As a pivotal pathogen of global concern, carbapenem-resistant Acinetobacter baumannii (CRAB) is intrinsically linked with severe, sometimes fatal, infections, prompting wide-ranging epidemiological research (Li et al., 2020; Cavallo et al., 2023; Diep et al., 2023). Efforts to understand and track the epidemiology of AB have employed a variety of genotyping methods, revealing the pathogen’s sophisticated population dynamics. This includes exploring virulence traits such as capsular polysaccharide (KL) and the lipooligosaccharide outer core (OCL), which are substantively connected to AB’s pathogenic properties (Deng et al., 2020; Li et al., 2020; Diep et al., 2023). The technological progress in whole-genome sequencing (WGS) has enriched genotyping capabilities, enabling more nuanced analysis through core genome multilocus sequence typing (cgMLST) or single nucleotide typing (SNP) for detailed typing and evolutionary studies.

An evident manifestation of CRAB’s genetic plasticity is its co-evolution toward both high virulence and drug resistance. One stark example is the KL49 AB type, similar in capsular polysaccharide type to the hypervirulent strain LAC-4 (Zhou et al., 2018; Deng et al., 2020), which has been implicated in several death-related outbreaks across continents (Valentine et al., 2008; Jones et al., 2015; Deng et al., 2020). Carbapenem-resistant hypervirulent AB (CR-hvAB) isolates with KL49 can cause fatal outcomes not only in immunodeficiency, but also in immunocompetent patients (Jones et al., 2015; Li et al., 2020). Moreover, as AB isolates, which can asymptomatically colonize various anatomical niches (Marchaim et al., 2007; Nutman et al., 2016), participate in co-infections in specific habitats, they likely engage in intraspecific competition, leveraging mechanisms such as the Type VI secretion system (T6SS) to deploy toxic effectors for direct killing of competitors (Hadjadj et al., 2018; Zhang et al., 2023).

Pregnant women who undergo physiological immunological changes, present a notable risk group for acquiring or reactivating infections (Hazenberg et al., 2021; Osei Sekyere et al., 2021), and who are carriers of AB are not only more predisposed to associated infections at an uncertain time during pregnancy, intrapartum or postpartum period, but also have a risk of maternal carriers transferring the AB to their newborns (Sood et al., 2019; Osei Sekyere et al., 2021). AB as a cause of pneumonia, urinary tract infections, and sepsis (Cavallo et al., 2023), has manifested among pregnant women and newborns in numerous countries (Sood et al., 2019; Osei Sekyere et al., 2021; Ghanchi et al., 2023; Odoyo et al., 2023; Woon et al., 2023), inciting adverse outcomes including spontaneous abortion, premature labor, and perinatal deaths (Aivazova et al., 2010; He et al., 2013; Osei Sekyere et al., 2021). Although the World Health Organization (WHO) estimates that puerperal sepsis accounts for 10.68% of maternal deaths, antepartum screening for AB remains scant, with prevailing data often emerging from retrospective studies and postpartum examinations (Say et al., 2014; Bebell et al., 2017; Osei Sekyere et al., 2021; Sousa et al., 2023).

Since the early 1970s, various reports have repeatedly emphasized the role of asymptomatic patients as a reservoir of pathogens, thus favoring their persistent colonization and extensive dissemination, and patients with positive surveillance cultures were eight times more likely to develop CRAB infections (Latibeaudiere et al., 2015), even after controlling for other variables, which emphasize the need for active surveillance for multidrug-resistant organisms and the value of molecular typing of strains to investigate their transmission and distribution features. Although there have been reported the skin or rectum being the site of higher carriage rate of CRAB (Nutman et al., 2020; Osei Sekyere et al., 2021), buccal mucosa also remains one of the most reliable sample sources to screen for its carriers (Nutman et al., 2016; Zhou et al., 2018; Cavallo et al., 2023; Da Silva et al., 2023). The oropharyngeal swabs, while may not be the best but the most viable option, could reduce sampling difficulty by healthcare professionals and enhance acceptability among pregnant women. Witnessing an upward trajectory in the dissemination and infection rates of CRAB, the objectives of this study were to assess the prevalence of oral and pharyngeal carriage of CRAB during pregnancy and investigate carriers’ high-risk factors and the genetic characteristics of related AB isolates.

A database selection of 114 isolates from Shenzhen in Guangdong Province, excluding the 41 isolates from this study, showcased that 59 (51.75%, 59/114) isolates belonged to Cluster^RS 1, followed by Cluster^RS 13 (35.09%, 40/114) and Cluster^RS 225 (3.51%, 4/114). Intriguingly, 90.35% (n = 103) of the total isolates shared the same Clusters^RS with the isolates found in pregnant women from Shenzhen, indicating that the genotypes of carriage isolates during pregnancy were the local prevalent AB or their closely related pathogens. However, a much higher proportion of Cluster^RS 1 isolates was observed among pregnant women compared with the previous proportion (75.61% vs. 51.75%; χ², 7.05; p < 0.01) in Shenzhen. Independent of whether cgMLST was performed exclusively on the 41 isolates in the current study or all 155 isolates in Shenzhen, the 31 Cluster^RS 1 isolates from pregnant women could be subdivided into three minor clusters, with CT3071 and CT2082 isolates forming an independent cluster (Supplementary Figure 4). Although there were at least 15 different alleles between the CT3071 isolates and other Cluster^RS 1 isolates in Shenzhen, an isolate with only five different alleles was identified in Guangzhou, a city adjacent to Shenzhen in Guangdong province. Cluster^RS 1, the largest Cluster^RS and host to substantial genetic diversity globally, had over half its isolates with novel CTs in this study. Upon excluding novel CTs isolates present only during pregnancy, the CRAB oropharyngeal carriage rate in pregnant women was halved to 13.04%, which was a rate similar to previous studies in the United States (13.46%, 49/364; Latibeaudiere et al., 2015), South Korea (15.06%, 168/1115; An et al., 2017), and Japan (13.52%, 172/1272; Yamamoto et al., 2019).

Several risk factors enhance the likelihood of CRAB carriers during pregnancy, aligning with findings from the general population (Alsultan et al., 2013; Ren et al., 2019; Diep et al., 2023). AMA has previously been shown to increase the risk of adverse pregnancy outcomes, maternal death, and maternal complications, such as GDM (Alsultan et al., 2013; Laopaiboon et al., 2014; Fink et al., 2023), and was suggested as an independent risk factor for CRAB carriers. Diabetes mellitus has been demonstrated as a significant risk factor for AB infections, and diabetic patients are significantly more likely to carry CRAB (Alsultan et al., 2013; Ren et al., 2019). It has previously been revealed that diabetes could destroy the control relationships between bacteria, disrupting the human micro-ecological balance, which is conducive to forming pan-resistant species of AB (Ren et al., 2019). The number of pregnant women with pre-existing diabetes was relatively low in the present study, whereas GDM was found to be an independent risk factor for pregnant women who carried the CRAB isolates; GDM also resulted in an increased risk of complications, such as leading to the development of type 2 diabetes in both the mother and infant (Guevara-Ramírez et al., 2023). Infections in pregnancy are common and are associated with numerous consequences for the mother, fetus, and neonate (Hazenberg et al., 2021). GBS infection, which was identified by VITEK 2, VITEK MS, and post-enrichment subculture methods in this study, also stood out as a notable independent risk factor for the carriage of CRAB in pregnant women. There was no high-risk group associated with certain Cluster^RS or CT isolates.

It is widely known that pathogen carriage is strongly associated with the subsequent development of infections. Although the results in the present study were consistent with previously published observations that there were no adverse maternal and neonatal effects due to AB during pregnancy (Sood et al., 2019), the presence of CR-hvAB with KL49 isolates could indicate that special internal environments or evolutionary strains control human micro-ecological balance and counterbalance this high pathogenicity and mortality during pregnancy. Hormonal alterations and reduced immunity during pregnancy confer a greater risk of emerging or resurgent infectious diseases. Meanwhile, there are many measures to help pregnant women fight disease, such as the supplementation of omega-3 polyunsaturated fatty acids during pregnancy, which has exhibited superior antimicrobial effects against the highly drug-resistant pathogen AB (Jiang et al., 2019).

Shenzhen is witnessing a surge in migrant population and is grappling with ensuing public health challenges such as healthcare service inequity and escalating infectious diseases, especially among vulnerable demographics such as pregnant women (Wang et al., 2023). The first KL49 AB (BioProject PRJNA388510) was found in the Third People’s Hospital of Shenzhen in 2014. Notably, a mother who had just given birth to a newborn baby played a central role in a fatal outbreak of KL49 strains at Shenzhen People’s Hospital in the Luohu district, with a deadly 77.78% mortality rate in 2017 (BioProject PRJNA533558; Supplementary Figure 5). The following year, KL49 strains were implicated in another severe outbreak with an 80% mortality rate, involving two departments, and the transmission was associated with contamination of the bedside chest roentgenogram machine (BioProject PRJNA510897); the KL49 strain was also identified in the Intensive Care Unit (ICU) portable ventilator (BioProject PRJNA546440). Of the 286 AB clinical isolates from the Department of Clinical Laboratory identified using a PCR rapid detection method (Deng et al., 2020), 53 (18.53%) KL49 isolates were detected across 11 departments between 2017 and 2019 at Shenzhen People’s Hospital. A total of 489 patients were incorporated on admission (<2 h) in the ICU at Shenzhen People’s Hospital for an ASC program, which revealed that 177 and 156 carbapenemase-producing organisms Acinetobacter isolates were oropharyngeal and intestinal carriage, respectively, from January to November 2019. To date, there has been less effort to monitor AB carriage in pregnancy.

KL49 AB isolates are associated with fatal outbreaks or severe infections in relatively immunocompetent patients; their high virulence was not only observed in clinical data, but also reproduced in animal models, including lethal to immunocompetent mice and G. mellonella (Jones et al., 2015; Zhou et al., 2018; Zeng et al., 2019; Deng et al., 2020; Li et al., 2020). The CC2^IP-KL49 isolates were divided into 16 Clusters^RS; among them, Cluster^RS 13 was the predominant group, accounting for 44.19% (76/172). In contrast to Cluster^RS 1, as “generalist pathogens”, able to adapt to several human populations and spread around the world, Cluster^RS 13 demonstrated surprising phylogeographical specificity to Guangdong province (Supplementary Figures 1, 3; Figure 1A). This geographical restriction could correspond to the local adaptation of these “ecological specialist” KL49 isolates to local human host populations. Although both previous studies in Guangdong, China, and many parts of the world outside of Guangdong have demonstrated that Cluster^RS 13 and other Cluster^RS KL49 isolates are more virulent than non-KL49 (Jones et al., 2015; Zhou et al., 2018; Deng et al., 2020; Li et al., 2020), the Cluster^RS 13 isolates did not support its high virulence to cause significant morbidity and mortality in pregnant women. In addition to host factors, no specific evolution of KL49 strains has been identified in pregnant women through multiple genotyping and the differential analysis of SNPs comparing KL49 strains with hosts’ death and survival information.

Two extensively drug-resistant AB, with significantly different mortality rates in the G. mellonella infection model, obtained at two-time points during a case, have previously been reported (Grier et al., 2021). In the present study, there were five participants from whom two samples were obtained at different interval times. The five pairs of isolates displayed more or less distinct genomic or phenotypic characteristics in comparison to two strains within the same host, including some critical drug-resistance phenotypes, which was also reported in a previous study of two AB isolates from a single patient, with subsequent change from tigecycline susceptibility to resistance (Hornsey et al., 2011). In general, the co-occurrence of two highly resistant bacteria in the same patient may lead to therapeutic failure and may lead to death (Ding et al., 2021). However, dual infections of two clinical strains of CRAB have been identified in the same sample from a patient (Hadjadj et al., 2018). In the present study, KL49 isolates and KL7 isolates (i.e., CT3071 isolates in pregnancy) were most common in the five participants with two isolates, accounting for 50% and 40% of the 10 total related CRAB isolates, respectively (Table 2).

The population bias for CT3071 was similar to a prior report that K14.K64-CRKP mainly occurred in adult patients, especially patients >65 years of age, and wzi209-CRKP mainly occurred in pediatric patients, especially infants (Zhu et al., 2022). The CT3071 isolates exhibiting KL7, as the most prevalent CRAB isolates of maternal carriage, were potentially able to adapt to the population of pregnant women (Table 3). The capsule thickness of the KL7 isolates was significantly higher than that of other capsular types (Hu et al., 2020), which was identified in Shenzhen for the first time. Compared with KL49 isolates, CT3071 isolates possess a T6SS that has the ability to mediate the killing of bacterial competitors (Jones et al., 2015; Zhou et al., 2018; Zhang et al., 2023). Considering CT3071 isolates have lower virulence than KL49 isolates (Supplementary Figure 2), their potential intraspecific competition might also be a possible reason for the absence of morbidity and mortality in pregnant women.

The limitations of this study prominently include the singular sampling site and hospital from which isolates were collected, especially on account of the multiple sampling populations and sites are important to compare and confirm the results, and the disruption caused by the COVID-19 pandemic affecting screening and participant follow-up processes. Such clinical information as, history of previous hospitalization (pregnancy-unrelated), smoking, and inappropriate nutritional status, were unavailable for analysis, since there was no positive carrier among the related populations in this small sample size. It is also likely that because of the strict disinfection procedure and widespread mask-wearing habits during the COVID-19 pandemic in China, no related genotype of the AB strain in pregnancy was found in the environment or healthcare workers during this study. Therefore, there was no direct evidence to indicate whether the origins of the relevant strains in pregnant women were from the hospital, the community environment, or other transmission chains, particularly the newly created CTs isolates. Despite these limitations, the findings in the present study are significant since, in the potential chain of mother-to-newborn transmission, all are very susceptible to infections, with quite limited antibiotics for therapeutic options, particularly in the face of previous fatal neonatal outbreaks and contamination over animate and inanimate environment (Osei Sekyere et al., 2021; Odoyo et al., 2023; Woon et al., 2023). In China and most developing countries, there needs to be more individual rooms to take contact precautions and enforce patient isolation in the Department of Obstetrics and Gynecology, especially in public hospitals, which is an issue that deserves more attention.

This is the first study to describe the situations of the carriage of CRAB among pregnant women in China. The independent risk factors for carriers included AMA, GDM, and GBS infection during pregnancy. The discovery of a significant proportion of newly created CT isolates during pregnancy is noteworthy and demands further study to decode pathogen-pathogen compatibility, understand the characteristics of emerging genotypes such as CT3071, and develop a broader surveillance network of CRAB isolates during pregnancy for effective detection and control in both hospital and community settings, especially in Guangdong for the hypervirulent KL49 isolates.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/Supplementary material.

The studies involving humans were approved by the Medical Ethics Committee of Shenzhen People’s Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants or the participants’ legal guardians/next of kin.

CZ: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. DL: Data curation, Formal analysis, Investigation, Resources, Software, Writing – review & editing. YW: Data curation, Formal analysis, Investigation, Methodology, Resources, Supervision, Validation, Writing – review & editing. LW: Investigation, Resources, Writing – review & editing. YH: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – review & editing. JY: Formal analysis, Investigation, Resources, Supervision, Validation, Writing – review & editing.