International Journal of medicine & biomedical sciences

Vol.1 Issue.1

A Comparative Study on Ziehl-Neelsen Staining (Light Microscopy), Auramine O Staining (Iled- Fluorescent Microscopy) and Culture on LJ Media of Sputum Samples for the Diagnosis of Pulmonary Tuberculosis

Bivek Timalsina1*, Bidur Kutu1, Rusna Pradhan1, Bhagwan Maharjan2
1 Department of Medical Microbiology, Nobel College, Pokhara University, Nepal
2 Laboratory Technologist, GENETUP, Kalimati, Nepal

Tuberculosis is a particular infectious disease caused by Mycobacterium tuberculosis [1]. The disease primarily affects the lungs and cause pulmonary tuberculosis diagnosed with smear positive [4]. Over 80,000 people in Nepal have the disease. Nearly 20,000 people develop infectious sputum positive TB every year and about 45,000 new cases of all forms of TB occur in the same period. It is estimated that about 5,000-7,000 people die from TB, every year [5]. Therefore, proper and efficient early screening and diagnosis of cases, along with good treatment strategies are needed for successful TB control.

The highly accurate diagnosis of pulmonary tuberculosis in developing countries relied mostly on light microscopy with ZN staining in most of the laboratory settings, and in very few settings with Fluorescent microscopy and culture method of sputum sample [5-6]. Though culture is regarded as gold standard highly sensitive method for diagnosis allowing susceptibility testing of the isolates, poor availability of culturing facilities, the long time span (6-9 weeks) required and chances of contamination make it difficult to follow [3]. Studies have shown that the rapid diagnosis with smear microscopy is highly specific in areas of high TB prevalence. The speed, feasibility and cost effectiveness of microscopy aided with high sensitivity make it valuable tool for TB diagnosis, but for this technique the yield requirement is between 5,000 to 10,000 organisms per ml sample [7-8]. The use of fluorescent microscopy enhances the visualization by providing contrast coloration to the bacilli present in the sample [9]. There are also other methods like ELISA, Mycodot, X-ray, which are not confirmatory tests, and similarly, the advanced techniques like BACTEC, gene probe, PCR, gas liquid chromatography are costly and only available in very few laboratories and lack in specificity [10-11].

Therefore, this study only focuses on the comparison of the commonly used diagnostic methods in developing countries such as microscopy, and culture, which is very useful to give idea about the effectiveness of diagnosis.

 

METHODOLOGY

The prospective case-control study was conducted in the Nepal Anti-Tuberculosis Association (NATA), GENETUP lab, Kalimati, Kathmandu from July 2010 to October 2010, on sputum samples from patient visiting at the GENETUP lab with suspected pulmonary tuberculosis cases without treatment and follow-up cases after DOTS and MDR treatment. A total of 299 sputum samples (170 from 78 suspected cases, 42 from 22 follow-up cases with DOTS treatment and 87 from Follow-up cases with MDR) were collected aseptically.

Sample Collection and Transportation

Individual were advised to rinse mouth with water, cough forcibly, and collect sputum in mouth and spit carefully and aseptically in to a sterile, wide mouth, unbreakable container. The lid was tightened properly and the container was transported to the lab immediately. Three sputum specimens were collected i.e. one spot, one early morning and one another spot when patient returns next day for suspected out-patients visiting GENETUP. For in patients of GENETUP, two early morning samples were collected. Similarly, one early morning sputum sample was collected for MDR patients and maximum two samples were collected for follow-up patients visiting GENETUP. The samples were transported in the tray for processing within the day of collection. Early morning sputum samples, collected at patient’s home, were transported by patients or their relatives to the laboratory. Samples from remote areas were transported through shipping in multilayered plastic packs. The minimum amount of sputum sample was 2 ml, the optimum being 5 ml. At the time of sample collection, data was collected with written consent from individuals taking part in this study.

Sample inclusion and exclusion criteria

Suspected pulmonary tuberculosis individuals, follow-up patients with DOTS treatment and MDR treatment referred from hospitals were taken for sampling. Those, with leakage sample and less than 2 ml of mucopurulent sputum sample were excluded.

Sample processing and smear preparation

The processing of sample was carried out in a biosafety cabinet (BSL-2) and subjected to two direct smear preparations from each sample with the help of sterile wooden stick in clean, dry, thin (1mm) glass slides free from scratches; as scratches may retain flurochrome and appear as fluorescent artifacts. The smear was air dried and fixed by flaming. The remaining sample was further processed with NALC-NaOH method for culture preparation on modified Lowenstein-Jensen media.

Staining and microscopic examination

From each sample, Ziehl-Neelsen staining and Auramine O staining was done on two prepared smear slides from each sample. Both slides were blinded by the reader and were read by two independent readers. For the ZN staining, solutions were prepared and staining was done as per the technique described in standard operative procedure [5]. Acid Fast Bacilli (AFB) was demonstrated by oil immersion lens using 1000x magnification in light microscopy. The AFB appeared as red rods against blue background (Fig. 1).

 

 

 

Fig. 1: (A) ZN stained sputum showing red TB bacilli in blue background as 1000x. (B) AO fluorescence stained sputum showing yellow luminous TB bacilli in green background as 400x.

 

For the Fluorescent AO staining, solutions were prepared and staining was done as per the technique recommended by WHO [1,7]. The fluorescence microscope used is the iLED Primostar Zeiss with an attached illuminator manufactured by Karl Zeiss and is fitted in a dark room. The film is examined at 400x magnification. The tubercle bacilli are seen as yellow luminous slight curved rods in a green background (Fig 1) which was further cross examined by another examiner. Artifacts are distinguished from bacilli by their hazy yellow or grey coloration lacking reddish tinge and were poorly delineated [3].

Smear reporting

Evaluation of smear was done by standardized procedure of scanning by grid pattern, proposed by National Tuberculosis Institute, with following reporting standards criteria proposed by IUATLD/WHO [8]. In this study, 2+, and 3+ were classified as multibacillary and scanty, and 1+ as paucibacillary.

Table 1: ZN and Fluorescence smear reporting according to IUATLD/WHO

IUATLD/WHO scale

(1000x field = HPF)

 

Result

Microscopy system used

Bright-field

(1000x magnification:

1 length = 2 cm = 100 HPF)

Fluorescence

(200–250x magnification:

1 length = 30 fields =

300 HPF)

Fluorescence

(400x magnification:

1 length = 40 fields =

200 HPF)

No AFB seen

Zero AFB / 1 length

Zero AFB / 1 length

Zero AFB / 1 length

Scanty

1–9 AFB / 1 length

or 100 HPF

1–29 AFB / 1 length

1–19 AFB / 1 length

1+

10–99 AFB / 1 length or 100 HPF

30–299 AFB / 1 length

20–199 AFB / 1length

2+

1–10 AFB / 1 HPF on average

10–100 AFB / 1 field on average

5–50 AFB / 1 field on average

3+

>10 AFB / 1 HPF on average

>100 AFB / 1 field on average

>50 AFB / 1 field on average

 

Culture

Modified Lowenstein-Jensen media were prepared in-house. After processing of sputum sample by NALC-NaOH method, 0.5 ml of sediment was inoculated on the surface of LJ media, using sterile dropper and spread over the surface. The tubes were incubated at 37°C and left in slanted position for a week to allow even distribution of the inoculums over the entire surface of the medium. The caps were tightened and tubes were placed upright and continued incubation for eight weeks. The tubes were examined once a week for eight weeks. Rough, tough and non-pigmented buff colonies with raised, nodular or wrinkled surface and irregular thin margin (Fig 2) indicated the growth of Mycobacterium spp. Rapid growers were excluded for further study, as Mycobacterium tuberculosis is slow grower. The reporting of culture was done according to the bacteriological index (Table 2).

Fig. 2: Growth of Acid Fast Bacilli in LJ Culture media with 3+, 2+, 1+, and no growth.

 

 

Table 2: Culture reporting according to the IUATLD/WHO.

 

Culture Reading

Report

No growth

Negative

1-19 colonies

Scanty (Record exact number of colonies)

20-100 colonies

1+

Innumerable discrete colonies

2+

Confluent growth

3+

Contaminated growth

C

 

 

Quality control

Mycobacterium fortuitum was inoculated in modified LJ media in two tubes and incubated for 48 hours. Normally it should show growth after 48 hours. If there is no growth after 48 hours, the media should not be used for culture. The sterility of media was also checked after incubation of 48 hours and any contaminated tubes must be removed from the media box.

 

Data entry and statistical analysis

All reports from sputum examination request form were taken into Microsoft Office Excel Worksheet, 2010 version for Windows and test accuracy results were calculated as sensitivity, and specificity using mycobacterium culture as a reference standard. Test characteristic were compared using the Chi-square test with p-values

 

RESULTS

Table 3 shows that, out of total 299 sputum samples of pulmonary tuberculosis, including general suspected cases and with follow-up cases having treatment, 19.06%, 29.1% and 24.41% were found pulmonary tuberculosis positive by ZN, AO and culture respectively. In respective category of cases, the case detection rates for general suspected patients without treatment were 20%, 25.88% & 28.24%; for follow up patients of DOTS treatment were 30.95%, 57.14% & 19.05%; and for MDR follow-up patients were 11.49%, 21.84% & 19.54% for ZN, AO and culture respectively. The rate of case detection is significantly higher with culture in case of general suspected cases without treatment followed by AO and ZN. But the follow-up cases showed decrease in case of detection rate by cultural methods and in these, AO staining proved to be more sensitive than the other two. The difference in their case detection rates was statistically significant (p < 0.01).

 

Table 3: Comparison of ZN microscopy and Fluorescent microscopy with Culture

 

 

Culture

 

 

Positive

Negative

Contaminated

 

 

A+B+C

A+B+C

A+B+C

Total

 

Positive

31+6+7 = 44

1+1+1 = 3

2+6+2 = 10

57

ZN

Microscopy

Negative

17+2+10 = 29

108+23+67 = 198

11+4+0 = 15

242

 

Total

48+8+17 = 73

109+24+70 = 201

13+10+2 = 25

299

 

Positive

38+8+15 = 61

3+7+2 = 12

3+9+2 = 14

87

Fluorescent

Microscopy

Negative

10+0+2 = 12

106+17+66 = 189

10+1+0 = 11

212

 

Total

48+8+17 = 73

109+24+70 = 201

13+10+2 = 25

299

 

 

A = Group I = 170 (General suspected cases without treatment)

B = Group II = 42 (DOTS Follow-up patients)

C= Group III = 87 (MDR Follow-up patients)

 

 

 

 

 

 

 

Out of total 299 samples, 73 (48+8+17) were culture positive and 25 were contaminated culture. Removing contaminated culture samples and taking culture as gold standard, the sensitivity and specificity of direct microscopic examination were found to be 60.03% and 98.51% for ZN method; and 83.56% and 94.53% for Fluorescent AO method respectively. The percentage of false negative by AO staining was only 16.44%, which was in sharp contrast to that of ZN (39.73%)

The sensitivity and specificity, false positive and false negative of ZN and AO, in respective types of cases are depicted in Figure 3.

The comparison between ZN and AO methods with respect to culture and their types of cases (Figure 4) points out that the sensitivity was the highest in case of follow-up patients with DOTS treatment, in both ZN and AO, but there was decrease in specificity and increase in false positivity in AO, in the same. The false negativity was highest with ZN microscopy in MDR cases.

 

 

Table 4: Comparison between ZN and Fluorescent AO microscopy in total cases.

 

 

 

Fluorescent Microscopy

 

 

Positive

Negative

Total

ZN Microscopy

Positive

57

0

57

Negative

30

212

242

total

87

212

299

 

The grade wise reporting with standard IUATLD/WHO pointed out that the ZN stained smears were able to detect 35 (31+4) multibacillary and 22 (5+17) paucibacillary cases whereas the AO stained smears were able to detect 36 (29+7) multibacillary and 49 (2+47) paucibacillary cases. More number of paucibacillary cases was detected by AO stained fluorescent microscopy, in which the ZN was not sensitive enough as shown in the Table 5.

 

 

 

 

 

Table 5: Grade-wise correlation of Ziehl-Neelsen and Fluorescent staining techniques (NS = No AFB seen; S = Scanty; PB = Paucibacillary; MB = Multibacillary)

Ziehl-Neelsen Microscopy

Fluorescent Microscopy

Total

Grading

NS

S

1+

2+

3+

 

NS

212

2

25

3

0

242

S

0

0

5

0

0

5

1+

0

0

15

2

0

17

2+

0

0

3

25

3

31

3+

0

0

0

1

3

4

Total

212

2

47

29

7

299

 

DISCUSSION

Early diagnosis of tuberculosis with aided sensitivity and reliability is very much important for reducing transmission, morbidity and mortality, especially in developing countries where resources lack in advanced methods of diagnosis. Because the clinical signs and symptoms of pulmonary tuberculosis are not specific, the fundamental principal for the diagnosis of tuberculosis is the accurate demonstration of M. tuberculosis in a suitable specimen from the suspected cases. The detection of smear positive cases is the highest priority in any TB control program, as these cases are infectious and contribute to transmission of disease. Therefore, the comparisons among the currently used methods in diagnosis are looked for in this study.

Smear microscopy using the conventional ZN stain and the recent AO stain are highly specific, rapid and cheapest method, used for the early diagnosis of Mycobacterium tuberculosis. Though the culture method requires longer time, it is regarded as gold standard for diagnosis and useful for Drug Susceptibility Test (DST). ZN stain can detect bacilli when they are in the order of 105/ml of the sputum, whereas a more sensitive AO stain can detect in the order of 104/ml of sputum (Forbes BA, Bailey and Scott). Several studies by various authors have been shown the different case detection rate as with Jain et.al. ZN 32.7%, AO 41.6%, Githui et. al ZN 65%, AO 80%, Laifangbam et. al. ZN 44.1%, AO 71.6%, culture 70%, Prasanthi et. al. ZN 50%, AO 69% [9,11-13] In most of the study, the case detection rates were higher with AO staining than ZN staining as was the case in this study, where 19.06%, 29.1% and 24.41% were found pulmonary tuberculosis positive by ZN, AO and culture respectively. The difference in the case detection rates was found to be statistically significant, with better method of microscopy by AO method than ZN method (p < 0.01). In respective category of cases, the case detection rates for general suspected patients with no treatment were 20%, 25.88%, and 28.24%; for follow up patients of DOTS treatment were 30.95%, 57.14% and 19.05%; and for MDR follow-up patients were 11.49%, 21.84% and 19.54% for ZN, AO and culture respectively. This showed the decrease in culture detection in case of follow up cases with treatment, where AO is most effective approach.

The range of sensitivity and specificity of ZN staining reported by various authors have been found in between 61% to 86.4% ; and 96.2% to 100% respectively ; whereas the same with AO staining (fluorescent microscopy) reports were 59.7% to 83% ; and 85.5% to 99% respectively [9,12-16]. Taking culture as gold standard and removing culture contaminated cases, the overall sensitivity and specificity in the present study in all cases were found to be 60.03 % and 98.51% for ZN method; and 83.56% and 94.53% for fluorescent AO method respectively. The sensitivity of AO method is significantly much higher than that of ZN method. The specificity of AO method (94.53%) was quite lower than that of ZN method (98.51%). In the present study, the percentage of false negative by AO staining was only 16.44 %, whereas the ZN method showed marked high false negative, 37.73% as also noted by Jain A et. al. that around 40-50% of active pulmonary TB (culture positive) cannot be detected by ZN microscopy [12]. No AO negative result with ZN positive samples was found, which makes the use of only AO staining fluorescent microscopy method is reliable microscopic method for diagnosis. There are also 25 culture contaminated samples thus the sensitivity of these microscopic techniques lies in only those with culture positive and negative samples.

In a study conducted by Kumar et. al., 85% of culture positive cases could be diagnosed by microscopy alone. In this study, the diagnosis by ZN light microscopy alone was achieved in 60.03% (44/73) of the culture positive cases which is remarkably increased with AO fluorescent microscopy alone, 83.56% (61/73) of the culture positive cases. All cases of ZN positive were found to be positive by AO fluorescent method. Hence, it is apparent that the number of cases missed by ZN stain is higher which can be detected by AO fluorescent method.

 

CONCLUSION

The most commonly and routinely used method of diagnosis of pulmonary tuberculosis is the sputum examination by microscopy and culture method. The cost effectiveness and easy to perform with limited resources made these methods most prominently approached in resource poor countries, where the detection by molecular techniques are very limited and not usually done. In microscopy, there are conventional light microscopy (ZN staining) and fluorescent microscopy (AO staining). These two methods differ with each other in several aspects such as efficacy, cost of processing and instrumentation. Similarly, the culture method is prerequisite for standard diagnosis and testing of drug.

The study clearly indicated that the case detection rate (efficacy) of fluorescent microscopy (AO stain) is remarkably higher than that of ZN (light microscopy) ,with aided advantages of less eye strain, easy visualization, less time consuming and even detection of low number of bacteria (paucibacillary cases) in comparison to ZN method. As the screening was done under lower power magnification (400x) i.e. larger area per field than ZN method (1000x), less time is consumed for examination of same area by AO method. Taking culture as gold standard, there is high agreement between AO staining and culture than that of ZN staining and culture. The use of AO staining alone could be reliable microscopic method as there were no cases of ZN positive where AO was negative. But ZN staining alone missed most of the positive pulmonary cases with respect to AO and culture. In case of Fluorescent microscopy, though the capital cost is higher for expensive instrumentation, the overall cost with large number of sample processing by limited manpower makes it no difference in cost. Thus, it has been recommended as very effective method of choice in high risk areas, where a large number of sputum samples are to be examined.

Similarly, culture examination is very efficient, most reliable and gold standard technique, which is the pre-requisite for determining strength of bacteria to antibiotics and differentiating from other non-pathogenic mycobacterium by growth rate and biochemical test. But the requirement of longer time duration (6-8 weeks), high cost, well trained manpower and chances of contamination are making it difficult to implement, in developing countries. Thus culture along with fluorescent microscopy should be method of diagnosis of pulmonary tuberculosis.

Hence, the correct diagnosis of pulmonary tuberculosis requires combination of AO (fluorescent microscopy), culture and biochemical analysis.

 

COMPETING INTERESTS

We declare that we don’t have competing of interest.

 

AUTHORS’ CONTRIBUTIONS

BT, BK, RP performed the sample collection, laboratory experiments and data recording. BM supervised and guided in the research. BT performed statistical analysis, conceived part of this study and prepared the manuscript. All authors read and approved the final manuscript.

 

Ethical Consideration

This study was approved by Institutional Review Committee of Nobel College, Sinamangal and GENETUP, Kalimati. Informed verbal agreement was taken from Patients.

 

ACKNOWLEDGEMENTS

We would like to thank German Nepal Tuberculosis Project (GENETUP), Kathmandu, Nepal and Nobel College, Kathmandu for the research platform.

 

REFERENCES

1. World Health Organization. Guidance on couples HIV testing and counselling including antiretroviral therapy for treatment and prevention in serodiscordant couples: recommendations for a public health approach. Online available at: http://apps.who.int/iris/handle/10665/44646

2. Tuberculosis Control SAARC Region Update, 2013 [Internet]. Available from: http://saarctb.org/attachments/article/23/TB update 2013.pdf

3. Bhatt CP, Timalsina B, Kutu B, Pradhan R, Maharjan B, Shrestha B. A Comparision of Laboratory Diagnostic Methods of Tuberculosis and Aetiology of Suspected Cases of Pulmonary Tuberculosis. SAARC Journal of Tuberculosis, Lung Diseases and HIV/AIDS. 2015 Apr 11; 11(2):1-6.

4.World Health Organization. World Health Organization global tuberculosis report. Online availanle at: http://www.who.int/tb/publications/global_report/ gtbr12_main.pdf

5. National Tuberculosis Center. National Tuberculosis Programme, a Clinical Manual for Nepal. 2009 ;( Third edition). Available from: http://nepalntp.gov.np/theme/images/uploads/137 3874048linical_Manual.pdf

6. World Health Organization. Definitions and reporting framework for tuberculosis–2013 revision. Online available at: http://apps.who.int/iris/handle/10665/79199

7. Parsons LM, Somoskövi Á, Gutierrez C, Lee E, Paramasivan CN, Abimiku AL, Spector S, Roscigno G, Nkengasong J. Laboratory diagnosis of tuberculosis in resource-poor countries: challenges and opportunities. Clinical microbiology reviews. 2011 Apr 1; 24(2):314-50.

8. Laszlo A. Sputum examination for tuberculosis by direct microscopy in low income countries. IUATLD Technical Guide. International Union against Tuberculosis and Lung Disease, Paris, France. 2000.

 

9. Gupta S, Shenoy VP, Bairy I, Muralidharan S. Diagnostic efficacy of Ziehl-Neelsen method against fluorescent microscopy in detection of acid fast bacilli. Asian Pacific Journal of Tropical Medicine. 2010 Apr 30; 3(4):328-9.

10. Kulkarni S, Singh P, Memon A, Nataraj G, Kanade S, Kelkar R, Rajan MG. An in-house multiplex PCR test for the detection of Mycobacterium tuberculosis, its validation & comparison with a single target TB-PCR kit. The Indian journal of medical research. 2012 May; 135(5):788.

11. Kivihya-Ndugga LE, Van Cleeff MR, Githui WA, Nganga LW, Kibuga DK, Odhiambo JA, Klatser PR. A comprehensive comparison of Ziehl-Neelsen and fluorescence microscopy for the diagnosis of tuberculosis in a resource-poor urban setting. The International Journal of Tuberculosis and Lung Disease. 2003 Dec 1; 7(12):1163-71.

12. Jain A, Bhargava A, Agarwal SK. A comparative study of two commonly used staining techniques for acid fast bacilli in clinical specimens. Indian Journal of Tuberculosis. 2002; 49(3):161-2.

13. Laifangbam S, Singh HL, Singh NB, Devi KM, Singh NT. A comparative study of fluorescent microscopy with Ziehl-Neelsen staining and culture for the diagnosis of pulmonary tuberculosis. Kathmandu University Medical Journal. 2009; 7(3):226-30.

14. Kivihya-Ndugga LE, Van Cleeff MR, Githui WA, Nganga LW, Kibuga DK, Odhiambo JA, Klatser PR. A comprehensive comparison of Ziehl-Neelsen and fluorescence microscopy for the diagnosis of tuberculosis in a resource-poor urban setting. The International Journal of Tuberculosis and Lung Disease. 2003 Dec 1; 7(12):1163-71.

15. Ulukanligil M, Aslan G, Tasçi S. A comparative study on the different staining methods and number of specimens for the detection of acid fast bacilli. Memorias do Instituto Oswaldo Cruz. 2000 Dec; 95(6):855-8.

16. Kondraske GV. A working model for human system-task interfaces. The biomedical engineering handbook. 1995; 2:147.

17. Holani AG, Ganvir SM, Shah NN, Bansode SC, Shende I, Jawade R, Bijjargi SC. Demonstration of Mycobacterium Tuberculosis in Sputum and Saliva Smears of Tuberculosis Patients Using Ziehl Neelsen and Flurochrome Staining-A Comparative Study. Journal of clinical and diagnostic research: JCDR. 2014 Jul; 8(7):ZC42.

 


IMPACT FACTOR

IndianScience IndianScience

SIF : 0.74

IF : 0.432

openaccess

CURRENT ISSUES