Gram-Negative Urinary Tract Isolates in Southwestern Ontario

Vol. 109, April

THE JOURNAL OF UROLOGY

Printed in U.S.A.

Copyright © 1973 by The Williams & Wilkins Co.

GRAM-NEGATIVE URINARY TRACT ISOLATES IN SOUTHWESTERN ONTARIO WILLIAM A. BLACK AND LESLIE A. HATCH

From the Department of Microbiology, St. Joseph's Hospital and the Department of Bacteriology and Immunology, University of Western Ontario, London, Ontario, Canada 1. Gram-negative bacilli isolated from 5,084 inpatient and outpatient urine° specimens

The introduction of semi-quantitative bacterial culture of urine and standardized methods of antibiotic sensitivity testing have facilitated the meaningful comparison of laboratory reports from different areas. 1 In view of the epidemiological value of such information, Blazevic and associates have drawn attention to the lack of potentially comparative data of this nature in the literature. 2 Herein we report on the identity and antibiotic sensitivity patterns of gram-negative urinary tract isolates in a 600-bed teaching hospital during a 5-month period.

TABLE

Inpatient

Species

No. Iso!ates

Outpatient

GramGramGramNega- No. Nega- No. Negative tive tive IsoIsoBaBaBa!ates !ates cilli cilli cilli (%)

MATERIALS AND METHODS

After preliminary cleansing of the urethral orifice, midstream urine specimens were collected from male and female inpatients and outpatients. Some specimens were taken by catheter. In most instances, early morning specimens were obtained. The dipspoon* method employing cystine-lactose-electrolyte-deficient agar was used by placing the spoon directly in the stream of urine, or by dipping it, within 5 minutes after the patient had voided, into midstream urine that had been collected in a sterile container. 3 The organisms were tested for sensitivity by a single diskt method based on the Kirby-Bauer technique with emphasis on standardization of inoculum, accurate measurement of zone sizes and correlation of zone size with those of standard sensitive strains set up in parallel tests daily.• The zone sizes of the latter were related to the minimum inhibitory concentration of each antimicrobial for the organism. Organisms with zone sizes greater than, equal to or not more than 20 per cent less than the diameter of the control strain were reported as sensitive. Organisms with Accepted for publication August 4, 1972. 1 Kass, E. H.: Pyelonephritis and bacteriuria. A major problem in preventive medicine. Ann. Intern. Med., 56: 46, 1962. 2 Blazevic, D. J., Stemper, J.E. and Matsen, J.M.: Organisms encountered in urine cultures over a 10-year period. Appl. Microbiol., 23: 421, 1972. * Modern Laboratories Ltd., Toronto, Ontario, Canada. 3 Mackey, J. P. and Sandys, G. H.: Laboratory diagnosis of infections of the urinary tract in general practice by means of a dip-inoculum transport medium. Brit. Med. J., 2: 1286, 1965. t Sensi-Discs, Baltimore Biological Laboratories, Baltimore, Maryland. 'B;mer, A. W., Kirby, W. M. M .. Sherris. J.C. and Turck, M.: Antibiotic susceptibility testing by a standardized single disc method. Amer. J. Clin. Path., 45: 493, 1966. 692

E.coli 350 124 Proteus Klebsiella-Entero- 100 bacter Serratia 65 Pseudomonas 39 Providence 28 Acinetobacter 7 Alcaligenes 2 Citrobader 2 Totals 717

Total

(%)

(%)

48.81 17.29 13.95

98 42 31

42.59 18.26 13.48

448 166 131

47.30 17.53 13.83

9.07 5.44 3.90 0.98 0.28 0.28 100.00

16 22 14 3 1 3 230

6.96 81 9.56 61 6.08 42 10 1.32 0.43 3 1.32 5 100.00 947

8.55 6.44 4.44 1.06 0.32 0.53 100.00

smaller zone sizes were reported as resistant. No other terms were used in reporting. The disks used were tetracycline 30 mcg., chlor- · amphenicol 30 mcg., nitrofurantoin 100 mcg., kanamycin 30 mcg., ampicillin 10 mcg., polymyxin B 50 units, gentamicin 10 mcg., nalidixic acid 30 mcg. and sulfacetamide 1.0 mg. The test medium was diagnostic sensitivity test agar (oxoid-CM 261) with 5 per cent lysed sheep blood added. Incubation was for 18 hours plus or minus 2 hours at 37C aerobically. Only urine specimens with counts of gram-negative bacilli, in either pure or mixed culture, of 100,000 per ml. or more were included in this study and no attempt was made to assign clinical significance to the individual isolates. RESULTS

Between October 1970 and February 1971, 5,084 urine examinations yielded 947 significant counts of gram-negative bacilli. Of these, 717 were isolated from inpatients and 230 from outpatients. Their distribution and identity are shown in table 1. Table 2 presents the percentage distribution of sensitivities to antibiotics in the most commonly isolated species. Table 3 shows the cumulative percentage distribution of those organisms sensitive to the oral antimicrobials tetracycline, nitrofurantoin, ampicillin, nalidixic acid and sulphonamides. DISCUSSION

The percentage distribution of species isolated was similar in outpatients. and inpatients. Just

693

GRAM-NEGATIVE URINARY TRACT ISOLATES

TABLE

2. Percentage distribution of sensitivity to 9 antimicrobials in 929 common gral"l,-negative bacilli

Species

E.coli: IP* OP Proteus: lP OP Klebsiella-Enterobacter: IP OP Serratia: IP OP Pseudomonas: IP OP Providence: IP OP

Ampicillin

Polymyxin

Gentamicin

Nalidixic Acid

Sulphonamide

95 94

81 80

100 100

100 100

99 99

79 79

350 98

48 55

90 93

73 78

3 5

98 98

93 90

73 62

124 42

72 74

90 77

94 90

36 29

94 84

98 94

92 84

80 84

100 31

3 31

6 13

11 0

9 19

5 0

5 0

100 100

37 13

49 19

65 16

44 55

28 36

2 0

10 0

2 0

87 100

97 95

.5 4

97 91

39 22

7 0

29 29

14 7

36 50

29 50

7 0

57 64

93 79

68 50

28 14

Tetracycline

Chloramphenicol

Nitrofurantoin

74 72

96 95

99 98

0.8 17

93 90

76 71

Kanamycin

No. Organisms Tested

*IP - inpatient; OP - outpatient.

less than half the strains were Escherichia coli. coli, Proteus and Klebsiella-Enterobacter species accounted for three-quarters of the total isolates. Serratia marcescens occurred more frequently than Pseudomonas in inpatients while the reverse was found in outpatients. Serratia, a common cause of hospital infection, has been seen as a urinary pathogen in this hospital since it was first recognized here in 1969. •. 6 Periodic surveys have shown that approximately 90 per cent of Proteus species isolated from urine specimens in this laboratory are Proteus mirabilis. Tables 2 and 3 reveal an unsuspected high incidence of sensitive strains. In this series, 75 per cent of the urinary tract infections caused by E. coli could have been treated by any of 4 oral antimicrobials and a choice of 2 was available for all 448 strains. Eighty per cent of the Proteus species were sensitive to at least 3 oral antimicrobials and all were sensitive to one. Of the Klebsiella-Enterobacter species, 75 per cent were sensitive to 3 or more, 90 per cent to 2 or more and only 3 of 131 were resistant to all oral antimicrobials. Almost 90 per cent of Pseudomonas species were sensitive to sulphonamide. The finding that 90 per cent of Serratia species were resistant to kanamycin reflects results obtained by Wilfert and associates.• On the other hand, Cabrera 6 and Allen and Conger 7 found a preponderance of

E.

5 Wilfert, J. N., Barrett, F. F., Ewing, W. H., Finland, M. and Kass, E. H.: Serratia marcescens: biochemical, serological, and epidemiological characteristics and antibiotic susceptibility of strains isolated at Boston City Hospital. Appl. Microbiol., 19: 345, 1970. 6 Cabrera, H. A.: An outbreak of Serratia marcescens, and its control. Arch. Intern. Med., 123: 650, 1969. 7 Allen, S. D. and Conger, K. B.: Serratia marcescens infection of the urinary tract: a nosocomial infection. J. Urol., 101: 621, 1969.

TABLE 3. Percentages of 929 common gram-negative urinary isolates sensitive to 5, 4, 3, 2, 1 or O of the 5 antimicrobials tetracycline, nitrofurantoin, ampicillin, nalidixic acid and sulphonamides administered orally

Percentages of Isolates Sensitive to Species 5 of 4 of 3 of 2 of 1 of Oof 5 5 5 5 5 5 E.coli: IP* OP Proteus: IP OP Klebsiella-Enterobacter: IP OP Serratia: IP OP Pseudomonas: IP OP Providence: IP OP

No. Isolates Tested

59 59

22 19

11 12

8 10

0 0

0 0

350 98

0 2

31 26

56 60

8 10

5 2

0 0

124 42

10 26

57 29

14 16

16 20

3 6

0 3

100 31

0 0

0 0

2 0

19 12

58 38

21 50

65 16

0 0

0 0

3 5

41 45

49 45

7 5

39 22

0 0

7 7

32 22

25 22

36 35

0 14

28 14

*IP - inpatients; OP - outpatients.

kanamycin-sensitive strains. A noteworthy finding was resistance to gentamicin in 40 per cent of the Providence species. Table 2 demonstrates little difference in the sensitivity patterns of outpatient and inpatient strains except against tetracycline. With tetracycline 17 and 31 per cent, respectively, of outpatient strains of Proteus and Serratia species were sensitive compared with 1 and 3 per cent for inpatient strains. No explanation could be found for these differences.

694

BLACK AND HATCH

This labor~tory's method of assessing sensitivity to antibiotics was designed to avoid the problem of interpreting intermediate zones of inhibition and to ensure the best possible correlation between in vitro patterns and in vivo results. It was accepted that some strains reported resistant in vitro might be moderately sensitive in vivo. Accordingly, the in vitro sensitivities of the organisms tabulated probably understate the in vivo possibilities. Gillespie and associates suggest that, in their area, sulphonamides remain the drugs of choice for treating urinary tract infections. 8 Table 2 demonstrates a high degree of in vitro activity of sulphonamides against our isolates and shows that nitrofurantoin, nalidixic acid and perhaps ampicillin would give similar results for most organisms. It is recognized that there is wide geographical variation in the sensitivity of urinary tract isolates.• The reasons for this are obscure but may be related to antibiotic usage patterns or other controllable factors. In this locality, there appears "Gillespie, W. A., Lee, P. A., Linton, K. B. and Rowland, A. J.: Antibiotic resistance of coliform bacilli in urinary infection acquired by women outside hospital. A 12-year survey. Lancet, 2: 675, 1971. • Robertson, M. H.: A 6-year survey of resistance patterns of urinary tract pathogens in general practice. Postgrad. Med. J., 47: 111, 1971.

to have been a considerable increase in sensitivity of gram-negative urinary tract isolates during the last 5 years. One explanation for this could be changes in laboratory methods but this is unlikely since current criteria for sensitivity reporting tend to understate the sensitivity of some strains. Another possibility is that altered therapeutic and administrative regimens in this hospital may have influenced the emergence of a more drug sensitive bacterial population. The mechanisms of this trend toward increasing sensitivity are being further investigated. We realize that our findings are not clinically applicable to other populations. However, they do accurately reflect the situation in this area and hopefully should provide interesting data for comparison with results obtained from laboratories elsewhere. SUMMARY

The identity of 94 7 gram-negative bacilli isolated in significant numbers from 5,084 specimens of urine during a 5-month period is presented. Sensitivity testing with 9 antimicrobials was done. Many of the most frequently isolated organisms were sensitive in vitro to a variety of orally administered antimicrobials. Comparison of this type of information from various areas may be of epidemiological interest.