methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus spp. (VRE), increasing cephalosporin resistance in the Enterobacteriaceae, and penicillin-resistant Streptococcus pneumoniae (PRSP) and Neisseria gonorrhoeae. Bermudian isolates do not exhibit the typical resistance patterns, and very little endemic resistance has been observed. For example, 99% of Escherichia coli and 98% of Pseudomonas aeruginosa strains are susceptible to gentamicin. King Edward VII Memorial Hospital, the only one in Bermuda, has established policies for rational antibiotic use and can monitor their effect on resistance patterns.

Bermuda is a British dependent territory 600 miles off the coast of North Carolina. It has a well-educated urban population of 60,000 and entertains nearly 1/2 million tourists annually. The King Edward VII Memorial Hospital (KEMH) is a Canadian accredited general hospital with 250 acute-care beds and 100 long-term-care beds. While it attempts to provide a full range of services with the latest technology for imaging and a sophisticated laboratory, patients requiring cardiac surgery, neurosurgery, or radiation therapy are referred to hospitals in Canada, the United States, or the United Kingdom.

Susceptibility profiles for organisms and selected antibiotics are presented in Table 1. The Bauer-Kirby disc diffusion method was used, and acceptable correlation of results was achieved when MIC determinations were performed by BBI Clinical Laboratories, New Britain, Conn. A number of unique characteristics are evident from the data. For example, virtually none of the P. aeruginosa isolates are resistant to gentamicin, compared to 10 to 30% resistance in the United States (4, 7). Many of the enteric isolates (E. coli, Klebsiella spp., and Proteus mirabilis) are virtually 100% susceptible to gentamicin with very little extended-spectrum cephalosporin resistance. In Barbados and Trinidad, 48 and 50%, respectively, of E. coli isolates were susceptible to ampicillin and 66 and 56% were susceptible to cephalothin, whereas in Bermuda 68 and 94% were suscepitible to ampicillin and cephalothin, respectively (1). Haemophilus influenzae and N. gonorrhoeae isolates show susceptibility profiles similar to those of strains isolated in a U.S. hospital of comparative size (4, 7).

TABLE 1.

Antibiotic susceptibility profiles of isolates at KEMH (August 1994 to July 1998)^a

Organism	No. of isolates	% of isolates susceptible to:
		AMP	AMC	1CEPH	3CEPH	CIP	GEN	IMI	NXN	PIP	SXT	PEN	SPEC	TET	CLIN	ERY	OX	VAN
Citrobacter spp.	150	0	97	98	99	100	100	100	99	NT	100
E. aerogenes/cloacae	311	0	0	0	90	100	99	100	100	NT	93
E. coli	4,109	68	90	95	99	98	99	100	99	NT	85
K. pneumoniae	679	0	96	97	99	98	99	100	98	NT	92
P. mirabilis	641	96	98	96	99	99	99	100	100	NT	99
P. aeruginosa	988	NT	NT	NT	98	98	98	94	93	95	NT
S. marcescens	177	0	0	0	95	100	100	100	98	NT	98
H. influenzae	198	69	96		NT						99	NT	NT	NT
N. gonorrhoeae	174	NT	99		99						NT	93	100	93
S. aureus	2,439		99	100			99b					21			97	92	100	100
MRSA	87		0	0			85					0			10	6	0	100

^aAMP, ampicillin; AMC, amoxicillin-clavulanic acid; 1CEPH, narrow-spectrum cephalosporin; 3CEPH, extended-spectrum cephalosporin; CIP, ciprofloxacin; CLIN, clindamycin; ERY, erythromycin; GEN, gentamicin; IMI, imipenem-cilastin; NXN, norfloxacin; OX, oxacillin; PEN, penicillin; PIP, piperacillin; SPEC, spectinomycin; SXT, trimethoprim-sulfamethoxazole; TET, tetracycline; VAN, vancomycin; NT, not tested. 

^bS. aureus isolates resistant to oxacillin are classified as MRSA. 

Methicillin-susceptible S. aureus (MSSA) showed 92% susceptibility to erythromycin, compared to 70% susceptibility in a U.S. hospital of similar size. The first outbreak of MRSA in Bermuda occurred in 1990. The MRSA rate is 3.5%, well below the U.S. rate of 10 to 30% (4, 7). Stringent hand-washing practices and a comprehensive MRSA-VRE screening policy for patients returning from hospitalization abroad may be responsible for the low MRSA rate.

In 1994, the first PRSP strain was isolated at KEMH by using a 1-μg oxacillin disc for screening (6). During the period August 1993 to July 1998, there were 502 S. pneumoniae isolates, of which 3% were resistant or of intermediate susceptibility to penicilllin. Only one was resistant to cefotaxime. In 1994 to 1995, the Centers for Disease Control reported that 23% of S. pneumoniae isolates in the United States were resistant to penicillin (3). In 1990, 100% of S. pneumoniae isolates in Iceland were susceptible to penicillin, and by 1996 only 60 to 70% were susceptible (9).

The first isolation of a VRE strain at KEMH was in 1995. Subsequently 13 patients have been colonized or infected with VRE. All VRE isolates have been imported from abroad. There has been no nosocomial transmission of VRE within KEMH. High-level aminoglycocide resistance has not been observed in Enterococcus spp. other than VRE isolates.

Antibiotic utilization controls have been in place for several years at KEMH. The pharmacy instituted formulary controls over 20 years ago. The microbiology laboratory has been selectively reporting antibiotic susceptibilities for 15 years. Three years ago, MRSA and VRE screening procedures were implemented for patients hospitalized abroad. We believe this collaborative effort has been a major factor in the control of antibiotic resistance in Bermuda.