Ceftriaxone- and ceftazidime-resistant Klebsiella species, Escherichia coli, and methicillin-resistant Staphylococcus aureus dominate caesarean surgical site infections at Mulago Hospital, Kampala, Uganda

Abstract

Objectives: The aim of this study was to determine the proportion and mechanism of resistance to ceftriaxone and ceftazidime among Klebsiella species and Escherichia coli and examine the burden of methicillin-resistant Staphylococcus aureus from caesarean section surgical site infections in Uganda.

Methods: Wound swabs from 109 caesarean section surgical site infections were cultured for pathogenic bacteria following standard microbiological procedures. The Kirby-Bauer disc diffusion technique was used for antimicrobial susceptibility testing. Methicillin-resistant S. aureus diagnosis was based on polymerase chain reaction testing for the mecA gene. Data were analysed using SPSS-IBM Statistics v.20.

Results: A total of 118 pathogens were recovered from 93 (85%) of 109 surgical site infections swabs. Of the 118 pathogens, gram-negative bacteria were 69 (58.5%), including 44 (37.3%) Klebsiella species, 11 (9.3%) E. coli, 6 (5.1%) Citrobacter species, and 8 (6.8%) other gram-negative bacteria. In total, 49 of the 118 pathogens were gram-positive bacteria, including 34 (28.8%) S. aureus and 15 (12.7%) Enterococci species. Resistance to ceftriaxone was detected in all 11 (100%) of the E. coli and in 43 (97.7%) of the 44 Klebsiella species and to ceftazidime in all 11 (100%) of the E. coli and 40 (91%) of the 44 Klebsiella species. Extended-spectrum beta-lactamase explained resistance to ceftazidime in 10 (91%) of the 11 E. coli and 19 (48%) of the 40 Klebsiella species. Carbapenemase production explained 15 (38%) of the 40 ceftazidime-resistant Klebsiella species. Methicillin-resistant S. aureus was detected in 91% of S. aureus.

Conclusion: Klebsiella species, E. coli, and S. aureus-majority methicillin-resistant S. aureus dominated the pathogens in caesarean section surgical site infections. Almost all of the E. coli and Klebsiella species were resistant to ceftriaxone or ceftazidime. Extended-spectrum beta-lactamase was the underlying resistance mechanism among almost all of the ceftriaxone- or ceftazidime-resistant E. coli. However, this mechanism accounted for less than half of ceftriaxone- or ceftazidime-resistant Klebsiella species, where carbapenemases accounted for 40% of the resistance, a finding previously unreported in Uganda.

Keywords: Caesarean section; extended-spectrum beta-lactamase; methicillin-resistant Staphylococcus aureus (MRSA); surgical site infections.

Figure 1.

ESBL confirmation in E. coli. Left: Ceftazidime (CAZ) 30 μg/mL disc where the zone diameter was 9 mm, indicating resistance to ceftazidime. Right: Ceftazidime/clavulanate (30/10 μg) disc with an enhanced growth inhibition zone diameter of 24 mm, that is, at least 5 mm diameter increase, confirming the E. coli as an ESBL strain.

Figure 2.

Inducible resistance to clindamycin (DA) in S. aureus caused by erythromycin (E). Note the flattening around the DA disc on the side nearest to the E disc, resulting in formation of a D-shaped zone around the DA disc.

Figure 3.

Gel electrophoresis image of the mecA gene. Lane 1: 100-bp DNA Ladder; Lane 2: blank with PCR reagents only; Lane 3: mecA-positive control (ATCC 43300); Lane 4: mecA-negative control (ATCC 29213); Lanes 5 and 8: S. aureus isolates negative for the mecA gene; Lanes 6, 7 and 9–12: S. aureus isolates positive for the mecA gene.