Urinary tract infections (UTIs) belong to the most common infections both in community and hospital settings. They account for 10–20% of all infections treated in primary care and 30–40% of infections treated in hospitals.
Urine samples constitute a large share in the daily workload of microbiological laboratories. A combination of blood agars, such as Columbia agar and MacConkey agar, are traditionally widely used for urine culture (Green, 2009; Akter
The aim of the study was to evaluate the usefulness of chromogenic media in detecting bacteria from urine and identifying UTI pathogens directly. The media were evaluated by using 100 urine specimens sent for routine diagnostic from paediatric and adult patients of two Polish hospitals: the Poviate Hospital in Wołomin, and the Baby Jesus University Hospital in Warsaw, between May and September 2016. Five chromogenic culture media were tested, namely chromID® CPS® Elite (CPSE; bioMérieux, France), BD CHROMagar Orientation Medium (ORI; Becton Dickinson, Germany), Brillance UTI Clarity Agar (UTI C; Oxoid, USA), CHROMagarTM Orientation (BMagar; BioMaxima, Poland), CHROMagarTM Orientation (ORIE; Graso, Poland). Blood agar (Columbia agar enriched with 5% sheep blood (BAP; Becton Dickinson, Germany) and MacConkey agar (MAC; Becton Dickinson, Germany) served as the reference media. All media were inoculated with a 0.01 ml disposable plastic loop as prescribed (Sharp
Presumptive identification of isolates using the manufacturer’s colour criteria was compared with the biochemical identification of bacteria Vitek 2 Compact system (bioMérieux, Marcy l’Etoile France) as a reference method, but complementary tests such as microscopic examination by Gram stain method, indol, oxidase and catalase detection (Perry, 2017) were also performed. Bacterial growth was recorded semi-quantitatively based on the colony count. All plates were recorded as having no growth (NG), 1, 2, 3, 4 or 5 colony types according to their morphology and colour. The number of each colony type was also recorded to facilitate the identification of pathogens in mixed cultures; 102 CFU/ml signified a growth of < 10 CFU on a plate; 103 CFU/ml signified 10–99 CFU on a plate,
In forty-one out of 100 (41%) urine samples no microbial growth (NG) was observed on any of the media used in the study. In the remaining 59 urine samples, 1 to 5 distinct microorganisms were cultured. Sixty-two Gram-negative rods (Enterobacteriaceae n = 61 and non-fermenting rods n = 1) and 47 Gram-positive cocci (enterococci n = 22; staphylococci n = 21; streptococci n = 4) were isolated from the urine samples. All of the isolates were screened for their colony colours using the colour criteria provided by manufacturers. Table I shows the analysis of bacterial growth on chromogenic media as compared with the reference method.
Comparison of microbial growth on chromogenic media
Bacterial strains | Number of isolates (n) | ||||||||
---|---|---|---|---|---|---|---|---|---|
The reference method | Chromogenic media | ||||||||
Family or genus (n) | Species (by VITEK 2 Compact) and isolates number | Columbia Agar + 5% sheep blood (COL) | MacConkey Agar (MAC) | ChromID® CPS® Elite (CPSE, bioMérieux) | BD CHROMagar Orientation Medium (ORI, Becton Dickinson) | Brillance UTI Clarity Agar (UTI C, Oxoid) | CHROMagar™ Orientation (BioMaxima) | CHROMagar™ Orientation (ORIE, Graso) | |
Gram-negative rods (n = 62) | |||||||||
Enterobacteriaceae (n = 61) | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | |
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | ||
33 | 32 | 31 | 32 | 30 | 33 | 31 | 33 | ||
16 | 16 | 15 | 16 | 16 | 16 | 16 | 16 | ||
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | ||
2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | ||
6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | ||
1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | ||
Non-fermenting rods (n = 1) | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | |
Gram-positive cocci (n = 47) | |||||||||
Enterococci (n = 22) | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | |
20 | 20 | 0 | 18 | 20 | 18 | 19 | 20 | ||
1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | ||
Staphylococci (n = 21) | 9 | 9 | 0 | 8 | 6 | 8 | 8 | 9 | |
4 | 4 | 0 | 4 | 3 | 3 | 3 | 3 | ||
7 | 7 | 0 | 6 | 6 | 6 | 6 | 6 | ||
1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | ||
Streptococci (n = 4) | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | |
3 | 3 | 0 | 3 | 3 | 3 | 3 | 3 |
As regards the Gram-positive cocci group, four streptococcal isolates grew on all media used in this study, but various results were obtained for twelve isolates – four
Monoculture was recorded in 31 (52.5%) “positive” samples; two morphologically different bacterial isolates were cultured in 12 (20.3%) urine samples; three different strains were found in 7 (11.9%) samples, four – in 7 (11.9%) samples, whereas one cultured sample (1.7%) yielded five different microorganisms. An analysis of the number of samples containing mixed bacterial population showed that all five chromogenic media evaluated in this study allowed for pre-differentiation of pathogen types when compared to the reference method. A direct comparison of these chromogenic media showed minor discrepancies between them in detecting all microorganisms when mixed culture was observed (Table II).
Detection of bacteria in mono- and mixed urine culture on chromogenic media for UTI diagnosis.
Number of isolates in a clinical specimen | Number of clinical specimens (urine) | Number of all isolates in all clinical specimens | Total number of isolates (% of the number cultured on reference media) | ||||
---|---|---|---|---|---|---|---|
Chromogenic media | |||||||
ChromID CPS Elite (CPSE, bioMérieux) | BD CHROMagar Orientation Medium (ORI, Becton Dickinson) | Brillance UTI Clarity Agar (UTI C, Oxoid) | CHROMagarTM Orientation (BioMaxima) | CHROMagarTM Orientation (ORIE, Graso) | |||
1 | 31 | 31 | 30 (96.8%)† | 29 (93.6%)† | 31 (100%) | 30 (96.6%)† | 31 (100%) |
2 | 12 | 24 | 23 (95.8%)† | 22 (91.7%)†, ¶ | 22 (91.7%)§ | 23 (95.8%)¶ | 24 (100%) |
3 | 7 | 21 | 21 (100%) | 18 (85.7%)†, ‡, †† | 17 (81.0%)†, ‡, § | 19 (90.5%)† | 20 (95.3%)† |
4 | 7 | 28 | 25 (89.3%)†, ¶ | 25 (89.3%)†, ‡, ¶ | 27 (96.4%)† | 25 (89.3%)†, §, ¶ | 26 (92.6%)†, ‡ |
5 | 1 | 5 | 5 (100%) | 5 (100%) | 5 (100%) | 5 (100%) | 5 (100%) |
– no growth of
– no growth of
– no growth of
– no growth of Gram-negative rods cultured on sheep blood-enriched Columbia agar or MacConkey agar with a colony count of 102 CFU/ml (clinical specimens no. 3866, 80)
– no growth of Gram-negative rods cultured on sheep blood-enriched Columbia agar and MacConkey agar with a colony count of 103 CFU/ml (clinical specimen no. 4181)
Table III summarises the sensitivity, specificity, PPV and NPV of chromogenic media for UTI diagnostic with qualitative and semi-quantitative colony count (for all pathogens) and the sensitivity for
Sensitivity, specificity, positive (PPV) and negative predictive values (NPV) of chromogenic media for UTI diagnosis.
Parameters | Chromogenic media | |||||
---|---|---|---|---|---|---|
ChromID® CPS® Elite (CPSE, bioMérieux) | BD CHROMagar Orientation Medium (ORI, Becton Dickinson) | Brillance UTI Clarity Agar (UTI C, Oxoid) | CHROMagarTM Orientation (BioMaxima) | CHROMagarTM Orientation (ORIE, Graso) | Mean value | |
Qualitative cultures for all detected pathogens (p > 0.99) | ||||||
Sensitivity (%) | 94.7 | 91.7 | 89.6 | 94.4 | 97.2 | 93.5 |
Specificity (%) | 97.7 | 95.5 | 97.7 | 97.7 | 97.7 | 97.3 |
Positive predictive value (PPV) (%) | 98.9 | 98.0 | 98.4 | 99.0 | 99.1 | 98.7 |
Negative predictive value (NPV) (%) | 89.4 | 82.4 | 85.7 | 87.8 | 93.3 | 87.7 |
Qualitative cultures of | ||||||
Sensitivity (%) | 96.8 | 90.1 | 100 | 93.3 | 100 | 96.0 |
Semi-quantitative cultures for all detected pathogens (p = 0.9) | ||||||
Sensitivity (%) | 85.2 | 80.2 | 75.0 | 81.0 | 85.1 | 81.3 |
Specificity (%) | 85.7 | 82.4 | 91.3 | 82.7 | 82.4 | 84.9 |
Positive predictive value (PPV) (%) | 91.5 | 90.0 | 92.3 | 90.0 | 90.5 | 90.9 |
Negative predictive value (NPV) (%) | 76.4 | 67.7 | 72.4 | 69.4 | 73.7 | 71.9 |
Semi-quantitative cultures of | ||||||
Sensitivity (%) | 93.1 | 84.0 | 95.2 | 87.1 | 93.6 | 90.6 |
A detailed analysis of the semi-quantitative assay of different bacteria species on chromogenic media when compared to the BAC and MAC reference media demonstrated a tendency for decreased colony count on some media, yet the differences were not statistically significant. The count of
Microbiology laboratories always attempt to reduce the turnaround time and the cost of pathogens identification and their susceptibility testing (Strauss and Bourbeau, 2015). In recent years, chromogenic culture media have been widely used in clinical microbial diagnostic for detection and preliminary identification of pathogens and antimicrobial resistance mechanisms (Fillius
ASM recommends culturing urinary samples for colony count on blood agar media only. Other media can be used for semi-quantitative tests, after being evaluated for possible inhibition of bacteria growth. MAC and chromogenic media can limit the growth of bacteria but according to the reference values, the recovery usually amounts to no less than 30%, (Pasek, 1999; Sharp and Clark, 2009; Sharp
Due to the high number of urine culture specimens processed annually, laboratories are constantly seeking ways to improve their effectiveness. Automated instruments for dispensing the urine samples onto culture plates have been introduced. Due to the high prices of new technical solutions, they are only utilised in big laboratories that diagnose a large number of specimens. In small laboratories, the basic research methods and techniques in UTI diagnostics, such as urine culture and counting colonies are still used. Using chromogenic media appears to be a good alternative to conventional microbial diagnostic of UTI, yet, the user has to know the limitations of chromogenic media. The benefits of using chromogenic media in UTI diagnostics will most likely be seen in a non-hospital laboratory, because the most frequently isolated species from uncomplicated UTI infections is
In conclusion, all the chromogenic media tested in our study are attractive and easy-to-use screening media that considerably reduce the daily workload and the number of identification kits required.