Mixed probiotics reduce the severity of stress-induced depressive-like behaviors

In recent years, the gut microbiome has gained significant attention in the spheres of research and public health. As a result, studies have increasingly explored the potential of probiotic dietary supplements as treatment interventions for conditions such as anxiety and depression. The present study examined the effect of mixed probiotics (Lacticaseibacillus rhamnosus and Enterococcus faecium) on inflammation, microbiome composition, and depressive-like behaviors in a macaque monkey model. The mixed probiotics effectively reduced the severity of depressive-like behaviors in macaque monkeys. Further, treatment with mixed probiotics gradually increased the abundance of beneficial bacteria in the gut, improving the balance of the gut microbiota. Additionally, macaques treated with the mixed probiotics showed decreased serum levels of inflammatory factors (P < 0.05), an increased rate of L-tryptophan metabolism (P < 0.05), and the restoration of 5-HT and 5-HTP levels (P < 0.05). Correlation analysis confirmed that Lacticaseibacillus and other beneficial bacteria exhibited a negative correlation with inflammation in the body (P < 0.05), and a positive correlation with tryptophan metabolism (P < 0.05). In conclusion, the mixed probiotics effectively restored intestinal homeostasis in macaques and enhanced tryptophan metabolism, ultimately alleviating inflammation and depressive-like behaviors.

GABA induced by sleep deprivation promotes the proliferation and migration of colon tumors through miR-223-3p endogenous pathway and exosome pathway

BACKGROUND

Research has indicated that long-term sleep deprivation can lead to immune dysfunction and participate in the occurance and progression of tumors. However, the relationship between sleep deprivation and colon cancer remains unclear. This study explored the specific mechanism through which sleep deprivation promotes the proliferation and migration of colon cancer, with a focus on the neurotransmitter GABA.

METHODS

Chronic sleep deprivation mice model were used to investigate the effect of sleep disorder on tumors. We detected neurotransmitter levels in the peripheral blood of mice using ELISA. CCK-8 assay, colony formation assay, wound healing assay, and transwell assay were performed to investigate the effect of GABA on colon cancer cells, while immunofluorescence showed the distribution of macrophages in lung metastatic tissues. We isolated exosomes from a GABA-induced culture medium to explore the effects of GABA-induced colon cancer cells on macrophages. Gain- and loss-of-function experiments, luciferase report analysis, immunohistochemistry, and cytokine detection were performed to reveal the crosstalk between colon cancer cells and macrophages.

RESULTS

Sleep deprivation promote peripheral blood GABA level and colon cancer cell proliferation and migration. Immunofluorescence analysis revealed that GABA-induced colon cancer metastasis is associated with enhanced recruitment of macrophages in the lungs. The co-culture results showed that GABA intensified M2 polarization of macrophage induced by colon cancer cells. This effect is due to the activation of the macrophage MAPK pathway by tumor-derived exosomal miR-223-3p. Furthermore, M2-like macrophages promote tumor proliferation and migration by secreting IL-17. We also identified an endogenous miR-223-3p downregulation of the E3 ligase CBLB, which enhances the stability of cMYC protein and augments colon cancer cells proliferation and migration ability. Notably, cMYC acts as a transcription factor and can also regulate the expression of miR-223-3p.

CONCLUSION

Our results suggest that sleep deprivation can promote the expression of miR-223-3p in colon cancer cells through GABA, leading to downregulation of the E3 ligase CBLB and inhibition of cMYC ubiquitination. Simultaneously, extracellular miR-223-3p promotes M2-like macrophage polarization, which leads to the secretion of IL-17, further enhancing the proliferation and migration of colon cancer cells.

Increasing rate of hospitalization for severe peptic ulcer in digestive disease emergencies after the pandemic

Since December 2019, the novel coronavirus has spread worldwide, affecting more than 510 million people, with more than 6 million deaths. However, some of the potential effects of the pandemic have not been thoroughly studied. We collected data from 2 regional emergency centers from May to November for the years 2015 to 2019, before the pandemic, and from May to November 2020, after the pandemic. We evaluated the incidence of each major type of digestive disease before and after the pandemic in adults at the 2 hospitals, which experienced coronavirus disease 2019 outbreaks with varying severity. A total of 11,394 patients were enrolled in the study Affiliated Hospital of Putian University (PUTIAN, n = 5503) Union Hospital, Tongji Medical college, Huazhong University of Science and Technology (UNION, n = 5891), and the proportion of male patients was approximately the same at both hospitals, with 3360 (61.1%) and 3680 (62.5%), respectively. The average ages of the patients were 55.8 ± 18.4 years PUTIAN and 54.3 ± 15.8 years UNION. The numbers of patients at the 2 hospitals increased steadily, but in 2020, the number of patients at UNION declined. The baseline characteristics of the 2 groups at the 2 hospitals showed significant differences for age before and after the pandemic but not for sex. The constituent ratios of diseases in each year in the 2 hospitals differed. The number of patients with peptic ulcers in 2020 was significantly different from those in each year from 2015 to 2019 (PUTIAN 2015-2020, 15.0%, 18.2%, 14.9%, 16.9%, 19.5%, 34.9%; UNION 2015-2020, 29.2%, 32.5%, 29.3%, 29.4%, 29.7%, 41.3%, respectively). The rates of peptic ulcer increased dramatically in both hospitals in 2020. An increase in the incidence of severe peptic ulcer was observed after the pandemic compared to the same period before the pandemic. Therefore, these factors should be considered in the formulation of public health strategies and the allocation of medical resources in the post pandemic era.

Telephone follow-up by clinical pharmacists can improve treatment outcomes in patients with peptic ulcers: A prospective randomized study

OBJECTIVE

The purpose of this study was to investigate the effect of pharmaceutical care by clinical pharmacists through telephone follow-up on the treatment outcomes in patients with peptic ulcers who had been discharged from the hospital.

METHODS

A total of 120 patients with peptic ulcers discharged from the hospital were randomly divided into an intervention group and a control group, with 60 patients in each group. The patients in the two groups received different services.

RESULTS

A total of 108 patients with peptic ulcers were enrolled in this study, including 53 in the intervention group and 55 in the control group. This study showed that the Helicobacter pylori eradication rate (19/23, 82.61% vs 13/29, 44.83%), awareness of peptic ulcer disease, medication compliance, diet compliance, and life compliance in the patients in the intervention group were higher than those in the patients in the control group. The H pylori eradication group had higher follow-up scores than the noneradication group. Sex and body mass index (BMI) did not affect the results in either group, but age did. In the control group, younger patients scored higher than older patients, whereas in the intervention group, this difference disappeared for diet compliance and life compliance, and significant differences remained for awareness of basic knowledge regarding peptic ulcer (AOKPU) and medication compliance.

CONCLUSION

As a form of clinical pharmaceutical care, telephone follow-up by clinical pharmacists is recommended for discharged patients with peptic ulcers because it can improve treatment outcomes after discharge.

Can an incomplete ERAS protocol reduce postoperative complications compared with conventional care in laparoscopic radical resection of colorectal cancer? A multicenter observational cohort and propensity score-matched analysis

Background

The patients undergoing laparoscopic radical colorectomy in many Chinese hospitals do not achieve high compliance with the ERAS (enhanced recovery programs after surgery) protocol.

Methods

The clinical data from 1,258 patients were collected and divided into the non-ERAS and incomplete ERAS groups.

Results

A total of 1,169 patients were screened for inclusion. After propensity score-matched analysis (PSM), 464 pairs of well-matched patients were generated for comparative study. Incomplete ERAS reduced the incidence of postoperative complications (p = 0.002), both mild (6.7% vs. 10.8%, p = 0.008) and severe (3.2% vs. 6.0%, p = 0.008). Statistically, incomplete ERAS reduced indirect surgical complications (27,5.8% vs. 59, 12.7) but not local complications (19,4.1% vs. 19, 4.1%). The subgroup analysis of postoperative complications revealed that all patients benefited from the incomplete ERAS protocol regardless of sex (male, p = 0.037, 11.9% vs. 17.9%; female, p = 0.010, 5.9% vs. 14.8%) or whether neoadjuvant chemotherapy was administered (neoadjuvant chemotherapy, p = 0.015, 7.4% vs. 24.5%; no neoadjuvant chemotherapy, p = 0.018, 10.2% vs. 15.8%). Younger patients (<60 year, p = 0.002, 7.6% vs. 17.5%) with a low BMI (<22.84, 9.4% vs. 21.1%, p < 0.001), smaller tumor size (<4.0 cm, 8.1% vs. 18.1%, p = 0.004), no fundamental diseases (8.8% vs. 17.0%, p = 0.007), a low ASA score (1/2, 9.7% vs. 16.3%, p = 0.004), proximal colon tumors (ascending/transverse colon, 12.2% vs. 24.3%, p = 0.027), poor (6.1% vs. 23.7%, p = 0.012)/moderate (10.3% vs. 15.3%, p = 0.034) tumor differentiation and no preoperative neoadjuvant radiotherapy (10.3% vs. 16.9%, p = 0.004) received more benefit from the incomplete ERAS protocol.

Conclusion

The incomplete ERAS protocol decreased the incidence of postoperative complications, especially among younger patients (<60 year) with a low BMI (<22.84), smaller tumor size (<4.0 cm), no fundamental diseases, low ASA score (1/2), proximal colon tumors (ascending/transverse colon), poor/moderate differentiation and no preoperative neoadjuvant radiotherapy. ERAS should be recommended to as many patients as possible, although some will not exhibit high compliance. In the future, the core elements of ERAS need to be identified to improve the protocol.

Lactobacillus Ameliorates SD-Induced Stress Responses and Gut Dysbiosis by Increasing the Absorption of Gut-Derived GABA in Rhesus Monkeys

Sleep deprivation (SD) has become a health problem in the modern society. Although probiotics supplementation has been proven to improve SD-induced gut dysbiosis, the potential neuroendocrine mechanisms remain elusive. In this study, thirty rhesus monkeys (RMs) were recruited. Paradoxical sleep, bright light, and noise were used to build an RM SD model. We examined the plasma γ-aminobutyric acid (GABA), stress hormones, and inflammatory cytokines using ELISAs. 16S ribosomal DNA sequencing and untargeted metabolomics sequencing were employed to detect gut microbial community and metabolites, respectively. The results of our study showed that RMs subjected to SD had elevated plasma stress hormones (such as cortisol and norepinephrine) and proinflammatory cytokines (such as TNF-α, IL-6, and IL-8), and a decreased anti‐inflammatory cytokine IL-10 level. Additionally, SD could give rise to a significant change in gut microbiota and metabolites. The differential gut microbiota and metabolites caused by SD were enriched in the signaling pathways related to GABA metabolism. Pearson correlation analysis revealed that there is a significant correlation between plasma GABA and SD-induced stress responses and gut dysbiosis. The supplementation of GABA-producing probiotics could significantly increase the relative abundance of Lactobacillus and plasma GABA levels, and reverse SD‐induced stress responses and gut dysbiosis. Therefore, we speculated that SD-induced stress response and gut dysbiosis might be an outcome of reduced gut-derived GABA absorption. The supplementation of GABA-producing Lactobacillus might be beneficial for the treatment of SD-induced intestinal dysfunction.

Insulin resistance induced by long-term sleep deprivation in rhesus macaques can be attenuated by Bifidobacterium

Long-term sleep deprivation (SD) is a bad lifestyle habit, especially among specific occupational practitioners, characterized by circadian rhythm misalignment and abnormal sleep/wake cycles. SD is closely associated with an increased risk of metabolic disturbance, particularly obesity and insulin resistance. The incretin hormone, glucagon-like peptide-1 (GLP-1), is a critical insulin release determinant secreted by the intestinal L-cell upon food intake. Besides, the gut microbiota participates in metabolic homeostasis and regulates GLP-1 release in a circadian rhythm manner. As a commonly recognized intestinal probiotic, Bifidobacterium has various clinical indications regarding its curative effect. However, few studies have investigated the effect of Bifidobacterium supplementation on sleep disorders. In the present study, we explored the impact of long-term SD on the endocrine metabolism of rhesus monkeys and determined the effect of Bifidobacterium supplementation on the SD-induced metabolic status. Lipid concentrations, body weight, fast blood glucose, and insulin levels increased after SD. Furthermore, after 2 mo of long-term SD, the intravenous glucose tolerance test showed that the glucose metabolism was impaired and the insulin sensitivity decreased. Moreover, 1 mo of Bifidobacterium oral administration significantly reduced blood glucose and attenuated insulin resistance in rhesus macaques. Overall, our results suggested that Bifidobacterium might be used to alleviate SD-induced aberrant glucose metabolism and improve insulin resistance. Also, it might help in better understanding the mechanisms governing the beneficial effects of Bifidobacterium.NEW & NOTEWORTHY Our findings demonstrated that long-term sleep deprivation is closely associated with metabolic syndromes. Bifidobacterium administration showed a superior effect on insulin resistance caused by sleep deprivation. Overall, we provide prevention and treatment methods for long-term sleep deprivation, a bad lifestyle habit among specific occupational practitioners, such as irregular shift workers.

Failure of enhanced recovery programs after laparoscopic radical gastrectomy: a single-center retrospective study

BACKGROUND

Enhanced recovery programs (ERPs), as a rapid rehabilitation method, have been widely used in gastric cancer patients. Although many related studies have confirmed their effectiveness, some patients may still experience poor clinical outcomes. This study analyzed risk factors associated with ERP failure after laparoscopic radical gastrectomy.

METHODS

We analyzed the outcomes of 212 patients who underwent ERP following laparoscopic radical gastrectomy between March 2017 and December 2019. The ERP included preoperative education, short periods of fasting, non-mechanical intestinal preparation, early ambulation and oral feeding. ERP failure was defined as more than 7 days of hospitalization due to postoperative complications, unplanned readmission within 30 days of surgery, or death.

RESULTS

The mean patient age was 62 years (range 39-89 years). Surgical procedures included total gastrectomy (n = 161) and distal gastrectomy (n = 51). Overall, 38 (17.9%) patients failed to complete the program, with no mortality. Univariable analysis (P < 0.15) revealed that ERP failure was associated with age, sex, body mass index (BMI), American Society of Anesthesiologists (ASA) grade, tumor location, preoperative education, combined operation, long operation time, and significant blood loss. Multivariable analysis (P < 0.05) showed that age, ASA grade III, combined operation and preoperative education were independent risk factors for ERP failure.

CONCLUSIONS

We showed that an advanced age, a high ASA grade, lack of a preoperative education and combined surgery were independent risk factors associated with ERP failure after laparoscopic gastrectomy. Therefore, a preoperative patient evaluations and education are important for the success of ERPs.

Single-port endoscopic mastectomy via the lateral chest approach for the treatment of grade II gynecomastia

To investigate the feasibility of single-port endoscopic mastectomy via the lateral chest approach in the treatment of Simon grade II gynecomastia.Data from 12 patients with grade II gynecomastia admitted from January 2017 to November 2018 were retrospectively analyzed, and related satisfaction surveys were conducted 6 months after the operation.All surgeries were successfully performed under single-port endoscopy, and no patients were converted to open surgery. There were no serious complications related to the surgery, and all the patients were satisfied with the postoperative appearance.The application of single-port endoscopy in the surgical treatment of grade II gynecomastia is safe and reliable.

Laser-engineered heavy hydrocarbons: Old materials with new opportunities

Polycyclic heavy hydrocarbons (HHs) such as coal, tar, and pitch are a family of materials with extremely rich and complex chemistry, representing a massive opportunity for their use in a range of potential applications. The present work shows that optimal selection of initial HHs based on molecular constituents is essential in tuning the material for a particular and targeted electronic application. Combining the selection of feedstock chemistry (H:C and aromatic content) and controlling variable laser treatment parameters (laser power, speed, and focus) lead to full control over the H:C ratio, sp² concentration, and degree of graphitic stacking order of the products. The broad intertunability of these factors results from a wide distribution of carbon material crystallinity from amorphous to highly graphitic and a broad distribution of electrical conductivity up to 10³ S/m.

[Application of contralateral mastoplasty in breast reconstruction after breast cancer surgery]

Objective

To introduce a contralateral mastoplasty in breast reconstruction with prosthesis after breast cancer surgery in order to gain bilateral breasts symmetry.

Methods

Between January 2016 and June 2018, 11 female patients with breast cancer were treated, aged 34-64 years old (mean, 49.6 years). There were 5 cases in left side and 6 cases in right side. There were 3 cases of invasive carcinoma and 8 cases of intraductal carcinoma. The diameter of tumor was 0.2-4.1 cm (mean, 2.5 cm). The disease duration ranged from 1 to 15 months (mean, 6 months). According to Regnault grading criteria, there were 7 cases of mild breast ptosis and 4 cases of moderate breast ptosis. Simple nipple-sparing mastectomy and reconstruction using prosthesis of the affected side, and folding and lifting of the nipple-areolar complex of the healthy side were performed.

Results

The operation time was 144-188 minutes (mean, 158 minutes). The hospital stay was 6-9 days (mean, 7.5 days). Postoperatively, poor incision healing occurred in 1 case and healed after symptomatic treatment. The other incisions healed well and no surgical-related complications occurred. All patients were followed up 6-30 months (mean, 16 months). At 3 months after operation, the expert group adopted the self-made rating scale to evaluate the bilateral breasts symmetry, and the score was 8-10 (mean, 8.9). The patients were evaluated for their satisfaction according to the self-made score scale, and the score was 8-10 (mean, 9.1).

Conclusion

After immediate breat reconstruction with prosthesis after breast cancer surgery, the satisfied bilateral breasts appearances and symmetry can be obtained by contralateral mastoplasty.

Effects of duodenal transection timing on clinical short-term outcomes of patients with laparoscopic spleen-preserving splenic hilar lymphadenectomy for advanced proximal gastric cancer

Background

To determine the optimal timing of duodenal transection in patients undergoing laparoscopic-assisted total gastrectomy (LATG) in combination with laparoscopic spleen-preserving splenic hilar lymphadenectomy (LSPL) for advanced proximal gastric cancer (APGC).

Methods

One hundred twenty-seven patients with APGC who received LATG with duodenal transection as well as LSPL between January 2017 and July 2018 were retrospectively recruited in this study. According to the different transection timing, the patients were allocated into two groups: a conventional group (CG) who received the duodenal transection prior to the LSPL and an experimental group (EG) who were given LSPL before the duodenum was transected. Clinical short-term outcomes were compared in the two groups.

Results

Analysis of the demographical and clinical characteristics showed that the two groups were comparable with no significant differences between CG and EG in the study patients regardless of their body mass indices (BMI). The intraoperative and postoperative indicators for clinical short-term outcomes were compared between the CG and EC, and results indicated that the EG had significant shorter mean time of LSPL and total operation time than those in the CG (P < 0.05). Of note, the numbers of patients with intraoperative injury and the volume of blood loss during the LSPL procedure were significantly reduced in the EG versus CG (P < 0.05). For the obese APGC patients, administration of LSPL prior to duodenal transection significantly increased the number of dissected No.10 lymph nodes (LNs) (P < 0.05). The other intraoperative and postoperative indicators did not show any differences between the two comparison groups.

Conclusions

Our findings demonstrated that duodenal transection timing was significantly associated with clinical short-term outcomes of APGC patients. The duodenal transection prior to the LSPL is superior overall to the conventional transection timing in the treatment of APGC patients with LATG and LSPL in combination.

Comparison of 16S rRNA gene PCR and blood culture for diagnosis of neonatal sepsis

Septicemia is a common cause of morbidity and mortality among newborns in the developing world. However, accurate clinical diagnosis of neonatal sepsis is often difficult because symptoms and signs are often nonspecific. Blood culture has been the gold standard for confirmation of the diagnosis. However, the sensitivity is low and results are usually not promptly obtained. Therefore, the diagnosis of sepsis is often based on clinical signs in association with laboratory tests such as platelets count, immature/total neutrophils ratio (I/T), and a rise in C-reactive protein (CRP). Polymerase chain reaction (PCR) methods for the detection of neonatal sepsis represent new diagnostic tools for the early identification of pathogens.

METHODS

During a 4-month prospective study, 16S rRNA PCR was compared with conventional blood culture for the diagnosis of neonatal bacterial sepsis. In addition, the relationship between known risk factors, clinical signs, laboratory parameters, and the diagnosis of sepsis was considered.

RESULTS

Sepsis was suspected in 706 infants from the intensive neonatal care unit. They all were included in the study. The number of positive cultures and positive PCR results were 95 (13.5%) and 123 (17.4%), respectively. Compared with blood culture, the diagnosis of bacterial sepsis by PCR revealed a 100.0% sensitivity, 95.4% specificity, 77.2% positive predictive value, and 100.0% negative predictive value. In this study, Apgar scores at 5 min, weight, icterus, irritability, feeding difficulties, gestational age (GA), premature rupture of membrane (PRM), platelets count, I/T, and a marked rise in CRP were important in establishing the diagnosis of sepsis in the newborn. In addition, weight, GA, PRM, irritability, duration of antibiotic usage, mortality rate, and number of purulent meningitis cases were significantly different between early-onset sepsis and late-onset sepsis.

CONCLUSION

16S rRNA PCR increased the sensitivity in detecting bacterial DNA in newborns with signs of sepsis, allowed a rapid detection of the pathogens, and led to shorter antibiotic courses. However, uncertainty about the bacterial cause of sepsis was not reduced by this method. 16S rRNA PCR needs to be further developed and improved. Blood culture is currently irreplaceable, since pure isolates are essential for antimicrobial drug susceptibility testing.

Changes in muscle sympathetic nerve activity and effects of breathing maneuvers in humans during microgravity induced by parabolic flight

The mechanism of cardiovascular deconditioning, such as an orthostatic intolerance after space flight, has not been well clarified. Several studies to investigate that mechanism have focused mainly on hemodynamic changes including heart rate, arterial blood pressure, cardiac output, etc., but no studies have yielded a direct insight into changes in the sympathetic nervous system. Among ground-based experiments, parabolic flight is the only maneuver to expose human subjects to actual microgravity although it lasts for only a short duration of approx. 20 sec. Using microneurography, the present study aimed to analyze the involvement of the sympathetic nervous system in regulating the acute effects of fluid shift induced by parabolic flight during the transitional changes from 1 G to hypergravity, hypergravity to microgravity, and microgravity to hypergravity by direct measurement of sympathetic outflow to the muscles. Some parts of the study were published elsewhere. We also investigated how the sympathetic outflow to muscle is modified during microgravity with elimination of the breathing effect by comparing the cardiovascular parameters under controlled and uncontrolled respiration.

[Cerebral hemodynamic impairment and therapeutic effect of external counterpulsation on elderly patients with brain infarction]

Hemodynamic parameters of middle cerebral artery(MCA) were measured with Transcranial Doppler (TCD) in 31 elderly patients with brain infarction during convalescence and 28 healthy elderly controls. Twenty-two elderly patients with brain infarction and cerebral hemodynamic impaired were treated by External Counterpulsation(ECP). The results showed that the Vp and Vm of MCA in patients were significantly lower than that in the healthy controls(P < 0.001), the DVp, DVm and asymmetry of MCA in patients were greater than that in the healthy elderly(P < 0.001, P < 0.005). The Vp and Vm of MCA in patients after ECP were significantly higher than before(P < 0.001). The DVp, DVm and asymmetry of MCA in patients after ECP were significantly lower than before(P < 0.001, P < 0.005). The hemodynamic therapeutic effect is 81.8%.

Biomechanical study of the bile duct system outside the liver

Diseases of the bile duct system in the digestive system after surgery are common. In order to clarify the cause of these diseases, research on the diseases from a biomechanical perspective is increasing; however, the same cannot be said of biochemical research. In this paper, by using a new, well-devised testing apparatus, specimens extracted from the bile duct system of canine body are tested. The test data are analyzed using the finite deformation theory, and mechanical properties of the bile duct system outside the liver are investigated. The conclusions show that the viscoelasticity of the bile duct system is very small. In its normal physiological condition, the bile duct wall has an almost uniform distribution of circumferential and longitudinal stress. However, when the diseases of the bile duct system cause high pressure at the bile duct, the circumferential stress and longitudinal stress at the bile inside wall suddenly increase and are much larger than those stresses at the outside wall. The elastic modulus gradually becomes small from the common bile duct and the common hepatic duct to hepatic duct, and the value of elastic modulus for the cystic duct is almost equal to that of the hepatic duct.

Development of a cloning system in Mycoplasma pulmonis

A system suitable for recombinant DNA manipulation in mycoplasmas was developed using the cloned antibiotic-resistance genes of Tn4001 and Tn916. An integrative plasmid containing one of the resistance markers was inserted into the genome of Mycoplasma pulmonis to form a recipient strain. This was accomplished by transformation and homologous recombination between chromosomal DNA sequences cloned onto the integrative plasmid. A second vector, the cloning vector, containing the same plasmid replicon and alternate resistance marker, carried cloned foreign DNA. When transformed into mycoplasmal recipients, homologous recombination between plasmid sequences resulted in integration of the cloning vector and foreign DNA. A Brucella abortus gene coding for a 31-kDa protein and the P1 structural gene and operon from Mycoplasma pneumoniae were introduced to examine the feasibility of developing mycoplasma as cloning hosts. Recombinant plasmids as large as 20 kb were inserted into M. pulmonis, and the integrated foreign DNA was stably maintained. The maximum size of clonable DNA was not determined, but plasmids larger than 22 kb have not been transformed into mycoplasmas using polyethylene glycol. Also the size of genome (800-1200 kb) may affect the stability of larger inserts of foreign DNA. This system is applicable to any mycoplasma capable of transformation, homologous recombination and expression of these resistance markers. Because of their lack of a cell wall, mycoplasmas may be useful cloning hosts for membrane or excreted protein genes from other sources.