Urinary Tract Infections
(January 2005)
(Download 
Urinary Tract Infections.pdf )
Urinary Tract Infections (UTIs) are very common especially amongst females. While Escherichia coli is by far the most common cause, several other bacteria can be responsible. The antibiotic susceptibility pattern of urinary bacterial isolates in this part of Australia is as follows:
% of bacterial isolates 'sensitive' to antibiotic
| Microbe in Urine | Amoxycillin | Augmentin | Cephalexin | Trimethoprim | Nitrofurantoin | Gentamicin | Norfloxacin |
|---|
| Escherichia coli |
57 |
92 |
81 |
86 |
99 |
99 |
99 |
| Klebsiella pneumoniae |
R |
96 |
90 |
87 |
68 |
99 |
97 |
| ESCPPM* Group |
R |
R |
R |
80 |
78 |
82 |
89 |
| Pseudomonas aeruginosa |
R |
R |
R |
R |
R |
95 |
95 |
| Enterococcus sp. |
S |
S |
R |
R |
S |
R |
R |
| Staphylococcus saprophyticus |
S |
S |
S |
S |
S |
R |
S |
| Group B Streptococcus |
S |
S |
S |
R |
S |
R |
S |
- E = Enterobacter sp. (some)
- S = Serratia sp
- C = Citrobacter sp.
- P = Providencia sp.
- P = Proteus sp. (some)
- M = Morganella sp.
- R = Uniformly resistant to this antibiotic
- S = Uniformly sensitive to this antibiotic
-
Recommended Antibiotics
Antibiotics recommended for treating a UTI before microbiology results available are
- Trimethoprim
- Cephalexin
- "Augmentin" (Amoxycillin / Clavulanate)
- Gentamicin (5mg/kg iv or im, once a day, one or two doses, in severe cases)
Amoxycillin is NOT recommended because only 57% of E.coli are sensitive to it.
Norfloxacin is NOT recommended as antibiotic-resistance develops quickly in bacteria. It is the only antibiotic available for oral therapy of Pseudomonas aeruginosa UTIs.
Frequently Asked Questions About Urine Cultures
When are urine bacterial counts significant in men and women?
In asymptomatic women:
- >108 cfu/L of a pathogen on one occasion = 80% probability of genuine bacteriuria
- <108cfu/L of a pathogen on one occasion = <5% probability of genuine bacteriuria. Urine specimen was probably contamination by perineal bacteria.
In symptomatic women:
- >105 cfu/L of a pathogen = genuine bacteriuria
In symptomatic men:
- >106 cfu/L of pathogen = genuine bacteriuria
(cfu = colony forming unit, where one cfu = one bacterial cell).
In what situations is urine culture indicated in the absence of symptoms?
Asymptomatic bacteriuria should be sought, and may require treatment, in the following patients: pregnant, neonates & preschool children with previous history of UTI, those with abnormal urinary tracts, preoperative patients eg. joint replacement, other major surgery (bacteriuria is a risk factor for post-operative catheter-associated UTI) and patients at risk of endocarditis who are undergoing a urinary tract procedure (refer to the Antibiotic Guidelines, (version 12, 2003) Prophylaxis Medical p.146).
Is it worth doing a urine culture when there is a change in the appearance of urine (eg. becoming murky or smelly) or in the chronically catheterised patient?
In general terms, only collect a urine culture if symptomatic infection is suspected. Please note that collection of urine from a patient with a long-term indwelling urinary catheter requires aseptic insertion of a new catheter to avoid contamination of the urine by bacteria colonising the plastic collecting system.
Notice
We wish to advise that starting 1st February 2005 HAPS Microbiology has decided to cease routine dipstick urine analysis (i.e. blood, glucose, protein & pH), as many doctors do this test in their rooms. However, should you still require this test on a particular urine, please request "dip-stick" or "urinalysis" on the pathology request form, in addition to "M/C/S" (microscopy, culture, sensitivities) and it will be done.
About the Authors
This HAPS Communique was written by Dr Stephen Graves, Director of Microbiology, and Dr John Ferguson, Microbiology & Infectious Diseases Staff Specialist
If you have any questions regarding this topic Microbiology can be contacted on Telephone: (02) 49214000, Facsimile: (02) 49214400.