Bacterial Epidemiology and Antimicrobial Resistance Profiles of Respiratory Specimens of Children with Pneumonia in Hainan, China

Introduction

Pneumonia is one of the major causes of childhood morbidity and mortality globally.¹ In 2015, an estimated 921,000 children younger than 5 years old died of pneumonia in the world.² In China, due to general improvements in living conditions, better healthcare and improved vaccines, the estimates of clinical pneumonia in children decreased from 25.9% in 2000 to 8.4% in 2015.^1,3,4 However, an estimated >700,000 children are still hospitalized with pneumonia in China each year, representing a huge disease burden.^1,5 These hospitalized pneumonia cases are a major cause of morbidity in children.^1,6

Bacteria such as H. influenzae, S. pneumoniae are common causes of pneumonia in children. Based on the 2015 Global Burden of Diseases (GBD) data approximately 64% of pneumonia deaths in children under 5-years old were due to bacterial infections.^1,2 For example, through direct transthoracic needle lung biopsy and autopsy, bacteria were found to be responsible for most pneumonia deaths in African children.⁷ More recently, bacteria were also recognized as causes for secondary pulmonary infections associated with coronavirus disease (COVID-19), increasing morbidity and mortality of COVID patients.⁸

Antimicrobial resistance (AMR) is recognized as one of the most serious global threats to human health and is commonly associated with high morbidity and mortality rates and large medical cost burdens.^9,10 The World Health Organization (WHO) has highlighted that infections by antibiotic-resistant bacteria are responsible for around 700,000 deaths per year worldwide, if left to persist at the current rate, may lead to 10 million deaths in 2050.¹¹ In particular, several recent reports described increases in multidrug resistant (MDR) bacteria during the COVID-19 pandemic, with the rise in MDR bacteria rendering infections increasingly difficult to treat.^12–23 Common MDR bacteria include Vancomycin resistant Enterococci (VRE), methicillin (oxacillin) resistant S. aureus (MRSA) and certain Gram-negatives such as E. coli and K. pneumoniae producing extended-spectrum β-lactamases or carbapenem-resistant Enterobacteriaceae (CRE).^24,25 Options for treating patients with MDR bacterial infections are often extremely limited.

To effectively prevent and treat infections by MDR bacteria, including those causing pneumonia, we need accurate diagnosis of both the disease agents and their antimicrobial susceptibilities. However, at present, relatively little is known about the bacterial species and antimicrobial susceptibility of respiratory specimens from children with pneumonia, especially in tropical and developing regions such as in Hainan Island, South China. In this study, we aim to investigate the bacterial species and their susceptibilities to commonly used antimicrobial drugs of respiratory specimens from children with pneumonia in Haikou Maternal and Child Health Hospital in Hainan, China. The prevalence of MDR bacteria was also investigated in this study.

Materials and Methods

Samples

A total of 5017 specimens including 4986 sputum samples, 19 bronchoalveolar lavage fluid samples and 12 tracheal tube tip samples from hospitalized children with pneumonia from April 1, 2021, to March 31, 2022, were collected, following standard clinical specimen collection protocols. Repeated strains of the same patient at the same hospitalization episode were excluded. The sputum samples were taken by a disposable sterile suction tube under negative pressure and sent for microscopic examination within 24 hours after admission. Sputum quality was considered adequate if it contained ≥25 leukocytes and ≤10 epithelial cells under low magnification. The Ethics Committee of Hainan Maternal and Child Health Hospital and Hainan Medical University approved our sampling and study. This study did not involve any medical intervention of any patients. The guardians of all patients were provided full information about this study and all of them signed a consent form. The study cohort consisted of 2994 males and 2023 females, of whom 1638 patients were less than 1 month old, 1762 patients were 1 month to 1 year old, 1403 patients were 2 to 5 years old, and 214 patients were 6 to 14 years old (Table S1).

Identification of Bacterial Species

To identify the bacteria, we plated the specimens on Columbia blood plate and chocolate plate.²⁵ The plates were cultured overnight at 35°C in a 5% CO₂ incubator. Actively growing and morphologically distinct colonies on each plate were identified to the species level using the VITEK 2 Compact microbial identification system (BioMérieux, France). The strains were stored in a −80°C freezer until being revived for antimicrobial susceptibility testing.

Antimicrobial Susceptibility Testing (AST)

For each bacterial isolate that we obtained from each of the patients, we determined its susceptibility to multiple selected antimicrobial agents. These selected agents differed among species with isolates from each species tested for their susceptibilities to a panel of the most commonly used antimicrobial drugs in China for treating the respective infections caused by each bacterial species. We used the Kirby-Bauer (KB) disk diffusion method to determine the antimicrobial susceptibilities of strains of H. influenzae and M. catarrhalis. For strains of other bacterial species, we used the VITEK 2 Compact automatic system with the AST-GN/GP cards (bioMérieux, France). The specific antibiotics tested for each species are shown in Tables 1 and 2. For the KB disk diffusion method, the disks (Oxoid Ltd., Basingstoke, UK) were placed onto Mueller–Hinton agar (Oxoid Ltd., Basingstoke, UK) in accordance with the Clinical and Laboratory Standards Institute (CLSI) 2021 guidelines.²⁶ H. influenzae ATCC49247 and S. aureus ATCC29213 were used for quality controls. CRE strains were defined as strains of Enterobacteriaceae that were resistant to either ertapenem and/or imipenem.

Table 1 Antibiotic Resistance Rates of Gram-Positive Bacteria Analyzed in This Study

Table 2 Antibiotic Resistance Rates of Gram-Negative Bacteria Analyzed in This Study

β-Lactamase Test

The nitrocefin discs were used to detect β-lactamase activity, following established protocol.²⁶ A positive result was defined as a disk color change from white to red. A negative result was defined as no color change. Strains S. aureus ATCC29213 and S. aureus ATCC25923 were used for positive and negative controls.

Extended-Spectrum β-Lactamase Test

For certain groups of bacteria, their ability to produce extended-spectrum β-lactamases was determined by means of a three-disk synergy test (with cefotaxime and cefotaxime/clavulanic acid, ceftazidime, and ceftazidime/clavulanic acid, cefepime and cefepime/clavulanic acid). Strains positive for the production of extended-spectrum β-lactamases were those that showed a greater than or equal to eightfold decrease in MICs for cefotaxime or ceftazidime when tested in combination with clavulanic acid, when compared with their MICs without clavulanic acid, following the Clinical and Laboratory Standards Institute (CLSI) 2021 guidelines.²⁶

Analyses of Data

All statistical comparisons among samples were conducted in GraphPad Prism 8 using the chi-square test. P value <0.05 was considered statistically significant.

Results

Among the 5017 respiratory tract specimens from hospitalized children with pneumonia, we successfully isolated 996 bacterial strains, yielding an overall 19.9% isolation rate for bacteria. Table S1 summarizes the bacteria carriage rates in the respiratory tract among host groups from Haikou Maternal and Child Health Hospital, of different sexes, ages, and different seasons. Our analyses revealed no statistically significant difference in bacteria isolation rates between the two sexes (P = 0.402). However, significant differences were found among the age groups (less than 1 month old, 1 month to 1 year old, 2 to 5 years old, and 6 to 14 years old) (P = 0.000); and among the four seasons (spring, summer, autumn and winter) (P = 0.000). Specifically, patients aged 1 month to 1 year old had the highest bacteria carriage rate (29.5%), followed by those aged 2 to 5 years old (22.7%), and those aged 6 to 14 years old (9.8%), patients aged less than 1 month old had the lowest bacteria carriage rate (8.4%). Pairwise age-group comparisons revealed that except between the <1 month old and the 6 to 14 years old (P > 0.05), all other age groups comparisons showed statistically significant differences in their bacterial carriage rates (P < 0.05). Among the four seasons, the winter samples had the highest bacterial carriage rate (26.2%), the summer samples had the lowest bacterial carriage rate (16.7%), and the other two seasons (spring and autumn) were in-between, at 20.4% and 18.4%, respectively.

We found no statistically significant difference in species composition between bacteria samples from the two sex groups (P = 0.949) (Figure 1). However, bacteria populations from the four age groups (Figure 2) and four seasons (Figure 3) differed significantly in their bacteria species distributions (P < 0.01 in both comparisons). Specifically, the samples from the 2 to 5 years old analyzed here had a significantly higher percentage of H. influenzae (55.2%) than those from less than 1 month (3.6%). In contrast, samples from less than 1 month had a significantly higher percentage of E. coli (27.0%) than those from 2 to 5 years old (0.3%) and 6 to 14 years old (0.0%) (Figure 2). The samples from spring and winter had the higher percentage of H. influenzae (45.0% and 47.4%) than those from summer and autumn (25.6% and 24.4%) (Figure 3).

Figure 1 Detection rate of respiratory tract bacteria by gender in children with pneumonia.

Figure 2 Detection rate of respiratory tract bacteria in different age groups.

Figure 3 Detection rate of respiratory tract bacteria in different seasons.

Bacteria Isolates

The 996 bacteria isolates belonged to 24 species. Among the 996 isolates, 234 were Gram-positive bacteria (23.5%) and 762 were Gram-negative bacteria (76.5%). Based on their overall frequencies, from the most common to the least common in our sample, the 24 species were H. influenzae (356 isolates, 35.7%), S. pneumoniae (128, 12.9%), M. catarrhalis (114, 11.5%), E. coli (89, 8.9%), S. aureus (89, 8.9%), K. pneumoniae (82, 8.2%), A. baumannii (31, 3.1%), P. aeruginosa (28, 2.8%), Enterobacter cloacae (18, 1.8%), S. agalactiae (13, 1.3%), Enterobacter aerogenes (12, 1.2%), Klebsiella oxytoca (9, 0.9%), Serratia marcescens (6, 0.6%), Citrobacter koseri (5, 0.5%), Acinetobacter junii (3, 0.3%), S. haemolyticus (3, 0.3%), Pseudomonas luteola (2, 0.2%), Raoultella planticola (2, 0.2%), and one each of Enterococcus faecalis, Serratia fonticola, Pseudomonas mendocina, Proteus mirabilis, Enterobacter gergoviae and Salmonella spp, each accounting for 0.1%, respectively (Table S1).

Antimicrobial Susceptibility Profile

The commonly prescribed antimicrobial drugs for clinical use in China were selected to determine the susceptibility pattern for each bacterial isolates obtained in this study. A total of 702 strains (70.5%) showed with the resistant (R) and/or intermediate (I) phenotypes to at least one of the tested drugs. The details are follows.

Gram-Positive Bacteria

All strains of the five Gram-positive bacteria (S. pneumoniae, S. aureus, S. agalactiae, S. haemolyticus and E. faecalis) were tested for their susceptibilities to antibiotics by the VITEK 2 Compact automatic system with GP cards. The summary results of antimicrobial susceptibility testing of these five species are presented in Table 1. Below are brief descriptions for each of the five species.

S. pneumoniae

All the 128 S. pneumoniae strains were tested for their susceptibilities to the following seven antibiotics: penicillin, erythromycin, trimethoprim-sulfamethoxazole, vancomycin, linezolid, meropenem, and ceftriaxone (Table 1). All the 128 S. pneumoniae strains were resistant to erythromycin. The rates of resistance to trimethoprim-sulfamethoxazole and ceftriaxone were 93.8% (120/128), and 39.8% (51/128), respectively. All the S. pneumoniae strains were sensitive to penicillin, vancomycin, linezolid, and meropenem (Table 1).

S. aureus and S. haemolyticus

All the 89 S. aureus strains and three S. haemolyticus strains were tested for their susceptibilities to the following seven antibiotics: penicillin, oxacillin, erythromycin, clindamycin, trimethoprim-sulfamethoxazole, vancomycin, and linezolid. The S. aureus and S. haemolyticus strains showed different resistance rates to five of the seven drugs but all strains were sensitive to linezolid, and vancomycin. The AMR rates of S. aureus to the five drugs, from the highest to lowest, were penicillin (78.7%, 70/89), erythromycin (24.7%, 22/89), oxacillin (MRSA) (22.5%, 20/89), clindamycin (22.5%, 20/89), and trimethoprim-sulfamethoxazole (7.9%, 7/89) (Table 2). All three S. haemolyticus strains were resistant to penicillin, erythromycin, and oxacillin, two S. haemolyticus strains were resistant to trimethoprim-sulfamethoxazole and one S. haemolyticus strain was resistant to clindamycin (Table 1).

S. agalactiae and E. faecalis

All the 13 S. agalactiae strains were tested for their susceptibilities to the following five antibiotics: penicillin, ampicillin, clindamycin, vancomycin, and linezolid. Our S. agalactiae population showed a high resistance rate to clindamycin (92.3%, 12/13), but all 13 strains were sensitive to the other four drugs (Table 1). The E. faecalis strain was sensitive to all the tested five drugs: penicillin, ampicillin, erythromycin, vancomycin, and gentamicin (Table 1).

Gram-Negative Bacteria

The H. influenzae and M. catarrhalis strains were all tested for their susceptibility to antibiotics by the KB disk diffusion method. For other Gram-negative bacterial strains, including those of E. coli, K. pneumoniae, A. baumannii, P. aeruginosa, E. cloacae, E. aerogenes, K. oxytoca, S. marcescens, C. koseri, A. junii, P. Luteola, R. planticola, S. fonticola, P. mendocina, P. mirabilis, E. gergoviae and Salmonella spp. their antibiotic susceptibilities were determined by the VITEK 2 Compact automatic system with GN cards. The summary results of these tests are presented in Figures 4, 5, and Table 2.

Figure 4 AMR rates of the H. influenzae population in this study. Abbreviations: AMP, ampicillin; AMC, amoxicillin-clavulanic acid; CXM, cefuroxime; CRO, ceftriaxone; MEM, meropenem; SXT, trimethoprim-sulfamethoxazole; AZM, azithromycin.

Figure 5 AMR rates of the M. catarrhalis population in this study. Abbreviations: AMC, amoxicillin-clavulanic acid; SXT, trimethoprim-sulfamethoxazole; AZM, azithromycin; ERY, erythromycin; CLA, clarithromycin; TET, tetracycline.

H. influenzae and M. catarrhalis

All the 356 H. influenzae strains were tested for their susceptibilities to the following seven antibiotics: ampicillin, amoxicillin-clavulanic acid, ceftriaxone, cefuroxime, meropenem, trimethoprim-sulfamethoxazole, and azithromycin (Figure 4). Among the 356 strains, 322 (90.4%) showed the R and/or I phenotypes to at least one of the seven drugs. The overall resistance rates of H. influenzae to the seven drugs, from the highest to lowest, were trimethoprim-sulfamethoxazole (80.3%, 286/356), ampicillin (76.7%, 273/356), cefuroxime (58.4%, 208/356), azithromycin (29.5%, 105/356), amoxicillin-clavulanic acid (18.3%, 65/356), ceftriaxone (5.3%, 19/356), and meropenem (0.6%, 2/356) (Figure 4).

All the 114 M. catarrhalis strains were tested for their susceptibilities to the following six drugs: amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole, azithromycin, erythromycin, clarithromycin, and tetracycline (Figure 5). All the M. catarrhalis strains were sensitive to tetracycline and clarithromycin, while the M. catarrhalis strains showed different resistance rates to other four drugs: amoxicillin-clavulanic acid (1.8%, 2/114), trimethoprim-sulfamethoxazole (29.8%, 34/114), azithromycin (41.2%, 47/114), and erythromycin (44.7%, 51/114) (Figure 5). In addition, 60.5% (69/114) of M. catarrhalis strains and 42.9% (153/356) of H. influenzae strains produced β-lactamases.

E. coli

All the 89 E. coli strains were tested for their susceptibilities to the following 12 antibiotics: ampicillin, ampicillin-sulbactam, piperacillin-tazobactam, cefazolin, ceftriaxone, ceftazidime, cefepime, imipenem, aztreonam, trimethoprim-sulfamethoxazole, tobramycin, and imipenem (Table 2). The E. coli strains showed different resistance rates to 10 of the 12 antibiotics except for amikacin and piperacillin-tazobactam where no resistant strain was isolated. The resistance rates of E. coli to the 10 drugs from the highest to lowest were ampicillin (68.5%, 61/89), ampicillin-sulbactam (52.8%, 47/89), trimethoprim-sulfamethoxazole (29.2%, 26/89), cefazolin (23.6%, 21/89), ceftriaxone (21.4%, 19/89), tobramycin (21.4%, 19/89), ceftazidime (20.2%, 18/89), aztreonam (19.1%, 17/89), cefepime (1.1%, 1/89), and amikacin (1.1%, 1/89). In addition, 19.1% (17/89) E. coli strains produced extended spectrum β-lactamases.

K. pneumoniae and K. oxytoca

All the 82 K. pneumoniae strains and nine K. oxytoca strains were tested for their susceptibilities to the following 11 antibiotics: ampicillin-sulbactam, piperacillin-tazobactam, cefazolin, ceftriaxone, ceftazidime, cefepime, imipenem, aztreonam, trimethoprim-sulfamethoxazole, tobramycin, and amikacin (Table 2). All the K. pneumoniae strains were sensitive to amikacin. One each of the 82 K. pneumoniae strains was resistant to piperacillin-tazobactam, cefepime, imipenem (CRE) and piperacillin-tazobactam respectively. The resistance rates of K. pneumoniae to the other six drugs from the highest to lowest were ampicillin-sulbactam (18.3%, 15/82), cefazolin (13.4%, 11/82), trimethoprim-sulfamethoxazole (13.4%, 11/82), ceftazidime (10.9%, 9/82), ceftriaxone (8.5%, 7/82), and aztreonam (4.9%, 4/82). The CRE strains were resistant to nine of the 11 drugs except tobramycin and amikacin. 6.1% (5/82) K. pneumoniae produced extended-spectrum β-lactamases. Three of the nine (33.3%) K. oxytoca strains were resistant to cefazolin. All the nine K. oxytoca strains were sensitive to the other ten drugs.

A. baumannii and A. junii

All the 31 A. baumannii strains and three A. junii were tested for their susceptibilities to the following eight antibiotics: ampicillin-sulbactam, ceftriaxone, ceftazidime, cefepime, imipenem, trimethoprim-sulfamethoxazole, tobramycin, and amikacin (Table 2). Two of the 31 (6.5%) A. baumannii strains were resistant to trimethoprim-sulfamethoxazole, 11 (35.5%) were resistance to ceftriaxone, while the other A. baumannii strains were sensitive to the other six drugs. All three A. junii strains were sensitive to all the eight drugs.

P. aeruginosa, P. luteola and P. mendocina

All the 28 P. aeruginosa strains were tested for their susceptibilities to the following six antibiotics: piperacillin-tazobactam, ceftazidime, cefepime, imipenem, tobramycin, and amikacin (Table 2). Two P. luteola and one P. mendocina strains were tested for their susceptibilities to the following eight antibiotics: piperacillin-tazobactam, ceftriaxone, ceftazidime, cefepime, imipenem, trimethoprim-sulfamethoxazole, tobramycin, and amikacin. The P. mendocina strain was resistant to ceftriaxone and ceftazidime. The other tested strains were all sensitive to the tested drugs.

E. cloacae, E. aerogenes and E. gergoviae

All the 18 E. cloacae, 12 E. aerogenes and one E. gergoviae strains were tested for their susceptibilities to the following nine antibiotics: piperacillin-tazobactam, ceftriaxone, ceftazidime, cefepime, imipenem, aztreonam, trimethoprim-sulfamethoxazole, tobramycin, and amikacin (Table 2). One E. aerogenes isolate was resistant to ceftriaxone, ceftazidime, cefepime, and aztreonam. Other tested strains were all sensitive strains to all tested antibiotics.

S. marcescens and S. fonticola

All the six S. marcescens and one S. fonticola strains were tested for their susceptibilities to the same antibiotics as Enterobacter sp. above (Table 2). The S. fonticola strain was resistant to ceftriaxone, ceftazidime, and aztreonam but sensitive to other six drugs. All the six S. marcescens strains were sensitive to the nine tested antibiotics.

Others

Five C. koseri, two R. planticola, one P. mirabilis, and one Salmonella strains were tested for their susceptibilities to different drugs (Table 2). All the strains were sensitive to the tested drugs except the P. mirabilis strain which was resistant to trimethoprim-sulfamethoxazole.

Discussion

Pneumonia is a major cause of morbidity and mortality. According to the 2015 and 2016 GBD data, the main causes of pneumonia deaths in children were bacteria.^1,27 Similar to those reported from Chengdu (southwest China) and Xiamen (southeast China),^25,28 the detected bacterial species in this study mainly belonged to Gram-negative taxa, and that the 1 month to 1 year old and 2 to 5 years old groups had higher bacteria carriage rates than those of less than 1 month and the 6 to 14 years old groups (p = 0.000). However, no statistically significant difference in bacterial species composition and isolate rate was found between the two sex groups. Our results are different from a study in India that demonstrated boys under 5 years old had a higher incidence of respiratory tract infection than girls.²⁹

H. influenzae, S. pneumoniae, and M. catarrhalis are the top three bacterial pathogens colonizing the lower respiratory tract of children with pneumonia. A previous study showed that these three bacteria were positively correlated with each other in their carriage rates at the population level.³⁰ However, differences among age groups were found for several species, similar to two previous reports.^27,31 For example, in our sample, H. influenzae (55.2%) were mainly isolated from the 2 to 5 years old group while only 3.6% was found in the less than 1 month age group. In contrast, samples from less than 1 month old had a significantly higher percentage of E. coli (27.0%) than those from 2 to 5 years old (0.3%) and 6 to 14 years old (0.0%).

Our results also observed significant influence of seasons on species distribution. For example, the samples from spring and winter had higher percentages of H. influenzae (45.0% and 47.4%) than those from summer and autumn (25.6% and 24.4%). Our results contrast those reported recently of a retrospective study from Chengdu, China. In that study, H. influenzae was detected more frequently in spring than other species, while S. pneumoniae and M. catarrhalis were detected more frequently in winter.²⁷ Seasonal differences have been found in many fungal pathogens, largely related to differences in temperature and moisture among seasons and the impact of those differences on fungal growth and reproduction in both our indoor and outdoor living environments.^10,32

AMR is a recognized global threat and increases the risk of infection-related death for patients of all age groups, including children. In our study, a total of 702 strains (70.5%) showed the R and/or I phenotypes to at least one of the tested drugs in this study. Our results suggest that susceptibility testing should be implemented before antibiotic treatment in Hainan to improve treatment success. The main bacteria detected in our cohort was H. influenzae and we observed high AMR rates of this species to sulfamethoxazole (80.3%) and ampicillin (76.9%), similar to those reported in southern parts of Mainland China^27,28 Ampicillin is a historical drug of choice for treating H. influenzae infection, but in recent years, ampicillin resistance has increased substantially,^33–37 suggesting that ampicillin should no longer be the first-line treatment for infections caused by H influenzae in China. Furthermore, strains of H. influenzae isolated here showed variable rates of resistance to 5 other commonly used antibiotics (Figure 4), with 42.9% of these strains producing β-lactamases. Interestingly, though the rate of β-lactamase production was high, it was lower than that reported in a national survey in China by the Infectious Disease Surveillance of Pediatrics (ISPED) program during 2016–2020.³⁸

The second most common bacterium was S. pneumoniae and we observed all strains of this species being resistant to erythromycin. In addition, we observed a high frequency resistance to trimethoprim-sulfamethoxazole. Interestingly, there was a low frequency of resistance to ceftriaxone and all S. pneumoniae strains in our collection were extremely sensitive to penicillin, vancomycin, linezolid, and meropenem (Table 2). These data are generally consistent with those reported previously.^27,28,35 Together, our results suggest that penicillin, vancomycin, linezolid, and meropenem can be used as the first-line antibiotics for the treatment of pneumoniae caused by S. pneumoniae in Hainan.

The third most common bacterial species was M. catarrhalis and we observed that 60.5% of M. catarrhalis strains produced β-lactamases. This rate is far lower than previously reported by ISPED (>95%).³⁷ However, all the M. catarrhalis strains were sensitive to tetracycline and clarithromycin, and with different degrees of resistance to amoxicillin-clavulanic acid, trimethoprim-sulfamethoxazole, azithromycin, and erythromycin.

Among the 89 S. aureus and three S. haemolyticus strains isolated in our study, 22.5% and 100% were resistant to oxacillin, respectively. A similar rate was reported by Zhu et al during 2018–2020 where 27% of S. aureus detected in the lower respiratory tract of children in Chengdu, southwest China were MRSA and with an increasing trend of resistance over the three years.²⁷ Reports from Japan suggested that the rapid spread of S. aureus carrying the resistance gene in the environment was associated with increased MRSA detection rate in hospitals.³⁹ Similarly, reports from Spain showed that the use of antibiotics in animal husbandry promoted the spread of Staphylococcus antibiotic resistance genes in the environment and wildlife.⁴⁰ We also found the oxacillin-resistant S. aureus and oxacillin-resistant S. haemolyticus strains were also resistant to penicillin and were more likely to be resistant to other antibiotics than the oxacillin-sensitive S. aureus and oxacillin-sensitive S. haemolyticus. Interestingly, all S. aureus and S. haemolyticus strains in our study were sensitive to vancomycin and linezolid. Our results suggest that these two drugs can be used as first-line drugs for treating infections caused by MRSA and MRSH in Hainan.

E. coli and K. pneumoniae were the most common species producing extended-spectrum β-lactamases. In this study, we found that the frequency of extended-spectrum β-lactamases production from E. coli and K. pneumoniae were 19.1% and 6.1%, respectively. These rates are far lower than those reported in the previous studies.^41,42 Studies conducted by Wang et al⁴³ and Rodriguez-Bano et al⁴⁴ showed statistically significant relationship between age groups and the percentage of extended-spectrum β-lactamases producers, with the oldest age group having a greater proportion of extended-spectrum β-lactamases-producing strains. Over half of the E coli strains in our sample were resistant to ampicillin and ampicillin-sulbactam, similar to those reported in a previous study.²⁸ However, our E. coli sample showed a lower frequency of resistance to other 10 antibiotics (trimethoprim-sulfamethoxazole, cefazolin, ceftriaxone, tobramycin, ceftazidime, aztreonam, cefepime, amikacin, and piperacillin-tazobactam) than previous reports^27,28,38 (Table 2). Among all strains isolated here, the CRE strain showed the broadest antibiotic resistance profile, being resistant to nine of the 11 tested drugs except tobramycin and amikacin (Table 2).

Conclusion

In conclusion, our analyses of the distribution and drug resistance characteristics of bacterial pathogens revealed significant age and seasonal patterns of bacterial infection epidemiology in children with pneumonia in Hainan. High drug resistance rates were observed for most bacterial species to several of the antibiotics. Our results call for greater effects in vaccination, hand hygiene, strengthening of personal protective measures, and aseptic operation of invasive medical treatment to reduce the spread of drug-resistant pathogens. In addition, the highly variable AMR rates among the pathogen species-antibiotic combinations call for the development of rapid and accurate detection of both the pathogens and their antibiotic susceptibilities in individual jurisdictions.³⁷ Such data could help shorten decision-making and improve treatment outcomes against these pathogens.