Jpn. J. Infect. Dis., 54, 64‑68, 2001

Original Article

Prevalence of Resistance to Antimicrobials of Escherichia coli
Isolates fTrom Clinical Sources at a Private Hospital in Trinidad
Fitzroy A. Orrett* and Simone M. Shurlandl
Department of Pathology and Microbiology, the UniversiOJ of the West Indies,
Faculo) of the Medical Sciences andlcollege of Health Sciences, NIHERST Medical Laboratory Technology Department,
Eric Williams Medical Sciences Complex,
Champs Fleurs, Trinidad and Tobago, West Indies(Received November 28, 2000. Accepted March 1, 2001)

SUMMARY: Antimicrobial susceptibility pattems of strains of Escherichia coli isolated between 1 994 and1998 were studied. Ofthe 1,283 strains examined, 75% were recovered from urine, 8.7% from wounds, 3.2%
from blood, 2.6% from pus, and 10.5% from other sources. Isolates from Inpatients and outpatients accounted
for 46. 1% and 53.9%, respectively. Gentamicin and nalidixic acid showed the greatest efficacy against isolates
from both inpatients and outpatients, revealing a >90% sensitivity･ Drugs with the lowest efrlCqCies were ampicillin
and amoxicillin‑clavulanic acid, which showed a >45% resistance. Tetracycline showed a significant decline inresistance from 1994 to 1998 among strains from both inpatients and outpatients (P < 0.001). This decline may
be related to a policy of restrictive antibiotic reportlng by the Microbiology Laboratory and seminars fわr generalpractitioners, subsequent to an island‑wide suⅣey an antibiotic resistance. A similar pattem of declining resistance

was also observed for cefuroxime. E. coli sensitivlty tO CO‑trimoxazole was relatively stable during the study
period. Although the overall prevalence of resistance among E. coli strains is relatively low, on‑golng Surveillance
ofbacterial resistance must continue. The microbial antibiogram can provide general practitioners and clinicianswith data essential for optlmum emPlrlC Choices. Further, the introduction of a policy of restrictive reportlng

may act "synerglStically" with the education of doctors on resistance pattems, to effect island‑Wide reduction of
antimicrobial resistance.

64%and 63%, re甲eCtively, have been rqportedfor trimethopnm.

lNTRODUCT10N

Although many studies have indicated that the overall

The prevalence of antibiotic resistance in Escherichia coli
strains has been increaslng progressively worldwide since theprevalence of bacterial resistance is increaslng WOrldwide,
scant documentation exists in Trinidad as to the prevalence of1970S (1‑3). These organisms are arpong the mostfrequently

resistance among common isolates, and E. colt in particular.

isolated in the laboratory as causative agents Of infectious

The present study was undertaken to assess the extent ofdiseases. The extent or bacterial resistance to a particularantibiotic resistance among local disease‑causlng Strains of

antimicrobial agent varies with the therapeutic practice in that

EI COli in Trinidad, where over‑the‑counter drugs are readily

reglOn and among Institutions at which the E. colt strains wereavailable and high rates ofbacterial diseases exist.

isolated. Variation among E. coli resistance pattems fromdifferent reg10nS Of the world has been previously observed

MATERIALS AND METHODS(4‑6).

The appearance and rapid spread of resistant organisms

Source of Specimens: E. coli strains from various clinicalhave followed the introduction of any new antimicrobial agent(7,8)I Although this is the case for many antibiotics, studies

sources were isolated in the Microbiology Laboratory of theErie Williams Medical Sciences Complex (EWMSC) between

have shown relative stability ln Susceptibility with pmdent

January l, 1994 and December 31, 1998 (Table 1). The

usage of antibiotics in many areas. In the United States,

EWMSC is a 560‑bed prlVate medical complex located insusceptibility of approximately 98% of E. coli strains to

the northwestem part of Trinidad, the larger of a twin‑island

cIPrOfloxacin has been reported, and the aminoglycosides andrepublic, Trinidad and Tobago, located about 1 1 km off thenitrofurantoin have been shown to be relatively stable fornorthem coast of Venezuela in South America. The popula‑tion of the Republic is about 1.25 million. Specimens were

many. years (9). A report on antibiotic susceptibilityof gram‑negatlVe bacteria causing SePtlCemia at 1 0 Canadian hospitals

obtained from inpatients and outpatients; the former include

showed that 98%, 93%, and 91% or isolates (>50% were

hospitalized patients, and the latter include those attending

E. coli) remained sensitive to imipenem, aztreonam, andcefazolin, respectively ( 1 0). However, the incidence of resis‑

the accident and emergency department, outpatient clinics,

general practice, and surrounding health centers. Only one

tance is higher in developlng than in developed countries. In

isolate with a glVen resistant phenotype was retained from

India (1 1) and Nigeria (12), for example, resistance rates ofeach patient fわr antibiotic analysts.

Specimen collection, isolation, and identification: Blood*Corresponding author: Mailing address: P･ 0･ Box 371 , Curepe

Post Office, Curepe, Trinidad and Tobago, West Indies. E‑mail:ヲamPles came in brain heart infusion (BHI) broth and werelnCubated at 370C fわr an initial period of48 h. Solution ln

drfao@tstt. net.tt

bottles in which growth was suspected (due to turbidity, gas,

64

Table L clinical sources of Escherichia colt strainsisolated at thewere incubated aerobically at 35‑37oC fわr 1 8‑24 h･ All speci一EWMSC*, 1994‑1998

mens were processed according to methods of standard
Strains fromprocedure (14)･ E･ Coli isolates †ere identified according toNature/S o urc eof specimen

Urinecolonial morphology, Gram reactlOn,and biochemical charac‑

Inpatients Outpatients
No.

%

No.

′LU一‑

tJ 07 ′hU 3 2 1 1 つJ 0 4 つJ 7 0ノ 1 5 4′人U 4

7 0 5 4 3 L o 5 4 0 ′LU ′LU 2 0ノ 0 7

5

‑4

%
00

1 0 0 ′h〉 ∠U ∠U tJ 4

L 6 LoooL 6

teristics.

Antimicrobial susceptibility testing: Susceptibility to1 0 2 0ノ ∩7 0ノ 0 4

Wbund swab

various antimicrobials was calculated uslng the agar disc

Blood

di飢ISion technique of Bauer et al. (15), on Mueller‑Hinton

Pus

agar (BBL Microbiology Systems, Cockeysville, Md･, USA),

Sputumaccording to the guideline recommendations of the National

HVSI

Committee for Clinical Laboratory Standards (NCCLS) ( 1 6).

Stool

Antibiotic discs containing the fわllowing concentrations (inMisccllancous2

brackets) were used: ampicillin ( I 0 jig), amOXicillin‑clavulanic

Total

591

1 00.0692

acid (20/10 jig), nalidixic acid (30 LLg), gentamicin (10 LLg),

100.0

tetracycline (30 LLg), trifnethoprim‑sulfamethoxazole ( 1 ･25/

*EWMSC ‑ Erie Williams Medical Scicnce Complex, lHVS ‑23.75 LLg) and cefuroxlme (30 LLg). Antibiotic discs were

higb vaglnal swab, 2Misccllaneous ‑ tissue biopsy, peritoneal

obtained from several local drug distributors rather than adialysatc, car swab.

slngle supplier. Results were read aRer 1 8‑24 h and interpreted

according to zone size. lntemediate zone sizes were occasionalor hemolysis) was subcultured onto blood, chocolate, andand were excluded from the study. The control organisms

MacConkey agar plates. BHI with negative results were

were E. colt ATCC 25922 strain and E. colt ATCC 35218
strain obtained from the Caribbean Epidemiology Center, abranch of the Pan American Health Organization. Statisticalanalysis was performed uslng the Statistical Package for theSocial Sciences (SPSS Inc., Chicago, Ill., USA).

reported after 10 days･ Cerebrospinalfluid (CSF), urine (mid‑stream and catheter) and sputum specimens were collectedin sterile containers. Specimens from wounds, genital tract,pus, and discharge were collected onto sterile cotton Culturettell swabs (Becton Dickinson Microbiology System, Cockeysville,

Md･, USA)･ Stool sa?ples came in wide‑nTOuth screw‑top

RES ULTS

plastic sterile contalnerS (Elicey PrecislOn Laboratory

Consumables, Shrewbury, Mass., USA).

During the 4‑year period, a total of34,928 Specimens werereceived at the EWMSC, Microbiology Laboratory for culture,of which 16.9% (5,903/34,928) were positive. From these
5,903 positive cultures, 1,283 (21.7%) were common E. colt

All specimens (except genital swabs) collected with sterilecotton‑tlpped applicators (Culturette II) were inoculated onto

sheep blood, chocolate, and MacConkey agar plates andincubated aerobically at 35‑37oC for 1 8‑24 h. Genital (highstrains. Outpatients accounted fわr 692 isolates (53･9%) andinpatients for 591 isolates (46.1%) (Table 1). The major†aginal) swabs were inoculated onto chocolate agar andlnCubated in a CO2 incubator at 35‑37oC fわr 18‑24 h. Bloody

sources were urine, wounds, blood, and pus, which together

fecal specimens were inoculated onto xylose lyslne deoxycho‑

accounted f♭r 1,145 (89.2%) ofall isolates.

late, and both lactose fermentlng and lactose non‑fermentlng

Table 2a and 2b show the resistance pattems of the strains

colonies were identified. The E. Coli isolates were subcultured

isolated from Inpatients and outpatients, respectively.

onto sorbitol‑MacConkey agar to screen presumptlVely fわr

Gentamicin and nalidixic acid showed the greatest efficacy

the 0157: H7 serotype. We wereunable to confirm with anti‑

against isolates in both inpatients and outpatients, showing aserum that the suspect strains were indeed 0157: H7. Urine>90% sensitivity. The drugs with the lowest efficacy were

samples were inoculated onto cysteine lactose electrolyte‑

tetracycline, ampicillin, and amoxicillin‑clavulanic acid, in

deficient and sheep blood agar plates uslng a Platinum wireloop delivering 0.00 1 ml of urine. A midstream (̀clean catch')descending order; lnpatients showed a <55% sensitivlty, andoutpatients a <67% sensitivity. Trimethoprim‑sulfamethoxazole

urine specimen containlng 100,000 bacteria per ml or in a

was relatively stable throughout the period or study in bothcatheter specimen containlng >3,000 bactena per ml of a slngle

Inpatients and outpatients. In both types of patients, however,species was considered as significant bacteriuria ( 1 3). Plates

cefuroxime showed a gradual but significant decrease in

Table 2a. Pcrccntagc ofantimicrobial resistance of 1 ,283 Escherichia coli strains isolated fromvarious sources at仙c EWMSC*, 1994‑1998

Inpaticnt isolates
1994

1995

1996

1997

N‑100

N‑96

N‑118

N‑140

1998

N‑137

% E. Colt resistant to
Ampicillin

5 つJ O 2 0

0 0 4 4 0ノ 0 40000000

4 2 1 7 2 97 L 5 5 4 5 3

Amoxicillin‑clavulanic acidGcntamicin
Nalidixic acidTctracycl in°

Trimcthoprlm‑Su胞methoxazole

Cefuroxime*EWMSC ‑ Erie Williams Medical SciellCeS Complex.

65

0ノ 07 2 /hV 0 0 父U

5 つJ 1 4 つJ 1 2 8 L 3 4 3 25｣940｣7

つJ 7 2 4 5 ∠U 4 上U qノ ｣ 3 2 4 3
5 つJ l一1 4 5 1′LU 2 1 2 2 2′0 7 0 7 4 0ノ 0

0 7 8 Lo 9 7

Table 2b. Pcrcentagc of antimicrobial resistance of 1 ,283 Eschen'chia colt strains isolated fromvarious sources at the EWMSC*, 1 994‑1998
Outpatient isolates
1994

1995

N‑146

N‑106

1996

N‑81

1997

198

N‑150

N‑209

% E. Colt resistant to
Ampicillin

521 727

つJ O7 5 2 0ノ 7 745｣｣544

4 2 1 7 4 0 7 5 つJ 7 0ノ tJ ∠U 2 5 2 5 2 4 0

4 つJ 1 l つJ 2 6 9 2 L oノ 7 2

0ノ 5 つJ 1 5 2 5∠U 2 1 2 2 1

4 7 つJ n7 5 7 0 7 つJ 3 つJ つJ つJ 0

5 2一1 4 つJ 3 3 7 3 6 L 3 5 ｣ 0 4 7 6 5 9

Amoxicillin‑clavulanic acidGcntamicin
Nalidixic acidTctracycl in°

Trimethoprlm‑Sul famcthoxazole
Cc凡lrOXime*EWMSC ‑ Erie Williams Medical Scicnccs Complex.

Table 3a. Proportion (%) of 398 EscherL‑chLla colt'strains isolated from urine specimens resistant
to common antibiotics at the EWMSC*, 1994‑1998
Inpatient isolatcs
I 994

1995

N‑65

N‑66

1996

1997

1998

N‑68

N‑95

N‑104

% E. Colt resistant to
AmpicillintJ 2 ′h〉 2 ′lU

3 ･3̲3･64･5to･653･｡朋N

3 0 L 3 0 9 L 805｣025

2 2 1 2 29 2 L 3 6 0 1

4｣52565tJ 2 1 3 つJ

5743477

0 4 2 7 7 0ノ 4

4 1 1 1 2 0 0ノ 2 ̲ 8 0 L 4 2 9 5 7 つJ 2

Amoxicillin‑clavulanic acid
Gentamicin
Nalidixic acidTctracycl in°

Trimethopnm‑sul famethoxazole

Cc furoxi me*EWMSC ‑ Erie Williams Medical Sciences Complex. LNT ‑ not tested.

Table 3b. Proportion (%) of 56 1 Escherichia colt strains isolated from urine specimens resistant

to common antibiotics at the EWMSC*, 1 994‑1998
Outpatient isolates
1994

1995

1996

1997

1998

N‑114

N‑92

N‑50

N‑130

N‑175

% E. Colt resistant to
Ampicill in

4 2 ′LU 2 ′0 3 4 L L 9 L 2

つJ 2 ′LU っJ 4

0ノ ′0 0 0 つJ一‑ つJ(‖8 2 4 ∠U tJ O 2

0 0 tJ 5 0 0 4

4 つJ 1 4 2 5 2 4 2 0 0 6 20000000

5 3 2 2 04 3 3 0ノ 5 ∠U 06｣｣2490舶242.6.28.28.防 0 0 n7 0ノ 0 ∠U 7

Amoxicillin‑clavulanic acid
Gentamicin
Nalidixic acidTctracycline

Trimcthoprlm‑Sul famethoxazolc
Cefuroxime*EWMSC ‑ Erie Williams Medical Sciences Complex.

and Kenya (29.2%) (1 8), but much lower than that reported
from Ghana (47.1%) (19).

resistance over the 4‑year period (X2‑ 90.75, P < 0.001).

The susceptibilitypattems for E. coli strainsrecovered fromurine of hospitalized and non‑hospitalized patients are shown

The prevalence of resistance to ampicillin and amoxicillin‑in Table 3a and 3b, respectively. E. Coli maintained a relative

clavulanic acid during the study period was relatively stable.

susceptibility to amoxicillin‑clavulanic acid, nalidixic acid,

Resistance to ampicillin was generally >50%. This may begentamicin, and trimethoprlm‑Sulfamethoxazole throughout
the period of study. For tetracycline, resistance rates fell indue in part to the high prevalence of 8‑1actamase‑producing
organisms within the country. In one island‑wide study inboth types of patients; from 89.1% in 1994 to 20.4% in 1998

1994 by Orrett and Shurland (20), β‑lactarpase production

among 1 ,572 bacterial isolates &om co.mmunltysources (83%in inpatients (X2 ‑ 95.25, P < 0.001), and from 79.7% in
1994 to 41.6% in 1998 in outpatients (X2 ‑ 30.41, P< 0.001).

of which were gram‑negative organlSmS) was fわund to be

73.3%. Resistance to amoxicillin‑clavulanic acid was relatively
low (32･0%) when compared to that to ampicillin, but
considerably higher than reports of 25% and 5.7% fromJ)ISCUSSION
The present study found that the frequency of isolation ofFrance (2 1) and Crete (22), respectively. Several mechanisms

E･ coli at the EWMSC (21.7%) among all bacterial isolates
was comparable to that reported from Ethiopia (2 1%) (17)for resistance to amoxicillin‑clavulanic acid among E. coltstrains have been proposed. These include TEM‑ I 8‑lactamase66

hyperproduction (2 1 ,23), and increased activityofthe SHV‑and SHV‑1 genes on plasmids, and are easily transmissible

1 β‑lactamases, including the CTX M 2‑4 group or β‑

斤om one organism to another (34).

1actamases and the amp C‑type 8‑lactamases such as CMY‑

increased use of the 3rd generation cephalosporins was

2, BILll , SAL‑ 1 , and LAT‑1 and LAT‑2 (24). Other resistancesucceeded by a nslng prevalence of resistance to血ese agentsmechanisms suggested were the altered pemeability of the(35). Several institutions have reported increased isolation ofouter cell membrane (25) and mutationsin the genes encoding

ESBL‑producing strains of E. coli, Klebsiella pneumoniae,

TEM‑1 β‑lactamases (26).

and Entey10bacter and SeTratia spp.from cases of nosocomial

ln commTnity and hospital situations, E･ colt strains showed

infections(36‑38). No documented data on the prevalence ofsignificant Improvement in sensitivity to tetracyclines (P <ESBLproducing organisms in the Caribbean could be fわund

0･001)･ ln 1994, sensitivity among hospital and community

in the literature. Therefore, the prevalence of ESBL‑producing

strains was 10.9% and 20.3%, respectively. By 1998, sensi‑
tivlty rose tO 79.6% among hospital strains and 58.4% amongcommunlty Strains･ Followlng the survey of Orrett andShurland (20), a series of seminars were held at the EWMSC

bacteria, in this hospital and the country, lS unknown. This isa cause f♭r concem as it has implications fわr management ofserious nosocomial infections.

along with a large gathering ofgeneral practitioners to discuss

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