A POCT to Rapid Detect GBS with Highly Sensitivity

Yang Chen

1,2,3

, Zhi-Rui Xie

1,2,3

and Yao-Gen Shu

1,2,3

Wenzhou Institute, University of Chinese Academy of Sciences, Wenzhou, Zhejiang 325000, P.R. China

Oujiang Laboratory (Zhejiang Lab for Regenerative Medicine, Vision and Brain Health),

Wenzhou, Zhejiang 325024, China

Research Center of Quantitative Detection Technology, NMPA Key Laboratory for Quality Monitoring

and Evaluation of Vaccines and Biological Products, Wenzhou, Zhejiang 325024, China

Keywords:

POCT, GBS, Spectral Absorption, Chromogenic Culture Media.

Abstract:

Group B streptococcus (GBS) i s a leading cause of invasive neonatal infections and a signiﬁcant pathogen

in immunocompromised adults. Screening of GB S colonization in pregnant women determines the need for

antibiotic prophylaxis in that pregnancy. Therefore, efﬁcient and rapid determination of the GBS colonization

status of pregnant women is crucial. Here, we set up a PO CT with speciﬁc spectral absorption of chromogenic

culture media to replace the traditional visual identity of GBS, which greatly improved the sensitivity of GBS

detection, and decreased the time to identify it.

1 INTRODUCTION

Group B streptococcus (GBS) is a Gram-positive en-

capsulated bacterium that belongs to the group of pyo-

genic streptococci, and an asymptomatic colonizer of

the digestive and genitourina ry tracts of healthy hu-

man adu lts. However, it can cause severe invasive in-

fections in neonates and immunocompro mised adult

patients. In 1960 s, GBS was identiﬁed into a lead-

ing cause of life-threatening neonatal infections(Hood

et al., 1961; Rosa-Fraile and Spellerberg, 2017).

In neonatology, there are two distinguish a ble clin-

ical syndromes: one is c a lled as early-onset disease

(EOD), in which GBS in fection oc curs within the ﬁrst

week of life (especially within the ﬁr st 24 h); a n-

other is called as late-onset disease (LOD), in which

GBS infection presents after 7 to 90 days postpartum.

EOD is caused by vertical transmission through either

ascending infection from the genital tract or during

labor and birth. Numerous studies have shown that

up to 30% of pregn ant women worldwide are colo-

nized with GBS, and vertica l transmission occurs for

roughly 50% of colonized m others. About 1% of col-

onized newborns develop EOD, which may be in con-

nection with rup tured mem branes because the infec-

tion of the fetus can happen only it exp osed in GBS.

Bacteremia without a focus is the most c ommon clin-

ical syndrome, followed by pneumonia and meningi-

tis. Even today th e case fatality rate for EOD is es-

timated to be 2 to 10%, and fatal outco mes are more

frequent amon g prematur e neonates(Edwards et al.,

2016).

Most EOD is due to the contact of the neonate

with GBS during delivery, therefore , intrapartum an-

tibiotic prophy la xis (IAP) administere d to GBS carri-

ers prevents vertical transmission in the vast majority

of cases, and its widespread use has resulted in sig-

niﬁcant reductions in the incidence of EOD. LOD,

however, is most likely acquired fr om breast milk,

or from nosocomial or community sources. Prema-

turity is the m ain risk factor for developing LOD, and

bacteremia without a focus of infection is the most

common presentation. The mortality rate for LOD

is lower, but meningitis and subsequent sequelae are

more frequently associate d with LOD(Verani et al.,

2010).

GBS also causes signiﬁcant maternal morbid ity,

including endometritis, chorioamnionitis, bacteremia,

and postpartum wound infections. GBS urinar y tract

infections are associate d with miscarriages, preterm

births, and low-birth-weight newborns. Although

GBS seldom causes disease in healthy adults, it is re-

sponsible for seriou s infections in diabetics, e lderly

individuals, reside nts in nursing ho mes, and other-

wise immunocompr omised patients. The successful

administration of IAP and the treatment of severe

GBS infections r e ly on efﬁcient and reliable detec-

tion of GBS in clinical samples(Edwards and Baker,

2005).

Chen, Y., Xie, Z. and Shu, Y.

A POCT to Rapid Detect GBS with Highly Sensitivity.

DOI: 10.5220/0012287600003657

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 17th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2024) - Volume 1, pages 91-94

ISBN: 978-989-758-688-0; ISSN: 2184-4305

In recent years, there has been rapid expansion

in the availability of chromogenic media for the de-

tection of GBS. Th ese culture media contain enzyme

substrates linked to ind oxyl chromogens, and the tar-

get microorganisms are characterized by speciﬁc en-

zyme systems that metabolize the substrate, result-

ing in release of the chromogen. Su bsequently, the

indigoid dye formed up on oxidation and dimeriza-

tion of indoxyl mo lecules in the p resence of oxy-

gen precipitates within the colonies, leading to typ-

ical brightly contrasting colors(Oren ga et al., 200 9).

Therefore, the amplitude of the contrasting is p osi-

tively to concentration of GBS. However, the tradi-

tional visual identity usua lly need at least 72 h to

determine whether the GBS colonize, thus, a rapid

highly sensitive detection of GBS is urgent.

2 MATERIALS AND METHODS

2.1 A POCT Based on the Speciﬁc

Spectral Absorption of Chromogen

We developed a POCT ( a point-o f-care testing(Shu

and Chen, 2022)) based o n chromogenic media to

rapid detect GBS, which meet the c linical nee ds with

highly sensitivity and rapid detection.

Figure 1 shows the mechanism of detection of the

POCT device. A parallel excitation light with a wave-

length of λ

is ﬁltrate from ﬁlter 1, and then inci-

dent to the sample by perpendicular to the bottom of

tube. As a result, the irradiated sample emits another

light (λ

), which is the so-called emission light, how-

ever, partial λ

light will be absorbed by indoxyl chro-

mogen, and the rest emission light will b e ﬁnally de-

tected by PMT through ﬁlter 2. The absolute detected

value of time progress is directly displayed in Fig.2.

The absorbed amount of light λ

is proportional

to the concentration of indoxy l chromogen, while the

latter is also proportional to the concentration of GBS.

Thus, the measurable absorbed amount of light λ

indirectly proportio nal to the concentration of GBS,

that is, the concentratio n of GBS (c) can be quan tita-

tively measured by the absorbed a mount of lig ht λ

− Q

) as deﬁned in Eq.(1).

2.2 Preparation of Samples and

Measuring

Two tubes of culture media with 1.2 mL were sup-

plied by Wenzhou Beikete Medical Equipment Co.,

Ltd. One contains indoxyl chromogens with higher

concentr ation and is labeled “5”, a nother is without

Figure 1: a: The mechanism of the POCT. LED is t he

source of excited l ight. A parallel excitation light with a

wavelength of λ

is ﬁltrate from ﬁlter 1, and then incident to

the sample by perpendicular to the bottom of tube. As a re-

sult, the i rradiated sample emits another light (λ

), which is

the so-called emission light, however, partial λ

light will be

absorbed by indoxyl chromogen, and the rest emission light

will be ﬁnally detected by PMT through ﬁlter 2. The abso-

lute value of time progress is directly displayed in Fig.2. b:

The sample of POCT i n experiment.

any chromogens and labeled “0”. Fig.2 shows the

samples of chromoge nic media with different concen-

tration of the mixture of chromogens and correspond-

ing measured absolute light intensity, which is pre-

pared and measured simultaneously as follows:

Firstly, We measured the value of the emission

light from tube “0”, and the platform “0” (the ﬁrst

higher platform from right) in Fig.2 is its time pro -

cess;

Secondly, a 5 µL samples of “5” is injected in tube

“0”, the new sample is labeled “1”, an d the measured

value is shown in platfor m “1” (the second higher

platform from right) in Fig.2;

Thirdly, Another 5 µL samples of “5” is injected

in tube “1”, the new sample is labeled “2”, and the

measured value is shown in platform “2” (the third

higher platform from right) in Fig.2;

Fourthly, A 10 µL samples of “5” is injected in

tube “2”, the new sample is labeled “3”, and the

BIODEVICES 2024 - 17th International Conference on Biomedical Electronics and Devices

measured value is shown in platform “3” (the fourth

higher platform from right) in Fig.2;

Fifthly, A 20 µL samples of “5” is injecte d in tu be

“3”, the new sample is labeled “4”, an d the measured

value is shown in platform “4” (the ﬁfth higher plat-

form from right) in Fig.2;

Finally, We measured the value o f the emission

light from tube “5”, and the platform “5” (the sixth

higher platform from right) in Fig.2 is its time pro-

cess;

The no rmalized concentrations of chromogens

of sample “0∼5”(with respect to that of the sam-

ple “5”), c, approximate to 0, 4.15 × 10

−3

, 8.26 ×

−3

, 1.64 × 10

−2

, 3.23 × 10

−2

, and 1.00 respec-

tively.

relative absorptive amplitude(ρ)

The normalized concentrations (c)

ρ=ac, R≈1.0

Figure 2: a: The measured absolute light intensity of sam-

ples by our POCT vs time. Each higher platform from right

to left corresponds to the value of sample 0,1,2,3,4 and 5

(The inserted panel) respectively, w hil e the lower platform

is the background value, so that the absolute light intensity

is t he higher one minus the lower one. The relative absorp-

tive amplitude of sample i, ρ

, can be deﬁned by Eq.(1),

and shown in bottom. b: The relat ive absorptive amplitude

(ρ) vs normalized concentrations of samples (c), which is

almost linear (ρ = ac, where a(= 3.75) is the ﬁtted con-

stant) at lower concentrations with regression coefﬁcient(R)

of 1.0. The inserted panel displays that the ρ

/ρ

is nearly

, which means our POCT is very much more sensitive

than the traditional visual one.

3 RESULTS

The absolute intensity of the measur ed emission light

) equals the value of higher platform minus the

backgr ound noise ( c orresponds th e value of lower

platform). Thus, the absorptive amp litude o f sample

is Q

− Q

, where Q

is supposed the value that there

is not any indoxyl chromogens in chr omogenic media

such as sample “0”.

The relative absorptive amplitude of sample “i”,

, c an be deﬁned by

≡ 1 −

, (1)

and shown in Fig.2. The relation between the rela-

tive absorptive amplitude (ρ) and the normalized con-

centrations of samples (c) is almo st linear (ρ = ac,

where a(= 3.75 ) is the ﬁtted constant) at lower con-

centrations with regression coefﬁcient(R) of 1.0. The

value of samples “ 1” ∼ “4” is obviously higher than

“ρ

(≡ 0)”, which mea ns that the sensitivity of our

method is much higher than th at of the traditional vi-

sual one as shown in Fig.2. The enormo us qua ntita-

tive difference b etween samples “1” and “5” further-

more displays the advance of the POCT. It is possible

for c hromo genic media to greatly decrease identiﬁca-

tion time if our POCT is loa ded.

4 CONCLUSIONS AND

DISCUSSION

The sensitivity of screening methods b ased on the cul-

ture identiﬁcation of maternal carriage of GBS de-

pends on the timing of specimen collection, the source

of the specimen, a nd the culture technique used by the

microbiology laboratory. The chromogenic media is

a good alternative for the identiﬁcation of GBS carrier

status among near-term pregnant women. Decreasing

identiﬁcation time of GBS as well as improving sen-

sitivity is our motivation to develop the POCT.

It is very difﬁculty for the traditional visual iden-

tity to de te rmine whether GBS colonized in samples 1

∼ 4 as shown in Fig.2. However, our POCT achieves

a rap id dete c tion of GBS, and reinforced the advance

of chromogenic media. Each platform of time course

displays difference in altitude in Fig.2, which means

our POCT is more sensitive tha n the traditional visual

one.

It has to be pointed that a quantitative measure-

ment of the number of GBS in sample “5 ” should

be done, so that the relation between ρ and number

of GBS can be determined, because it is important

for clinical trial to decid e the “threshold” of posi-

tive/negitive.

A POCT to Rapid Detect GBS with Highly Sensitivity

ACKNOWLEDGEMENTS

The authors thank Wenzhou Beikete Medical Equip-

ment Co., Ltd. for their supplying of samples and

chromogenic me dia, and the ﬁnancial supports by

Wenzhou Institute of UCAS (WIUCASQD2020009

and WIUCASICTP2022), the Discipline Cluster

for Oncology of Wenzhou Medical University (z1-

2023005), and Oujiang Laboratory (Zhejiang Lab

for Regenerative Medicine, Vision and Brain Health)

(OJQDJQ2022001).

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